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Diseño de Nanomateriales y Microestructuras

Broad objectives:
New procedures to improve the control of the micro- and nanostructure of materials, Microstructural and chemical characterization in the nanoscale to understand the behaviour of materials
Specific objectives:
Development of nanostructured and nanocomposite coatings for mechanical, tribological and protective applications. Simulation of mechanical properties on nanostructured materials and correlation with the microstructural characterization and the experiment
Specific advantages
Very well positioned in the magnetron sputtering technology for deposition of nanostructured coatings for mechanical, tribological and protective applications, Very well positioned in the physical and chemical approach synthesis methodologies of nanostructured materials like sol-gel, colloidal synthesis and gas phase condensation, A multidisciplinary approach combining chemists, physicist and materials engineers. Experimental approach complemented by the incorporation of simulation and modelling. Strong simulation capabilities for mechanical properties of nanostructured materials, Strong experience in high resolution microscopies: Atomic force, transmission and scanning electron microscopies. Understanding of nanomaterials processes by controlling and determining the microstructure. Multitechnique approach (XPS, XAS, TEM/EELS, XRD), Line with strong participation in European projects

Profesores de Investigación
Nombre Teléfono email web
Fernández Camacho, Asunción 954 48 95 31 asuncion@icmse.csic.es nanomatmicro
Catedráticos
Nombre Teléfono email web
Esquivias Fedriani, Luis M. 954 55 95 03 luisesquivias@us.es sisius
Gómez García, Diego 954 55 44 49 dgomez@us.es sisius
Investigadores Científicos
Nombre Teléfono email web
Sánchez López, Juan Carlos 954 48 95 79 jcslopez@icmse.csic.es jcslopez
Científicos Titulares
Nombre Teléfono email web
Poyato Galán, Rosalía 954 48 96 28 rosalia.poyato@icmse.csic.es
Rojas Ruiz, Cristina 954 48 95 00 + ext. 90 96 25 tcrojas@icmse.csic.es
Investigadores/Doctores Contratados
Nombre Teléfono email web
Arzac Di Tomaso, Gisela M. 954 48 95 00 + ext. 90 92 45 gisela@icmse.csic.es nanomatmicro
Fortio Godinho, Vanda Cristina 954 48 95 76 godinho@icmse.csic.es nanomatmicro
Morales Flórez, Víctor vmorales@us.es
Becarios Predoctorales
Nombre Teléfono email web
Paladini San Martín, Mariana 954 48 96 31 mariana.paladini@icmse.csic.es nanomatmicro
Personal Contratado
Nombre Teléfono email web
García Gil, María del Rocío 954 48 95 31 mrocio.garcia@icmse.csic.es nanomatmicro
Hufschmidt, Dirk 954 48 95 00 + ext. 90 92 45 dirk@icmse.csic.es
López Viejobueno, Jennifer 954 48 95 31 jennifer.lopez@icmse.csic.es nanomatmicro

Cerámicas Nanoestructuradas a Base de Carburo de Boro y Nitruro de Titanio para Aplicaciones Estructurales



Investigador Principal: Diego Gómez García / Arturo Domínguez Rodríguez
Periodo: 01-01-2016 / 31-12-2019
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2015-71411-R
Componentes: Francisco L. Cumbreras Hernández, Felipe Gutíerrez Mora, Ana Morales Rodríguez

Resumen [+]

El proyecto tiene como misión la fabricación de forma controlada científicamente de nanocerámicos de carburo de boro y de nitruro de titanio mediante la técnica de chispa de plasma. Se estudiarán las propiedades mecánicas de ambos cerámicos a temperatura ambiente (dureza y tenacidad), así como su plasticidad a alta temperatura (resistencia a la fluencia, deformación a velocidad constante).

Se pretende estudiar la influencia de la microestructura en la respuesta mecánica, así como dilucidar los mecanismos que controlan la plasticidad (particularmente la interacción de dislocaciones con maclas). Los resultados se modelarán analíticamente o mediante simulación a escala mesoscópica (vía modelos de campos de fases).


Desarrollo de catalizadores soportados sobre estructuras porosas para aplicaciones de generación y combustión catalítica de hidrógeno en el contexto de energías renovables



Investigador Principal: Asunción Fernández Camacho
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: CTQ2015-65918-R
Componentes: Asunción Fernández, Mª Carmen Jiménez de Haro, Vanda Godinho, Gisela Arzac, Dirk Hufschmidt, Rocio García

Resumen [+]

El agotamiento de combustibles fósiles a corto y medio plazo y los cambios climáticos producidos por el efecto invernadero son algunas de las principales consecuencias del uso extendido de estos combustibles. En este escenario el hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo en el contexto de un mayor uso de las energías renovables y limpias. En consecuencia se plantean actualmente retos importantes para el desarrollo de tecnologías adecuadas,  tanto en la producción de hidrógeno libre de CO2, como en su transporte y almacenamiento seguro, y en su combustión eficiente para producir calor ó electricidad en una pila de combustible. Sobre la base de los proyectos previos del grupo en el estudio de hidruros complejos para almacenamiento de hidrógeno y en el desarrollo de catalizadores y procesos integrados  de generación y uso del hidrógeno en aplicaciones portátiles; se abordarán en este proyecto nuevas investigaciones  para desarrollar catalizadores novedosos soportados sobre estructuras porosas: membranas y espumas de materiales poliméricos, metálicos y cerámicos de alto interés actual. Los catalizadores se desarrollarán y estudiarán en reacciones seleccionadas de generación y combustión de acuerdo a las siguientes líneas de actuación:

1) Desarrollo de materiales novedosos con alto valor añadido del conjunto soporte-catalizador. Por un lado los soportes porosos basados en membranas de PTFE, espumas metálicas de Ni y espumas cerámicas de SiC. El objetivo es desarrollar los nuevos catalizadores sobre soportes de interés  como membranas separadoras, electrolitos, electrodos ó combustores de hidrógeno. Los nuevos catalizadores persiguen la reducción del uso de metales nobles (i.e. bimetálicos Pt-Cu, Ni-Fe) y el desarrollo de nuevos materiales metal-metaloide (carburos, boruros, etc.). Se usarán métodos químicos de impregnación, y muy especialmente la tecnología de deposición de películas delgadas,  pulverizacón catódica, que hemos aplicado recientemente con éxito a la fabricación de catalizadores de Co. La metodología abre un campo de investigación de gran interés al permitirnos el control de la microestructura y/o la composición (i.e. Co, Co-B, Co-C) de los catalizadores a demanda.

2) La caracterización microestructural y química de los nuevos materiales y catalizadores desarrollados en el proyecto. Se trata típicamente de materiales con una microestructura y nanoestructura controlada en donde las modernas técnicas nanoscopicas van a jugar un papel fundamental en la fabricación a medida de estos.

3) Estudio de actividad en tres ensayos catalíticos: i) la generación hidrolítica de hidrógeno, ii) la descomposición fotocatalítica del agua y iii) la combustión catalítica del hidrógeno. Todas ellas reacciones de alto interés en el contexto del uso del hidrógeno como vector de transporte y almacenamiento de energías renovables.

--Sobre la base de los resultados obtenidos en estas líneas de actuación, el proyecto se ha diseñado para alcanzar un conocimiento fundamental y un diseño racional en la nanoescala de catalizadores soportados en sustratos porosos. Las relaciones composición-estructura-propiedades se investigarán usando los ensayos catalíticos y fotocatalíticos acoplados a la microscopía electrónica de alta resolución analítica y otras técnicas espectroscópicas.


Recubrimientos para aplicaciones en energía y alta temperatura



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2015-65539-P
Componentes: Iñigo Braceras Izaguirre (INASMET), Teresa Cristina Rojas Ruiz, Maria Belinda Sigüenza Carballo

Resumen [+]

La protección de las superficies frente a la temperatura, los fenómenos de oxidación o el desgaste ha logrado un progreso substancial mediante el desarrollo de nuevos materiales y recubrimientos con propiedades mejoradas tales como dureza extrema, baja fricción y tasas de desgaste, elevada resistencia ante la temperatura y la oxidación. Estas mejoras suponen un enorme ahorro de energía y reducción de costes debido a la vida media de los componentes mecánicos sin necesidad de sustitución, así como, a una reducción del impacto medioambiental. Este campo de investigación tiene una profunda repercusión en una gran variedad de sectores industriales (energía, herramientas de mecanizado, automoción, aeronáutico, metalurgia, etc.). El reto para la mayoría de estos procesos de funcionalización superficial residen en un control estricto de la micro y nanoestructura de la superficie y de las intercaras que hagan posible la aparición de nuevas propiedades y aplicaciones que la nanotecnología ofrece.

En este proyecto, se prepararán recubrimientos nanoestructurados para la protección de componentes sometidos a altas temperaturas y ambientes agresivos buscando un comportamiento mejorado. Este objetivo será abordado para tres diferentes aplicaciones que contribuirían a procesos energéticos más eficientes, energías renovables y soluciones para disminuir el impacto medioambiental. Basándonos en el sistema Cr-Al-N, se depositarán diferentes recubrimientos mediante la técnica de pulverización catódica reactiva cambiando la composición química (contenido en metal, incorporación de dopantes tales como Y o Si); microestructura; distribución de fases; arquitectura (multicapa/nanocomposite) o estructuras más complejas (tándem, multicapa en gradiente) sobre los sustratos apropiados dependiendo de la aplicación prevista: a) resistencia a la oxidación a alta temperatura (hasta 1000ºC) para herramientas; b) absorbedores solares selectivos estables térmicamente a medias (300-500ºC) y alta temperatura (>600ºC); resistencia a la corrosión para componentes en turbinas de vapor supercríticos (650ºC/100% vapor).

La investigación sobre los mecanismos de oxidación, transformaciones de fases, modificaciones estructurales, etc. serán objeto de un estudio detallado sobre los sustratos definidos para lograr un conocimiento fundamental sobre los procesos de degradación y los efectos protectores. El establecimiento de correlaciones entre las propiedades iniciales y el comportamiento funcional permitirá una mejor comprensión de los mecanismos de protección y por ende, una optimización de tales sistemas en forma de recubrimientos nanoestructurados para las aplicaciones previstas.

 

Palabras clave: Recubrimientos, alta temperatura, resistencia oxidación, corrosión, nanoestructurado, energía, absorbedor solar, multicapas


Procesado y caracterización microestructural, mecánica y eléctrica de compuestos cerámica-grafeno



Investigador Principal: Angela Gallardo López (UEI) / Rosalía Poyato Galán
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2015-67889-P
Componentes: Antonio Muñoz Bernabé, Felipe Gutiérrez Mora, Ana Morales Rodríguez

Resumen [+]

En la actualidad se plantean interesantes expectativas sobre los compuestos cerámica/grafeno, propuestos para aplicaciones en catálisis, almacenamiento y conversión de energía, protección del medio ambiente y biotecnología. Pero aún se requieren importantes esfuerzos para dar respuesta a cuestiones abiertas. Hay que incidir en aspectos como la resistencia a la cizalla de las intercaras cerámica-grafeno -esencial para asegurar la transferencia de carga efectiva sobre las láminas de grafeno-, la distribución homogénea del grafeno en la matriz cerámica y la relación de tamaños entre matriz y refuerzo, para maximizar el aumento de tenacidad y de conductividad eléctrica, así como también explorar sus propiedades mecánicas a alta temperatura.
En este proyecto se plantea un estudio sistemático de compuestos de matrices cerámicas con grafeno, desde la fabricación hasta la caracterización microestructural, mecánica y eléctrica, con el objetivo de mejorar la comprensión de los mecanismos que controlan estas propiedades al incorporar nanoestructuras de grafeno a una matriz cerámica. Se procesarán compuestos de dos matrices cerámicas diferentes, de alúmina y de circona tetragonal dopada con óxido de itrio (3YTZP), con grafeno mediante técnicas coloidales, prestando especial atención a la dispersión del grafeno en la matriz cerámica, aspecto no exento de dificultades y que es clave para conseguir la mejora de las propiedades. La sinterización se realizará en un horno de descarga de plasma (SPS, spark plasma sintering) de última generación, optimizando las condiciones para conseguir compuestos densos y de tamaño de grano nanométrico. Para el análisis microestructural se utilizarán técnicas como la difracción de rayos X, la espectroscopía Raman, y la microscopía electrónica de barrido y transmisión. Con ellas se evaluarán las fases cristalográficas presentes, el tamaño de grano, la distribución de las nanoestructuras de grafeno, etc.
Desde el punto de vista del diseño de materiales avanzados, es fundamental investigar la relación entre microestructura y propiedades mecánicas y eléctricas. Las propiedades mecánicas a temperatura ambiente (dureza, tenacidad a la fractura y resistencia a flexión) se abordarán mediante indentación y ensayos de flexión, a escalas macro y microscópica. A alta temperatura, se estudiará la deformación plástica de los compuestos cerámica-grafeno mediante ensayos de fluencia en atmósferas controladas. También se estudiará el comportamiento tribológico de los compuestos y se evaluará su conductividad eléctrica, una de las propiedades más interesantes ya que se modifica de forma notoria como resultado de la incorporación del grafeno a estos sistemas cerámicos. La respuesta eléctrica se analizará en un amplio rango de temperaturas, bien mediante espectroscopía de impedancia compleja, bien mediante medidas de conductividad en corriente continua en el caso de los compuestos menos resistivos. 


Aplicación de técnicas avanzadas de microscopía electrónica para la caracterización de recubrimientos nano-estructurados para aplicaciones en energías limpias



Investigador Principal: Ana María Beltrán Custodio
Periodo: 01-03-2015 / 28-02-2017
Organismo Financiador: Junta de Andalucía
Código: TAHUB-050. Programa Talent HUB
Componentes:

Resumen [+]

Este proyecto se centra en la generación y almacenamiento de hidrógeno con el objetivo de producir hidrógeno para energías limpias. Esto sucede durante una reacción exotérmica en la que es necesaria la presencia de un catalizador para que se lleve a cabo en condiciones de seguridad. Los catalizados basados en metales nobles son buenos candidatos para este objetivo (cobalto, cobre…). Aquí, los sistemas completos catalizador-soporte son estudiados. Estos sistemas son crecidos mediante técnicas de pulverización catódica (“magnetron sputtering”). La estructura y la composición son estudiadas a escala nanométrica mediante técnicas avanzadas de microscopía electrónica de transmisión-barrido (STEM), como la microscopía electrónica de alta resolución (HRTEM), imágenes adquiridas en modo campo oscuro con detector de alto ángulo (HAADF), energía dispersiva de rayos X, espectroscopia de pérdida de energía de electrones (EELS), para análisis químico. Además, el uso de la técnica de caracterización tridimensional, tomografía electrónica, aporta un completo conocimiento del sistema analizado. La combinación de técnicas de análisis estructural y de composición, en modo TEM y STEM, nos permite obtener una completa nano-caracterización del sistema. Estos análisis STEM son una herramienta esencial para determinar la relación entre la microestructura, las condiciones de crecimiento y el comportamiento final y las propiedades del sistema, que nos ayudará a mejorarlos y, por tanto, contribuir a la producción de energía limpia.

Este proyecto tiene cuatro objetivos estratégicos.

1. Nano-materiales para aplicaciones en energía limpia. Materiales para la producción, uso y almacenamiento de hidrógeno.
2. Desarrollo de la técnica de magnetron sputtering para la fabricación de nano‑estructuras (capas delgadas, recubrimientos y micro-estructuras multicapas).
3. Potenciación de las facilidades LANE (Laboratorio de microscopía del centro ICMSE-CSIC).
4. Uso de técnicas avanzadas de caracterización estructural y de análisis para el estudio a nano-escala de nuevos nano-materiales. 


Desarrollo de procesos de combustión catalítica de hidrógeno y estudio de su integración en dispositivos para aplicaciones portátiles



Investigador Principal: Asunción Fernández Camacho
Periodo: 16-05-2014 / 15-05-2016
Organismo Financiador: Junta de Andalucía
Código: P12-TEp-862
Componentes: Julián Martínez, Gisela Arzac, Dirk Hufschmidt, Joaquín Ramírez, M.Carmen Vera, Vanda Godinho, Lionel Cervera, T.Cristina Rojas, Olga Montes, Mariana Paladini, Jaime Caballero-Hernández

Resumen [+]

El hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo en el contexto de un mayor uso de las energías renovables y limpias. La producción y el uso de la energía basada en la tecnología del hidrógeno es de especial relevancia en pequeña escala para aplicaciones portátiles (y potencialmente escalable para aplicaciones estacionarias). En el presente proyecto se abordará el estudio del proceso de combustión catalítica o controlada de hidrógeno en los distintos aspectos que puedan conducir a una configuración final integrada con un sistema de generación de H2 en aplicaciones portátiles. Para ello se aprovecharán las sinergias integrando investigadores de dos grupos del PAI: i) Del grupo TEP217, especialistas en almacenamiento y generación de hidrógeno en sistemas basados en hidruros metálicos, hidruros complejos y composites de hidruros reactivos; así como en el uso de catalizadores y aditivos para controlar y mejorar las cinéticas de estos procesos. ii) Del grupo FQM342, especialistas en la obtención de cerámicos porosos de alto interés como soportes de catalizadores en entornos agresivos de combustión. Además la colaboración se completa con la participación de la empresa Abengoa Hidrógeno S.A. que participa en calidad de subcontratada como especialistas en sistemas de producción y almacenamiento de hidrógeno.
En particular se trabajará en este proyecto en las siguientes líneas de actuación:
1.- Desarrollo de catalizadores y soportes para la combustión controlada. Típicamente cerámicas porosas biomórficas de carburo de silicio y catalizadores clásicos tipo metal noble y nuevos catalizadores de bajo coste a desarrollar en el proyecto.
2.- Desarrollo de los reactores necesarios para el estudio de la combustión controlada. Típicamente para flujos de hidrógeno de unos pocos ml/min y para la escala de un generador de H2 ya disponible de 0.5 a 1.5 L/min.
3.- Acoplamiento al sistema de combustión controlada de los sistemas portátiles de generación de hidrógeno que hemos desarrollado en proyectos anteriores.
4.- Aplicación de la tecnología de pulverización catódica de una manera exploratoria en este proyecto para depositar los catalizadores de combustión catalítica en sustratos porosos.
5.- Caracterización microestructural y química de los soportes y catalizadores en la nanoescala para seguir los procedimientos de síntesis y evolución en operación.
 


Desarrollo de nuevos materiales y procesos para la generación y uso del hidrógeno principalmente en aplicaciones portátiles



Investigador Principal: Asunción Fernández Camacho
Periodo: 01-01-2013 / 31-12-2015
Organismo Financiador: Ministerio de Economía y Competitividad
Código: CTQ2012-32519
Componentes: Gisela Arzac, Jaime Caballero, Lionel Cervera, Vanda Fortio, Carlos Negrete, Dirk Hufschmidt, Cristina Rojas Ruiz, Roland Schierholz

Resumen [+]

El hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo en el contexto de un mayor uso de las energías renovables y limpias. En el presente proyecto se abordará el estudio de los distintos procesos que conducen a la configuración final integrada de sistemas de generación y uso del hidrógeno principalmente en aplicaciones portátiles (y potencialmente escalables para aplicaciones estacionarias). En particular se trabajará en este proyecto en las siguientes líneas de actuación:
a) Investigación en nuevos compuestos ligeros para su uso en procesos de generación de hidrógeno en pequeña escala por vía química (hidrólisis). Típicamente reacciones de hidrólisis de borohidruros (i.e. NaBH4) y compuestos tipo borano de amoníaco, hidrazinas ó borano hidrazina. Este area incluye el desarrollo de catalizadores en la nanoescala utilizando métodos de vía húmeda para su síntesis: Nanoestructuras metal-metaloide (tipo Co-B, Co-B-P y similares) y catalizadores bimetálicos (que incluyan ó no metaloide) de bajo coste potenciando efectos sinérgicos (tipo CoRu, NiPt ó Co-Ru-B). Incluye también el desarrollo de reactores portátiles para estos procesos y el desarrollo de nuevos sustratos y monolitos, estudios de adherencia del catalizador y durabilidad.
b) Investigación en nuevos sistemas anfitrión-huésped (host-guest) que contengan hidrógeno para el almacenamiento reversible (carga/descarga). Principalmente soportes (anfitrión) porosos del tipo “nanoscaffolds” (basados en C ó BN) infiltrados con borohidruros (huésped) (i.e. borohidruro de titanio) típicamente utilizados para el almacenamiento reversible de hidrógeno. Estos nuevos materiales deben presentar cinéticas de carga y descarga mejoradas.
c) Estudios de acoplamiento de un sistema generador de hidrógeno de bajo coste a una celda de combustible. Típicamente un reactor continúo para la hidrólisis del NaBH4 con catalizador Co-B que suministra H2 en condiciones de flujo constante para alimentar directamente una pila de combustible tipo PEM de 60 W.
d) Estudios fundamentales para el desarrollo de catalizadores y soportes para la combustión controlada de hidrógeno. Es una línea nueva en el grupo de investigación que se basa en preparar por vía húmeda catalizadores nanoparticulados de metal noble sobre soportes comerciales de cerámicas porosas (tipo SiC). Incluye el diseño de un reactor para el estudio en escala laboratorio de la producción de calor por combustión controlada de hidrógeno.
e) Desarrollo de la tecnología de pulverización catódica (“magnetrón sputtering”) para la preparación de catalizadores y nano-estructuras sobre diversos sustratos de aplicación en los procesos desarrollados en los apartados anteriores. El grupo tiene una amplia experiencia en esta tecnología que se aplicaría de manera novedosa en este proyecto permitiendo una gran versatilidad en cuanto a la nanoestructura, composición y aditivos para mejorar la actividad, durabilidad y selectividad de los catalizadores.
f) Caracterización microestructural y química de los nuevos materiales y catalizadores desarrollados en el proyecto. Se trata típicamente de materiales con una nanoestructura controlada en donde las modernas técnicas nanoscopicas van a jugar un papel fundamental en la fabricación a medida de estos materiales.
 


Desarrollo de recubrimientos nanoestructurados protectores para su uso en condiciones extremas (NANOPROTEXT)



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-01-2012 / 31-12-2014
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2011-29074-C02-01
Componentes: T. Cristina Rojas Ruiz; Francisco Javier Pérez Trujillo;Maria del Pilar Hierro de Bengoa;Germán Alcalá Penades; Maria Sonia Mato Díaz; Marta Brizuela; Pablo Corengia; José Luis Viviente; Alberto García;Daniel González

Resumen [+]

En muchas operaciones industriales, los componentes de las maquinas o piezas que están en contacto se hallan sometidos a condiciones extremas de carga, fricción, temperatura o atmósfera variable. La investigación dirige sus esfuerzos hacia al desarrollo de nuevos recubrimientos multicomponentes capaces de aumentar su eficiencia protegiendo su superficie contra el desgaste y la oxidación, que ocasionan fallos ulteriores de funcionamiento. Mediante el control del tamaño y distribución de las fases componentes, la composición química y su microestructura en el rango nanométrico es posible obtener propiedades multifuncionales tales como baja fricción, dureza y estabilidad térmica.
En este proyecto se propone el desarrollo de tres tipos de recubrimientos nanoestructurados mediante el proceso de magnetron sputtering para aplicaciones protectoras en condiciones extremas o singulares de funcionamiento (presión, temperatura, atmósferas oxidantes, vacío, etc). Los sistemas elegidos comprenden cristales de materiales duros (nitruros o carburos) combinados con una segunda fase o elemento que mejore su comportamiento. De este modo se ensayarán recubrimientos nanocomposite formados por nanocristales de WC dispersos en una segunda fase amorfa de tipo calcogenuro (WS2 or WSe2) para su uso como lubricante sólido en aplicaciones espaciales o bajo atmósferas inertes. En el segundo caso, Y ó Zr serán usados como elementos dopantes dentro de recubrimientos de CrAlN con objeto de incrementar la resistencia a la oxidación a baja y alta temperatura, y el comportamiento tribológico, muy válido en numerosos sectores industriales tales como (herramientas de mecanizado, metalúrgico, aeronaútico, automoción, etc.). Finalmente, se desarrollaran recubrimientos nanocomposite duros y transparentes basados en la familia del Al-Si-N para protección de sistemas ópticos.
En todos los casos, el proyecto comprende su síntesis, caracterización estructural y química, así como su validación práctica en ensayos tribológicos y de oxidación que simulan las condiciones finales de operación. En el caso concreto de las capas duras y transparentes también se evaluarán sus propiedades ópticas. El estudio de la relación existente entre la microestructura y las propiedades medidas será un objetivo esencial puesto que permitirá una mayor comprensión de los mecanismos de actuación, y por ende, la optimización de tales sistemas nanoestructurados para su mejor aprovechamiento tecnológico.
 


Estudio de las interacciones intermoleculares entre hidroxiacidos carboxilicos de cadena larga como modelo para el diseño de poliesteres biomimeticos



Investigador Principal: José Jesús Benítez Jiménez
Periodo: 01-01-2012 / 31-12-2014
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: CTQ2011-24299
Componentes: Alejandro Heredia Guerrero, Miguel Angel San Mibuel Barrera, Jaime Oviedo López, Miguel Salmerón Batalle

Resumen [+]

El objetivo de este proyecto de investigación es el estudio y determinación de las interacciones que se ponen de manifiesto entre las moléculas de ácidos carboxílicos lineales de cadena larga en función del nivel y tipo de funcionalización con grupos hidroxilos. Para ello se proponen sistemas modelos basados en capas autoensambladas de estas moléculas sobre un soporte plano de baja energía de interacción para que sean las propias interacciones intrermoleculares las que condicionen la estructura del empaquetamiento. La metodología de estudio de estos sistemas confinados combinará, fundamentalmente, las microscopías de sonda de proximidad, las simulaciones atomísticas de dinámica molecular y el análisis químico por espectroscopía infrarroja. La información fundamental obtenida se empleará para el diseño de una ruta de síntesis química de poliésteres miméticos a la cutina vegetal, un biopolímero de barrera hidrófobo, inocúo y completamente biodegradable. Se determinarán las propiedades físicas (mecánicas, permeabilidad, de transporte iónico, etc…) y químicas (grado de esterificación, degradabilidad, etc…) de estos materiales sintéticos y se relacionarán con sus estructuras primarias (red de enlaces ester) y secundarias (interacciones por puente de hidrógeno entre grupos hidroxilos  remanentes). A partir de esta relación estructura-función, se modificará el protocolo de síntesis empleando elementos no propagadoras del  entrecruzamiento de la red primaria (moléculas con bajo grado de hidroxilación) y modificadores de de la red secundaria (ácidos carboxílicos con distinto grado de hidroxilación), con vistas a la obtención de polímeros con propiedades “a la carta”. Finalmente, se explorará el potencial de  aplicación de estos poliésteres sintéticos como sustitutos de plásticos obtenidos a partir de hidrocarburos con vistas a reducir residuos, tanto en el proceso de fabricación como los asociados a su desecho.


Laboratorio avanzado para el análisis de nanomateriales funcionales



Investigador Principal: María Asunción Fernández Camacho
Periodo: 01-10-2011 / 30-03-2015
Organismo Financiador: Unión Europea
Código: REGPOT-CT-2011-285895
Componentes: T. Cristina Rojas, M.Carmen Jiménez, Gisela Arzac, Olga Montes, Inmaculada Rosa, Rafael Alvarez, Vanda Godinho, Juan Carlos Sánchez-López, Hernán Míguez, Agustín R. González-Elipe, Manuel Ocaña, M. Jesús Sayagués, Lionel Cervera, Roland Schierholz, Salah Rouillon, Lucia Castillo, Rocío García, Carlos García-Negrete, Jaime Caballero

Resumen [+]

El proyecto AL-NANOFUNC ha sido diseñado para poner en marcha en el Instituto de Ciencia de los Materiales de Sevilla (ICMS, CSIC-Univ.Sevilla, España) un laboratorio avanzado para el Nano-análisis de nuevos materiales funcionales. Las técnicas de Nanoscopía avanzada, basadas en equipos de microscopía electrónica de última generación, se dedicarán a la investigación de vanguardia en temas específicos de gran interés: i) Nanomateriales para aplicaciones energéticas sostenibles; ii) películas delgadas multifuncionales y recubrimientos nanoestructurados; iii) materiales nano-estructurados para fotónica y sensores. Para situar a los laboratorios del ICMS en una posición de liderazgo que sea competiti-va en un escenario mundial, el proyecto AL-NANOFUNC contempla la puesta al día del poten-cial investigador actual en varias direcciones: i) Mejorar las capacidades de equipamiento en relación a la microscopía electrónica analítica de alta resolución; ii) mejorar el impacto de la investigación básica a través de la contratación de investigadores especializados y el intercambio transnacional con los centros de referencia en Europa, iii) desarrollar y mejorar el potencial de innovación de la investigación del ICMS abriendo las nuevas instalaciones a empresas y centros relacionados; iv ) organizar talleres, conferencias y actividades de difusión para mejorar la visibilidad de la investigación. En el proyecto se propone también una estrecha colaboración con centros de referencia y empresas de Lieja (Bélgica), Graz (Austria), Jülich (Alemania), Oxford (Inglaterra), Cambridge (Inglaterra), Dübendorf (Suiza) y Rabat (Marruecos), así como con laboratorios de Universidades Andaluzas. Cinco empresas en Andalucía colaborarán también en estrecha sinergia para promover las líneas estratégicas de interés a largo plazo de la región en los productos de piedra natural y artificial y los sectores de energía solar y energías renovables.


Recubrimientos nanoestructurados para operar en vacío



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-10-2011 / 31-12-2011
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2010-21597-C02-01
Componentes: T. Cristina Rojas Ruiz, Santiago Domínguez Meister

Resumen [+]

En este proyecto se desarrollarán recubrimientos nanoestructurados por la técnica de magnetron sputtering para lubricación de componentes mecánicos en aplicaciones aeroespa-ciales. Estos materiales deben proporcionar protección frente al desgaste y baja fricción cuando se usen en condiciones atmosféricas o vacío. Los sistemas elegidos para lograr este compromiso están formados por nanocristales de WC dispersados en una fase amorfa de dicalcogenuro (WS2 or WSe2). Estos lubricantes se esperan que pueden mejorar la resistencia al desgaste, mecánica y a la oxidación en comparación con los recubrimientos convencionales (MoS2 or DLC) usados para estos fines.


Desarrollo de recubrimientos composite de carbono para aplicaciones biomédicas



Investigador Principal: Juan Carlos Sánchez López
Periodo: 15-03-2011 / 15-03-2014
Organismo Financiador: Junta de Andalucía
Código: P10-TEP 06782
Componentes: T. Cristina Rojas, Carlos López Cartes, David Abad, Vanda Godinho, Santiago Domínguez, Inmaculada Rosa

Resumen [+]

El proyecto comprende el desarrollo de recubrimientos basados en carbono desde su síntesis a medida, caracterización, evaluación en tests de desgaste y estudios de biocompatibilidad para su uso en implantes artificiales. El control del tipo de enlace químico del carbono (sp2/sp3) y la composición química, incluyendo metales como (Ag, Ti) u otros elementos (B, N, O), permitirá modular las propiedades mecánicas y tribológicas (dureza, fricción y resistencia al desgaste) con objeto de incrementar su comportamiento final. Para ello se propone el empleo de la técnica de pulverización catódica (del inglés magnetron sputtering) para depositar estos recubrimientos avanzados sobre los materiales usados en los implantes (acero, aleaciones de Ti o polímeros) bajo diferentes condiciones de síntesis. Seguidamente, éstos composites de carbono serán evaluados de forma comparativa en ensayos de fricción y desgaste que simulen las condiciones que estos materiales se encontrarán en la aplicación final. De esta manera será posible establecer una correlación entre el comportamiento observado y las características químicas y estructurales de las capas preparadas bajo diferentes condiciones de síntesis. Finalmente, la biocompatibilidad será estudiada en ensayos de adhesión celular, citotoxicidad y actividad antibacteriana. Este completo conjunto de análisis aportará una excelente perspectiva de las posibilidades de transferencia tecnológica de estos materiales avanzados a la biomedicina.


Nanopartículas funcionalizadas para aplicaciones de hipertermia y evaluación de su ecotoxicidad



Investigador Principal: Asunción Fernández Camacho
Periodo: 03-02-2010 / 02-02-2013
Organismo Financiador: Junta de Andalucía
Código: P09-FQM-4554
Componentes: J. Blasco, M. Hampel, Carlos López, L.M. Lubián, I. Moreno, Miguel Angel Muñoz, David Philippon, T. Cristina Rojas, Inmaculada Rosa, Carlos García-Negrete

Resumen [+]

En este Proyecto de Excelencia se parte de la experiencia previa del grupo TEP-217 en el desarrollo y caracterización de nanopartículas funcionalizadas potencialmente biocompatibles y se pretende avanzar en cuatro direcciones. a) Continuar con el desarrollo de nanopartículas basadas principalmente en Au, Ag y óxidos magnéticos con distintas funcionalizaciones y microestructura. b) Profundizar en la fisico-química de su interacción con campos electromagnéticos (en un amplio rango de frecuencias desde kHz a GHz) para producir calentamientos localizados. Actualmente se han propuesto distintos mecanismos (corrientes inducidas, histéresis, relajación de momentos magnéticos y movimiento browniano) sin que existan todavía suficientes datos para comprender e interpretar los resultados experimentales. c) Establecer una colaboración multidisciplinar con el grupo RNM-306, especialista en ensayos de ecotoxicidad, que permita mejorar el conocimiento del impacto ambiental de las nanopartículas (principalmente de oro y plata) en los ecosistemas marinos, que son el sumidero final de una buena parte de los nanomateriales producidos en la actualidad. d) Realizar estudios preliminares de la toxicidad de las nanopartículas en función del campo electromagnético aplicado. En cualquier proyecto dedicado a la nanotecnología resulta extremadamente valioso introducir estudios que nos permitan determinar el impacto toxicológico y ambiental de los nuevos materiales que se están desarrollando en la actualidad.

Un objetivo fundamental de este proyecto es la formación de personal investigador a través de la realización de una Tesis Doctoral en el Instituto de Ciencia de Materiales de Sevilla.


Acoplamiento dinámica de fronteras de grano - segregación de impurezas en policristales nanoestructurados: aplicación a la circonia tetragonal dopada con itrio policristalina (YTZP)



Investigador Principal: Diego Gómez García
Periodo: 01/01/2010 – 31/12/2012
Organismo Financiador: Ministerio de Educación y Ciencia
Código: MAT2009-14351-C02-01
Componentes: Francisco Luis Cumbrera Hernández (USE), Arturo Domínguez Rodríguez (USE), Robert Luis González Romero (becario AECID)

Resumen [+]

El proyecto que se presenta estudiará, mediante simulación por ordenador a distintas escalas, la evolución microestructural de un policristal a temperatura constante y bajo la apli-cación de un campo de tensiones mecánicas; en particular, se prestará especial atención a los sistemas nanométricos. Para abordar con rigor este problema es indispensable conocer la ley de movilidad de las fronteras de grano en función de la temperatura y de las tensiones locales. En presencia de impurezas, esta ley depende crucialmente de la concentración de especies atómicas segregadas en dichas fronteras y su evolución durante el régimen dinámico (i. e. durante la deformación). A su vez, la segregación se ve alterada por el propio movimiento de la frontera de grano, de modo que ambos fenómenos están acoplados entre sí. El estudio de la segregación se realizará mediante simulación por Dinámica Molecular (DM); asimismo, se utilizará la DM para caracterizar la movilidad de una única frontera de grano conteniendo impurezas. Estos datos serán empleados en un modelo mesoscópico que se usará para estudiar la dinámica de un conjunto de granos de tamaño nanométrico y, por ende, la plasticidad de este sistema policristalino modelo. El objetivo último de este proyecto es el de determinar la ley de evolución de los cen-tros de masas de los granos para obtener, previo tratamiento estadístico, la ley constitutiva para la plasticidad en un policristal nanométrico. Esta ley macroscópica se contrastará final-mente con resultados experimentales en el sistema itria-zirconia policristalino (YTZP) nanométrico, en el que el equipo ha adquirido amplia experiencia en los últimos años.


Papel de los aditivos en los sistemas composites de hidruros metálicos reactivos para almacenamiento de hidrógeno



Investigador Principal: Asunción Fernández Camacho
Periodo: 01/01/2010 - 31/12/2012
Organismo Financiador: Ministerio de Educación y Ciencia
Código: CTQ2009-13440
Componentes: Carlos López, Cristina Rojas Ruiz, Gisela Arzac, Dirk Hufschmidt, Raimondo Ceccini, Emilie Deprez

Resumen [+]

Dada la problemática actual por el agotamiento a corto-medio plazo de los combusti-bles fósiles y los cambios climáticos causados por el efecto invernadero, se hace necesaria la reconsideración de una política energética global. El hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo por tratarse de una alternativa viable y limpia. En el presente proyecto se propone el estudio de los llamados sistemas composites de hidruros reactivos (RHC) para almacenamiento de hidrógeno. Estos sistemas se basan en acoplar un hidruro metálico sencillo (i.e. MgH2) con un hidruro complejo (típicamente un compuesto borohidruro, i.e LiBH4) para dar una reacción reversible que produce o consume hidrógeno. El sistema puede así usarse como material para almacenamiento de hidrógeno de acuerdo a la siguiente reacción: MgH2+2LiBH4 ↔ MgB2+LiH+4H2 (11.4 wt% capacidad de almacenamiento de hidrógeno). La reacción mejora el balance de calor, en comparación con el MgH2 puro, al reducir la liberación de calor durante el proceso de carga. Para mejorar los aspectos cinéticos (reducción de las temperaturas y tiempos de operación) se ha propuesto el uso de catalizadores y/o aditivos. El principal objetivo del proyecto es comprender el papel de estos aditivos para mejorar las cinéticas de sorción de hidrógeno. En particular se han seleccionado como aditivos para este estudio los productos comerciales Ti-Isopropoxide (TiO4C12H28), TiO2 y VCl3 . También se prepararan en nuestro laboratorio otros catalizadores como Co3B, Ni3B o RuCo que igualmente se ensayarán. Los sistemas se prepararán y activarán por molienda de alta energía de los dos mate-riales hidruros molidos juntos con ó sin aditivos (5-10 mol%). Los estudios cinéticos se llevarán a cabo a través de medidas de sorción gravimétrica y volumétrica de hidrógeno (desorción o absorción vs. tiempo a T constante) y de la calorimetría de barrido diferencial (DSC). Se llevará también a cabo un estudio exhaustivo de caracterización microestructural y química de los sistemas en las diferentes etapas (tras la molienda, desorbidos y re-absorbidos) con las si-guientes técnicas: Difracción de rayos X (XRD), microscopía electrónica de transmisión (TEM) acoplada al análisis EDX (energía dispersiva de rayos X) y EELS (espectroscopía de pérdida de energía de electrones), espectroscopía de fotoemisión (XPS) y espectroscopía de absorción de rayos X (XAS). El estudio comparativo de las muestras con y sin aditivos y la correlación entre los estudios cinéticos y el análisis microestructural y químico, deben clarificar el mecanismo de la mejora cinética producida por los aditivos. Estos mecanismos están a día de hoy lejos de ser comprendidos. Sobre la base del conocimiento adquirido se espera mejorar de manera significativa estos sistemas en relación a sus aplicaciones para almacenamiento de hidrógeno.


Estructura, empaquetamiento y propiedades tribológicas de monocapas autoensambladas de alquilaminas lineales de cadena larga



Investigador Principal: José Jesús Benítez Jiménez
Periodo: 01-01-2009 / 31-12-2011
Organismo Financiador: Ministerio de Ciencia y Tecnología
Código: CTQ2008-00188
Componentes: Miguel Salmerón, Eduardo Garzón Garzón, Pedro J. Sánchez Soto, J. Alejandro Heredia Guerrero

Resumen [+]

El presente proyecto se encuadra en la línea de investigación que analiza las propiedades tribológicas de monocapas autoensamblas. Más concretamente en la contribución de eventos a escala molecular en la propiedades fricciónales de sistemas modelos a base de monocapas autoensambladas de moléculas alquílicas. La información de que se dispone para sistemas modelo a base de tioles sobre oro y alquisilanos sobre mica empleando técnicas de sonda de proximidad, fundamentalmente AFM (atomic force microscopy), es muy amplia. La aportación que proporciona este proyecto es más novedosa y parte del empleo de otro sistema modelo, alquilaminas de cadena larga sobre mica. La interacción del grupo funcional amino con el soporte mica es considerablemente menor que la propia del tiol-oro y el silano-mica lo que se traduce en una menor calidad del empaquetamiento molecular. El control de la calidad del empaquetamiento mediante el ajuste de las condiciones de preparación permitiría disponer de un sistema con gran contenido de defectos sobre el que establecer la influencia de éstos en las propiedades friccionales. La consistencia mecánica de las capas de alquilaminas sobre mica impide su resolución estructural a nivel molecular empleando el microscopio AFM en modo de contacto, por lo que se propone una metodología que englobe y complemente el característico análisis friccional y la microscopia SPFM (scanning polarization force microsco-py). La técnica SPFM se basa en la medida de la fuerza electrostática que se establece entre una sonda polarizada y las cargas, dipolos permanentes o inducidos a nivel superficial. Dadas las marcadas diferencias entre las magnitudes dieléctricas de la mica y la monocapa alquílica, la metodología propuesta parte del análisis del efecto de pantalla de la capa autoensamblada sobre la señal en polarización del soporte y su relación con el grado de compactación de ésta. La técnica SPFM es especialmente sensible a la presencia de agua dado su elevada constante dieléctrica por lo que resulta muy adecuada para la detección de vacantes o intersticios sus-ceptibles de adsorber agua en el seno de la capa autoensamblada. En último extremo, el pro-yecto tiene por objeto la correlación de las propiedades friccionales con la evaluación SPFM del grado de empaquetamiento de las capas preparadas.


Estudio de la viabilidad de procesos de carbonatación de CO2 mediante compuestos tipo Wollastonita para su aplicación en procesos industriales de captura y reutilización de CO2



Investigador Principal: Luis Esquivias Fedriani
Periodo: 01/01/2009 – 31/12/2011
Organismo Financiador: Ministerio de Educación y Ciencia
Código: CIT-44000-209-1
Componentes: Alberto Santos Sánchez, Víctor Morales Flórez, Cristián Cárdenas Escudero, Laura Pereda Briones

Resumen [+]

El proyecto Wollastonita aborda el reto actual de reducir las emisiones de dióxido de carbono asociadas a los procesos energéticos e industriales. Es por ello que su principal consiste en el desarrollo de un sistema capaz de capturar grandes cantidades de CO2 y otros gases de efecto invernadero (GEI) de misión localizada, típicamente plantas térmicas de generación de energía eléctrica u cementeras, escalable a nivel industrial. Con la realización de este Proyecto se tratará por una parte de analizar la viabilidad técnica y económica de los procesos de secuestro de CO2 mediante compuestos de sílice y calcio, como es el caso de la wollastonita, y por otra parte, se tratarán de identificar las especificaciones requeridas para el diseño de un sistema integrado de captura y secuestro de CO2 aplicado a una instalación industrial generadora de grandes cantidades de este gas. Dado que el subproducto de la carbonatación puede ser un mineral valioso, medioambientalmente seguro y termodinámicamente estable, este puede ser reutilizado como materia prima en determinados procesos industriales, dependiendo de su morfología, pureza y tamaño de partícula. Por ello, se estudiarán las posibles aplicaciones de este producto, tratando de establecer en cada caso la relación coste/beneficio. Estas posibilidades supondrían el hecho de conseguir un ciclo completo para el proyecto, desarrollando un proceso viable para la reducción de los GEI y su eliminación o reutilización completa ulterior.


Desarrollo y diseminación de nuevas técnicas de caracterización nanomecánica y standars



Investigador Principal: Asunción Fernández Camacho
Periodo: 01-09-2008 / 31-08-2011
Organismo Financiador: Unión Europea
Código: NMP3-CA-2008-218659
Componentes: Godinho, V., Philippon, D.

Resumen [+]

El proyecto se dedica al desarrollo, mejora, y standarización de las técnicas de caracterización, los métodos y los equipos en los ensayos nano-mecánicos. Las actividades a nivel Europeo, coordinadas por un centro virtual, mejorarán la metrología de nanoindentación actual y permitirán un conocimiento más profundo de la relación estructura-propiedades en la nano-escala. Estos métodos son una herramienta única para caracterizar el comportamiento mecánico en la nanoescala de nanocomposites, nanocapas e interfases. Este trabajo también producirá una base sólida para definer y preparer nuevos standards que soporten la metodología de caracterización de los nanomateriales. Las etapas incluyen el desarrollo de los métodos clásicos de nanoindentación dinámica y su aplicación a campos nuevos como el rayado y las medidas de desgaste y la aplicación de nano-indentadores modificados. También se trabajará en la determinación uniforme de los parámetros instrumentals y en la definición de standards par alas nuevas aplicaciones. El centro virtual diseminará la información sobre la base de una nueva "base de datos para la caracterización Nano-mecánica". Esto se conseguirá a través de los trabajos de "round robin" entre los socios é incluirá igualmente datos de de otras fuentes de investigación y la búsqueda bibliográfica.


Recubrimientos nanoestructurados multifuncionales para aplicaciones mecánicas y tribológicas (NANOMETRIB)



Investigador Principal: Juan Carlos Sánchez López
Periodo: 01-10-2007 / 30-09-2011
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: MAT2007-66881-C02-01
Componentes: Asunción Fernández Camacho, Cristina Fernández, Miguel Angel Muñoz-Márquez, Said El Mrabet, Vanda Godinho, M. David Abad

Resumen [+]

En el campo de las aplicaciones mecánicas y tribológicas, las investigaciones se dirigen al desarrollo de nuevos sistemas que consigan aumentar la eficiencia de operaciones industriales, equipos o herramientas mediante el incremento de la dureza, la reducción de la fricción y la velocidad del desgaste de los materiales en contacto o la resistencia a la oxidación. Estas mejoras suponen un ingente ahorro económico y energético al alargar la vida media de los materiales sin necesidad de su reparación o cambio, como también, una reducción del empleo de emulsiones lubricantes con aceites o grasas. Este proyecto se propone el desarrollo de nuevos recubrimientos nanoestructurados multifuncionales por la técnica de PVD-Magnetron Sputtering para aplicaciones mecánicas y tribológicas en los que se alcance un equilibrado compromiso entre todas las propiedades mencionadas de fricción, dureza, estabilidad térmica. La combinación de múltiples funciones en un mismo material dota de un extraordinario valor añadido al sistema. Para lograr este objetivo general se van a preparar recubrimientos caracterizados donde el tamaño y distribución de las fases componentes, la composición química y su microestructura estén confinados en el rango nanométrico. Los sistemas elegidos comprenden cristales de materiales duros (nitruros, carburos o boruros de metales de transición: Cr, Ti, W) que pueden estar rodeados de una segunda fase que actúe como lubricante a base de C o dicalcogenuros de W) y dopados con ciertos metales para incrementar su resistencia térmica (V ó Nb). En todos los casos, el proyecto comprende su síntesis, caracterización estructural y química, así como su validación práctica en ensayos mecánicos y tribológicos. El estudio de la relación existente entre la microestructura y las propiedades medidas será un objetivo esencial puesto que permitirá una mayor comprensión de los mecanismos de actuación, y por ende, la optimización de tales sistemas nanoestructurados para su mejor aprovechamiento tecnológico.


2017


Titulo: Effect of acid-treatment and colloidal-processing conditions on the room temperature mechanical and electrical properties of 3YTZP/MWNT ceramic nanocomposites
Autores: Poyato, R.; Morales-Rodríguez, A.; Gutiérrez-Mora, F.; Muñoz, A.; Gallardo-López, A.
Revista: Ceramics International, 43 (2017) 16560-16568
resumen | texto completo


Different colloidal powder processing routines have been used to prepare composites of 3 mol% Y2O3 -ZrO2 (tetragonal zirconia polycrystals, 3YTZP) with 2.5 vol% multiwall carbon nanotubes (MWNT) with the aim of achieving a homogeneous distribution of the MWNTs in the ceramic, eliminating agglomerates but also minimizing carbon nanotube (CNT) damage during processing. Modifications of the acid treatment applied to the nanotubes, including subjecting them to stirring or ultrasonic agitation, and use of acid or basic pH during composite powder mixing have been approached.
No MWNT damage during processing was detected by Raman spectroscopy. CNT bundles were found in all the composites forming different patterns depending on the processing route. Similar values of hardness were obtained for all the composites, while different anisotropy in fracture propagation was found when studying parallel and perpendicular directions to the sintering pressing axis on the cross sections of the composites due to the MWNT preferential alignment. The CNT bundles were found to act as fracture short paths. A similar anisotropic behavior was observed for the electrical conductivity. These results have been correlated to the different microstructures obtained in the composites prepared with different processing routines.

Diciembre, 2017 | DOI: 10.1016/j.ceramint.2017.09.043

Titulo: Determination of the thickness of the embedding phase in 0D nanocomposites
Autores: Martinez-Martinez, D; Sanchez-Lopez, JC
Revista: Applied Surface Science, 421 (2017) 179-184
resumen | texto completo


0D nanocomposites formed by small nanoparticles embedded in a second phase are very interesting systems which may show properties that are beyond those observed in the original constituents alone. One of the main parameters to understand the behavior of such nanocomposites is the determination of the separation between two adjacent nanoparticles, in other words, the thickness of the embedding phase. However, its experimental measurement is extremely complicated. Therefore, its evaluation is performed by an indirect approach using geometrical models. The ones typically used represent the nanoparticles by cubes or spheres. 
In this paper the used geometrical models are revised, and additional geometrical models based in other parallelohedra (hexagonal prism, rhombic and elongated dodecahedron and truncated octahedron) are presented. Additionally, a hybrid model that shows a transition between the spherical and tessellated models is proposed. Finally, the different approaches are tested on a set of titanium carbide/amorphous carbon (TiC/a-C) nanocomposite films to estimate the thickness of the a-C phase and explain the observed hardness properties. 

Noviembre, 2017 | DOI: 10.1016/j.apsusc.2016.12.081

Titulo: Towards Extending Solar Cell Lifetimes: Addition of a Fluorous Cation to Triple Cation-Based Perovskite Films
Autores: Salado, M; Fernandez, MA; Holgado, JP; Kazim, S; Nazeeruddin, MK; Dyson, PJ; Ahmad, S
Revista: Chemsuschem, 10 (2017) 3846-3853
resumen | texto completo


Organohalide perovskites have emerged as highly promising replacements for thin-film solar cells. However, their poor stability under ambient conditions remains problematic, hindering commercial exploitation. The addition of a fluorous-functionalized imidazolium cation during the preparation of a highly stable cesium-based mixed perovskite material Cs-0.05(MA(0.15)FA(0.85))(0.95)Pb(I0.85Br0.15)(3) (MA= methylammonium; FA= formamidinium) has been shown to influence its stability. The resulting materials, which vary according to the amount of the fluorous-functionalized imidazolium cation present during fabrication, display a prolonged tolerance to atmospheric humidity (> 100 days) along with power conversion efficiencies exceeding 16%. This work provides a general route that can be implemented in a variety of perovskites and highlights a promising way to increase perovskite solar cell stability.

Octubre, 2017 | DOI: 10.1002/cssc.201700797

Titulo: HoF3 and DyF3 Nanoparticles as Contrast Agents for High-Field Magnetic Resonance Imaging
Autores: Gonzalez-Mancebo, Daniel; Becerro, Ana I.; Rojas, T. Cristina; Garcia-Martin, Maria L.; de la Fuente, Jesus M.; Ocana, Manuel
Revista: Particle & particle systems characterization, 34 (2017) art. 1700116
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Clinical contrast agents (CAs) currently used in magnetic resonance imaging (MRI) at low fields are less effective at high magnetic fields. The development of new CAs is mandatory to improve diagnostic capabilities of the new generation of high field MRI scanners. The purpose of this study is to synthesize uniform, water dispersible LnF3 (Ln = Ho, Dy) nanoparticles (NPs) and to evaluate their relaxivity at high magnetic field (9.4 T) as a function of size and composition. Two different types of HoF3 NPs are obtained by homogeneous precipitation in ethylene glycol at 120 °C. The use of holmium acetate as holmium precursor leads to rhombus-like nanoparticles, while smaller, ellipsoid-like nanoparticles are obtained when nitrate is used as the holmium salt. To explain this behavior, the mechanism of formation of both kinds of particles is analyzed in detail. Likewise, rhombus-like DyF3 nanoparticles are prepared following the same method as for the rhombus-like HoF3 nanoparticles. We have found, to the best of knowledge, the highest transverse relaxivity values at 9.4 T described in the literature for this kind of CAs. Finally, the LnF3 NPs have shown negligible cytotoxicity for C6 rat glioma cells for concentrations up to 0.1 mg mL−1.

Octubre, 2017 | DOI: 10.1002/ppsc.201700116

Titulo: Incorporation of Calcium Containing Mesoporous (MCM-41-Type) Particles in Electrospun PCL Fibers by Using Benign Solvents
Autores: Liverani, L.;Boccardi, E.; Beltrán, A.M.; Boccaccini, A.R.
Revista: Polymers, 9 (2017) 487
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The electrospinning technique is a versatile method for the production of fibrous scaffolds able to resemble the morphology of the native extra cellular matrix. In the present paper, electrospinning is used to fabricate novel SiO2particles (type MCM-41) containing poly(epsilon-caprolactone) (PCL) fibers. The main aims of the present work are both the optimization of the particle synthesis and the fabrication of composite fibers, obtained using benign solvents, suitable as drug delivery systems and scaffolds for soft tissue engineering applications. The optimized synthesis and characterization of calcium-containing MCM-41 particles are reported. Homogeneous bead-free composite electrospun mats were obtained by using acetic acid and formic acid as solvents; neat PCL electrospun mats were used as control. Initially, an optimization of the electrospinning environmental parameters, like relative humidity, was performed. The obtained composite nanofibers were characterized from the morphological, chemical and mechanical points of view, the acellular bioactivity of the composite nanofibers was also investigated. Positive results were obtained in terms of mesoporous particle incorporation in the fibers and no significant differences in terms of average fiber diameter were detected between the neat and composite electrospun fibers. Even if the Ca-containing MCM-41 particles are bioactive, this property is not preserved in the composite fibers. In fact, during the bioactivity assessment, the particles were released confirming the potential application of the composite fibers as a drug delivery system. Preliminary in vitro tests with bone marrow stromal cells were performed to investigate cell adhesion on the fabricated composite mats, the positive obtained results confirmed the suitability of the composite fibers as scaffolds for soft tissue engineering.

Octubre, 2017 | DOI: 10.3390/polym9100487

Titulo: Dense graphene nanoplatelet/yttria tetragonal zirconia composites: Processing, hardness and electrical conductivity
Autores: Gallardo-Lopez, A; Marquez-Abril, I; Morales-Rodriguez, A; Munoz, A; Poyato, R
Revista: Ceramics International, 43 (2017) 11743-11752
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Yttria tetragonal zirconia ceramic composites with 1, 2.5, 5 and 10 vol% nominal contents of graphene nanoplatelets (GNPs) were fabricated and characterized. First, the GNP dispersion in isopropanol was optimized to de-agglomerate the GNPs without damaging their structure. Then, submicrometric fully dense composites were obtained via spark plasma sintering (SPS) at 1250 degrees C with a 5 min holding time. The processing routine produced a nearly homogeneous GNP dispersion in the ceramic matrix, and the GNPs preferential orientation was perpendicular to the sintering compression axis. A ceramic grain refinement due to the GNPs was also detected. The Vickers hardness measured on the plane perpendicular to the sintering compression axis (basal plane) was lower than on the cross sections. This anisotropy increased with the increasing GNP content, while the average hardness decreased. The electrical conductivity was also highly anisotropic, up to seven times higher for the basal planes. The electrical percolation threshold for these composites was estimated to be between 2.2 and 4.4 vol% of the GNP measured content.

Octubre, 2017 | DOI: 10.1016/j.ceramint.2017.06.007

Titulo: Carbon nanofibers replacing graphene oxide in ceramic composites as a reinforcing-phase: Is it feasible?
Autores: Cano-Crespo, Rafael; Malmal Moshtaghioun, Bibi; Gomez-Garcia, Diego; Dominguez-Rodriguez, Arturo; Moreno, Rodrigo
Revista: Journal of the European Ceramic Society, 37 (2017) 3791-3796
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In recent years, the interest of graphene and graphene-oxide has increased extraordinarily due to the outstanding properties concurring in this material. In ceramic science, the possibility of combining excellent electrical conductivities together with an enhancement of mechanical properties has motivated the research in fabrication of graphene oxide-reinforced ceramic composites despite the intrinsic difficulties for sintering. In this work a comparison is made between graphene oxide-reinforced alumina composites and carbon nanofiber-reinforced alumina ones. It will be concluded that the improvement of mechanical properties is scarce, if any. Since carbon nanofibers have also a good electrical conductivity their importance for future applications as a replacement of more sophisticated but expensive graphene-based ceramic composites will be stressed.

Septiembre, 2017 | DOI: 10.1016/j.jeurceramsoc.2017.03.027

Titulo: The role of cobalt hydroxide in deactivation of thin film Co-based catalysts for sodium borohydride hydrolysis
Autores: Paladini, M; Arzac, GM; Godinho, V; Hufschmidt, D; de Haro, MCJ; Beltran, AM; Fernandez, A
Revista: Applied Catalysis B-Environmental, 210 (2017) 342-351
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Deactivation of a Co catalyst prepared as thin film by magnetron sputtering was studied for the sodium borohydride (SB) hydrolysis reaction under different conditions. Under high SB concentration in single run experiments, the formation of a B-O passivating layer was observed after 1.5 and 24 h use. This layer was not responsible for the catalyst deactivation. Instead, a peeling-off mechanism produced the loss of cobalt. This peeling-off mechanism was further studied in cycling experiments (14 cycles) under low SB concentrations. Ex-situ study of catalyst surface after use and solid reaction products (precipitates) was performed by X-Ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The presence of cobalt hydroxide and oxyhydroxide was detected as major components on the catalyst surface after use and as precipitates in the supernatant solutions after washing. Cobalt borate, cobalt carbonate and oxycarbonate were also formed but in lesser amounts. These oxidized cobalt species were formed and further detached from the catalyst at the end of the reaction and/or during catalyst washing by decomposition of the unstable in-situ formed cobalt boride. Leaching of cobalt soluble species was negligible. Thin film mechanical detachment was also found but in a smaller extent. To study the influence of catalyst composition on deactivation processes, cycling experiments were performed with Co-B and Co-C catalysts, also prepared as thin films. We found that the deactivation mechanism proposed by us for the pure Co catalyst also occurred for a different pure Co (prepared at higher pressure) and the Co-B and Co-C samples in our experimental conditions. 

Agosto, 2017 | DOI: 10.1016/j.apcatb.2017.04.005

Titulo: Plasma assisted deposition of single and multistacked TiO2 hierarchical nanotube photoanodes
Autores: Filippin, AN; Sanchez-Valencia, JR; Idigoras, J; Rojas, TC; Barranco, A; Anta, JA; Borras, A
Revista: Nanoscale, 9 (2017) 8133-8141
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We present herein an evolved methodology for the growth of nanocrystalline hierarchical nanotubes combining physical vapor deposition of organic nanowires (ONWs) and plasma enhanced chemical vacuum deposition of anatase TiO2 layers. The ONWs act as vacuum removable 1D and 3D templates, with the whole process occurring at temperatures ranging from RT to 250 degrees C. As a result, a high density of hierarchical nanotubes with tunable diameter, length and tailored wall microstructures are formed on a variety of processable substrates as metal and metal oxide films or nanoparticles including transparent conductive oxides. The reiteration of the process leads to the development of an unprecedented 3D nanoarchitecture formed by stacking the layers of hierarchical TiO2 nanotubes. As a proof of concept, we present the superior performance of the 3D nanoarchitecture as a photoanode within an excitonic solar cell with efficiencies as high as 4.69% for a nominal thickness of the anatase layer below 2.75 mu m. Mechanical stability and straightforward implementation in devices are demonstrated at the same time. The process is extendable to other functional oxides fabricated by plasma-assisted methods with readily available applications in energy harvesting and storage, catalysis and nanosensing.

Julio, 2017 | DOI: 10.1039/c7nr00923b

Titulo: High-temperature creep of carbon nanofiber-reinforced and graphene oxide-reinforced alumina composites sintered by spark plasma sintering
Autores: Cano-Crespo, Rafael; Malmal Moshtaghioun, Bibi; Gomez-Garcia, Diego; Dominguez-Rodriguez, Arturo; Moreno, Rodrigo
Revista: Ceramisc International, 43 (2017) 7136-7141
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Alumina (Al2O3) ceramic composites reinforced with either graphene oxide (GO) or carbon nanofibers (CNFs) were prepared using Spark Plasma Sintering. The effects of GO and CNFs on the microstructure and in consequence on their mechanical properties were investigated. The microstructure of the sintered materials have been characterized quantitatively prior to and after the creep experiments in order to discover the deformation mechanism. Graphene-oxide reinforced alumina composites were found to be more creep resistant than carbon nanofibers-reinforced alumina ones or monolithic alumina with the same grain size distribution. In all the cases, grain boundary sliding was identified as the deformation mechanism

Junio, 2017 | DOI: 10.1016/j.ceramint.2017.02.146

Titulo: New method for carbon dioxide mineralization based on phosphogypsum and aluminium-rich industrial wastes resulting in valuable carbonated by-products
Autores: Romero-Hermida, I; Santos, A; Perez-Lopez, R; Garcia-Tenorio, R; Esquivias, L; Morales-Florez, V
Revista: Journal of CO2 Utilization, 18 (2017) 15-22
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A new carbon mineralization method was designed based on a sequestration agent synthesised exclusively from industrial wastes. Phosphogypsum waste from the fertiliser industry was dissolved into caustic aqueous waste from the aluminium anodising industry. The resulting precipitate consisted of katoite (Ca3Al2(OH) 12, a Si-free hydrogrossular solid solution end-member of the Al-containing hydrogarnet) and thenardite (Na2SO4); the latter easily removed by rinsing with water. The carbonation performance of this katoite-rich sequestration agent was evaluated using two different methods, by bubbling in aqueous media and by weathering. Both procedures yielded high carbonation efficiencies (80% and 100%, respectively), and resulted in a solid precipitate composed primarily of calcite (CaCO3) and aluminium hydroxide (Al(OH)(3)). Priority attention was given to the transfer of trace elements and radionuclides of the uranium series typically present in the phosphogypsum. Results confirmed that the traces were transferred to resulting final solid carbonate at concentrations similar to those present in the raw phosphogypsum. In conclusion, these carbonated minerals would trap substantial amounts of CO2 and produce final materials with similar civil engineering uses to those proposed for current phosphogypsum wastes. This work offers new methods for jointly managing specific industrial wastes oriented to more sustainable industrial processes and controlling CO2 emissions.

Marzo, 2017 | DOI: 10.1016/j.jcou.2017.01.002

Titulo: Solid lubricant behavior of MoS2 and WSe2-based nanocomposite coatings
Autores: Dominguez-Meister, S; Rojas, TC; Brizuela, M; Sanchez-Lopez, JC
Revista: Science and Tecnology of Advances Materials, 18 (2017) 1
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Tribological coatings made of MoS2 and WSe2 phases and their corresponding combinations with tungsten carbide (WC) were prepared by non-reactive magnetron sputtering of individual targets of similar composition. A comparative tribological analysis of these multiphase coatings was done in both ambient air (30-40% relative humidity, RH) and dry nitrogen (RH<7%) environments using the same tribometer and testing conditions. A nanostructural study using advanced transmission electron microscopy of the initial coatings and examination of the counterfaces after the friction test using different analytical tools helped to elucidate what governs the tribological behavior for each type of environment. This allowed conclusions to be made about the influence of the coating microstructure and composition on the tribological response. The best performance obtained with a WSe x film (specific wear rate of 2 x 10(-8) mm(3) N(-1)m(-1) and a friction coefficient of 0.03-0.05) was compared with that of the well-established MoS2 lubricant material.

Marzo, 2017 | DOI: 10.1080/14686996.2016.1275784

Titulo: Ceramics of Ta-doping stabilized orthorhombic ZrO2 densified by spark plasma sintering and the effect of post-annealing in air
Autores: Sponchia, G; Moshtaghioun, BM; Benedetti, A; Riello, P; Gomez-Garcia, D; Dominguez-Rodriguez, A; Ortiz, AL
Revista: Scripta Materialia, 130 (2017) 128-132
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16 mol% Ta-doped ZrO2 powders were synthesized and densified by spark-plasma sintering (SPS) in vacuum, followed by post-SPS annealing in air, thus obtaining two ultrafine-grained ceramics consisting of Ta-doping stabilized orthorhombic ZrO2. The as-SPSed ceramic is black because it is actually a suboxide essentially with reduced cations and abundant oxygen vacancies, whereas the post-annealed ceramic is white because it is an oxide without vacancies and with only partially reduced cations. Both ceramics are relatively hard and brittle, but the as-SPSed ceramic was slightly more so, attributable to crystallographic and microstructural differences. Implications of interest for the ceramics community are discussed.

Marzo, 2017 | DOI: 10.1016/j.scriptamat.2016.11.021

Titulo: Absorption capacity, kinetics and mechanical behaviour in dry and wet states of hydrophobic DEDMS/TEOS-based silica aerogels
Autores: Morales-Florez, V; Pinero, M; Braza, V; Mesa, MD; Esquivias, L; La Rosa-Fox, N
Revista: Journal of Sol-Gel Science and Technology, 81 (2017) 600-610
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This work is a new approach to the study of the structural, mechanical and absorption properties of hybrid organic/inorganic silica-based aerogels. Diethoxydimethylsilane and tetraethoxysilane have been used as precursors. Changes in properties such as specific surface area, porous volume, pore radius, and surface texture and chemistry were researched as a function of the relative organic content. In addition, the absorption properties were tested for different organic liquids. The discrepancy in the absorption mechanisms and the kinetics of pure inorganic and hybrid samples were discussed. It was confirmed that swelling occurs in samples with high organic content, which, in turn, governs the absorption process. Finally, the mechanical behaviour was studied by uniaxial compression. A significant rise of the rupture strain up to 0.45 and a 10-fold decrease in the Young's modulus to 7.8 MPa were measured in the dry samples by increasing the organic content. The mechanical response of the samples after saturation by the absorption of two reference oily liquids, namely, common motor oil and liquid polydimethylsiloxane, was also compared with the behaviour of dry samples. The presence of liquid within the sample reduced the value of the mechanical parameters in almost all cases. Moreover, the inclusion of organic chains also made the wet aerogels highly deformable. In summary, these first results suggest that tuning the organic ratio of the hybrid aerogels allows the control of not only the structural and mechanical properties but also the absorption properties.

Febrero, 2017 | DOI: 10.1007/s10971-016-4203-0

Titulo: Pt-impregnated catalysts on powdery SiC and other commercial supports for the combustion of hydrogen under oxidant conditions
Autores: Arzac, G. M.; Montes, O.; Fernandez, A.
Revista: Applied Catalysis B-Envionmental, 201 (2017) 391-399
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We report the study of the catalytic hydrogen combustion over Pt-impregnated powdery silicon carbide (SiC) using H2PtCl6 as precursor. The reaction was conducted in excess of oxygen. beta-SiC was selected for the study because of its thermal conductivity, mechanical properties, chemical inertness and surface area. The obtained Pt particles over SiC were medium size (average particle diameter of 5 nm for 0.5 wt% Pt). The activity of the Pt-impregnated catalyst over SiC was compared to those obtained in oxidized form over TiO2 and Al2O3 commercial supports (Pt particles very small in size, average particle diameter of 1 nm for 0.5 wt% Pt in both cases). The case of a SiO2 support was also discussed. Those Pt/SiC particles were the most active because of their higher contribution of surface Pt, indicating that partially oxidized surfaces have better activity than those totally oxidized in these conditions. SiC was modified with an acid treatment and thus bigger (average particle diameter of 7 nm for 0.5 wt% Pt) and more active Pt particles were obtained. Durability of the SiC and TiO2 supported catalysts was tested upon 5 cycles and both have shown to be durable and even more active than initially. Exposure to the oxidative reaction mixture activates the catalysts and the effect is more pronounced for the completely oxidized particles. This is due to the surface oxygen chemisorption which activates catalystsi surface.

Enero, 2017 | DOI: 10.1016/j.apcatb.2016.08.042

Titulo: Spark plasma sintering of fine-grained alumina ceramics reinforced with alumina whiskers
Autores: Tamura, Y; Moshtaghioun, BM; Gomez-Garcia, D; Rodriguez, AD
Revista: Ceramis International, 43 (2017) 658-663
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Densification of alumina whisker-reinforced alumina ceramics by spark plasma sintering (SPS) has been investigated with the aim of obtaining a fine-grained microstructure and also studying the effect of whisker addition on the room-temperature mechanical properties. It was found that whisker addition retards slightly the sinterability of alumina by whisker hindering of particle rearrangement. Besides, the internal stress on the alumina matrix particles reduced due to the presence of a whisker network structure of strong rigid boundaries. Nevertheless near fully-dense and fine-grained alumina ceramics with alumina whisker content between 3 wt% and 10 wt% could be obtained under appropriate SPS conditions. The hardness of alumina ceramics with 3 wt% was comparable to that of pure alumina ceramics (similar to 26 GPa) whereas its fracture toughness (5.6 MPa m(1/2)) was higher (4.2 MPa m(1/2)). Crack bridging by well-dispersed whiskers and whiskers pull-out were identified as the main toughening mechanisms.

Enero, 2017 | DOI: 10.1016/j.ceramint.2016.09.210

2016


Titulo: Characterization and Validation of a-Si Magnetron-Sputtered Thin Films as Solid He Targets with High Stability for Nuclear Reactions
Autores: Godinho, V; Ferrer, FJ; Fernandez, B; Caballero-Hernandez, J; Gomez-Camacho, J; Fernandez, A
Revista: ACS Omega, 1 (2016) 1229-1238
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In this work, we present our magnetron sputtering based methodology to produce amorphous silicon coatings with closed porosity, as a strategy to fabricate solid helium targets, in the form of supported or self-supported thin films, for nuclear reactions. We show how by changing the He working pressure it is possible to obtain highly porous homogeneous structures incorporating different He amounts. These porous coatings (a-Si: He) are very reproducible from run to run, and the high He amount incorporated makes them excellent candidates for solid He targets. The possibility of producing self-supported films is illustrated here, and its potential use in inverse kinematics experiments with radioactive beams is shown through the dispersion in forward geometry of a stable Li-6 beam. Also the elastic scattering cross-sections for proton from helium were determined using an a-Si: He coating. The results agree well with the ones reported in the literature. These two examples validate our coatings as good candidates to be used as solid He targets in nuclear reactions. The stability of He inside the coatings, fundamental for its use as solid He targets, was investigated, both over time and after irradiation. The coatings proved to be very stable, and the amount of He inside the pores remains unaltered at least 2 years after deposition and after high irradiation fluence (5 x 10(17) particles/cm(2); with a dose rate of 5 x 10(12) particles/(cm(2) s)).

Noviembre, 2016 | DOI: 10.1021/acsomega.6b00270

Titulo: Tailor-made preparation of Co-C, Co-B, and Co catalytic thin films using magnetron sputtering: insights into structure-composition and activation effects for catalyzed NaBH4 hydrolysis
Autores: Paladini, M; Godinho, V; Arzac, GM; de Haro, MCJ; Beltran, AM; Fernandez, A
Revista: RSC Advances, 6 (2016) 108611-108620
resumen | texto completo


The magnetron sputtering (MS) methodology is a powerful tool for tailor-made fabrication of Co-based thin film catalysts with controlled microstructures and compositions for sodium borohydride (SBH) hydrolysis. In particular, Co-C catalysts were tested in this reaction and compared to Co-B and Co catalyst coatings. The microstructural and chemical analyses by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Rutherford back scattering (RBS) and X-ray photoelectron spectroscopy (XPS) were used to characterize a complete library of thin film catalysts. Pure Co materials were characterized by their nanocrystalline microstructure, and grain refinement was achieved via an increase in the deposition pressure. The incorporation of boron or carbon via co-deposition results in amorphization and dispersion of the active metallic Co phase. The composition can be tuned while keeping a controlled microstructure, and a comparison of activity at 25 degrees C was performed on catalysts deposited on Ni foam substrates. A comparison of the initial activities showed that the Co-B samples were more active than the Co-C samples because of electronic effects. However, a strong activation was found for the Co-C catalysts after the first use. This effect was dependent upon the incorporation of cobalt boride (CoxB) species on the catalysts' surface, as shown by XPS. After the first several uses, the activity of the Co-C samples (values up to 2495 mL min(-1) g(catalyst)(-1)) were as high as that of fresh Co-B, and the surface composition of both the catalysts was similar. This activation was not observed for the pure Co and was very weak for the Co-B catalysts. The use of polymeric (PTFE) substrates (flexible membranes) illustrated the versatility of the methodology to obtain catalytic membranes and allowed for a TEM microstructural analysis at the nanoscale. Catalytic activities at 60 degrees C were as high as 16.7 and 20 L min(-1) g(Co)(-1) for the Co-C and Co-B membranes, respectively. We determined the optimized conditions to increase the catalytic activity of Co-based coatings prepared via magnetron sputtering.

Noviembre, 2016 | DOI: 10.1039/c6ra23171c

Titulo: Enhanced carbon nanotube dispersion in 3YTZP/SWNTs composites and its effect on room temperature mechanical and electrical properties
Autores: Gallardo-Lopez, A; Morales-Rodriguez, A; Vega-Padillo, J; Poyato, R; Munoz, A; Dominguez-Rodriguez, A
Revista: Journal of Alloys and Compounds, 682 (2016) 70-79
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In this work, several modifications of the colloidal processing technique and spark plasma sintering (SPS) to prepare yttria tetragonal zirconia composites (YTZP) with single walled carbon nanotubes (SWNT) have been tested with the aim of eliminating SWNT agglomerates. These modifications include high versus low energy ultrasonic agitation during colloidal processing, lyophilization of the 3YTZP/SWNT slurry and electrical insulation during sintering of the composites. Semi-quantitative microstructural characterization of the carbon nanotube distribution in the sintered composites showed that high energy ultrasonic agitation reduces drastically agglomerate size. Lyophilization of the mixed suspensions avoids SWNT bundle size growth. Combination of both produces an enhanced carbon nanotube network distribution along the grain boundaries (GB) due to the absence of carbon nanotube agglomerates and to a limited SWNT bundle size. This results in an increase of the real SWNT content in the GBs up to nominal SWNT content and therefore an enhanced SWNT efficiency in the composites. The agglomerate-free highly-dispersed composites exhibit a decrease in density together with grain size refinement, a decrease in room temperature hardness, an increase in flexural strength and a most significant increase in room temperature electrical conductivity. Improved SWNT distribution also lowers electrical percolation threshold to a very low level in SWNT ceramic composites, <1 vol% SWNT.

Octubre, 2016 | DOI: 10.1016/j.jallcom.2016.04.262

Titulo: Timing of calcium nitrate addition affects morphology, dispersity and composition of bioactive glass nanoparticles
Autores: Zheng, K; Taccardi, N; Beltran, AM; Sui, BY; Zhou, T; Marthala, VRR; Hartmann, M; Boccaccini, AR
Revista: RSC Advances, 6 (2016) 95101-95111
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Bioactive glass nanoparticles (BGN) are promising materials for a number of biomedical applications. Many parameters related to the synthesis of BGN using sol–gel methods can affect their characteristics. In this study, the influence of timing of calcium nitrate (calcium precursor) addition during processing on BGN characteristics was investigated. The results showed that the addition timing could affect the morphology, dispersity and composition of BGN. With delayed addition of calcium nitrate, larger, more regular and better dispersed BGN could be synthesized while the gap between nominal and actual compositions of BGN was widened. However, the addition timing had no significant influence on structural characteristics, as BGN with different addition-timing of calcium nitrate exhibited similar infrared spectra and amorphous nature. The results also suggested that monodispersed BGN could be synthesized by carefully controlling the addition of calcium nitrate. The synthesized monodispersed BGN could release Si and Ca ions continuously for up to at least 14 days. They also showed in vitro bioactivity and non-cytotoxicity towards rat bone marrow-derived mesenchymal stem cells (rBMSCs). In conclusion, the timing of calcium precursor addition is an essential parameter to be considered when producing BGN which should exhibit monodisperse characteristics for biomedical applications.

Septiembre, 2016 | DOI: 10.1039/C6RA05548F

Titulo: Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen
Autores: Arzac, G. M.; Ramirez-Rico, J.; Gutierrez-Pardo, A.; Jimenez de Haro, M. C.; Hufschmidt, D.; Martinez-Fernandez, J.; Fernandez, A.
Revista: RSC Advances, 6 (2016) 66373-66384
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Catalytic hydrogen combustion was studied with H-2/air mixtures in conditions that simulate the H-2 concentration of the exhaust gases from fuel cells (3-4% v/v H-2 in air). Pt-impregnated monoliths based on porous biomorphic SiC (bio-SiC) substrates were employed for the first time for this reaction. Capillary forces were exploited for the incipient impregnation of supports with H2PtCl6 solutions. Freeze drying permitted us to obtain a homogeneous distribution of the active phase reducing accumulation at the monolith's outer shell. The supports and catalysts were characterized from a structural and thermal point of view. Catalytic tests were performed in a homemade reactor fed with up to 1000 ml min(-1) H-2/air mixtures and a diffusional regime (non-isothermal) was achieved in the selected conditions. Catalyst loading was tested in the range of 0.25-1.5 wt% Pt and 100% conversion was achieved in all cases. Temperatures were recorded at different points of the monoliths during the reaction showing anisotropic thermal behavior for selected bio-SiC substrates. These effects are of interest for heat management applications and were explained in correlation with thermal conductivity measurements performed on the supports. Pt-impregnated monoliths were also tested in less than 100% conversion conditions (1% v/v H-2 in air) and in powder form in kinetic conditions for comparative purposes.

Septiembre, 2016 | DOI: 10.1039/c6ra09127j

Titulo: Colloidal crystals and water: Perspectives on liquid-solid nanoscale phenomena in wet particulate media
Autores: Gallego-Gomez, F; Morales-Florez, V; Morales, M; Blanco, A; Lopez, C
Revista: Advances in Colloid and Interface Science, 234 (2016) 142-160
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Solid colloidal ensembles inherently contain water adsorbed from the ambient moisture. This water, confined in the porous network formed by the building submicron spheres, greatly affects the ensemble properties. Inversely, one can benefit from such influence on collective features to explore the water behavior in such nanoconfinements. Recently, novel approaches have been developed to investigate in-depth where and how water is placed in the nanometric pores of self-assembled colloidal crystals. Here, we summarize these advances, along with new ones, that are linked to general interfacial water phenomena like adsorption, capillary forces, and flow. Water-dependent structural properties of the colloidal crystal give clues to the interplay between nanoconfined water and solid fine particles that determines the behavior of ensembles. We elaborate on how the knowledge gained on water in colloidal crystals provides new opportunities for multidisciplinary study of interfacial and nanoconfined liquids and their essential role in the physics of utmost important systems such as particulate media.

Agosto, 2016 | DOI: 10.1016/j.cis.2016.05.004

Titulo: Flue gas adsorption by single-wall carbon nanotubes: A Monte Carlo study
Autores: Romero-Hermida, MI; Romero-Enrique, JM; Morales-Florez, V; Esquivias, L
Revista: Journal of Chemical Physics, 145 (2016) 074701
resumen | texto completo


Adsorption of flue gases by single-wall carbon nanotubes (SWCNT) has been studied by means ofMonte Carlo simulations. The flue gas is modeled as a ternary mixture of N2, CO2, and O2, emulating realistic compositions of the emissions from power plants. The adsorbed flue gas is in equilibrium with a bulk gas characterized by temperature T, pressure p, and mixture composition. We have considered different SWCNTs with different chiralities and diameters in a range between 7 and 20 Å. Our results show that the CO2 adsorption properties depend mainly on the bulk flue gas thermodynamic conditions and the SWCNT diameter. Narrow SWCNTs with diameter around 7 Å show high CO2 adsorptioncapacity and selectivity, but they decrease abruptly as the SWCNT diameter is increased. For wideSWCNT, CO2 adsorption capacity and selectivity, much smaller in value than for the narrow case, decrease mildly with the SWCNT diameter. In the intermediate range of SWCNT diameters, the CO2adsorption properties may show a peculiar behavior, which depend strongly on the bulk flue gas conditions. Thus, for high bulk CO2 concentrations and low temperatures, the CO2 adsorption capacity remains high in a wide range of SWCNT diameters, although the corresponding selectivity is moderate. We correlate these findings with the microscopic structure of the adsorbed gas inside the SWCNTs.

Agosto, 2016 | DOI: 10.1063/1.4961023

Titulo: Effects of electronic and nuclear stopping power on disorder induced in GaN under swift heavy ion irradiation
Autores: Moisy, F; Sall, M; Grygiel, C; Balanzat, E; Boisserie, M; Lacroix, B; Simon, P; Monnet, I
Revista: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 381 (2016) 39-44
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Wurtzite GaN epilayers, grown on the c-plane of sapphire substrate, have been irradiated with swift heavy ions at different energies and fluences, and thereafter studied by Raman scattering spectroscopy, UV–visible spectroscopy and transmission electron microscopy. Raman spectra show strong structural modifications in the GaN layer. Indeed, in addition to the broadening of the allowed modes, a large continuum and three new modes at approximately 200 cm−1, 300 cm−1 and 670 cm−1 appear after irradiation attributed to disorder-activated Raman scattering. In this case, spectra are driven by the phonon density of states of the material due to the loss of translation symmetry of the lattice induced by defects. It was shown qualitatively that both electronic excitations and elastic collisions play an important role in the disorder induced by irradiation. UV–visible spectra reveal an absorption band at 2.8 eV which is linked to the new mode at 300 cm−1observed in irradiated Raman spectra and comes from Ga-vacancies. These color centers are produced by elastic collisions (without any visible effect of electronic excitations).

Agosto, 2016 | DOI: 10.1016/j.nimb.2016.05.024

Titulo: Electrical properties of reduced 3YTZP ceramics consolidated by spark plasma sintering
Autores: Poyato, R; Macias-Delgadoa, J; Garcia-Valenzuela, A; Gonzalez-Romero, RL; Munoz, A; Dominguez-Rodriguez, A
Revista: Ceramics International, 42 (2016) 6713-6719
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3 mol% Yttria doped zirconia ceramics were consolidated by spark plasma sintering (SPS) at two sintering temperatures with the aim of achieving two different reduction levels. Microstructural characterization of the ceramics was performed by scanning electron microscopy (SEM). Electrical properties were investigated by means of impedance spectroscopy from room temperature up to 500 degrees C. The two ceramics presented a remarkably different electrical behavior. The effect of the extra electrons introduced by reduction during SPS on both the bulk and the grain boundary conductivity was analyzed and discussed.

Mayo, 2016 | DOI: 10.1016/j.ceramint.2016.01.040

Titulo: Obtention of Li3xLa2/3−xTiO3 ceramics from amorphous nanopowders by spark plasma sintering
Autores: Leyet, Y.; Guerrero, F.; Anglada-Rivera, J.; Martinez, I.; Amorin, H.; Romaguera-Barcelay, Y.; Poyato, R.; Gallardo-Lopez, A.
Revista: Ferroelectrics, 498 (2016) 62-66
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In this work, Li3xLa2/3-xTiO3 powder with nominal lithium content (x = 0.08) was synthesized by mechano synthesis method. Spark plasma sintering (SPS) was employed to prepare lithium lanthanum titanium oxide solid-state ceramic. The techniques of X-ray diffraction, high resolution scanning electron microscopy, and Raman spectroscopy were used to characterize the composition and microstructure of samples. The results showed that fine-grained ceramics with relative density of 95.5% were obtained by sintering the oxide powders at 1100 degrees C for only 5min.

Mayo, 2016 | DOI: 10.1080/00150193.2016.1167538

Titulo: Structure, electrochemical properties and functionalization of amorphous CN films deposited by femtosecond pulsed laser ablation
Autores: Maddi, C; Bourquard, F; Tite, T; Loir, AS; Donnet, C; Garrelie, F; Barnier, V; Wolski, K; Fortgang, P; Zehani, N; Braiek, M; Lagarde, F; Chaix, C; Jaffrezic-Renault, N; Rojas, TC; Sanchez-Lopez, JC
Revista: Diamond and Related Materials,65 (2016) 17-25
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Amorphous carbon nitride (a-C:N) material has attracted much attention in research and development Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 10 Pa) and DC bias (0 to -350 V) were used in order to explore a wide range of nitrogen content into the films. The structure and chemical composition of the films have been studied by using Raman spectroscopy, electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 21 at%. Nitrogen content increase induces a higher sp(2) character of the film. However DC bias has been found to increase the film structural disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurements, investigated by cyclic voltammetry (CV), demonstrated that a-C:N film with moderate nitrogen content (10 at.%) exhibited the best behavior, in terms of reversibility and electron transfer kinetics. Electrochemical grafting from diazonium salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene molecules. Such a film may be a promising electrode material in electrochemical detection of electroactive pollutants on bare film, and of biopathogen molecules after surface grafting of the specific affinity receptor. 

Abril, 2016 | DOI: 10.1016/j.diamond.2016.01.001

Titulo: Nitrogen Nanobubbles in a-SiOxNy Coatings: Evaluation of Its Physical Properties and Chemical Bonding State by Spatially Resolved Electron Energy-Loss Spectroscopy
Autores: Lacroix, B.; Godinho, V.; Fernández, A.
Revista: Journal of Physical Chemistry C, 120 (2016) 5651-5658
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Nanoporous silicon-based materials with closed porosity filled with the sputtering gas have been recently developed by magnetron sputtering. In this work the physical properties (density and pressure) of molecular nitrogen inside closed pores in a SiOxNy coating are investigated for the first time using spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope. The paper offers a detailed methodology to record and process multiple EELS spectrum images (SIs) acquired at different energy ranges and with different dwell times. An adequate extraction and quantification of the N–K edge contribution due to the molecular nitrogen inside nanopores is demonstrated. Core-loss intensity and N chemical bond state were evaluated to retrieve 2D maps revealing the stable high density of molecular nitrogen (from 40 to 70 at./nm3) in nanopores of different size (20–11 nm). This work provides new insights into the quantification of molecular N2 trapped in porous nitride matrices that could also be applied to other systems.

Marzo, 2016 | DOI: 10.1021/acs.jpcc.5b09036

Titulo: Intensification of hydrogen production by methanol steam reforming
Autores: Sanz, O; Velasco, I; Perez-Miqueo, I; Poyato, R; Odriozola, JA; Montes, M
Revista: International Journal Hydrogen Energy, 41 (2016) 5250-5259
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This paper studies the methanol steam reforming intensification to enhance the hydrogen production in a multi-channel block type micro-reformer. The effects of operating parameters such as reforming temperature, space velocity and catalyst layer thickness on reforming performance are investigated. For optimized design and operating conditions, the 8 cm(3) reformer unit produced 170 LH2/h containing on dry basis 75.0% H-2, 23.5% CO2, 0.06% CH3OH and 1.44% CO at 648 K allowing the production of 218-255 Win a commercial PEMFC with 80% hydrogen utilization. This study shows that high methanol conversion can be achieved with high Pd/ZnO catalyst loading at 648 K with very low CO content (<1.5%) in the outlet stream. 

Marzo, 2016 | DOI: 10.1016/j.ijhydene.2016.01.084

Titulo: Determination of the Anisotropic Elastic Properties of Rocksalt Ge2Sb2Te5 by XRD, Residual Stress, and DFT
Autores: Cecchini, R; Kohary, K; Fernandez, A; Cabibbo, M; Marmier, A
Revista: Journal of Physical Chemistry C, 120 (2016) 5624-5629
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The chalcogenide material Ge2Sb2Te5 is the prototype phase-change material, with widespread applications for optical media and random access memory. However, the full set of its independent elastic properties has not yet been published. In this study, we determine the elastic constants of the rocksalt Ge2Sb2Te5, experimentally by X-ray diffraction (XRD) and residual stress and computationally by density functional theory (DFT). The stiffnesses (XRD-stress/DFT) in GPa are C-11 = 41/58, C-12 = 7/8, and C-44 = 8/12, and the Zener ratio is 0.46/0.48. These values are important to understand the effect of elastic distortions and nonmelting processes on the performances of increasingly small phase change data bits.

Febrero, 2016 | DOI: 10.1021/acs.jpcc.5b09867

Titulo: Investigation of a Pt containing washcoat on SiC foam for hydrogen combustion applications
Autores: Fernandez, A; Arzac, GM; Vogt, UF; Hosoglu, F; Borgschulte, A; de Haro, MCJ; Montes, O; Zuttel, A
Revista: Applied Catalysis B: Environmental, 180 (2016) 336-343
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A commercial Pt based washcoat, used for catalytic methane combustion, was studied supported on a commercial SiC foam as catalytic material (Pt/SiC) for catalytic hydrogen combustion (CHC). Structural and chemical characterization was performed using Electron Microscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The reaction was monitored following water concentration by Fourier Transform Infrared spectra (FTIR). The FTIR method was compared with H2 detection by Gas Cromatography (GC) and has shown to be adequate to study the kinetics of the CHC reaction in steady state under our experimental conditions (very lean 1% (v/v) H2/air mixtures). The catalyst is composed of 5–20 nm disperse Pt nanoparticles decorating a mixture of high surface area Al2O3 and small amounts of ceria supported on the SiC foam which also contains alumina as binder. The Pt/SiC catalytic material has demonstrated to be active enough to start up the reaction in a few seconds at room temperature. The material has been able to convert at least 18.5 Lhydrogen min−1 gPt−1 at room temperature in conditions of excess of catalyst. The Pt/SiC material was studied after use using XPS and no significant changes on Pt oxidation states were found. The material was characterized from a kinetic point of view. From the conversion-temperature plot a T50(temperature for 50% conversion) of 34 °C was obtained. Activation energy measured in our conditions was 35 ± 1 kJ mol−1.

Enero, 2016 | DOI: 10.1016/j.apcatb.2015.06.040

Titulo: High temperature internal friction in a Ti-46Al-1Mo-0.2Si intermetallic, comparison with creep behaviour
Autores: Castillo-Rodriguez, M; No, ML; Jimenez, JA; Ruano, OA; Juan, JS
Revista: Acta Materialia, 103 (2016) 46-56
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Advanced gamma-TiAl based intermetallics Mo-bearing have been developed to obtain the fine-grained microstructure required for superplastic deformation to be used during further processing. In the present work we have studied an alloy of Ti-46.8Al-1Mo-0.2Si (at%) with two different microstructures, ascast material with a coarse grain size above 300 mu m, and the hot extruded material exhibiting a grain size smaller than 20 mu m. We have used a mechanical spectrometer especially developed for high temperature internal friction measurements to study the defect mobility processes taking place at high temperature. The internal friction spectra at different frequencies has been studied and analyzed up to 1360 K in order to characterize the relaxation processes appearing inthis temperature range. A relaxation peak, with a maximum in between 900 K and 1080 K, depending on the oscillating frequency, has been attributed to Ti-atoms diffusion by the stress-induced reorientation of Al-V-Ti-Al elastic dipoles. The high temperature background in both microstructural states, as-cast and extruded, has been analyzed, measuring the apparent activation parameters, in particular the apparent energies of E-cast(IF) = 4.4 +/- 0.05 eV and E-ext(IF) = 4.75 +/- 0.05 eV respectively. These results have been compared to those obtained on the same materials by creep deformation. We may conclude that the activation parameters obtained by internal friction analysis, are consistent with the ones measured by creep. Furthermore, the analysis of the high temperaturebackground allows establish the difference on creep resistance for both microstructural states. 

Enero, 2016 | DOI: 10.1016/j.actamat.2015.09.052

Titulo: High-Temperature Deformation Mechanisms in Monolithic 3YTZP and 3YTZP Containing Single-Walled Carbon Nanotubes
Autores: Castillo-Rodriguez, M; Munoz, A; Dominguez-Rodriguez, A
Revista: Journal of The American Ceramic Society, 99 (2016) 286-292
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Monolithic 3YTZP and 3YTZP containing 2.5 vol% of single-walled carbon nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250 degrees C. Microstructural characterization of the as-fabricated 3YTZP/SWCNTs composite shows a homogeneous CNTs dispersion throughout the ceramic matrix. The specimens have been crept at temperatures between 1100 degrees C and 1200 degrees C in order to investigate the influence of the SWCNTs addition on high-temperature deformation mechanisms in zirconia. Slightly higher stress exponent values are found for 3YTZP/SWCNTs nanocomposites (n similar to 2.5) compared to monolithic 3YTZP (n similar to 2.0). However, the activation energy in 3YTZP (Q=715 +/- 60kJ/mol) experiences a reduction of about 25% by the addition of 2.5vol% of SWCNTs (Q=540 +/- 40kJ/mol). Scanning electron microscopy studies indicate that there is no microstructural evolution in crept specimens, and Raman spectroscopy measurements show that SWCNTs preserved their integrity during the creep tests. All these results seem to indicate that the high-temperature deformation mechanism is grain-boundary sliding (GBS) accommodated by grain-boundary diffusion, which is influenced by yttrium segregation and the presence of SWCNTs at the grain boundary.

Enero, 2016 | DOI: 10.1111/jace.13974

Titulo: Disorder-order phase transformation in a fluorite-related oxide thin film: In-situ X-ray diffraction and modelling of the residual stress effects
Autores: Gaboriaud, RJ; Paumier, F; Lacroix, B
Revista: Thin Solid Films, 601 (2016) 84-88
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This work is focused on the transformation of the disordered fluorite cubic-F phase to the ordered cubic-C bixbyite phase, induced by isothermal annealing as a function of the residual stresses resulting from different concentrations of microstructural defects in the yttrium oxide, Y2O3. 

This transformation was studied using in-situ X-ray diffraction and was modelled using Kolmogorov-Johnson-Mehl-Avrami (KJMA) analysis. The degree of the disorder of the oxygen network was associated with the residual stress, which was a key parameter for the stability and the kinetics of the transition of the different phases that were present in the thin oxide film. When the degree of disorder/residual stress level is high, this transition, which occurs at a rather low temperature (300 degrees C), is interpreted as a transformation of phases that occurs by a complete recrystallization via the nucleation and growth of a new cubic-C structure. Using the KJMA model, we determined the activation energy of the transformation process, which indicates that this transition occurs via a one-dimensional diffusion process. Thus, we present the analysis and modelling of the stress state. When the disorder/residual stress level was low, a transition to the quasi-perfect ordered cubic-C structure of the yttrium oxide appeared at a rather high temperature (800 degrees C), which is interpreted as a classic recovery mechanism of the cubic-C structure.

Enero, 2016 | DOI: 10.1016/j.tsf.2015.08.030

2015


Titulo: High-temperature deformation of fully-dense fine-grained boron carbide ceramics: Experimental facts and modeling
Autores: Moshtaghioun, BM; Garcia, DG; Rodriguez, AD
Revista: Materials & Design, 88 (2015) 287-293
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Boron carbide ceramics are the hardest material in Nature after diamond and the cubic phase of boron nitride. Due to this fact, their room-temperature fracture properties are the object of intense research. Paradoxically, high-temperature deformation is essentially unknown, because very high temperatures and stresses are necessarily required and high-quality specimens have not been available until recently. In this paper, the high-temperature compressive creep of fine-grained boron carbide polycrystals is reported. The breakdown of the classical power-law for high-temperature plasticity in ceramics is found. An analytical model is proposed. The model assumes that deformation is produced by dislocation glide. However, since the formation of twins is energetically favorable in this material and they act as strong barriers for dislocation glide, their motion turns to become progressively more difficult as elongation proceeds. The combination of increasing twin barriers and dislocations in mutual interaction is proposed to be the mechanism for high-temperature plasticity in this material. The model is validated with the experimental results. Final elongation of boron carbide specimens is reported to be over 100%, although this material cannot be described as a superplastic ceramic. 

Noviembre, 2015 | DOI: 10.1016/j.matdes.2015.08.134

Titulo: Microstructure and impedance spectroscopy of 3YTZP/SWNT ceramic nanocomposites
Autores: Poyato, R; Macias-Delgado, J; Gallardo-Lopez, A; Munoz, A; Dominguez-Rodriguez, A
Revista: Ceramics International, 41 (2015) 12861-12868
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This work provides new insights on microstructure and electrical properties of 3 mol% Y2O3-ZrO2 (3YTZP) composites with 0.5, 1, and 1.5 vol% single walled carbon nanotubes (SWNTs). The composites were spark plasma sintered (SPS) in identical conditions at 1250 degrees C from powder prepared by two different processing routines, with the aim of optimizing the SWNTs dispersion throughout the ceramic matrix. High densification and submicrometric grain size were achieved in all the composites. Electrical properties of the composites were characterized in a wide temperature range, and modeling of the impedance properties was approached by means of an equivalent circuit that allows separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles. Effects of the homogeneous distribution of SWNTs at the ceramic grain boundaries on the crystalline phases, percolation threshold, total conductivity and evolution of junctions' resistivity with temperature were analyzed and discussed. 

Noviembre, 2015 | DOI: 10.1016/j.ceramint.2015.06.123

Titulo: Atomic scale characterization of SiO2/4H-SiC interfaces in MOSFETs devices
Autores: Beltran, AM; Duguay, S; Strenger, C; Bauer, AJ; Cristiano, F; Schamm-Chardon, S
Revista: Solid State Communications, 221 (2015) 28-32
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The breakthrough of 4H-SiC MOSFETs is stemmed mainly due to the mobility degradation in their channel in spite of the good physical intrinsic material properties. Here, two different n-channel 4H-SiC MOSFETs are characterized in order to analyze the elemental composition at the SiC/SiO2 interface and its relationship to their electrical properties. Elemental distribution analyses performed by EELS reveal the existence of a transition layer between the SiC and the SiO2 regions of the same width for both MOSFETs despite a factor of nearly two between their electron mobility. Additional 3D compositional mapping by atom probe tomography corroborates these results, particularly the absence of an anomalous carbon distribution around the SiC/SiO2interface.

Octubre, 2015 | DOI: 10.1016/j.ssc.2015.08.017

Titulo: Full solution processed mesostructured optical resonators integrating colloidal semiconductor quantum dots
Autores: Calvo, ME; Hidalgo, N; Schierholz, R; Kovacs, A; Fernandez, A; Bellino, MG; Soler-Illia, GJAA; Miguez, H
Revista: Nanoscale, 7 (2015) 16583-16589
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Herein we show a solution based synthetic pathway to obtain a resonant optical cavity with embedded colloidal semiconductor quantum dots (CSQDs). The optical cavity pore network, surrounded by two dense Bragg mirrors, was designed ad hoc to selectively host the quantum dots, while uncontrolled infiltration of those in the rest of the layered structure was prevented. Coupling between the optical resonant modes of the host and the natural emission of the embedded nanoparticles gives rise to the fine tuning of the luminescence spectrum extracted from the ensemble. Our approach overcomes, without the need for an encapsulating agent and exclusively by solution processing, the difficulties that arise from the low thermal and chemical stability of the CSQDs. It opens the route to achieving precise control over their location and hence over the spectral properties of light emitted by these widely employed nanomaterials. Furthermore, as the porosity of the cavity is preserved after infiltration, the system remains responsive to environmental changes, which provides an added value to the proposed structure.

Septiembre, 2015 | DOI: 10.1039/C5NR03977K

Titulo: Role of Y in the oxidation resistance of CrAlYN coatings
Autores: Dominguez-Meister, S; El Mrabet, S; Escobar-Galindo, R; Mariscal, A; de Haro, CJ; Justo, A; Brizuela, M; Rojas, TC; Sanchez-Lopez, JC
Revista: Applied Surface Science, 363 (2015) 504-511
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CrAlYN coatings with different aluminum (4–12 at.%) and yttrium (2–5 at.%) contents are deposited by d.c. reactive magnetron sputtering on silicon and M2 steel substrates using metallic targets and Ar/N2 mixtures. The influence of the nanostructure and chemical elemental distribution on the oxidation resistance after heating in air at 1000 °C is studied by means of cross-sectional scanning electron microscopy (X-SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GD-OES). The sequential exposure to the metallic targets during the synthesis leads to a multilayer structure where concentration of metallic elements (Cr, Al and Y) is changing periodically. A good oxidation resistance is observed when Al- and Y-rich regions are separated by well-defined CrN layers, maintaining crystalline coherence along the columnar structure. This protective behavior is independent of the type of substrate and corresponds to the formation of a thin mixed (Al, Cr)-oxide scale that protects the film underneath. The GD-OES and XRD analysis have demonstrated that Y acts as a reactive element, blocking the Fe and C atoms diffusion from the steel and favoring higher Al/Cr ratio in the passivation layer after heating. The coating with Y content around 4 at.% exhibited the best performance with a thinner oxide scale, a delay in the CrN decomposition and transformation to Cr2N, and a more effective Fe and C blocking.

Septiembre, 2015 | DOI: 10.1016/j.apsusc.2015.06.099

Titulo: Preparation of phase pure, dense fine grained ceramics by conventional and spark plasma sintering of La-substituted BiFeO3 nanoparticles
Autores: Perejon, Antonio; Sanchez-Jimenez, Pedro E.; Poyato, Rosalia; Maso, Nahum; West, Anthony R.; Criado, Jose M.; Perez-Maqueda, Luis A.
Revista: Journal of the European Ceramic Society, 35 (2015) 2283-2293
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High density ceramics of the system Bi1-xLaxFeO3, 0 <= x <= 0.15, have been prepared starting from nanoparticles obtained by mechanosynthesis. The ceramics have been sintered conventionally at 850 degrees C and by spark plasma sintering (SPS). Sintering conditions have been optimized to obtain single phase ceramics, and the microstructure of the ceramics has been compared. Ceramics prepared conventionally present grain sizes from 5 mu m to less than 1 mu m, whereas grain sizes by SPS are in the range from 50 to 100 nm, which demonstrates that it is possible to obtain nanostructured ceramics of La-substituted BiFeO3 using mechanosynthesis followed by SPS at low temperature (625-650 degrees C). The as-prepared SPS ceramics show low resistivity, indicating some reduction in the samples. However, after an oxidative anneal in air, ceramics are highly insulating at room temperature and electrically homogeneous. The high quality of the ceramics has also been demonstrated by XRD, EDX, Raman and DSC.

Julio, 2015 | DOI: 10.1016/j.jeurceramsoc.2015.01.030

Titulo: Mechanical and electrical properties of low SWNT content 3YTZP composites
Autores: Poyato, R; Macias-Delgado, J; Garcia-Valenzuela, A; Gallardo-Lopez, A; Morales-Rodriguez, A; Munoz, A; Dominguez-Rodriguez, A
Revista: Journal of the European Ceramic Society, 35 (2015) 2351-2359
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Fully dense 3 mol% Y2O3-ZrO2 (3YTZP) composites with low single wall carbon nanotube content (0.5, 1 and 1.5 vol% SWNT) were prepared by colloidal processing and spark plasma sintering (SPS). SWNT were distributed at ceramic grain boundaries and also into agglomerates. Characterization of SWNT agglomerates indicated that increase in SWNT vol% does not imply an increase in agglomeration. SWNT agglomerate density was related to the evolution of hardness and fracture toughness with SWNT vol%. Electrical properties of the composites were characterized in a wide temperature range, and percolation threshold was estimated. A model allowing separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles was proposed for composites with a percolating SWNT network.

Julio, 2015 | DOI: 10.1016/j.jeurceramsoc.2015.02.022

Titulo: Direct observation of doping incorporation pathways in self-catalytic GaMnAs
Autores: Kasama, T.; Thuvander, M.; Siusys, A.; Gontard, L. C.; Kovacs, A.; Yazdi, S.; Duchamp, M.; Gustafsson, A.; Dunin-Borkowski, R. E.; Sadowski, J.
Revista: Journal of Applied Physics, 118 (2015) 054302
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Doping mechanisms of Mn in GaAs nanowires (NWs) that have been grown self-catalytically at 600 °C by molecular beam epitaxy (MBE) are investigated using advanced electron microscopy techniques and atom probe tomography. Mn is found to be incorporated primarily in the form of non-magnetic tetragonal Ga0.82Mn0.18 nanocrystals in Ga catalyst droplets at the ends of the NWs, while trace amounts of Mn (22 ± 4 at. ppm) are also distributed randomly in the NW bodies without forming clusters or precipitates. The nanocrystals are likely to form after switching off the reaction in the MBE chamber, since they are partially embedded in neck regions of the NWs. The Ga0.82Mn0.18 nanocrystals and the low Mn concentration in the NW bodies are insufficient to induce a ferromagnetic phase transition, suggesting that it is difficult to have high Mn contents in GaAs even in 1-D NW growth via the vapor-liquid-solid process.

Julio, 2015 | DOI: 10.1063/1.4927623

Titulo: Fabrication of Optical Multi layer Devices from Porous Silicon Coatings with Closed Porosity by Magnetron Sputtering
Autores: Caballero-Hernandez, Jaime; Godinho, Vanda; Lacroix, Bertrand; Jimenez de Haro, Maria C.; Jamon, Damien; Fernandez, Asuncion
Revista: ACS Applied Materials & Interfaces, 7 (2015) 13880-13897
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The fabrication of single-material photonic-multilayer devices is explored using a new methodology to produce porous silicon layers by magnetron sputtering. Our bottom-up methodology produces highly stable amorphous porous silicon films with a controlled refractive index using magnetron sputtering and incorporating a large amount of deposition gas inside the closed pores. The influence of the substrate bias on the formation of the closed porosity was explored here for the first time when He was used as the deposition gas. We successfully simulated, designed, and characterized Bragg reflectors and an optical microcavity that integrates these porous layers. The sharp interfaces between the dense and porous layers combined with the adequate control of the refractive index and thickness allowed for excellent agreement between the simulation and the experiments. The versatility of the magnetron sputtering technique allowed for the preparation of these structures for a wide range of substrates such as polymers while also taking advantage of the oblique angle deposition to prepare Bragg reflectors with a controlled lateral gradient in the stop band wavelengths.

Junio, 2015 | DOI: 10.1021/acsami.5b02356

Titulo: Removing the effects of the "dark matter" in tomography
Autores: Gontard, Lionel C.
Revista: Ultramicroscopy, 154 (2015) 64-72
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Electron tomography (ET) using different imaging modes has been progressively consolidating its position as a key tool in materials science. The fidelity of a tomographic reconstruction, or tomogram, is affected by several experimental factors. Most often, an unrealistic cloud of intensity that does not correspond to a real material phase of the specimen ("dark matter") blurs the tomograms and enhances artefacts arising from the missing wedge (MW). Here we show that by simple preprocessing of the background level of any tomographic tilt series, it is possible to minimise the negative effects of that "dark matter". Iterative reconstruction algorithms converge better, leading to tomograms with fewer streaking artefacts from the MW, more contrast, and increased accuracy. The conclusions are valid irrespective of the imaging mode used, and the methodology improves the segmentation and visualisation of tomograms of both crystalline and amorphous materials. We show examples of HAADF STEM and BF TEM tomography.

Junio, 2015 | DOI: 10.1016/j.ultramic.2015.03.017

Titulo: Island-type growth of Au–Pt heterodimers: direct visualization of misfit dislocations and strain-relief mechanisms
Autores: Garcia-Negrete, CA; Knappett, BR; Schmidt, FP; Rojas, TC; Wheatley, AEH; Hofer, F; Fernandez, A
Revista: RSC Advances, 5 (2015) 55262-55268
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Structural and analytical characterization related to the formation mechanism of Au–Pt heterodimers from polyhedral Pt nanocrystals is reported. The observation of specific lattice strain effects and the emergence of misfit dislocations point to the relevance of the Stranski–Krastanov growth mode as a means of explaining the previously reported dimerisation reaction between Au and Pt. Two size-dependent strain relief mechanisms were identified. For dimers grown from 4.7 nm seeds, the mechanism is related to bulk lattice strain accumulation at {111} planes along with lattice relaxation effects on other crystalline planes. However, for dimers grown from 11.2 nm seed sizes, the formation of misfit dislocations proved to be a highly efficient mechanism by which to release interface mismatch strain. Nanoscale chemical mapping at Au–Pt interfaces also revealed Au–Pt alloying to be unlikely under the mild temperature conditions employed in this work for Au–Pt heterodimer synthesis.

Mayo, 2015 | DOI: 10.1039/C5RA09808D

Titulo: STEM-in-SEM high resolution imaging of gold nanoparticles and bivalve tissues in bioaccumulation experiments
Autores: C.A. García-Negrete; M.C. Jiménez de Haro; J. Blasco; M. Soto; A. Fernández
Revista: Analyst, 140 (2015) 3082-3089
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The methodology termed scanning transmission electron microscopy in scanning electron microscopy (STEM-in-SEM) has been used in this work to study the uptake of citrate stabilized gold nanoparticles (AuNPs) (average particle sizes of 23.5 ± 4.0 nm) into tissue samples uponin vitro exposure of the dissected gills of the Ruditapes philippinarum marine bivalve to the nanoparticle suspensions. The STEM-in-SEM methodology has been optimized for achieving optimum resolution under SEM low voltage operating conditions (20–30 kV). Based on scanning microscope assessments and resolution testing (SMART), resolutions well below 10 nm were appropriately achieved by working at magnifications over 100k×, with experimental sample thickness between 300 and 200 nm. These relatively thick slices appear to be stable under the beam and help avoid NP displacement during cutting. We herein show that both localizing of the internalized nanoparticles and imaging of ultrastructural disturbances in gill tissues are strongly accessible due to the improved resolution, even at sample thicknesses higher than those normally employed in standard TEM techniques at higher voltages. Ultrastructural imaging of bio-nano features in bioaccumulation experiments have been demonstrated in this study.

Abril, 2015 | DOI: 10.1039/C4AN01643B

Titulo: Self-lubricity of WSex nanocomposite coatings
Autores: S. Dominguez-Meister; M. Conte; A. Igartua; T.C. Rojas; J.C. Sánchez-López
Revista: ACS Applied Materials & Interfaces, 7 (2015) 7979-7986
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Transition metal chalcogenides with lamellar structure are known for their use in tribological applications although limited to vacuum due to their easy degradation in the presence of oxygen and/or moisture. Here we present a tailored WSex coating with low friction (0.07) and low wear rates (3 × 10–7 mm3 Nm–1) even in ambient air. To understand the low friction behavior and lower chemical reactivity a tribological study is carried out in a high-vacuum tribometer under variable pressure (atmospheric pressure to 1 × 10–8 mbar). A detailed investigation of the film nanostructure and composition by advanced transmission electron microscopy techniques with nanoscale resolution determined that the topmost layer is formed by nanocrystals of WSe2 embedded in an amorphous matrix richer in W, a-W(Se). After the friction test, an increased crystalline order and orientation of WSe2 lamellas along the sliding direction were observed in the interfacial region. On the basis of high angle annular dark field, scanning transmission electron microscopy, and energy dispersive X-ray analysis, the release of W atoms from the interstitial basal planes of the a-W(Se) phase is proposed. These W atoms reaching the surface, play a sacrificial role preventing the lubricant WSe2 phase from oxidation. The increase of the WSe2 crystalline order and the buffer effect of W capturing oxygen atoms would explain the enhanced chemical and tribological response of this designed nanocomposite material.

Marzo, 2015 | DOI: 10.1021/am508939s

Titulo: Hydration and carbolenation reactions of calcium oxide by weathering: Kinetics and changes in the nanostructure
Autores: Morales-Florez, V; Santos, A; Romero-Hermida, I; Esquivias, L
Revista: Chemical Engineering Journal, 265 (2015) 194-200
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The weathering reactions of hydration and carbonation of nanostructured calcium oxide with atmospheric moisture and carbon dioxide have been characterized. This work is the first-to-date combined kinetic and nanostructural research on CaO oriented to two key processes for different systems, i.e. hardening of construction materials and carbon mineral sequestration. The evolution of the precipitated crystalline phases was monitored by X-ray diffraction and thermogravimetry, along with structural characterization by nitrogen physisorption, electron microscopy and small-angle scattering. Complete hydration of the samples was always found prior to the onset of carbon sequestration, which depended on the nanostructure of the samples. Hence, carbonation started after 300 h of weathering for samples with a specific surface area of 40 m(2)/g, whereas carbonation of the samples with 20 m(2)/g occurred after 550 h. Full carbonation from atmospheric CO2 (100% efficiency) was obtained in all cases. This combined research was completed by developing an empirical description of the weathering reactions in terms of a two-process Random Pore Model. Finally, this work aimed to determine the role of the nanostructure of samples based on industrial wastes as one of the most important factors for developing efficient carbon sequestration technologies.

Marzo, 2015 | DOI: 10.1016/j.cej.2014.12.062

Titulo: Hydrogen production through sodium borohydride ethanolysis
Autores: Arzac, GM; Fernandez, A
Revista: International Journal of Hydrogen Energy, 40 (2015) 5326-5332
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In this work, sodium borohydride (SB) ethanolysis was explored for the first time as a method to generate hydrogen for Polymer Exchange Membrane Fuel Cells. Ethanolysis by-product was characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, and Nuclear Magnetic Resonance. Metal and acid catalysts were tested. RuCl3 center dot 3H(2)O was the best metal catalyst. Acetic acid was selected for the study because of its effectiveness, low cost and relative greenness. The maximum gravimetric hydrogen density obtained was 2.1% wt. The addition of water produces an increase in hydrogen generation rate and a decrease in conversion. The use of ethanol-methanol mixtures produces an increase in reaction rates in absence of catalyst. As a proof of concept the reaction was performed in a small reactor which operates by the addition of ethanolic acetic acid solutions to solid SB (in the form of granules). The reactor produces stable and constant hydrogen generation in the range of 20-80 ml min(-1) during 1 h at constant temperature (around 27-35 degrees.

Marzo, 2015 | DOI: 10.1016/j.ijhydene.2015.01.115

Titulo: High N-content a-C:N films elaborated by femtosecond PLD with plasma assistance
Autores: Maddi, C; Donnet, C; Loir, AS; Tite, T; Barnier, V; Rojas, TC; Sanchez-Lopez, JC; Wolski, K; Garrelie, F
Revista: Applied Surface Science, 332 (2015) 346-353
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Amorphous carbon nitride (a-C:N) thin films are a interesting class of carbon-based electrode materials. Therefore, synthesis and characterization of these materials have found lot of interest in environmental analytical microsystems. Herein, we report the nitrogen-doped amorphous carbon thin film elaboration by femtosecond pulsed laser deposition (fs-PLD) both with and without a plasma assistance. The chemical composition and atomic bonding configuration of the films were investigated by multi-wavelength (MW) Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The highest nitrogen content, 28 at.%, was obtained with plasma assistance. The I(D)/I(G) ratio and the G peak position increased as a function of nitrogen concentration, whereas the dispersion and full width at half maximum (FWHM) of G peak decreased. This indicates more ordered graphitic like structures in the films both in terms of topological and structural, depending on the nitrogen content. EELS investigations were correlated with MW Raman results. The interpretation of XPS spectra of carbon nitride films remains a challenge. Plasma assisted PLD in the femtosecond regime led to a significant high nitrogen concentration, which is highlighted on the basis of collisional processes in the carbon plasma plume interacting with the nitrogen plasma.

Febrero, 2015 | DOI: 10.1016/j.apsusc.2015.01.123

Titulo: Transmission electron microscopy of thiol-capped Au clusters on C: Structure and electron irradiation effects
Autores: Lionel C. Gontard, Rafal E. Dunin-Borkowski
Revista: Micron
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High-resolution transmission electron microscopy is used to study interactions between thiol-capped Au clusters and amorphous C support films. The morphologies of the clusters are found to depend both on their size and on the local structure of the underlying C. When the C is amorphous, larger Au clusters are crystalline, while smaller clusters are typically disordered. When the C is graphitic, the Au particles adopt either elongated shapes that maximize their contact with the edge of the C film or planar arrays when they contain few Au atoms. We demonstrate the influence of electron beam irradiation on the structure, shape and stability of the Au clusters, as well as on the formation of holes bounded by terraces of graphitic lamellae in the underlying C.

Febrero, 2015 | DOI: 10.1016/j.micron.2014.12.001

Titulo: Ultra-fast and energy-efficient sintering of ceramics by electric current concentration
Autores: Zapata-Solvas, E; Gomez-Garcia, D; Dominguez-Rodriguez, A; Todd, RI
Revista: Scientific Reports, 5 (2015) art n. 8513
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Electric current activated/assisted sintering (ECAS) techniques, such as electrical discharge sintering (EDS) or resistive sintering (RS), have been intensively investigated for longer than 50 years. In this work, a novel system including an electrically insulated graphite die for Spark Plasma Sintering (SPS) is described, which allows the sintering of any refractory ceramic material in less than 1 minute starting from room temperature with heating rates higher than 2000°C/min and an energy consumption up to 100 times lower than with SPS. The system alternates or combines direct resistive sintering (DRS) and indirect resistive sintering (IRS). Electrical insulation of the die has been achieved through the insertion of a film made of alumina fibers between the graphite die and the graphite punches, which are protected from the alumina fiber film by a graphite foil. This system localized the electric current directly through the sample (conductive materials) as in DRS and EDS, or through the thin graphite foil (non-conductive materials) as in IRS, and is the first system capable of being used under EDS or RS conditions independently combining current concentration/localization phenomena.

Enero, 2015 | DOI: 10.1038/srep08513

Titulo: STEM-EELS analysis reveals stable highdensity He in nanopores of amorphous silicon coatings deposited by magnetron sputtering
Autores: Schierholz, Roland; Lacroix, Bertrand; Godinho, Vanda; Caballero-Hernandez, Jaime; Duchamp, Martial; Fernandez, Asuncion
Revista: Nanotechnology, 26 (2015) 075703
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A broad interest has been showed recently on the study of nanostructuring of thin films and surfaces obtained by low-energy He plasma treatments and He incorporation via magnetron sputtering. In this paper spatially resolved electron energy-loss spectroscopy in a scanning transmission electron microscope is used to locate and characterize the He state in nanoporous amorphous silicon coatings deposited by magnetron sputtering. A dedicated MATLAB program was developed to quantify the helium density inside individual pores based on the energy position shift or peak intensity of the He K-edge. A good agreement was observed between the high density (~35–60 at nm−3) and pressure (0.3–1.0 GPa) values obtained in nanoscale analysis and the values derived from macroscopic measurements (the composition obtained by proton backscattering spectroscopy coupled to the macroscopic porosity estimated from ellipsometry). This work provides new insights into these novel porous coatings, providing evidence of high-density He located inside the pores and validating the methodology applied here to characterize the formation of pores filled with the helium process gas during deposition. A similar stabilization of condensed He bubbles has been previously demonstrated by high-energy He ion implantation in metals and is newly demonstrated here using a widely employed methodology, magnetron sputtering, for achieving coatings with a high density of homogeneously distributed pores and He storage capacities as high as 21 at%.

Enero, 2015 | DOI: 10.1088/0957-4484/26/7/075703

Titulo: Influence of the Processing Route on the Carbon Nanotubes Dispersion and Creep Resistance of 3YTZP/SWCNTs Nanocomposites
Autores: Castillo-Rodriguez, M; Munoz, A; Morales-Rodriguez, A; Poyato, R; Gallardo-Lopez, A; Dominguez-Rodriguez, A
Revista: Journal of the American Ceramic Society, 98 (2015) 645-653
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3YTZP matrix composites containing 2.5 vol% of single-walled carbon nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250°C, following different processing routines with the aim of optimizing the SWCNTs dispersion throughout the ceramic matrix. Microstructural characterization of the as-fabricated samples has been performed by means of scanning electron microscopy (SEM). The specimens have been crept at 1200°C to correlate creep resistance and SWCNTs distribution. There are no creep experimental results on these nanocomposites reported in literature. Mechanical results show that the incorporation of SWCNTs into a 3YTZP matrix produces an increase in the strain rate at high temperature with respect to monolithic zirconia. The creep resistance of these nanocomposites decreases with the improvement of the SWCNTs dispersion, where a smaller SWCNTs agglomerate size and consequently a higher concentration of carbon nanotubes surrounding the 3YTZP grain boundaries is found. This fact indicates that SWCNTs act as a lubricant making grain-boundary sliding easier during deformation of these composites.

Enero, 2015 | DOI: 10.1111/jace.13348

Titulo: Tribocorrosion behavior of TiBxCy/a-C nanocomposite coating in strong oxidant disinfectant solutions
Autores: Gracia-Escosa, E; Garcia, I; Sanchez-Lopez, JC; Abad, MD; Mariscal, A; Arenas, MA; de Damborenea, J; Conde, A
Revista: Surface & Coatings Technology, 263 (2015) 78-85
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Corrosion and tribocorrosion studies of a TiBxCy/a-C coating deposited on AISI 316L steel have been performed in an aqueous solution of 026 vol.% acetic, 0.16 vol.% peracetic and 0.18 vol.% hydrogen peroxide (commercial product Oxonia I vol.%). The corrosion current density of the TiBxCy/a-C coating ranges on the same order as bare steel but with a significantly decreasing friction (0.1 vs. 0.6) and wear rate (similar to 10 times lower). The compact microstructure of the coating hinders the access of the aggressive electrolyte to the substrate, preventing the onset of the corrosion attack, while maintaining an excellent tribological behavior in strong oxidant solutions.

Enero, 2015 | DOI: 10.1016/j.surfcoat.2014.12.047

Titulo: Biotribological behavior of Ag–ZrCxN1−x coatings against UHMWPE for joint prostheses devices
Autores: Calderon, SV; Sanchez-Lopez, JC; Cavaleiro, A; Carvalho, S
Revista: Journal of the Mechanical Behavior of Biomedical Materials, 41 (2015) 83-91
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This study aims to evaluate the structural, mechanical and tribological properties of zirconium carbonitrides (ZrCxN1−x) coatings with embedded silver nanoparticles, produced with the intention of achieving a material with enhanced multi-functional properties, including mechanical strength, corrosion resistance, tribological performance and antibacterial behavior suitable for their use in joint prostheses. The coatings were deposited by direct current (DC) reactive magnetron sputtering onto 316 L stainless steel, changing the silver content from 0 to 20 at% by modifying the current density applied to the targets. Different nitrogen and acetylene gas fluxes were used as reactive gases. The coatings revealed different mixtures of crystalline ZrCxN1−x, silver nanoparticles and amorphous carbon phases. The hardness of the films was found to be mainly controlled by the ratio between the hard (ZrCxN1−x) and soft (Ag and amorphous carbon) phases in the films, fluctuating between 7.4 and 20.4 GPa. The coefficient of friction, measured against ultra-high molecular weight polyethylene (UHMWPE) in Hank’s balanced salt solution with 10 g L−1albumin, is governed by the surface roughness and hardness. The UHMWPE wear rates were in the same order of magnitude (between 1.4 and 2.0×10−6 mm3 N−1 m−1), justified by the effect of the protective layer of albumin formed during the tests. The small differences were due to the hydrophobic/hydrophilic character of the surface, as well as to the silver content.

Diciembre, 2014 | DOI: 10.1016/j.jmbbm.2014.09.028

2014


Titulo: Improvement of Vickers hardness measurement on SWNT/Al2O3 composites consolidated by spark plasma sintering
Autores: Rodriguez, AM; Lopez, AG; Fernandez-Serrano, A; Poyato, R; Munoz, A; Dominguez-Rodriguez, A
Revista: Journal of the European Ceramic Society, 34 (2014) 3801-3809
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Dense alumina composites with different carbon nanotube content were prepared by colloidal processing and consolidated by Spark Plasma Sintering (SPS). Single-wall carbon nanotubes (SWNTs) were distributed at grain boundaries and also into agglomerates homogeneously dispersed. Carrying out Vickers hardness tests on the cross-section surfaces instead of top (or bottom) surfaces has shown a noticeable increase in the reliability of the hardness measurements. This improvement has been mainly attributed to the different morphology of carbon nanotube agglomerates, which however does not seem to affect the Vickers hardness value. Composites with lower SWNT content maintain the Vickers hardness of monolithic alumina, whereas it significantly decreases for the rest of compositions. The decreasing trend with increasing SWNT content has been explained by the presence of higher SWNT quantities at grain boundaries. Based on the results obtained, a method for optimizing Vickers hardness tests performance on SWNT/Al2O3 composites sintered by SPS is proposed.

Noviembre, 2014 | DOI: 10.1016/j.jeurceramsoc.2014.05.048

Titulo: Effect of La2O3 addition on long-term oxidation kinetics of ZrB2-SiC and HfB2-SiC ultra-high temperature ceramics
Autores: Zapata-Solvas, E; Jayaseelan, DD; Brown, PM; Lee, WE
Revista: Journal of European Ceramic Society, 34 (2014) 3535-3548
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Long-term oxidation kinetics of SiC-reinforced UHTCs and La2O3-doped UHTCs over an intermediate temperature range (1400-1600 degrees C) reveal partially protective behavior for the former characterized by an oxidation kinetic exponent 1 < n < 2. In addition, unstable oxidation behavior was observed in HfB2-based UHTCs due to the presence of SiC agglomerates. On the other hand, La2O3-doped UHTCs were found to be protective over the whole temperature range studied (n = 2), in particular at 1600 degrees C, where oxidation kinetic exponents as high as 8 were observed as a consequence of formation of new oxidation protective particles, MeOxCy, where Me is Zr, Hf or Si. Adsorption of oxygen-containing species formed protective MeOxCy), phases, which enhanced the thermal stability of the oxide scale as well as providing protection against oxidation for long exposure times at 1600 degrees C.

Noviembre, 2014 | DOI: 10.1016/j.jeurceramsoc.2014.06.004

Titulo: High temperature internal friction measurements of 3YTZP zirconia polycrystals. High temperature background and creep
Autores: Simas, P; Castillo-Rodriguez, M; No, ML; De-Bernardi, S; Gomez-Garcia, D; Dominguez-Rodriguez, A; Juan, JS
Revista: Journal of the European Ceramic Society, 34 (2014) 3859-3863
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This work focuses on the high-temperature mechanic properties of a 3 mol% yttria zirconia polycrystals (3YTZP), fabricated by hot-pressureless sintering. Systematic measurements of mechanical loss as a function of temperature and frequency were performed. An analytical method, based on the generalized Maxwell rheological model, has been used to analyze the high temperature internal friction background (HTB). This method has been previously applied to intermetallic compounds but never to ceramics, except in a preliminary study performed on fine grain and nanocrystalline zirconia. The HTB increases exponentially and its analysis provides an apparent activation enthalpy which correlates well with that obtained from creep experiments. This fact shows on the one hand the plausibility of applying the generalized Maxwell model to ceramics, and on the other hand indicates the possibility of using mechanical spectroscopy as a complementary helpful technique to investigate the high temperature deformation mechanism of materials.

Noviembre, 2014 | DOI: 10.1016/j.jeurceramsoc.2014.05.016

Titulo: Transmission electron microscopy of unstained hybrid Au nanoparticles capped with PPAA (plasma-poly-allylamine): Structure and electron irradiation effects
Autores: Gontard, LC; Fernandez, A; Dunin-Borkowski, RE; Kasama, T; Lozano-Perez, S; Lucas, S
Revista: Micron, 67 (2014) 1-9
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Hybrid (organic shell–inorganic core) nanoparticles have important applications in nanomedicine. Although the inorganic components of hybrid nanoparticles can be characterized readily using conventional transmission electron microscopy (TEM) techniques, the structural and chemical arrangement of the organic molecular components remains largely unknown. Here, we apply TEM to the physico-chemical characterization of Au nanoparticles that are coated with plasma-polymerized-allylamine, an organic compound with the formula C3H5NH2. We discuss the use of energy-filtered TEM in the low-energy-loss range as a contrast enhancement mechanism for imaging the organic shells of such particles. We also study electron-beam-induced crystallization and amorphization of the shells and the formation of graphitic-like layers that contain both C and N. The resistance of the samples to irradiation by high-energy electrons, which is relevant for optical tuning and for understanding the degree to which such hybrid nanostructures are stable in the presence of biomedical radiation, is also discussed.

Noviembre, 2014 | DOI: 10.1016/j.micron.2014.06.004

Titulo: Calcium silicates synthesised from industrial residues with the ability for CO2 sequestration
Autores: Morales-Florez, V; Santos, A; Lopez, A; Morina, I; Esquivias, L
Revista: Waste Management & Research, 32 (2014) 1178-1185
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This work explored several synthesis routes to obtain calcium silicates from different calcium-rich and silica-rich industrial residues. Larnite, wollastonite and calcium silicate chloride were successfully synthesised with moderate heat treatments below standard temperatures. These procedures help to not only conserve natural resources, but also to reduce the energy requirements and CO2 emissions. In addition, these silicates have been successfully tested as carbon dioxide sequesters, to enhance the viability of CO2 mineral sequestration technologies using calcium-rich industrial by-products as sequestration agents. Two different carbon sequestration experiments were performed under ambient conditions. Static experiments revealed carbonation efficiencies close to 100% and real-time resolved experiments characterised the dynamic behaviour and ability of these samples to reduce the CO2 concentration within a mixture of gases. The CO2 concentration was reduced up to 70%, with a carbon fixation dynamic ratio of 3.2mgCO(2) per g of sequestration agent and minute. Our results confirm the suitability of the proposed synthesis routes to synthesise different calcium silicates recycling industrial residues, being therefore energetically more efficient and environmentally friendly procedures for the cement industry.

Noviembre, 2014 | DOI: 10.1177/0734242X14542148

Titulo: Chemistry, nanostructure and magnetic properties of Co-Ru-B-O nanoalloys
Autores: Arzac, GM; Rojas, TC; Gontard, LC; Chinchilla, LE; Otal, E; Crespo, P; Fernandez, A
Revista: RSC Advances, 4 (2014) 46576-46586
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In our previous works, Co–B–O and Co–Ru–B–O ultrafine powders with variable Ru content (xRu) were studied as catalysts for hydrogen generation through sodium borohydride hydrolysis. These materials have shown a complex nanostructure in which small Co–Ru metallic nanoparticles are embedded in an amorphous matrix formed by Co–Ru–B–O based phases and B2O3. Catalytic activity was correlated to nanostructure, surface and bulk composition. However, some questions related to these materials remain unanswered and are studied in this work. Aspects such as: 3D morphology, metal nanoparticle size, chemical and electronic information on the nanoscale (composition and oxidation states), and the study of the formation or not of a CoxRu1−x alloy or solid solution are investigated and discussed using XAS (X-ray Absorption Spectroscopy) and Scanning Transmission Electron Microscopy (STEM) techniques. Also magnetic behavior of the series is studied for the first time and the structure–performance relationships discussed. All Co-containing samples exhibited ferromagnetic behavior up to room temperature while the Ru–B–O sample is diamagnetic. For the xRu = 0.13 sample, an enhancement in the Hc (coercitive field) and Ms (saturation magnetization) is produced with respect to the monometallic Co–B–O material. However this effect is not observed for samples with higher Ru content. The presence of the CoxB-rich (cobalt boride) amorphous ferromagnetic matrix, very small metal nanoparticles (Co and CoxRu(1−x)) embedded in the matrix, and the antiferromagnetic CoO phase (for the higher Ru content sample, xRu = 0.7), explain the magnetic behavior of the series.

Octubre, 2014 | DOI:

Titulo: Supported Co catalysts prepared as thin films by magnetron sputtering for sodium borohydride and ammonia borane hydrolysis
Autores: Paladini, M; Arzac, GM; Godinho, V; De Haro, MCJ; Fernandez, A
Revista: Applied Catalysis B: Environmental, 158-159 (2014) 400-409
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Supported Co catalysts were prepared for sodium borohydride and ammonia borane hydrolysis by magnetron sputtering for the first time under different conditions. Ni foam was selected as support. Deposition conditions (time, pressure, and power) were varied to improve catalytic activity. A decrease in deposition power from 200 to 50 W, leads to a decrease in crystallite and column size and a higher activity of catalysts. The increase in deposition pressure from 1.5 × 10−2 to 4.5 × 10−2 mbar produces same effect but in this case the enhancement in activity is higher because amorphous materials were obtained. The highest activity for SB hydrolysis was 2650 ml min−1 gcat−1 for the 50 W Co 4.5 (4 h) sample (Ea = 60 ± 2 kJ mol−1). For AB hydrolysis activity for the 50 W Co 3.2 (4 h) sample was similar. Durability of the thin films was tested for both reactions upon cycling (14 cycles). Diluted acid washing was effective to recover the activity for sodium borohydride reaction but not for ammonia borane hydrolysis. The strong Co–NH3 interactions explain the non-efficiency of the acid washing.

Septiembre, 2014 | DOI: 10.1016/j.apcatb.2014.04.047

Titulo: Shape-defined nanodimers by tailored heterometallic epitaxy
Autores: Garcia-Negrete, Carlos A; Rojas, Teresa C; Knappett, Benjamin R; Jefferson, David A; Wheatley, Andrew E H; Fernandez, Asuncion
Revista: Nanoscale, 6 (2014) 11090-11097
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The systematic construction of heterogeneous nanoparticles composed of two distinct metal domains (Au and Pt) and exhibiting a broad range of morphologically defined shapes is reported. It is demonstrated that careful Au overgrowth on Pt nanocrystal seeds with shapes mainly corresponding to cubeoctahedra, octahedra and octapods can lead to heterometallic systems whose intrinsic structures result from specific epitaxial relationships such as {111} + {111}, {200} + {200} and {220} + {220}. Comprehensive analysis shows also that nanoparticles grown from octahedral seeds can be seen as comprising of four Au tetrahedral subunits and one Pt octahedral unit in a cyclic arrangement that is similar to the corresponding one in decahedral gold nanoparticles. However, in the present case, the multi-component system is characterized by a broken five-fold rotational symmetry about the [011] axis. This set of bimetallic dimers could provide new platforms for fuel cell catalysts and plasmonic devices.

Septiembre, 2014 | DOI: 10.1039/C4NR01815J

Titulo: Hardness and flexural strength of single-walled carbon nanotube/alumina composites
Autores: Gallardo-Lopez, A; Poyato, R; Morales-Rodriguez, A; Fernandez-Serrano, A; Munoz, A; Dominguez-Rodriguez, A
Revista: Journal of Materials Science, 20 (2014) 7116-7123
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This work adds new experimental facts on room temperature hardness and flexural strength of alumina and composites with 1, 2, 5 and 10 vol% single-walled carbon nanotubes (SWNT) with similar grain size. Monolithic Al2O3 and composites were spark plasma sintered (SPS) in identical conditions at 1300 A degrees C, achieving high density, submicrometric grain size and a reasonably homogeneous distribution of SWNT along grain boundaries for all compositions with residual agglomerates. Vickers hardness values comparable to monolithic alumina were obtained for composites with low (1 vol%) SWNT content, though they decreased for higher concentrations, attributed to the fact that SWNT constitute a softer phase. Three-point bending flexural strength also decreased with increasing SWNT content. Correlation between experimental results and microstructural analysis by electron microscopy indicates that although SWNT agglomerates have often been blamed for detrimental effects on the mechanical properties of these composites, they are not the main cause for the reported decay in flexural strength.

Septiembre, 2014 | DOI: 10.1007/s10853-014-8419-5

Titulo: Impregnation of carbon black for the examination of colloids using TEM
Autores: Gontard, LC; Knappett, BR; Wheatley, AEH; Chang, SLY; Fernandez, A
Revista: Carbon, 76 (2014) 464-468
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Nanoparticles are frequently synthesised as colloids, dispersed in solvents such as water, hexane or ethanol. For their characterisation by transmission electron microscopy (TEM), a drop of colloid is typically deposited on a carbon support and the solvent allowed to evaporate. However, this method of supporting the nanoparticles reduces the visibility of fine atomic details, particularly for carbonaceous species, due to interference from the 2-dimensional carbon support at most viewing angles. We propose here the impregnation of a 3 dimensional carbon black matrix that has been previously deposited on a carbon film as an alternative means of supporting colloidal nanoparticles, and show examples of the application of this method to advanced TEM techniques in the analysis of monometallic, core@shell and hybrid nanoparticles with carbon-based shells.

Nanoparticles represent one of the most studied structures in nanotechnology and nanoscience because of the wide range of applications arising from their unique optical, physical and chemical properties [1]. Often they have core@shell structures, or are coated with organic molecules. Nanoparticle functionality is largely affected by the specific configuration of the outer surface atoms. For example, in heterogeneous catalysis activity and selectivity are mostly determined by the type of atomic defects present at the surface of metallic nanoparticles, and in the field of biomedicine the surface coating of hybrid (inorganic core@organic shell) nanoparticles regulates their stability, solubility and targeting.

Nanoparticles are frequently synthesised using solution techniques that yield colloids, i.e., a solid–liquid mixture containing solid particles that are dispersed to various degrees in a liquid medium; most frequently water, ethanol or hexane. Colloid characterisation generally employs a variety of techniques to establish understanding and control over nanoparticle synthesis and properties. Electron microscopy in transmission mode (TEM) and in scanning transmission mode (STEM) are widely used for particle characterisation, and advances in these techniques mean that it is now routinely possible to resolve single atoms at the surfaces of nanoparticles using aberration-corrected microscopes, to elucidate the three-dimensional shapes of nanoparticles using electron tomography, and to enhance the contrast in very low density materials (e.g., carbonaceous materials) using electron holography [2] and [3]. However, the significant potential of these (S)TEM techniques is ultimately limited by the sample and the techniques available for sample preparation.

Typically, examination by (S)TEM requires that a nanoparticulate sample be prepared by depositing a drop of colloid on a thin, electron-transparent support. It is usual that an amorphous carbon film, silicon nitride film or graphene layers deposited on a copper grid constitute the support [4]. Crucially, these sample preparation techniques suffer from the major limitation that the contrast from the support often shadows atomic details at the particle surface. Moreover, it has been established that the thinnest supports can degrade under electron-beam irradiation, affecting particle stability [5], and also that hydrocarbon contamination can be an issue [6]. The most widely used commercially available TEM support is holey carbon, which comprises of a perforated carbon thin film. In this case, sample preparation aims to locate at least some of the nanoparticles of interest at the edges of the perforations. However, the concave nature of the holes means that solvent contaminants tend to accumulate preferentially at these sites. Moreover, if the TEM sample holder is tilted a particle attached to the edge of a hole is very likely to be shadowed by the carbon film. Taken together, these drawbacks significantly limit the application of techniques such as electron tomography [6].

We propose here a method of circumventing some of these fundamental problems by developing a technique for mounting nanoparticulate samples using a carbon matrix that is inspired by the way samples used in electrocatalysis are prepared [7]. Fig. 1 shows an image of a typical Pt-based electrocatalyst supported on carbon black as used in proton-electron membrane fuels cells, and which consists of Pt nanoparticles formed by calcination of a carbon black impregnated with a solution of salt precursor. Carbon black is a low-grade form of graphite, which is composed of nanocrystallites and no long-range order [8]. In Fig. 1 the carbon black is Vulcan XC-72R, which is widely used as a catalyst support in fuel cells because it provides high electrical conductivity, good reactant gas access, adequate water handling and good corrosion resistance, whilst allowing high dispersion of the particles. In electrocatalyst samples it is common to find particles, like the 5 nm Pt particle shown in Fig. 1, attached strongly to the surface of the support and viewed edge-on against a vacuum so as to provide optimal conditions for high-resolution TEM (HRTEM). Fig. 1B is a quantitative phase image of a Pt particle obtained from a defocus series of 20 images at intervals of 5 nm acquired in a FEGTEM JEOL 2020 at 200 kV with spherical aberration of −30 μm and applying the exit-wave restoration technique [2]. The contrast between details of the particle finestructure is very high compared to conventional HRTEM images, and details such as the presence of monoatomic carbon ribbons surrounding the particle can be seen.

Agosto, 2014 | DOI: 10.1016/j.carbon.2014.05.006

Titulo: On the formation of the porous structure in nanostructured a-Si coatings deposited by dc magnetron sputtering at oblique angles
Autores: Godinho, V; Moskovkin, P; Alvarez, R; Caballero-Hernandez, J; Schierholz, R; Bera, B; Demarche, J; Palmero, A; Fernandez, A; Lucas, S
Revista: Nanotechnology, 25 (2014) 355705
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The formation of the porous structure in dc magnetron sputtered amorphous silicon thin films at low temperatures is studied when using helium and/or argon as the processing gas. In each case, a-Si thin films were simultaneously grown at two different locations in the reactor which led to the assembly of different porous structures. The set of four fabricated samples has been analyzed at the microstructural level to elucidate the characteristics of the porous structure under the different deposition conditions. With the help of a growth model, we conclude that the chemical nature of the sputter gas not only affects the sputtering mechanism of Si atoms from the target and their subsequent transport in the gaseous/plasma phase towards the film, but also the pore formation mechanism and dynamics. When Ar is used, pores emerge as a direct result of the shadowing processes of Si atoms, in agreement with Thornton's structure zone model. The introduction of He produces, in addition to the shadowing effects, a new process where a degree of mobility results in the coarsening of small pores. Our results also highlight the influence of the composition of sputtering gas and tilt angles (for oblique angle deposition) on the formation of open and/or occluded porosity.

Agosto, 2014 | DOI: 10.1088/0957-4484/25/35/355705

Titulo: Technological Proposals for Recycling Industrial Wastes for Environmental Applications
Autores: Romero-Hermida, I; Morales-Florez, V; Santos, A; Villena, A; Esquivias, L
Revista: Minerals, 4 (2014) 746-757
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A two-fold objective is proposed for this research: removing hazardous and unpleasant wastes and mitigating the emissions of green house gasses in the atmosphere. Thus, the first aim of this work is to identify, characterize and recycle industrial wastes with high contents of calcium or sodium. This involves synthesizing materials with the ability for CO2 sequestration as preliminary work for designing industrial processes, which involve a reduction of CO2 emissions. In this regard, phosphogypsum from the fertilizer industry and liquid wastes from the green olive and bauxite industries have been considered as precursors. Following a very simple procedure, Ca-bearing phosphogypsum wastes are mixed with Na-bearing liquid wastes in order to obtain a harmless liquid phase and an active solid phase, which may act as a carbon sequestration agent. In this way, wastes, which are unable to fix CO2 by themselves, can be successfully turned into effective CO2 sinks. The CO2 sequestration efficiency and the CO2 fixation power of the procedure based on these wastes are assessed.

Agosto, 2014 | DOI: 10.3390/min4030746

Titulo: Simultaneous quantification of light elements in thin films deposited on Si substrates using proton EBS (Elastic Backscattering Spectroscopy)
Autores: Ferrer, FJ; Alcaire, M; Caballero-Hernandez, J; Garcia-Garcia, FJ; Gil-Rostra, J; Terriza, A; Godinho, V; Garcia-Lopez, J; Barranco, A; Fernandez-Camacho, A
Revista: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 332 (2014) 449-453
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Quantification of light elements content in thin films is an important and difficult issue in many technological fields such as polymeric functional thin films, organic thin film devices, biomaterials, and doped semiconducting structures.

Light elements are difficult to detect with techniques based on X-ray emission, such as energy dispersive analysis of X-rays (EDAX). Other techniques, like X-ray photoelectron spectroscopy (XPS), can easily quantify the content of light elements within a surface but often these surface measurements are not representative of the lights elements global composition of the thin film. Standard Rutherford backscattering spectroscopy (RBS), using alpha particles as probe projectiles, is not a good option to measure light elements deposited on heavier substrates composed of heavier elements like Si or glass. Nuclear Reaction Analysis (NRA) offers a good quantification method, but most of the nuclear reactions used are selective for the quantification of only one element, so several reactions and analysis are necessary to measure different elements.

In this study, Elastic Backscattering Spectroscopy (EBS) using proton beams of 2.0 MeV simultaneously quantified different light elements (helium, carbon, nitrogen, oxygen, and fluorine) contained in thin films supported on silicon substrates. The capabilities of the proposed quantification method are illustrated with examples of the analysis for a series of thin film samples: amorphous silicon with helium bubbles, fluorinated silica, fluorinated diamond-like carbon and organic thin films. It is shown that this simple and versatile procedure allows the simultaneous quantification of light elements in thin films with thicknesses in the 200–500 nm range and contents lower than 10 at.%.

Julio, 2014 | DOI: 10.1016/j.nimb.2014.02.124

Titulo: Bifunctional, Monodisperse BiPO4-Based Nanostars: Photocatalytic Activity and Luminescent Applications
Autores: Becerro, AI; Criado, J; Gontard, LC; Obregon, S; Fernandez, A; Colon, G; Ocana, M
Revista: Crystal Growth & Design, 14 (2014) 3319-3326
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Monodisperse, monoclinic BiPO4 nanostars have been synthesized by a homogeneous precipitation reaction at 120 °C through controlled release of Bi3+ cations from a Bi–citrate chelate, in a mixture of glycerol and ethylene glycol, using H3PO4 as the phosphate source. The set of experimental conditions necessary to obtain uniform nanoparticles is very restrictive, as the change in either the polyol ratio or the reactant concentrations led to ill-defined and/or aggregated particles. The morphology of the particles consists of a starlike, hierarchical structure formed by the ordered arrangement of nanorod bundles. Transmission electron tomography has revealed that the nanostars are not spherical but flattened particles. Likewise, Fourier transform infrared spectroscopy and thermogravimetry have shown that the synthesized nanostars are functionalized with citrate groups. The mechanism of formation of the nanostars has been analyzed to explain their morphological features. The as-synthesized BiPO4 nanostars exhibit an efficient photocatalytic performance for the degradation of Rhodamine B. Finally, it has been demonstrated that the stars can be Eu3+-doped up to 2 mol % without any change in the particle morphology or symmetry, and the doped samples show emission in the orange-red region of the visible spectrum after ultraviolet excitation. These experimental observations make this material a suitable phosphor for biotechnological applications.

Junio, 2014 | DOI: 10.1021/cg500208h

Titulo: A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques
Autores: Lapresta-Fernandez, A; Salinas-Castillo, A; de la Llana, SA; Costa-Fernandez, JM; Dominguez-Meister, S; Cecchini, R; Capitan-Vallvey, LF; Moreno-Bondi, MC; Marco, MP; Sanchez-Lopez, JC; Anderson, IS
Revista: Critical Reviews in Solid State and Materials Sciences, 39 (2014) 423-458
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This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described.

Mayo, 2014 | DOI: 10.1080/10408436.2014.899890

Titulo: Effect of high SWNT content on the room temperature mechanical properties of fully dense 3YTZP/SWNT composites
Autores: Poyato, R; Gallardo-Lopez, A; Gutierrez-Mora, F; Morales-Rodriguez, A; Munoz, A; Dominguez-Rodriguez, A
Revista: Journal of the European Ceramic Society, 34 (2014) 1571-1579
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This paper is devoted to correlate the microstructure and room temperature mechanical properties of single-wall carbon nanotube (SWNT) reinforced 3 mol% yttria stabilized tetragonal zirconia with high SWNT content (2.5, 5 and 10 vol%). Fully dense composites were prepared by using a combination of aqueous colloidal powder processing and Spark Plasma Sintering. SWNTs were located at the ceramic grain boundaries and they were not damaged during the sintering process. The weak interfacial bonding between SWNTs and ceramic grains together with the detachment of SWNTs within thick bundles have been pointed out as responsible for the decrease of hardness and fracture toughness of the composites in comparison with the monolithic 3YTZP ceramic.

Mayo, 2014 | DOI: 10.1016/j.jeurceramsoc.2013.12.024

Titulo: Phase assembly and electrical conductivity of spark plasma sintered CeO2-ZrO2 ceramics
Autores: Poyato, R; Cruz, SA; Cumbrera, FL; Moreno, B; Chinarro, E; Odriozola, JA
Revista: Journal of Materials Science, 49 (2014) 6353-6362
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Cex Zr1−x O2 (x = 0.10, 0.16 and 0.33) nanocrystalline powders were obtained by a two-step synthesis technique and sintered by spark plasma sintering (SPS). As consequence of the reduction of Ce4+ to Ce3+ species by carbon in the graphite environment in SPS, phase assemblies including tetragonal, monoclinic and pyrochlore phases were generated in the ceramics during the sintering process. The electrical conductivity was highly dependent on phase assembly and atmosphere (N2, H2 and O2). A significant decrease in the activation energy was noticed in the ceramics with high pyrochlore content when measuring the conductivity in H2 atmosphere, consequence of the strong reduction promoted in these ceramics during the measurement. Equal conduction behavior with similar activation energy was observed in all the ceramics when measuring in O2 atmosphere.

Mayo, 2014 | DOI: 10.1007/s10853-014-8361-6

Titulo: Tomographic Heating Holder for In Situ TEM: Study of Pt/C and PtPd/Al2O3 Catalysts as a Function of Temperature
Autores: Gontard, LC; Dunin-Borkowski, RE; Fernandez, A; Ozkaya, D; Kasama, T
Revista: Microscoy and Microanalysis, 20 (2014) 982-990
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A tomographic heating holder for transmission electron microscopy that can be used to study supported catalysts at temperatures of up to similar to 1,500 degrees C is described. The specimen is placed in direct thermal contact with a tungsten filament that is oriented perpendicular to the axis of the holder without using a support film, allowing tomographic image acquisition at high specimen tilt angles with minimum optical shadowing. We use the holder to illustrate the evolution of the active phases of Pt nanoparticles on carbon black and PtPd nanoparticles on gamma-alumina with temperature. Particle size distributions and changes in active surface area are quantified from tilt series of images acquired after subjecting the specimens to increasing temperatures. The porosity of the alumina support and the sintering mechanisms of the catalysts are shown to depend on distance from the heating filament.

Mayo, 2014 | DOI: 10.1017/S1431927614000373

Titulo: Detecting single-electron events in TEM using low-cost electronics and a silicon strip sensor
Autores: Gontard, LC; Moldovan, G; Carmona-Galn, R; Lin, C; Kirkland, AI
Revista: Microscopy, 63(2) (2014) 119-130
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There is great interest in developing novel position-sensitive direct detectors for transmission electron microscopy (TEM) that do not rely in the conversion of electrons into photons. Direct imaging improves contrast and efficiency and allows the operation of the microscope at lower energies and at lower doses without loss in resolution, which is especially important for studying soft materials and biological samples. We investigate the feasibility of employing a silicon strip detector as an imaging detector for TEM. This device, routinely used in high-energy particle physics, can detect small variations in electric current associated with the impact of a single charged particle. The main advantages of using this type of sensor for direct imaging in TEM are its intrinsic radiation hardness and large detection area. Here, we detail design, simulation, fabrication and tests in a TEM of the front-end electronics developed using low-cost discrete components and discuss the limitations and applications of this technology for TEM.

Marzo, 2014 | DOI: 10.1093/jmicro/dft051

Titulo: Long-term high temperature oxidation of CrAl(Y)N coatings in steam atmosphere
Autores: Mato, S; Alcala, G; Brizuela, M; Galindo, RE; Perez, FJ; Sanchez-Lopez, JC
Revista: Corrosion Science, 80 (2014) 453-460
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The oxidation resistance of CrAl(Y)N coatings deposited by reactive magnetron sputtering on P92 steel substrates was tested at 650 °C in 100% steam atmosphere up to 2000 h of oxidation. Mass gain measurements and characterisation of coatings and scales after oxidation show the enhanced oxidation resistance provided by the coatings with respect to that of the substrate. The dominant influence of the film microstructure developed due to the presence of an adhesion interlayer of CrN at the coating/substrate interface over Y additions is evidenced. The best performance is achieved by a CrAlN dense coating of around 6 μm without adhesion interlayer.

Febrero, 2014 | DOI: 10.1016/j.corsci.2013.11.066

Titulo: Additive-free superhard B4C with ultrafine-grained dense microstructures
Autores: Moshtaghioun, BM; Cumbrera, FL; Ortiz, AL; Castillo-Rodriguez, M; Gomez-Garcia, D
Revista: Journal of the European Ceramic Society, 34 (2014) 841-848
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A unique combination of high-energy ball-milling, annealing, and spark-plasma sintering has been used to process superhard B4C ceramics with ultrafine-grained, dense microstructures from commercially available powders, without sintering additives. It was found that the ultrafine powder prepared by high-energy ball-milling is hardly at all sinterable, but that B2O3 removal by gentle annealing in Ar provides the desired sinterability. A parametric study was also conducted to elucidate the role of the temperature (1600–1800 °C), time (1–9 min), and heating ramp (100 or 200 °C/min) in the densification and grain growth, and thus to identify optimal spark-plasma sintering conditions (i.e., 1700 °C for 3 min with 100 °C/min) to densify completely (>98.5%) the B4C ceramics with retention of ultrafine grains (∼370 nm). Super-high hardness of ∼38 GPa without relevant loss of toughness (∼3 MPa m1/2) was thus achieved, attributable to the smaller grain size and to the transgranular fracture mode of the B4C ceramics.

Febrero, 2014 | DOI: 10.1016/j.jeurceramsoc.2013.10.006

Titulo: Mechanical and phase stability of TiBC coatings up to 1000 degrees C
Autores: Abad, MD; Veldhuis, SC; Endrino, JL; Beake, BD; Garcia-Luis, A; Brizuela, M; Sanchez-Lopez, JC
Revista: Journal of Vacuum Science & Technology A, 32 (2014) 021508
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TiBC coatings with different phase compositions (nanocrystalline TiBxCy or TiB2 phases mixed or not with amorphous carbon, a-C) were prepared by magnetron sputtering. These coatings were comparatively studied in terms of phase stability after thermal annealing at 250, 500, 750, and 1000 °C in argon using Raman and x-ray absorption near-edge spectroscopy techniques. The main differences were observed at temperatures above 500 °C when oxidation processes occur and the mechanical properties deteriorate. At 1000 °C, the samples were fully oxidized forming a-C, TiO2, and B2O3 as final products. Higher hardness and reduced indentation modulus values and better tribological properties were observed at 750 °C for nanocomposite structures including amorphous carbon and ternary TiBxCy phases. This behavior is attributed to a protective effect associated with the a-C phase which is achieved by the encapsulation of the nanocrystals in the coating and the better hard/lubricant phase ratio associated with this type of coating.

Febrero, 2014 | DOI: 10.1116/1.4861365

Titulo: A Nanoscale Characterization with Electron Microscopy of Multilayered CrAlYN Coatings: A Singular Functional Nanostructure
Autores: Rojas, TC; Dominguez-Meister, S; Brizuela, M; Garcia-Luis, A; Fernandez, A; Sanchez-Lopez, JC
Revista: Microscoy and Microanalysis, 20 (2014) 14-24
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A combination of transmission electron microscopy techniques and spatially resolved microanalysis is used to investigate the nanostructure, constituting phases, and chemical elemental distribution in CrAlYN multilayered coatings. The location of the metallic elements and their chemical state are needed to understand their functional properties. Samples were prepared with variable Al (4-12 at%) and Y (2-5 at%) contents by direct current reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N-2 mixtures under different deposition parameters (power applied to the target and rotation speed of the sample holder). The changes produced in the nanostructure and chemical distribution were investigated. Nanoscale resolution electron microscopy analysis has shown that these coatings present a singular nanostructure formed by multilayers containing at a certain periodicity nanovoids filled with molecular nitrogen. Spatially resolved energy dispersive spectroscopy and electron energy loss elemental mappings and profiles showed that the chromium, aluminum, and yttrium atoms are distributed in a sequential way following the position of the targets inside the deposition chamber. Analysis of the different atomic distribution and phases formed at the nanoscale is discussed depending on the deposition parameters.

Enero, 2014 | DOI: 10.1017/S1431927613013962

Titulo: Comparative Study of Micro- and Nano-structured Coatings for High-Temperature Oxidation in Steam Atmospheres
Autores: Perez, FJ; Castaneda, SI; Hierro, MP; Galindo, RE; Sanchez-Lopez, JC; Mato, S
Revista: Oxidation of Metals, 81 (2014) 227-236
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For many high-temperature applications, coatings are applied in order to protect structural materials against a wide range of different environments: oxidation, metal dusting, sulphidation, molten salts, steam, etc. The resistance achieved by the use of different kind of coatings, such as functionally graded material coatings, has been optimized with the latest designs. In the case of supercritical steam turbines, many attempts have been made in terms of micro-structural coatings design, mainly based on aluminides, and other diffusion coating systems in order to consider alternatives, nano-structured coatings based on Cr and Al compositions and deposited by a physical vapor deposition technique, were assessed to high-temperature oxidation resistance in steam environments. The oxidation kinetics where analyzed for up to 2,000 h at 650 °C by means of gravimetric measurements. The evaporation behavior was also analyzed by thermogravimetric-mass spectrometry. Excellent results where observed for some of the nano-structured coatings tested. Those results where compared to results obtained for micro-structured coatings. Based on that comparison, it was deduced that the nano-structured coatings have a potential application as protective systems in high-temperature steam environments.

Enero, 2014 | DOI: 10.1007/s11085-013-9447-2

Titulo: Tribological behaviour at high temperature of hard CrAlN coatings doped with Y or Zr
Autores: Sanchez-Lopez, JC; Contreras, A; Dominguez-Meister, S; Garcia-Luis, A; Brizuela, M
Revista: Thin Solid Films, 550 (2014) 413-420
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The tribological properties of CrAlN, CrAlYN and CrAlZrN coatings deposited by direct current reactive magnetron sputtering are studied by means of pin-on-disc experiments at room temperature, 300, 500 and 650 °C using alumina balls as counterparts. The influence of the metallic composition (Al, Y and Zr) on the friction, wear properties and oxidation resistance is studied by means of scanning electron microscopy, energy dispersive X-ray analysis and Raman analysis of the contact region after the friction tests. The results obtained allow us to classify the tribological behaviour of the CrAl(Y,Zr)N coatings into three groups according to the nature of the dopant and aluminium content. The sliding wear mechanism is characterized by the formation of an overcoat rich in chromium and aluminium oxides whose particular composition is determined by the initial chemical characteristics of the coating and the testing temperature. The fraction of Cr2O3 becomes more significant as the Al content decreases and the temperature increases. The addition of Y, and particularly Zr, favours the preferential formation of Cr2O3 versus CrO2 leading to a reduction of friction and wear of the counterpart. Conversely, the tribological behaviour of pure CrAlN coatings is characterized by higher friction but lower film wear rates as a result of higher hardness and major presence of aluminium oxides on the coating surface.

Diciembre, 2013 | DOI: 10.1016/j.tsf.2013.10.041

Titulo: Thermal properties of La2O3-doped ZrB2- and HfB2-based ultra-high temperature ceramics
Autores: Zapata-Solvas, E; Jayaseelan, DD; Brown, PM; Lee, WE
Revista: Journal of the European Ceramic Society, 33 (2013) 3467-3472
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Thermal properties of La2O3-doped ZrB2- and HfB2-based ultra high temperature ceramics (UHTCs) have been measured at temperatures from room temperature to 2000 °C and compared with SiC-doped ZrB2- and HfB2-based UHTCs and monolithic ZrB2 and HfB2. Thermal conductivities of La2O3-doped UHTCs remain constant around 55–60 W/mK from 1500 °C to 1900 °C while SiC-doped UHTCs showed a trend to decreasing values over this range.

Noviembre, 2013 | DOI: 10.1016/j.jeurceramsoc.2013.06.009

Titulo: Tribological comparison of different C-based coatings in lubricated and unlubricated conditions
Autores: Ciarsolo, I; Fernandez, X; de Gopegui, UR; Zubizarreta, C; Abad, MD; Mariscal, A; Caretti, I; Jimenez, I; Sanchez-Lopez, JC
Revista: Surface and Coatings Technology, 257 (2014) 278-285
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The use of carbon-based coatings (hydrogenated and non-hydrogenated DLC, doped and alloyed-DLC) is of wide interest due to its applications in mechanical components submitted to friction and wear including sliding parts in automotive engines. A tribological comparative analysis using a reciprocating (SRV) tester in lubricated and unlubricated conditions with a 4-stroke motor oil has been carried out on six currently relevant state-of-the-art coatings (namely WC/a-C, TiBC/a-C and TiC/a-C:H nanocomposites, Ti-doped DLC, BCN film and a crystalline monolithic TiC film as reference). The quantification of the fraction of the sp(2)-bonded matrix has been done by fitting of C 1s XPS peak and the mechanical properties evaluated by nanoindentation. The comparative analysis has allowed us to identify the capabilities of each system depending on the testing conditions and the possible synergies as a function of the chemical composition and film nature. Under lubricated harsh conditions (max. contact pressure 1.7 GPa) only coatings displaying hardness superior to 20 GPa could stand the sliding motion without failure. At lower contact pressures, a significant fraction of sp(2) carbon (>= 75%) is advantageous for reducing wear in boundary lubrication. WC/a-C, BCN and Ti-DLC films showed the best tribological response in dry sliding conditions. This fundamental information would be of relevance for assisting engineers in selecting best partnership for lubrication systems. 

Septiembre, 2013 | DOI: 10.1016/j.surfcoat.2014.07.068

2013


Titulo: Preliminary investigation of flash sintering of SiC
Autores: Zapata-Solvas, E; Bonilla, S; Wilshaw, PR; Todd, RI
Revista: Journal of the European Ceramic Society, 33 (2013) 2811-2816
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The feasibility of flash sintering a covalent ceramic, SiC, has been investigated for the first time. Flash sintering involves the application of an electrical potential difference across a powder compact during heating, which leads to sintering at low furnace temperatures in a few seconds and has only been demonstrated with ionic ceramics previously. Near-theoretical density was achieved using Al2O3 + Y2O3 sintering aids at a furnace temperature of only 1170 degrees C and in a time of 150 s. Specimen temperatures were significantly higher than the furnace temperature owing to Joule heating and consequently heat loss limited densification in the near surface region. It was not possible to reach high densities using "ABC" sintering aids (aluminium-boron-carbon) or pure SiC. The mechanisms involved and potential commercial advantages are briefly discussed.

Octubre, 2013 | DOI: 10.1016/j.jeurceramsoc.2013.04.023

Titulo: In situ imaging and strain determination during fracture in a SiC/SiC ceramic matrix composite
Autores: Ramirez-Rico, J; Stolzenburg, F; Almer, JD; Routbort, JL; Singh, D; Faber, KT
Revista: Scripta Materialia, 69 (2013) 497-500
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A combined imaging and microdiffraction technique using high-energy synchrotron X-rays is described and used to reveal microstructure, damage and strain evolution around notches in SiC/SiC composites. This technique allows for monitoring the material for cracks while loading and mapping the strain distribution in fibers and matrix with a resolution of tens of microns. We show that at current resolutions this technique is capable of measuring the strain distribution near crack tips in ceramic matrix composites and observe load transfer effects.

Septiembre, 2013 | DOI: 10.1016/j.scriptamat.2013.05.032

Titulo: Evidence of nanograin cluster coalescence in spark plasma sintered α-Al2O3
Autores: Morales-Rodriguez, A; Poyato, R; Gallardo-Lopez, A; Munoz, A; Dominguez-Rodriguez, A
Revista: Scripta Materialia, 69 (2013) 529-532
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The aim of this study is to elucidate the coarsening kinetics involved during densification of fine-grained pure α-alumina by spark plasma sintering. Low temperature and short dwell time sintering conditions were used to preserve the nanocrystalline structure of the starting commercial powder (about 50 nm). Notwithstanding the above, submicron grain coarsened microstructures have been developed. The microstructure evolution of alumina under different sintering conditions points to a nanograin rotation densification mechanism as being responsible for the fast grain growth observed.

Septiembre, 2013 | DOI: 10.1016/j.scriptamat.2013.06.019

Titulo: Synthesis and tribological properties of WSex films prepared by magnetron sputtering
Autores: Dominguez-Meister, S; Justo, A; Sanchez-Lopez, JC
Revista: Materials Chemistry and Physics, 142 (2013) 186-194
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WSex films with variable Se/W ratio were deposited by non-reactive r.f. magnetron sputtering from WSe2 target changing the applied d.c. pulsed bias conditions and substrate temperature. The structural and chemical properties were measured by cross-sectional scanning electron microscopy (X-SEM), energy dispersive analysis (EDX), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The tribological properties were measured in ambient air (RH = 30–40%) and dry nitrogen by means of a reciprocating ball-on-disk tribometer. A clear correlation was found between the Se/W ratio and the measured friction coefficient displaying values below 0.1 (in ambient air) and 0.03 (in dry N2) for ratios Se/W ≥ 0.6 as determined by electron probe microanalysis (EPMA). The results demonstrated that notable tribological results could be obtained even in ambient air (friction ≤ 0.07 and wear rate ≈10−7 mm3 Nm−1) by controlling the film microstructure and chemical composition. By incorporating carbon, wear and chemical resistance can be gained by formation of non-stoichiometric carbides and/or alloying into the defective WSex hexagonal structure. The existence of a WSe2 rich interfacial layer (either on the ball scar or embedded in the film track) was evidenced by Raman in low friction conditions. The improvement in tribological performance is therefore obtained by means of layered WSex, the formation of gradient composition from metallic W (hard) to WSe2 (lubricant) and carbon incorporation.

Septiembre, 2013 | DOI: 10.1016/j.matchemphys.2013.07.004

Titulo: Spectroscopic properties of electrochemically populated electronic states in nanostructured TiO2 films: anatase versus rutile
Autores: Berger, T; Anta, JA; Morales-Florez, V
Revista: Physical Chemistry Chemical Physics, 15 (2013) 13790-13795
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A thorough characterization of nanostructured materials under application-relevant conditions is a prerequisite for elucidating the interplay between their physicochemical nature and their functional properties in practical applications. Here, we use a spectroelectrochemical approach to study the population of electronic states in different types of nanostructured anatase and rutile TiO2 films in contact with an aqueous electrolyte. The spectroscopic properties of the two polymorphs were addressed under Fermi level control in the energy range between the fundamental absorption threshold and the onset of lattice absorption (3.3–0.1 eV). The results evidence the establishment of an equilibrium between localized Ti3+ centers absorbing in the vis/NIR and shallow (e−)(H+) traps absorbing in the MIR upon electron accumulation in anatase electrodes. The absence of the MIR-active (e−)(H+) traps on all rutile electrodes points to a crystal structure-dependent electron population in the films.

Agosto, 2013 | DOI: 10.1039/C3CP52324A

Titulo: Dissociation of basal dislocations in 4 H - SiC single crystals deformed around the transition temperature
Autores: Castillo-Rodriguez, M; Lara, A; Munoz, A; Dominguez-Rodriguez, A
Revista: Journal of the American Ceramic Society, 96 (2013) 2921-2925
resumen | texto completo


The dislocation microstructure was studied in 4H–SiC samples plastically deformed by basal slip activation around the transition temperature (1000°C–1100°C). Dissociation of basal dislocations takes place over a wide temperature range (800°C–1300°C), but its influence on dislocation motion is different in the high- and low-temperature regimes due to the difference in mobility of partials. Consequently, this material exhibits a completely different mechanical behavior below and above its transition temperature, indicating a change in the deformation mechanism. In this work, the dislocation microstructure was studied around the transition temperature at which both mechanisms are still operative, thus providing a richer number of different configurations generated by dissociation of basal dislocations. They were observed and analyzed by means of the complementary use of weak-beam dark-field imaging and high-resolution transmission electron microscopy. Firstly, 3C band nucleation in the 4H–SiC matrix was identified and its appearance discussed from an energy standpoint. Secondly, the attractive interaction between partials in dipoles and the difference in mobility between the leading and the trailing partial have remarkable effects on the dissociation width, and explain the absence of work hardening above the transition temperature.

Agosto, 2013 | DOI: 10.1111/jace.12434

Titulo: High temperature plasticity in yttria stabilised tetragonal zirconia polycrystals (Y-TZP)
Autores: Dominguez-Rodriguez, A; Gomez-Garcia, D; Wakai, F
Revista: International Materials Reviews, 58 (2013) 399-417
resumen | texto completo


The literature data on the superplastic deformation of high purity yttria stabilised tetragonal zirconia polycrystals is reviewed in detail. It is shown that, based on the existence of a threshold stress, the single mechanism of grain boundary sliding (GBS) accommodated by diffusional processes can explain the superplasticity of these materials over all the ranges of temperature, stress, grain size, and surrounding atmosphere that have been studied. The origin of the threshold stress and its quantitative dependence on temperature and grain size is explained in terms of the segregation of yttrium atoms at the grain boundaries. A new model for GBS accommodated by lattice or grain-boundary diffusion is presented which can explain the transition of the stress exponent from 2 to 1.

Julio, 2013 | DOI: 10.1179/1743280413Y.0000000018

Titulo: Spark plasma sintering of TixTa1−xC0.5N0.5-based cermets: Effects of processing conditions on chemistry, microstructure and mechanical properties
Autores: Cordoba, Jose M.; Chicardi, Ernesto; Poyato, Rosalia; Gotor, Francisco J.; Medri, Valentina; Guicciardi, Stefano; Melandri, Cesare
Revista: Chemical Engineering Journal, 230 (2013) 558-566
resumen | texto completo


Nanometric powdered TixTa1−xC0.5N0.5-based cermets were fabricated using a mechanically induced self-sustaining reaction and consolidated by spark plasma sintering. Highly dense cermets were obtained, and their chemistry, microstructure and mechanical properties were characterised by X-ray diffraction, scanning electron microscopy, image analysis, microindentation and nanoindentation. The microhardness was found to depend directly on the contiguity and size of the ceramic hard particles. The samples synthesised at the lowest temperature (1150 °C) exhibited more homogeneous microstructures and smaller ceramic particles and the best combination of microhardness and fracture toughness.

Julio, 2013 | DOI: 10.1016/j.cej.2013.06.104

Titulo: Removal of basic yellow cationic dye by an aqueous dispersion of Moroccan stevensite
Autores: Ajbary, M; Santos, A; Morales-Florez, V; Esquivias, L
Revista: Applied Clay Science. 80-81 (46-51)
resumen | texto completo


The aim of this study was to investigate the adsorption of basic yellow, a cationic dye, from aqueous solution by natural stevensite, with 104 m2/g of specific surface area. The kinetics and the effects of several experimental parameters such as the pH of the solution, adsorbent dose and initial dye concentration were researched using a batch adsorption technique. The results showed that an alkaline pH favoured basic yellow adsorption and the adsorption reached equilibrium in about 20 min. It was concluded that the adsorption process was governed by the electrostatic interaction. The isothermal data were fitted by means of Langmuir and Freundlich equations, and a monolayer adsorption capacity of 454.54 mg/g was calculated. Finally, a good agreement was found between the pseudo-second order model and the experimental data. A high maximum adsorption capacity was obtained (526 mg/g) and a maximum surface density of ~ 9 dye molecules/nm2 was estimated, involving a columnar arrangement of the adsorbed molecules.

Julio, 2013 | DOI: 10.1016/j.clay.2013.05.011

Titulo: Characterisation of Co@Fe3O4 core@shell nanoparticles using advanced electron microscopy
Autores: Knappett, BR; Abdulkin, P; Ringe, E; Jefferson, DA; Lozano-Perez, S; Rojas, TC; Fernandez, A; Wheatley, AEH
Revista: Nanoscale, 5 (2013) 5765-5772
resumen | texto completo


Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.

Junio, 2013 | DOI: 10.1039/C3NR33789H

Titulo: A new bottom-up methodology to produce silicon layers with a closed porosity nanostructure and reduced refractive index
Autores: Godinho, V; Caballero-Hernandez, J; Jamon, D; Rojas, TC; Schierholz, R; Garcia-Lopez, J; Ferrer, FJ; Fernandez, A
Revista: Nanotechnology, 24 (2013) 275604
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A new approach is presented to produce amorphous porous silicon coatings (a-pSi) with closed porosity by magnetron sputtering of a silicon target. It is shown how the use of He as the process gas at moderated power (50–150 W RF) promotes the formation of closed nanometric pores during the growth of the silicon films. The use of oblique-angle deposition demonstrates the possibility of aligning and orientating the pores in one direction. The control of the deposition power allows the control of the pore size distribution. The films have been characterized by a variety of techniques, including scanning and transmission electron microscopy, electron energy loss spectroscopy, Rutherford back scattering and x-ray photoelectron spectroscopy, showing the incorporation of He into the films (most probably inside the closed pores) and limited surface oxidation of the silicon coating. The ellipsometry measurements show a significant decrease in the refractive index of porous coatings (n500 nm = 3.75) in comparison to dense coatings (n500 nm = 4.75). The capability of the method to prepare coatings with a tailored refractive index is therefore demonstrated. The versatility of the methodology is shown in this paper by preparing intrinsic or doped silicon and also depositing (under DC or RF discharge) a-pSi films on a variety of substrates, including flexible materials, with good chemical and mechanical stability. The fabrication of multilayers of silicon films of controlled refractive index in a simple (one-target chamber) deposition methodology is also presented.

Junio, 2013 | DOI: 10.1088/0957-4484/24/27/275604

Titulo: Mechanical properties of ZrB2- and HfB2-based ultra-high temperature ceramics fabricated by spark plasma sintering
Autores: Zapata-Solvas, E; Jayaseelan, DD; Lin, HT; Brown, P; Lee, WE
Revista: Journal of the European Ceramic Society, 33 (2013) 1373-1386
resumen | texto completo


Flexural strengths at room temperature, at 1400 °C in air and at room temperature after 1 h oxidation at 1400 °C were determined for ZrB2- and HfB2-based ultra-high temperature ceramics (UHTCs). Defects caused by electrical discharge machining (EDM) lowered measured strengths significantly and were used to calculate fracture toughness via a fracture mechanics approach. ZrB2 with 20 vol.% SiC had room temperature strength of 700 ± 90 MPa, fracture toughness of 6.4 ± 0.6 MPa, Vickers hardness at 9.8 N load of 21.1 ± 0.6 GPa, 1400 °C strength of 400 ± 30 MPa and room temperature strength after 1 h oxidation at 1400 °C of 678 ± 15 MPa with an oxide layer thickness of 45 ± 5 μm. HfB2 with 20 vol.% SiC showed room temperature strength of 620 ± 50 MPa, fracture toughness of 5.0 ± 0.4 MPa, Vickers hardness at 9.8 N load of 27.0 ± 0.6 GPa, 1400 °C strength of 590 ± 150 MPa and room temperature strength after 1 h oxidation at 1400 °C of 660 ± 25 MPa with an oxide layer thickness of 12 ± 1 μm. 2 wt.% La2O3 addition to UHTCs slightly reduced mechanical performance while increasing tolerance to property degradation after oxidation and effectively aided internal stress relaxation during spark plasma sintering (SPS) cooling, as quantified by X-ray diffraction (XRD). Slow crack growth was suggested as the failure mechanism at high temperatures as a consequence of sharp cracks formation during oxidation.

Junio, 2013 | DOI: 10.1016/j.jeurceramsoc.2012.12.009

Titulo: Structure of supercritically dried calcium silicate hydrates (C–S–H) and structural changes induced by weathering
Autores: Morales-Florez, V; de la Rosa-Fox, N
Revista: Journal of Materials Science, 48 (2013) 5022-5028
resumen | texto completo


The nanostructure of supercritically dried calcium silicate hydrates was researched. This particular drying procedure was used to avoid nanostructure modifications due to conventional drying processes. Thus, in this study, the as-precipitated cementitious C–S–H structure was obtained for the first time. A specific surface area 20 % larger than conventionally dried C–S–H was measured. Given the importance of this nanostructured phase for the properties of hydrated cements, especially when in contact with CO2-rich environments, the supercritically dried C–S–H was weathered for 2 weeks. The structural effects of this weathering process on the C–S–H were researched and calcium carbonate microcrystal precipitation or the presence of silica by-product are reported. Calcite and aragonite polymorphs were observed, as well as nanoporous silica forming globular arrangements. In addition, 2 weeks of weathering was not enough to carbonate the entire C–S–H sample.

Junio, 2013 | DOI: 10.1007/s10853-013-7289-6

Titulo: Surface properties of anatase TiO2 nanowire films grown from a fluoride-containing solution
Autores: Berger, T; Anta, JA; Morales-Florez, V
Revista: Chemphyschem, 14 (2013) 1676-1685
resumen | texto completo


Controlling the surface chemistry of nucleating seeds during wet-chemical synthesis allows for the preparation of morphologically well-defined nanostructures. Synthesis conditions play a key role in the surface properties, which directly affect the functional properties of the material. Therefore, it is important to establish post-synthesis treatments to facilitate the optimization of surface properties with respect to a specific application, without losing the morphological peculiarity of the nanostructure. We studied the surface properties of highly crystalline and porous anatase TiO2 nanowire (NW) electrodes, grown by chemical-bath deposition in fluoride-containing solutions, using a combined electrochemical and spectroscopic approach. As-deposited films showed low capacity for catechol adsorption and a poor photoelectrocatalytic activity for water oxidation. Mild thermal annealing at 200 °C resulted in a significant improvement of the electrode photoelectrocatalytic activity, whereas the bulk properties of the NWs (crystal structure, band-gap energy) remained unchanged. Enhancement of the functional properties of the material is discussed on the basis of adsorption capacity and electronic properties. The temperature-induced decrease of recombination centers, along with the concomitant increase of adsorption and reaction sites upon thermal annealing are called to be responsible for such improved performance.

Mayo, 2013 | DOI: 10.1002/cphc.201300024

Titulo: Exploring the benefits of depositing hard TiN thin films by non-reactive magnetron sputtering
Autores: Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A; Sanchez-Lopez, JC
Revista: Applied Surface Science, 275 (2013) 121-126
resumen | texto completo


The aim of this paper is to compare the mechanical and tribological properties of TiN coatings prepared in a conventional magnetron sputtering chamber according to two different routes: the usual reactive sputtering of a Ti target in an Ar/N2 atmosphere vs. the comparatively more simple sputtering of a TiN target in a pure Ar atmosphere. Improved properties in term of hardness and wear rates were obtained for films prepared by non-reactive sputtering route, due to the lower presence of oxynitride species and larger crystalline domain size. Additionally, a significant hardness enhancement (up to 45 GPa) is obtained when a −100 V d.c. bias is applied during growth. This behaviour is explained by non-columnar growth and small grain size induced by effective ion bombarding. These results demonstrate that non-reactive sputtering of TiN target appears a simple and efficient method to prepare hard wear-resistant TiN films.

Mayo, 2013 | DOI: 10.1016/j.apsusc.2013.01.098

Titulo: Structure and tribological properties of MoCN-Ag coatings in the temperature range of 25–700 °C
Autores: Shtansky, DV; Bondarev, AV; Kiryukhantsev-Korneev, PV; Rojas, TC; Godinho, V; Fernandez, A
Revista: Applied Surface Science, 273 (2013) 408-414
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The preparation of hard coatings with low friction coefficient over a wide temperature range is still a challenge for the tribological community. The development of new nanocomposite materials consisting of different metal-ceramic phases, each of which exhibiting self-lubricating characteristics at different temperatures, may help to solve this problem. We report on the structure and tribological properties of MoCN-Ag coatings deposited by magnetron co-sputtering of Mo and C (graphite) targets and simultaneous sputtering of an Ag target either in pure nitrogen or in a gaseous mixture of Ar + N2. The structure and elemental composition of the coatings were studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, Raman spectroscopy, and glow discharge optical emission spectroscopy. The tribological properties of the coatings against an Al2O3 ball were investigated first at discrete temperatures of 25, 500, and 700 °C, and then during continuous heating in the temperature range of 25–700 °C. The coating structure and their respective wear tracks were also examined to elucidate their phase transformations during heat treatments. The lowest friction coefficients (<0.4) were observed in the temperature ranges of 25–100 °C and 400–700 °C and can be explained by the presence of a free amorphous carbon phase, which served as a lubricant at low temperatures, and by a positive role of silver and two phases forming at elevated temperatures, molybdenum oxide and silver molybdate, which provided lubrication above 400 °C. In the temperature range between 100 and 400 °C, the friction coefficient was relatively high. This problem is to be addressed in future works.

Abril, 2013 | DOI: 10.1016/j.apsusc.2013.02.055

Titulo: Segregation to the grain boundaries in YSZ bicrystals: A Molecular Dynamics study
Autores: Gonzalez-Romero, RL; Melendez, JJ; Gomez-Garcia, D; Cumbrera, FL; Dominguez-Rodriguez, A
Revista: Solid State Ionics, 237 (2013) 8-15
resumen | texto completo


A Molecular Dynamics study about the segregation of yttrium at 1500 K to a Σ5 grain boundary in 8 mol% YSZ has been performed. Segregation has been induced by explicitly taking into account the excess energy associated to the elastic misfit effect for yttrium cations located nearby the grain boundary planes. After an initial transient, a steady regime is reached, in which the number of yttrium cations does not increase with time. Accumulation of yttrium cations is accompanied by that of zirconium ones and oxygen vacancies at some distance of the grain boundary planes. The changes in the radial distribution functions for different ionic pairs are discussed, as also the effect of segregation on oxygen diffusion along the grain boundaries and in volume. Finally, the possibility that segregated yttrium located at available free sites at the grain boundaries is pointed out.

Marzo, 2013 | DOI: 10.1016/j.ssi.2013.02.002

Titulo: Behaviour of Au-citrate nanoparticles in seawater and accumulation in bivalves at environmentally relevant concentrations
Autores: Garcia-Negrete, C. A.; Blasco, J.; Volland, M.; Rojas, T. C.; Hampel, M.; Lapresta-Fernandez, A.; Jimenez de Haro, M. C.; Soto, M.; Fernandez, A.
Revista: Environmental Pollution, 174 (2013) 134-141
resumen | texto completo


The degree of aggregation and/or coalescence of Au-citrate nanoparticles (AuNPs, mean size 21.5 ± 2.9 nm), after delivery in simulated seawater, are shown to be concentration-dependent. At low concentrations no coalescence and only limited aggregation of primary particles were found. Experiments were performed in which the marine bivalve (Ruditapes philippinarum) was exposed to AuNPs or dissolved Au and subsequently, bivalve tissues were studied by Scanning and Transmission Electron Microscopy and chemical analyses. We show that the bivalve accumulates gold in both cases within either the digestive gland or gill tissues, in different concentrations (including values of predicted environmental relevance). After 28 days of exposure, electron-dense deposits (corresponding to AuNPs, as proven by X-ray microanalysis) were observed in the heterolysosomes of the digestive gland cells. Although non-measurable solubility of AuNPs in seawater was found, evidence is presented of the toxicity produced by Au3+ dissolved species (chloroauric acid solutions) and its relevance is discussed.

Febrero, 2013 | DOI: 10.1016/j.envpol.2012.11.014

Titulo: Solvent-Controlled Synthesis and Luminescence Properties of Uniform Eu:YVO4 Nanophosphors with Different Morphologies
Autores: Nunez, N; Sabek, J; Garcia-Sevillano, J; Cantelar, E; Escudero, A; Ocana, M
Revista: European Journal of Inorganic Chemistry, 8 (2013) 1301-1309
resumen | texto completo


A facile solvothermal route has been developed for the preparation of tetragonal europium-doped yttrium orthovanadate nanoparticles (Eu:YVO4) and is based on a homogeneous precipitation reaction at 120 °C from solutions of rare earth precursors (yttrium acetylacetonate and europium nitrate) and sodium orthovanadate in ethylene glycol or ethylene glycol/water mixtures. The nature of the solvent has a dramatic effect on the morphology and crystallinity of the resulting nanoparticles. Polycrystalline nanoellipsoids (130 × 60 nm) were obtained in pure ethylene glycol, whereas quasispherical nanoparticles (100 nm) with monocrystalline character precipitated in ethylene glycol/water (7:3 by volume) mixtures. To explain these different morphological and structural features, the mechanism of particles formation was investigated. The effects of the doping level on the luminescence properties (emission spectra and luminescence lifetime) were also evaluated to find the optimum nanophosphors. Finally, it is shown that the luminescent efficiency of the quasispherical nanoparticles was higher than that of the nanoellipsoids; this can be related to differences in crystallinity and in impurity content.

Febrero, 2013 | DOI: 10.1002/ejic.201201016

Titulo: Strong quantum confinement effects in SnS nanocrystals produced by ultrasound-assisted method
Autores: Azizian-Kalandaragh, Y; Khodayari, A; Zeng, ZP; Garoufalis, CS; Baskoutas, S; Gontard, LC
Revista: Journal of Nanoparticle Research, 15 (2013) 1388
resumen | texto completo


Nanocrystalline SnS powder has been prepared using tin chloride (SnCl2) as a tin ion source and sodium sulfide (Na2S) as a sulfur ion source with the help of ultrasound irradiation at room temperature. The as-synthesized SnS nanoparticles were quantitatively analyzed and characterized in terms of their morphological, structural, and optical properties. The detailed structural and optical properties confirmed the orthorhombic SnS structure and a strongly blue shifted direct band gap (1.74 eV), for synthesized nanoparticles. The measured band gap energy of SnS nanoparticles is in a fairly good agreement with the results of theoretical calculations of exciton energy based on the potential morphing method in the Hartree–Fock approximation.

Diciembre, 2012 | DOI: 10.1007/s11051-012-1388-1

Titulo: Tribological properties of surface-modified Pd nanoparticles for electrical contacts
Autores: Abad, MD; Sanchez-Lopez, JC
Revista: Wear, 297 (2013) 943-951
resumen | texto completo


A fully comprehensive study of the tribological behavior of palladium nanoparticles (Pd NPs) capped by tetrabutylammonium chains using a ball-on-disk tribometer under different conditions of applied load, concentration, tribometer motion, linear speed and nature of the counterface is revised. A low concentration of NPs (2 wt%) in tetrabutylammonium acetate was found sufficient to improve the tribological properties due to the formation of a protective transfer film (TF) comprised of metallic Pd. The increase of the applied load (up to 20 N, 1.82 GPa of contact pressure) confirmed the excellent extreme-pressure behavior avoiding the counterfaces from severe wear. After a running-in period whose duration depends on the operating conditions, the TF build-up allows to maintain a low contact electrical resistance through the contact (<0.1 kΩ) during the entire test. When the Pd NPs are used with ceramic counterfaces, the nanoparticles increase the load-bearing capabilities and performance of the base without forming TF, likely by mixed or boundary lubrication and healing effects. Finally, the Pd NPs are demonstrated to be useful as a thin solid lubricant film in reciprocating motion yielding a comparable tribological behavior. Hence, the presented surface Pd NPs can be very helpful to extend life of sliding components due to their high strength resistance providing a gateway to electrical conduction as well.

Diciembre, 2012 | DOI: 10.1016/j.wear.2012.11.009

2012


Titulo: Chemical–physical characterization of isolated plant cuticles subjected to low-dose γ-irradiation
Autores: Heredia-Guerrero, Jose A; de Lara, Rocio; Dominguez, Eva; Heredia, Antonio; Benavente, Juana; Benitez, Jose J
Revista: Chemistry and physics of lipids, 165 (2012) 803-808
resumen | texto completo


Isolated tomato fruit cuticles were subjected to low dose (80 Gy) γ-irradiation, as a potential methodology to prevent harvested fruit and vegetables spoilage. Both irradiated and non-irradiated samples have been morphologically and chemically characterized by scanning electron (SEM), atomic force (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopies. Additionally, electrochemical measurements comprising membrane potential and diffusive permeability were carried out to detect modifications in transport properties of the cuticle as the fruit primary protective membrane. It has been found that low dose γ-irradiation causes some textural changes on the surface but no significant chemical modification. Texture modification is found to be due to a partial removal of outermost (epicuticular) waxes which is accompanied by mild changes of electrochemical parameters such as the membrane fixed charge, cation transport number and salt permeability. The modification of such parameters indicates a slight reduction of the barrier properties of the cuticle upon low dose γ-irradiation.

Noviembre, 2012 | DOI: 10.1016/j.chemphyslip.2012.10.003

Titulo: New insights into the synergistic effect in bimetallic-boron catalysts for hydrogen generation: The Co–Ru–B system as a case study
Autores: Arzac, G. M.; Rojas, T. C.; Fernandez, A.
Revista: Applied Catalysis B-Environmental, 128 (2012) 39-47
resumen | texto completo


Catalysed sodium borohydride hydrolysis is a high-potential method to produce hydrogen for portable applications. Co–B catalysts are the most chosen because they are easily prepared, cheap and efficient. The addition of small amounts of Ru produces a significant enhancement in catalytic activity.

In the present work a series of Co–Ru–B catalysts with variable Ru content was prepared, isolated and characterized. The comprehension of the synergistic effect was achieved trough the incorporation of the nanostructural dimension to the study of surface and bulk chemical states of the involved atoms along the series. It was found that up to 70% (of total metal) atomic content of Ru the catalysts can be considered isostructural to the single Co–B catalyst in the nanoscale. A structural transition occurs in the case of the pure Ru–B material to produce a boron deficient material with higher nanoparticle size. This structural transition together with Co segregation and Ru dispersion play a key role when explaining a [OH−] dependent effect.

The inexistence of borate layers in Ru rich catalysts is suggestive in the research for non deactivating catalysts.

Octubre, 2012 | DOI: 10.1016/j.apcatb.2012.02.013

Titulo: Deactivation, reactivation and memory effect on Co–B catalyst for sodium borohydride hydrolysis operating in high conversion conditions
Autores: Arzac, GM; Hufschmidt, D; De Haro, MCJ; Fernandez, A; Sarmiento, B; Jimenez, MA; Jimenez, MM
Revista: International Journal of Hydrogen Energy, 37 (2012) 14373-14381
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A system with a continuous reactor to produce hydrogen by sodium borohydride hydrolysis was designed and built. The purpose was to test a supported Co–B catalyst durability upon cycling and long life experiments in high conversion conditions. A Stainless Steel monolith was built and calcined to improve adherence. For comparison a Ru–B catalyst was tested upon cycling. Both Co–B and Ru–B catalysts are durable during 6 cycles and then deactivate. A known reactivation procedure has proven to be more effective for the Co–B than for the Ru–B catalyst. This is related to stronger adsorption of B–O based compounds on the Co–B catalyst which is reversible upon acid washing. For the Ru–B catalyst deactivation may be more related to particle agglomeration than to the adsorption of B–O based species. The continuous system enlarges the catalysts durability because of the continuous borate elimination at elevated temperatures.

Septiembre, 2012 | DOI: 10.1016/j.ijhydene.2012.06.117

Titulo: Chemical and microstructural characterization of (Y or Zr)-doped CrAlN coatings
Autores: Rojas, T. C.; El Mrabet, S.; Dominguez-Meister, S.; Brizuela, M.; Garcia-Luis, A.; Sanchez-Lopez, J. C.
Revista: Surface and Coatings Technology, 211 (2012) 104-110
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Magnetron sputtered chromium aluminium nitride films are excellent candidates for advanced machining and protection for high temperature applications. In this work CrAlN-based coatings including Y or Zr as dopants (≈ 2 at.%) are deposited by d.c. reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N2 mixtures. The hardness properties are found in the range of 22–33 GPa with H/E ratios close to 0.1. The influence of the dopant element in terms of oxidation resistance after heating in air at 1000 °C is studied by means of X-ray diffraction (XRD), cross-sectional scanning electron microscopy (X-SEM) and energy dispersive X-ray analysis (EDX). The microstructure and chemical bonding are investigated using a transmission electron microscope (TEM) and electron energy-loss spectroscopy (EELS) respectively. The improvement in oxidation resistance as compared to pure CrN coating is manifested in the formation of a Al-rich outer layer that protects the underneath coating from oxygen diffusion. The best performance obtained with the CrAlYN film is investigated by in situ annealing of this sample inside the TEM in order to gain knowledge about the structural and chemical transformations induced during heating.

Septiembre, 2012 | DOI: 10.1016/j.surfcoat.2011.07.071

Titulo: Phase composition and tribomechanical properties of Ti-B-C nanocomposite coatings prepared by magnetron sputtering
Autores: Sanchez-Lopez, JC; Abad, MD; Justo, A; Gago, R; Endrino, JL; Garcia-Luis, A; Brizuela, M
Revista: Journal of Physics D: Applied Physics, 45 (2012) 375401
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Protective nanocomposite coatings based on hard ceramic phases (TiC, TiB2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, Ti–B–C nanocomposite coatings were prepared by co-sputtering of graphite and TiB2 targets. Varying the discharge power ratio applied to the graphite and TiB2 targets from 0 to 2, the a-C content in the coatings could be tuned from 0 to 60%, as observed by means of Raman and x-ray photoelectron spectroscopy (XPS). The microstructural characterization demonstrated a progressive decrease in crystallinity from an initial nanocrystalline (nc) TiB2-like structure to a distorted TiBxCy ternary compound with increasing C concentration. X-ray absorption near-edge structure measurements on the B K-edge helped to determine a hexagonal arrangement around the B atoms in the ternary TiBxCy phase. A fitting analysis of the C 1s XPS peak allowed us to evaluate the relative amount of a-C and TiBxCy components. A drastic change in hardness (from 52 to 13 GPa) and friction coefficient values (from 0.8 to 0.2) is noticed when moving from nc-TiB2 to TiBC/a-C nanocomposites. The fraction of a-C necessary to decrease the friction below 0.2 was found to be 45%. Raman observation of the wear tracks determined the presence of disordered sp2-bonded carbon phase associated with the diminution of the friction level.

Agosto, 2012 | DOI: 10.1088/0022-3727/45/37/375401

Titulo: Microstructural characterization of hydrophobic Ti1−xAlxN coatings with moth-eye-like surface morphology
Autores: Godinho, V; Lopez-Santos, C; Rojas, TC; Philippon, D; de Haro, MCJ; Lucas, S; Fernandeza, A
Revista: Journal of Alloys and Compounds, 536 (2012) S398-S406
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Ti1−xAlxN thin films with different Al content were deposited by magnetron sputtering. The combination of electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) was used to evaluate the composition of the coatings. The effect of Al content on the morphology and properties of the coatings was investigated. High resolution electron microscopy and related techniques revealed the formation of a pillared moth-eye-like nanostructure with variable size and distribution of meso- and nano-columns and different degree of open porosity that depends on the Al content on the coating. For low Al content (x ≤ 0.21) c-(Ti,Al)N highly porous columns ending in a sharp pyramidal shape present low reflectivity and high hydrophobicity. While the precipitation of h-AlN phase at the column boundaries for x = 0.71 suppresses the c-(Ti,Al)N columnar growth and produces a smother surface, with higher reflectivity and less hydrophobic character.

Agosto, 2012 | DOI: 10.1016/j.jallcom.2012.02.178

Titulo: Water-dependent micromechanical and rheological properties of silica colloidal crystals studied by nanoindentation
Autores: Gallego-Gomez, Francisco; Morales-Florez, Victor; Blanco, Alvaro; de la Rosa-Fox, Nicolas; Lopez, Cefe
Revista: Nano Letters, 12 (2012) 4920-4924
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Here we show the suitability of nanoindentation to study in detail the micromechanical response of silica colloidal crystals (CCs). The sensitivity to displacements smaller than the submicrometer spheres size, even resolving discrete events and superficial features, revealed particulate features with analogies to atomic crystals. Significant robustness, long-range structural deformation, and large energy dissipation were found. Easily implemented temperature/rate-dependent nanoindentation quantified the paramount role of adsorbed water endowing silica CCs with properties of wet granular materials like viscoplasticity. A novel "nongranular" CC was fabricated by substituting capillary bridges with silica necks to directly test water-independent mechanical response. Silica CCs, as specific (nanometric, ordered) wet granular assemblies with well-defined configuration, may be useful model systems for granular science and capillary cohesion at the nanoscale.

Julio, 2012 | DOI: 10.1021/nl3024998

Titulo: Rapid carbothermic synthesis of silicon carbide nano powders by using microwave heating
Autores: Moshtaghioun, BM; Poyato, R; Cumbrera, FL; de Bernardi-Martin, S; Monshi, A; Abbasi, MH; Karimzadeh, F; Dominguez-Rodriguez, A
Revista: Journal of the European Ceramic Society, 32 (2012) 1787-1794
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This paper reports an improved procedure for synthesis of silicon carbide nanopowders from silica by carbothermic reduction under fast microwave-induced heating. The powders have been prepared by direct solid-state reaction in a 2.45 GHz microwave field in nitrogen atmosphere after 40 h milling. For the first time, the formation of silicon carbide (beta-SiC) as a major phase can be achieved at 1200 degrees C in 5 min of microwave exposure, resulting in nano sized particles ranging from 10 to 40 nm under optimized synthesis condition. The Rietveld quantitative phase-composition analysis confirmed that the major SiC polytype is cubic SiC (beta-SiC) with 98.5(4) weight fraction and the remained is minor hexagonal SiC polytypic (alpha-SiC) phases. Therefore this method is the most efficient one for SiC powder synthesis in terms of energy and time saving as well as preparation of SiC nano powders.

Junio, 2012 | DOI: 10.1016/j.jeurceramsoc.2011.12.021

Titulo: Processing of Swnt-Reinforced Yttria Stabilized Zirconia by Spark Plasma Sintering and Microstructure Characterization
Autores: S. de Bernardi-Martín, R. Poyato, Diego Gómez García, Arturo Domínguez-Rodríguez
Revista: Journal of Nano Research, 18-19 (2012) 317-323
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Single wall carbon nanotube reinforced yttria stabilized zirconia ceramic materials have been obtained by means of spark plasma sintering technique. Single wall carbon nanotubes were treated in an acid solution before mixing with zirconia powders to obtain a uniform distribution of both powders. This method allows obtaining ceramic materials with a grain size between 200 nanometers and 1 micron and with a grain size distribution which depends on processing conditions. This new route opens a new perspective for new ceramic composites tailoring with enhanced mechanical properties as structural materials

Junio, 2012 | DOI: 10.4028/www.scientific.net/JNanoR.18-19.317

Titulo: Three-dimensional fabrication and characterisation of core-shell nano-columns using electron beam patterning of Ge-doped SiO2
Autores: Gontard, LC; Jinschek, JR; Ou, HY; Verbeeck, J; Dunin-Borkowski, RE
Revista: Applied Physics Letters, 100 (2012) 263113
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A focused electron beam in a scanning transmission electron microscope (STEM) is used to create arrays of core-shell structures in a specimen of amorphous SiO2 doped with Ge. The same electron microscope is then used to measure the changes that occurred in the specimen in three dimensions using electron tomography. The results show that transformations in insulators that have been subjected to intense irradiation using charged particles can be studied directly in three dimensions. The fabricated structures include core-shell nano-columns, sputtered regions, voids, and clusters.

Mayo, 2012 | DOI: 10.1063/1.4731765

Titulo: Microstructural and chemical characterization of nanostructured Tialsin coatings with nanoscale resolution
Autores: Godinho, V; Rojas, TC; Trasobares, S; Ferrer, FJ; Delplancke-Ogletree, MP; Fernandez, A
Revista: Microscopy and Microanalysis, 18 (2012) 568-581
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Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa).

Mayo, 2012 | DOI: 10.1017/S1431927612000384

Titulo: Electrons in the Band Gap: Spectroscopic Characterization of Anatase TiO2 Nanocrystal Electrodes under Fermi Level Control
Autores: Berger, T; Anta, JA; Morales-Florez, V
Revista: Journal of Physical Chemistry C, 116 (2012) 11444-11455
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Macroscopic properties of semiconductor nanoparticle networks in functional devices strongly depend on the electronic structure of the material. Analytical methods allowing for the characterization of the electronic structure in situ, i.e., in the presence of an application-relevant medium, are therefore highly desirable. Here, we present the first spectral data obtained under Fermi level control of electrons accumulated in anatase TiO 2 electrodes in the energy range from the MIR to the UV (0.1-3.3 eV). Band gap states were electrochemically populated in mesoporous TiO 2 films in contact with an aqueous electrolyte. The combination of electrochemical and spectroscopic measurements allows us for the first time to determine both the energetic location of the electronic ground states as well as the energies of the associated optical transitions in the energetic range between the fundamental absorption threshold and the onset of lattice absorption. On the basis of our observations, we attribute spectral contributions in the vis/NIR to d-d transitions of Ti 3+ species and a broad MIR absorption, monotonically increasing toward lower wavenumbers, to a quasi-delocalization of electrons. Importantly, signal intensities in the vis/NIR and MIR are linearly correlated. Absorbance and extractable charge show the same exponential dependence on electrode potential. Our results demonstrate that signals in the vis/NIR and MIR are associated with an exponential distribution of band gap states.

Abril, 2012 | DOI: 10.1021/p212436b

Titulo: Electrostatic Induced Molecular Tilting in Self-Assembled Monolayers of n-Octadecylamine on Mica
Autores: Oviedo, J; San-Miguel, MA; Heredia-Guerrero, JA; Benitez, JJ
Revista: Journal of Physical Chemistry C, 116 (2012) 7099-7105
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Self-assembled monolayers of n-octadecylamine on mica (ODA/mica SAMs) have been investigated by atomic force microscopy (AFM) and by attenuated total reflectance infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopies. Topographic data characterizes a stable configuration with the alkyl skeleton tilted approximate to 46 degrees from the surface normal that is rationalized according to a well established structural alkyl chain packing model. Extended contact with air increases molecular tilting up to approximate to 58 degrees. ATR-FTIR and XPS reveal the presence of protonated amino groups within the monolayer and its increment upon exposure to air. The transition between both tilted states is explained assuming the protonation reaction as the driving force and introducing a model to evaluate an electrostatic repulsions term in the overall cohesive energy balance of the system. ODA molecules in the self-assembled monolayer respond to their spontaneous protonation by atmospheric water by tilting as a mechanism to relax the repulsions between -NH3+ heads.

Febrero, 2012 | DOI: 10.1021/jp300829g

Titulo: How Important is Working with an Ordered Electrode to Improve the Charge Collection Efficiency in Nanostructured Solar Cells?
Autores: Gonzalez-Vazquez, JP; Morales-Florez, V; Anta, JA
Revista: Journal of Physical Chemistry Letters, 3 (2012) 386-393
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The collection efficiency of carriers in solar cells based on nanostructured electrodes is determined for different degrees or morphological one-dimensional order. The transport process is modeled by random walk numerical simulation in a mesoporous electrode that resembles the morphology of nanostructured TiO2 electrodes typically used in dye-sensitized solar cells and related systems. By applying an energy relaxation procedure in the presence of an external potential, a preferential direction is induced in the system. It is found that the partially ordered electrode can almost double the collection efficiency with respect to the disordered electrode. However, this improvement depends strongly on the probability of recombination. For too rapid or too slow recombination, working with partially ordered electrodes will not be beneficial. The computational method utilized here makes it possible to relate the charge collection efficiency with morphology. The collection efficiency is found to reach very rapidly a saturation value, meaning that, in the region of interest, a slight degree of ordering might be sufficient to induce a large improvement in collection efficiency.

Enero, 2012 | DOI: 10.1021/jz2015988

Titulo: Nanoecotoxicity effects of engineered silver and gold nanoparticles in aquatic organisms
Autores: Lapresta-Fernandez, A; Fernandez, A; Blasco, J
Revista: TrAC Trends in Analytical Chemistry, 32 (2012) 40-59
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Engineered nanoparticles (ENPs) are increasingly being incorporated into commercial products. A better understanding is required of their environmental impacts in aquatic ecosystems.

This review deals with the ecotoxicity effects of silver and gold ENPs (AgNPs and AuNPs) in aquatic organisms, and considers the means by which these ENPs enter aquatic environments, their aggregation status and their toxicity. Since ENPs are transported horizontally and vertically in the water column, we discuss certain factors (e.g., salinity and the presence of natural organic materials), as they cause variations in the degree of aggregation, size range and ENP toxicity. We pay special attention to oxidative stress induced in organisms by ENPs.

We describe some of the main analytical methods used to determine reactive oxygen species, antioxidant enzyme activity, DNA damage, protein modifications, lipid peroxidation and relevant metabolic activities. We offer an overview of the mechanisms of action of AgNPs and AuNPs and the ways that relevant environmental factors can affect their speciation, agglomeration or aggregation, and ultimately their bio-availability to aquatic organisms.

Finally, we discuss similarities and differences in the adverse effects of ENPs in freshwater and salt-water systems.

Enero, 2012 | DOI: 10.1016/j.trac.2011.09.007

Titulo: Public concern over ecotoxicology risks from nanomaterials: Pressing need for research-based information
Autores: Lapresta-Fernandez, A; Fernandez, A; Blasco, J
Revista: Environment International, 39 (2012) 148-149
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[No abstract available]

Enero, 2012 | DOI: 10.1016/j.envint.2011.10.012

Titulo: Magnetron sputtered a-SiO xN y thin films: A closed porous nanostructure with controlled optical and mechanical properties
Autores: Godinho, V; Rojas, TC; Fernandez, A
Revista: Microporous and Mesoporous Materials, 149 (2012) 142-146
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Amorphous silicon oxynitride coatings with similar composition and different closed porosity were prepared by magnetron sputtering. Pores size, shape and distribution were evaluated by scanning electron microscopy and transmission electron microscopy. Raman and EELS analysis proved that the pores are filled with molecular nitrogen trapped during deposition. The mechanical properties evaluated by nanoindentation shows that the presence of closed nano-porosity does not compromise the mechanical integrity of these coatings. The introduction of closed porosity is shown as a good strategy for obtaining lower dielectric constant silicon oxynitride coatings with similar composition while keeping the good mechanical properties (∼13 GPa) characteristic of this type of coatings. The presence of close porosity gives also a good stability of coatings properties as compared to open porosity microstructures where gas phase in contact with the coatings can affect coatings properties.

Enero, 2012 | DOI: 10.1016/j.micromeso.2011.08.018

Titulo: An international round-robin calibration protocol for nanoindentation measurements
Autores: Cabibbo, M; Ricci, P; Cecchini, R; Rymuza, Z; Sullivan, J; Dub, S; Cohen, S
Revista: Micron, 43 (2012) 215-222
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Nanoindentation has become a common technique for measuring the hardness and elastic–plastic properties of materials, including coatings and thin films. In recent years, different nanoindenter instruments have been commercialised and used for this purpose. Each instrument is equipped with its own analysis software for the derivation of the hardness and reduced Young's modulus from the raw data. These data are mostly analysed through the Oliver and Pharr method. In all cases, the calibration of compliance and area function is mandatory. The present work illustrates and describes a calibration procedure and an approach to raw data analysis carried out for six different nanoindentation instruments through several round-robin experiments. Three different indenters were used, Berkovich, cube corner, spherical, and three standardised reference samples were chosen, hard fused quartz, soft polycarbonate, and sapphire. It was clearly shown that the use of these common procedures consistently limited the hardness and reduced the Young's modulus data spread compared to the same measurements performed using instrument-specific procedures. The following recommendations for nanoindentation calibration must be followed: (a) use only sharp indenters, (b) set an upper cut-off value for the penetration depth below which measurements must be considered unreliable, (c) perform nanoindentation measurements with limited thermal drift, (d) ensure that the load–displacement curves are as smooth as possible, (e) perform stiffness measurements specific to each instrument/indenter couple, (f) use Fq and Sa as calibration reference samples for stiffness and area function determination, (g) use a function, rather than a single value, for the stiffness and (h) adopt a unique protocol and software for raw data analysis in order to limit the data spread related to the instruments (i.e. the level of drift or noise, defects of a given probe) and to make the H and Er data intercomparable.

Enero, 2012 | DOI: 10.1016/j.micron.2011.07.016

Titulo: Analysis and application of the theories that rationalize the crystalline structures of fluorite-related rare earth oxides
Autores: Lopez-Cartes, C; Perez-Omil, JA; Rodriguez-Izquierdo, JM; Calvino, JJ
Revista: Catalysis Today, 180 (2012) 161-180
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The main current theories dealing with the crystalline structures of the fluorite related rare earth oxides, including those corresponding to reduced oxides, one based on the distribution of the coordination defect inside the fluorite structure, and the other which proposes the establishment of modular sequences constituted by modules with fluorite structure, are presented and comparatively explored in detail. Our in-depth analysis of both approximations indicates that they in fact provide smart and efficient rationalizations of the currently known intermediate rare earth oxides structures. We prove however that the strict application of the principles and rules proposed by each theory does not yield unique and unambiguous results for most of the members of the homologous series, as it has been claimed up to now. Moreover, the controversy about the reliability of these two, apparently different and competing, theories is definitely clarified and the exact equivalence of their structural predictions is demonstrated. Finally, we propose new extra systematization rules, not considered up to now in neither of these theoretical approaches, to overcome the observed limitations to properly rationalize the structure of this so technologically important family of oxides.

Diciembre, 2011 | DOI: 10.1016/j.cattod.2011.04.032

Titulo: Nanoscale mechanically induced structural and electrical changes in Ge 2Sb 2Te 5 films
Autores: Cecchini, R; Benitez, JJ; Sanchez-Lopez, JC; Fernandez, A
Revista: Journal of Applied Physics, 111 (2012) 016101 (3 pages)
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We demonstrate that the microstructure and electrical properties of Ge2Sb2Te5 films can be changed by a nanoscale mechanical process. Nanoscratching is used to define modified areas onto an as-deposited crystalline Ge2Sb2Te5 film. Scanning tunneling microscopy measurements show that the modified areas have a very low electrical conductivity. Micro-Raman measurements indicate that the mechanically induced microstructural changes are consistent with a phase transformation from crystalline to amorphous, which can be reversed by laser irradiation.

Diciembre, 2011 | DOI: 10.1063/1.3673592

Titulo: Changes on the nanostructure of cementitius calcium silicate hydrates (C-S-H) induced by aqueous carbonation
Autores: Morales-Florez, V; Findling, N; Brunet, F
Revista: Journal of Materials Science, 47 (2012) 764-771
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The nanostructure of the main binding phase of the hydrated cements, the calcium silicate hydrates (C–S–H), and their structural changes due to aqueous carbonation have been characterized using TEM, nitrogen physisorption, and SAXS. Synthetic C–S–H has been used for this purpose. Two different morphologies were identified, similar to the high density and low density C–S–H types. When submitting the sample to a CO2 flux, the low density phase was completely carbonated. The carbonation by-products, calcium carbonate, and silica gel were also identified and characterized. The precipitation of the silica gel increased the specific surface area from 95 to 132 m2/g, and its structure, formed by particles of ~5 nm typical radius, was observed by small angle X-ray scattering. In addition, the resistance of the high density C–S–H to carbonation is reported, and the passivating effect of the precipitated calcium carbonate is also discussed. Finally, the results have been compared with carbonation features observed in Portland cement carbonated experimentally at downhole conditions.

Diciembre, 2011 | DOI: 10.1007/s10853-011-5852-6

Titulo: Influence of silver content on the tribomechanical behavior on Ag-TiCN bioactive coatings
Autores: Sanchez-Lopez, JC; Abad, MD; Carvalho, I; Galindo, RE; Benito, N; Ribeiro, S; Henriques, M; Cavaleiro, A; Carvalho, S
Revista: Surface and Coatings Technology, 206 (2012) 2192-2198
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Surface modification of bulk materials used in biomedical applications has become an important prerequisite for better biocompatibility. In particular, to overcome the particle generation, low-wear coatings based on carbon (nitrogen) and containing antimicrobial elements such as silver are promising candidates. Thus, the present work explores the potentialities of silver-containing carbonitride-based (Ag-TiCN) thin films prepared by direct current unbalanced reactive magnetron sputtering. The silver content in the coatings was varied from 0 to 26.7at.% by changing the targets and the fraction of C 2H 2 and N 2 in the gas mixture with Ar. The obtained Ag-TiCN based coatings were characterized in terms of composition and microstructure. Mechanical and tribological properties of the films were studied by nanoindentation and reciprocating pin-on disk testing in a fetal bovine serum solution, respectively. Raman, scanning electron microscope and energy dispersive X-ray analysis was carried out in the contact region after tribological tests to obtain information about the friction mechanism. The cytotoxicity of the coatings was assessed by in vitro tests using fibroblast cells. The coatings comprised a mixture of TiC xN 1-x, Ag and a-C(N) x phases whose relative proportion varied depending on the Ag/Ti ratio. The mechanical, tribological and cytotoxicity properties were correlated with the chemical and phase composition. When the Ag/Ti ratios were below 0.20 (Ag contents <6.3at.%) the films resulted harder (~18GPa) with higher wear resistance (~10 -6mm 3/Nm), showing similar friction coefficient (~0.3) and good biocompatibility.

Diciembre, 2011 | DOI: 10.1016/j.surfcoat.2011.09.059

2011


Titulo: Magnetic core-shell fluorescent pH ratiometric nanosensor using a Stöber coating method
Autores: Lapresta-Fernández, A., Doussineau, T., Moro, A.J., Dutz, S., Steiniger, F., Mohr, G.J.
Revista: Analytica Chimica Acta, 707 (2011) 164-170
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We describe the use of a modified Stöber method for coating maghemite (&#947;-Fe2O3) nanocrystals with silica shells in order to built magnetic fluorescent sensor nanoparticles in the 50-70nm diameter range. In detail, the magnetic cores were coated by two successive silica shells embedding two fluorophores (two different silylated dye derivatives), which allows for ratiometric pH-measurements in the pH range 5-8. Silica coated magnetic nanoparticles were prepared using maghemite nanocrystals as cores (5-10nm in diameter) coated by tetraethoxyorthosilicate via hydrolysis/condensation in ethanol, catalyzed by ammonia. In the inner shell was covalently attached a sulforhodamine B, which was used as a reference dye; while a pH-sensitive fluorescein was incorporated into the outer shell. Once synthesized, the particles were characterized in terms of morphology, size, composition and magnetization, using dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). TEM analysis showed the nanoparticles to be very uniform in size. Wide-angle X-ray diffractograms showed, for uncoated as well as coated nanoparticles, typical peaks for the spinel structure of maghemite at the same diffraction angle, with no structural changes after coating. When using VSM, we obtained the magnetization curves of the resulting nanoparticles and the typical magnetization parameters as saturation magnetization (Ms), coercivity (Hc), and remanent magnetization (Mr). The dual-dye doped magnetic-silica nanoparticles showed a satisfactory magnetization that could be suitable for nanoparticle separation and localized concentration of them. Changes in fluorescence intensity of the pH indicator in the different pH buffered solutions were observed within few seconds indicating an easy accessibility of the embedded dye by protons through the pores of the silica shell. The relationship between the ratio in fluorescence (sensor/reference dyes) and pH was adjusted to a sigmoidal fit using a Boltzmann type equation. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% (w/v) of horse serum added, indicating that there are no significant statistical differences at a 95% confidence level.

Octubre, 2011 | DOI: 10.1016/j.aca.2011.09.008

Titulo: Procedure to use phosphogypsum industrial waste for mineral CO2 sequestration
Autores: Cárdenas-Escudero, C., Morales-Flórez, V., Pérez-López, R., Santos, A., Esquivias, L.
Revista: Journal of Hazardous Materials, 196 (2011) 431-435
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Industrial wet phosphoric acid production in Huelva (SW Spain) has led to the controversial stockpiling of waste phosphogypsum by-products, resulting in the release of significant quantities of toxic impurities in salt marshes in the Tinto river estuary. In the framework of the fight against global climate change and the effort to reduce carbon dioxide emissions, a simple and efficient procedure for CO2 mineral sequestration is presented in this work, using phosphogypsum waste as a calcium source. Our results demonstrate the high efficiency of portlandite precipitation by phosphogypsum dissolution using an alkaline soda solution. Carbonation experiments performed at ambient pressure and temperature resulted in total conversion of the portlandite into carbonate. The fate of trace elements present in the phosphogypsum waste was also investigated, and trace impurities were found to be completely transferred to the final calcite. We believe that the procedure proposed here should be considered not only as a solution for reducing old stockpiles of phosphogypsum wastes, but also for future phosphoric acid and other gypsum-producing industrial processes, resulting in more sustainable production.

Octubre, 2011 | DOI: 10.1016/j.jhazmat.2011.09.039

Titulo: Electrical properties and applications of carbon based nanocomposite materials: An overview
Autores: Sanjinés, R., Abad, M.D., Vâju, C., Smajda, R., Mionić, M., Magrez, A.
Revista: Surface and Coatings Technology, 206 (2011) 727-733
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The allotropic forms of carbon (amorphous and polycrystalline graphite, carbon black, fullerenes, nanotubes, graphene) exhibit a large variety of charge transport properties which have been stimulating fundamental and applied research for the development of new devices based on micro and nano-sized electronic systems. Carbon based nanocomposites offer the possibility to improve the device performances and to develop novel multifunctional material systems by combining the properties of each individual phase. In this paper we review the electrical properties of carbon materials and some of the most exciting carbon based nanocomposites, as well as their potential technological applications. First, the electrical properties of amorphous and polycrystalline graphitic materials and those of their related nanocomposites materials are discussed. Second, an overview of the state-of-art on research and applications of carbon nanotube-based composites is presented. Third, we discuss briefly the emerging area of research related to graphene materials. Finally, the electrical properties and applications of conducting carbon black aggregates and carbon black/polymer composites are overviewed.

Octubre, 2011 | DOI: 10.1016/j.surfcoat.2011.01.025

Titulo: Structure and Chemical State of Octadecylamine Self-Assembled Monolayers on Mica
Autores: Benitez, JJ; San-Miguel, MA; Dominguez-Meister, S; Heredia-Guerrero, JA; Salmeron, M
Revista: Journal of Physical Chemistry C, 115 (40) (2011) 19716-19723
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Structural and chemical data on n-octadecylamine self-assembled monolayers on mica (ODA/mica SAMs) have been obtained from ATR-FTIR and XPS spectroscopies. The analysis of the methylene modes concludes that alkylamine molecules are arranged in a rigid and well-ordered packing. Besides, the magnitude of the splitting of the methylene scissoring deflection is consistent with a molecular tilted configuration within the self-assembled layer, as already reported from topographic AFM data. Molecular dynamics simulations have supported this conclusion. XPS has revealed the presence of an important fraction of protonated amino groups (-NH3+) even in freshly prepared ODA/mica SAMs in air at RT. Two sources of protonation are proposed: (i) the acid-base reaction of (-NH2) end groups with the water adlayer on the surface of hydrophilic mica and (ii) the formation of an alkylamonium alkylcarbamate by a fast reaction with the atmospheric CO2 dissolved in such water adlayer. Though the water induced amino protonation is hypothetical, the presence of carbamate is univocally confirmed by ATR-FTIR. Upon extended contact with air (ripening) the conformational ordering in ODA/mica SAMs is slightly improved. Besides, further amino group protonation takes place with no additional carbamate formation. The process is described by a tentative mechanism in which protons are transferred from water molecules at the edges of SAMs islands to the inside. On the other side, carbamation is hindered by the steric effect of CO2 molecules trying to penetrate the close packed structure of octadecylamine molecules.

Septiembre, 2011 | DOI: 10.1021/jp203871g

Titulo: Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing
Autores: Lapresta-Fernndez, A., Doussineau, T., Dutz, S., Steiniger, F., Moro, A.J., Mohr, G.J.
Revista: Nanotechnology, 22 (2011), Article number 415501
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This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (&#8764;10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (&#8764;3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.

Septiembre, 2011 | DOI: 10.1088/0957-4484/22/41/415501

Titulo: Recent insights into xerogel and aerogel mineral composites for CO 2 mineral sequestration
Autores: Morales-Flórez, V., Santos, A., Esquivias, L.
Revista: Journal of Sol-Gel Science and Technology, 59 (2011) 417-423
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Supercritically dried composites have already been analysed and proposed as carbon dioxide sequesters. However, the economical and energetic costs of the supercritical drying process had to be re-evaluated, and were eventually found not to enhance the feasibility of the proposed route for CO2 mineral sequestration. Different composites series were synthesised with the only difference being the drying method. The structures of the porous matrix were characterised as well as their ability to capture CO2. The first results showed that the xerogel matrix is as good a host as the aerogel one, and also avoids expensive procedures such as supercritical drying for sample preparation without losing CO2 capture capacity and enhancing the efficiency of the whole carbon sequestration process. In this case, the sample preparation was simplified as much as possible, with the aim of reducing energetic and economic costs. Although good carbonation efficiencies were obtained with these cheap samples, the first results showed that previous high carbonation efficiencies could not be repeated.

Agosto, 2011 | DOI: 10.1007/s10971-010-2276-8

Titulo: Boron Compounds as Stabilizers of a Complex Microstructure in a Co-B-based Catalyst for NaBH4 Hydrolysis
Autores: Arzac, G.M., Rojas, T.C., Fernández, A.
Revista: ChemCatChem, 3 (2011) 1305-1313
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Co-B-based materials are widely used as catalysts for hydrogen generation through sodium borohydride self-decomposition. In the mid 1990s, the aqueous and organic chemistry involved in Co-B synthesis and handling was studied. Nevertheless, the exact microstructure of these catalysts has remained unsolved. Herein we present an exhaustive study which shows a new and complete microstructural view of a Co-B-based material together with the chemistry of the cobalt and boron involved. By using nanoscale-resolution microscopy and spectroscopy techniques, we have elucidated the role of boron compounds as stabilizers in a complex microstructure, which also explains its high catalytic performance and long-term stability. The catalyst is proposed to be made up of 1-3nm hcp Co0 nanoparticles embedded in amorphous CoxB (x=1, 2, 3), CoxOy, Co(BO2)2, and B2O3 phases alternatively or all together. All of these amorphous phases protect the nanocrystalline metallic core from growth and oxidation.

Julio, 2011 | DOI: 10.1002/cctc.201100101

Titulo: Identification of Ternary Phases in TiBC/a-C Nanocomposite Thin Films: Influence on the Electrical and Optical Properties
Autores: Manuel David Abad, Rosendo Sanjinés, Jose Luis Endrino, Raúl Gago, Joakim Andersson, Juan Carlos Sánchez-López
Revista: Plasma Processes and Polymers, 8 (2011) 579-588
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The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB2 (60:40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Grazing incidence X-ray diffraction reveals that the microstructure of the films is amorphous with small nanocrystallites emerging by increasing the C content that could be attributed to the formation of ternary (TiBxCy) or mixed binary (TiB2 and TiC) phases. Further information was then obtained by studying the chemical bonding by measuring the near-edge fine structure (NES) by electron energy-loss (B K-, C K-, and Ti L-edges) and X-ray absorption (B K- and Ti L-edges) spectroscopies. The NES analysis indicates the formation of a nanocrystalline ternary TiBxCy compound concomitant with the segregation of an a-C phase as the carbon content is increased. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the Van der Pauw method between 20 and 300 K. The films continuously lose their metallic character in terms of optical constants and resistivity with increasing carbon content. Theoretical fitting of the electrical properties using the grain-boundary scattering model supported the formation of a nanocomposite structure based on a ternary TiBxCy phase embedded in a matrix of a-C. The electron transport properties are mainly limited by the high density of point defects, grain size, and transmission probability.

Junio, 2011 | DOI: 10.1002/ppap.201000182

Titulo: Mechanical, microstructural and oxidation properties of reactively sputtered thin Cr-N coatings on steel
Autores: Cecchini, R., Fabrizi, A., Cabibbo, M., Paternoster, C., Mavrin, B.N., Denisov, V.N., Novikova, N.N., Haïdopoulo, M.
Revista: Thin Solid Films, 519 (2011) 6515-6521
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Thin (40 nm and 160 nm) CrN coatings were deposited on steel by reactive magnetron sputtering deposition, varying the N2 flow. The coatings were characterized in the as-deposited condition and after annealing in air at 500 °C for 1 h, by X-Ray Diffraction, Transmission Electron Microscopy, Raman and Fourier Transform Infrared spectroscopies. Hardness was measured by nanoindentation. Coatings have a nanocrystalline microstructure with the phase shifting from Cr2N to CrN, increasing grain size, thermal stability and resistance to oxidation with increasing N2. Also intrinsic coating hardness is influenced by both N2 flow during deposition and film thickness, as a result of changes in phase composition and microstructural properties.

Junio, 2011 | DOI: 10.1016/j.tsf.2011.04.115

Titulo: Microstructure and chemical bonding of DLC films deposited on ACM rubber by PACVD
Autores: Martinez-Martinez, D., Schenkel, M., Pei, Y.T., Sánchez-López, J.C., De Hosson, J.T.H.M.
Revista: Surface and Coatings Technology, 205 (2011) S75-S78
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The microstructure and chemical bonding of DLC films prepared by plasma assisted chemical vapor deposition on acrylic rubber (ACM) are studied in this paper. The temperature variation produced by the ion impingement during plasma cleaning and subsequent film deposition was used to modify the film microstructure by controlling the different degrees of strain applied to the substrate. The film microstructure is studied by top view and cross sectional SEM. The observed patch sizes are correlated with the variation of temperature that occurred during deposition. Finally, the chemical bonding of the samples is studied by Raman spectroscopy. All the samples show similar spectra regardless the bias voltage used.

Junio, 2011 | DOI: 10.1016/j.surfcoat.2011.02.067

Titulo: Surface-functionalized fluorescent silica nanoparticles for the detection of ATP
Autores: Moro, AJ; Schmidt, J; Doussineau, T; Lapresta-Fernandez, A; Wegener, J; Mohr, GJ
Revista: Chemical Communications, 47 (2011) 6066-6068
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The design of two-dyed fluorescent silica nanoparticles for ATP detection is presented. The indicator dye possesses a dipicolyl-amine (DPA) unit complexed with Zn(ii) as a receptor function for ATP while a rhodamine derivative is used as the reference dye. The nanoparticles were fully characterized regarding analytical performance, morphology and cytocompatibility.

Mayo, 2011 | DOI: 10.1039/C1CC10419E

Titulo: Comparative investigation of Al- and Cr-doped TiSiCN coatings
Autores: D.V. Shtansky, K.A. Kuptsov, Ph.V. Kiryukhantsev-Korneev, A.N. Sheveiko, A. Fernandez and M.I. Petrzhik
Revista: Surface and Coatings Technology, 205 (2011) 4640-4648
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The aim of this work was a comparative investigation of the structure and properties of Al- and Cr-doped TiSiCN coatings deposited by magnetron sputtering of composite TiAlSiCN and TiCrSiCN targets produced by self-propagating high-temperature synthesis method. Based on X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy data, the Al- and Cr-doped TiSiCN coatings possessed nanocomposite structures (Ti,Al)(C,N)/a-(Si,C) and (Ti,Cr)(C,N)/a-SiCxNy/a-C with cubic crystallites embedded in an amorphous matrix. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum at 1000, 1100, 1200, and 1300°C or in air at 1000°C for 1h. The results obtained show that the hardness of the Al-doped TiSiCN coatings increased from 41 to 46GPa, reaching maximum at 1000°C, and then slightly decreased to 38GPa at 1300°C. The Cr-doped TiSiCN coatings demonstrated high thermal stability up to 1100°C with hardness above 34GPa. Although both Al- and Cr-doped TiSiCN coatings possessed improved oxidation resistance up to 1000°C, the TiAlSiCN coatings were more oxidation resistant than their TiCrSiCN counterparts. The TiCrSiCN coatings showed better tribological characteristics both at 25 and 700°C and superior cutting performance compared with the TiAlSiCN coatings.

Mayo, 2011 | DOI: 10.1016/j.surfcoat.2011.04.012

Titulo: Surface-modified Pd and Au nanoparticles for anti-wear applications
Autores: J.C. Sánchez-López, M.D. Abad, L. Kolodziejczyk, E. Guerrero and A. Fernández
Revista: Tribology International, 44 (2011) 720-726
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This work reports the employment of metallic nanoparticles (palladium and gold) with a mean particle size of 2.2 nm surface-protected with tetraalkylammonium and alkanethiolate chains, respectively, as lubricant additives. Dispersions of both types of nanoparticles (5 wt%) are prepared using tetrabutylammonium acetate (TBA) and paraffin as base oils, respectively. The tribological properties are then evaluated by a ball-on-disc tribometer at two different loads (7 and 15 N) with excellent results: friction (<0.1), wear rate (not, vert, similar10&#8722;10 mm3/Nm). The excellent anti-wear response is explained by the formation of a metal-containing transfer film and their action as counterface spacers avoiding direct contact.

Mayo, 2011 | DOI: 10.1016/j.triboint.2009.12.013

Titulo: Structure and support induced structure disruption of soft nanoparticles obtained from hydroxylated fatty acids
Autores: Heredia-Guerrero, JA; San-Miguel, MA; Luna, M; Dominguez, E; Heredia, A; Benitez, JJ
Revista: Soft Matter, 7 (2011) 4357-4363
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Soft and spherical nanoparticles, named as cutinsomes, have been prepared from concentrated 9(10),16-dihydroxypalmitic acid (diHPA) in aqueous solution. After isolation, cutinsomes have been chemically and structurally characterized by ATR-FTIR, TEM and dynamic atomic force microscopy (dynamic AFM). The nanoparticle can be described as a lipidic, liquid-like and mostly esterified core surrounded by a polar shell of carboxylate/carboxylic acid molecules. Molecular dynamic (MD) simulations have been used to support this model. The structural stability of soft cutinsomes has been tested by deposition on both non-polar (HOPG) and polar (mica) flat substrates. It has been found that the magnitude of the interaction between the polar shell of cutinsomes and the support determines their structure conservation or its spreading or rupture and spill out of the liquid-like content. The structural consistence of these nanoparticles as a function of the polarity of substrate is of interest in elucidating the formation mechanism of cutin, the most abundant biopolyester in nature and a very interesting biomaterial to be mimetized.

Abril, 2011 | DOI: 10.1039/c0sm01545h

Titulo: Structural, chemical surface and transport modifications of regenerated cellulose dense membranes due to low-dose γ-radiation
Autores: Vazquez, MI; Heredia-Guerrero, JA; Galan, P; Benitez, JJ; Benavente, J
Revista: Materials Chemistry and Physics, 126 (2011) 734-740
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Modifications caused in commercial dense regenerated cellulose (RC) flat membranes by low-dose &#947;-irradiation (average photons energy of 1.23 MeV) are studied. Slight structural, chemical and morphological surface changes due to irradiation in three films with different RC content were determined by ATR-FTIR, XRD, XPS and AFM. Also, the alteration of their mechanical elasticity has been studied. Modification of membrane performance was determined from solute diffusion coefficient and effective membrane fixed charge concentration obtained from NaCl diffusion measurements. Induced structural changes defining new and effective fracture propagation directions are considered to be responsible for the increase of fragility of irradiated RC membranes. The same structural changes are proposed to explain the reduction of the membrane ion permeability through a mechanism involving either ion pathways elongation and/or blocking.

Marzo, 2011 | DOI: 10.1016/j.matchemphys.2010.12.051

Titulo: The biophysical design of plant cuticles: an overview
Autores: Dominguez, E; Heredia-Guerrero, JA; Heredia, A
Revista: New Phytologist, 189 (2011) 938-949
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The outer surfaces of epidermal cell walls are impregnated with an extracellular matrix called the cuticle. This composite matrix provides several functions at the interface level that enable plants to thrive in different habitats and withstand adverse environmental conditions. The lipid polymer cutin, which is the main constituent of the plant cuticle, has some unique biophysical properties resulting from its composition and structure. This review summarizes the progress made towards understanding the biophysical significance of this biopolymer with special focus on its structural, thermal, biomechanical, and hydric properties and relationships. The physiological relevance of such biophysical properties is discussed in light of existing knowledge on the plant cuticle.

Febrero, 2011 | DOI: 10.1111/j.1469-8137.2010.03553.x

Titulo: A comparative study of the role of additive in the MgH2 vs. the LiBH4&#8211;MgH2 hydrogen storage system
Autores: A. Fernández, E. Deprez, O. Friedrichs
Revista: International Journal of Hydrogen Energy, 36 (2011) 3932-3940
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The objective of the present work is the comparative study of the behaviour of the Nb- and Ti-based additives in the MgH2 single hydride and the MgH2 + 2LiBH4 reactive hydride composite. The selected additives have been previously demonstrated to significantly improve the sorption reaction kinetics in the corresponding materials. X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-Ray Photoelectron Spectroscopy (XPS) and Electron Microscopy (TEM) analysis were carried out for the milled and cycled samples in absence or presence of the additives. It has been shown that although the evolution of the oxidation state for both Nb- and Ti-species are similar in both systems, the Nb additive is performing its activity at the surface while the Ti active species migrate to the bulk. The Nb-based additive is forming pathways that facilitate the diffusion of hydrogen through the diffusion barriers both in desorption and absorption. For the Ti-based additive in the reactive hydride composite, the active species are working in the bulk, enhancing the heterogeneous nucleation of MgB2 phases during desorption and producing a distinct grain refinement that favours both sorption kinetics. The results are discussed in regards to possible kinetic models for both systems.

Febrero, 2011 | DOI: 10.1016/j.ijhydene.2010.12.112

Titulo: Endurance of TiAlSiN coatings: Effect of Si and bias on wear and adhesion
Autores: Philippon, D; Godinho, V; Nagy, PM; Delplancke-Ogletree, MP; Fernandez, A
Revista: Wear, 270 (2011) 541-549
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In this work, the endurance of TiAlSiN nanocomposite thin films subjected to tribological solicitation is studied. These coating were deposited on M2 steel substrate by magnetron sputtering. Dry sliding experiments were conducted at ambient temperature against WC-Co ball. Coefficients of friction, wear rates and endurances were correlated with the composition, microstructure, mechanical properties, residual stress and adhesion of the coatings. The hardness and elastic modulus were found dependent not only on the composition but also on the residual stress induced by the deposition process. Friction coefficient was found to be independent on Si content while the wear rate is strongly reduced for higher Si contents. The formation of a nanocomposite microstructure, the amount of amorphous Si-based phase and both, wear resistance and adhesion are shown as the critical factors to determine the endurance of the coating.

Febrero, 2011 | DOI: 10.1016/j.wear.2011.01.009

Titulo: Artificial weathering pools of calcium-rich industrial waste for CO2 sequestration
Autores: Morales-Florez, V; Santos, A; Lemus, A; Esquivias, L
Revista: Chemical Engineering Journal, 166 (2011) 132-137
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Processes of carbonation of calcium-rich aqueous industrial wastes from acetylene production were performed mimicking rock weathering, using the atmospheric carbon dioxide as reactant. This residue was carbonated exposing it to the air in artificial pools with controlled solid-to-liquid and surface-to-volume ratios, and the efficiency of this simple mineral carbonation process was maximized. Considering realistic values of just one acetylene production plant, the intelligent handling of the calcium-rich waste would make it possible to counteract the emission of around 800t of carbon dioxide per year, so the CO2 emissions of the acetylene production could be completely compensated and its carbon footprint significantly reduced.X-ray diffraction patterns and thermogravimetric analyses reported the conversion, up to 88%, of the calcium hydroxide into calcium carbonate under atmospheric conditions. So, considering a realistic industrial scale-up, 476kg of CO2 could be captured with 1t of dry waste. The morphology of the grains is resolved by electron microscopy, and can be described as needles 15nm wide and 200nm long arranged in grains smaller than 1 micron. We exploit these nanometric textural parameters (nanometric pores and particles having a specific surface area &#8764;50m2/g) to design an efficient carbon fixation procedure. The aim of this work is to propose this simple carbonation technology, based on aqueous alkaline industrial waste, as a contribution to reducing global CO2 emissions.

Diciembre, 2010 | DOI: 10.1016/j.cej.2010.10.039

Titulo: Combined x-ray photoelectron spectroscopy and scanning electron microscopy studies of the LiBH4-MgH2 reactive hydride composite with and without a Ti-based additive
Autores: Deprez, E; Munoz-Marquez, MA; de Haro, MCJ; Palomares, FJ; Soria, F; Dornheim, M; Bormann, R; Fernandez, A
Revista: Journal of Applied Physics, 109 (2011) 014913 (10 pages)
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A detailed electronic and microstructural characterization is reported for the LiBH4-MgH2 reactive hydride composite system with and without titanium isopropoxide as additive. Surface characterization by x-ray photoelectron spectroscopy combined to a morphological study by scanning electron microscopy as well as elemental map composition analysis by energy dispersive x-ray emission are presented in this paper for the first time for all sorption steps. Although sorption reactions are not complete at the surface due to the unavoidable superficial oxidation, it has been shown that the presence of the additive is favoring the heterogeneous nucleation of the MgB2 phase. Ti-based phases appear in all the samples for the three sorption steps well dispersed and uniformly distributed in the material. Li-based phases are highly dispersed at the surface while the Mg-based ones appear, either partially covered by the Li-based phases, or forming bigger grains. Ball milling is promoting mixing of phases and a good dispersion of the additive what favors grain refinement and heterogeneous reactions at the interfaces.

Diciembre, 2010 | DOI: 10.1063/1.3525803

2010


Titulo: A first study of the high-temperature plasticity of ceria-doped zirconia polycrystals
Autores: de Bernardi-Martin, S; Gomez-Garcia, D; Dominguez-Rodriguez, A; de Portu, G
Revista: Journal of the European Ceramic Society, 30 (2010) 3357-3362
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Ceria zirconia ceramic alloys were sintered by high-temperature annealing, considering several synthesis temperatures to obtain a full-dense ceria zirconia ceramic material using a temperature as low as possible. It was found that fully density is achieved at temperatures of 1450 degrees C. Monolithic specimens were crept under compression at high temperatures. The creep results fitted an empirical constitutive equation consistent with a classical Ratchinger mechanism for grain switching. This result was confirmed through microstructural characterization of as-received and post-mortem specimens. Since the conventional Ashby-Verrall model is contrary to the mechanism controlling creep in other zirconia alloys, the results are considered in the framework of a new grain boundary sliding model, with particular discussion of the validity of that model for the ceria zirconia case.

Noviembre, 2010 | DOI: 10.1016/j.jeurceramsoc.2010.07.043

Titulo: Effect of process parameters on mechanical and tribological performance of pulsed-DC sputtered TiC/a-C:H nanocomposite films
Autores: Shaha, KP; Pei, YT; Martinez-Martinez, D; Sanchez-Lopez, JC; De Hosson, JTM
Revista: Surface and Coatings Technology, 205 (2010) 2633-2642
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Mechanical, structural, chemical bonding (sp(3)/sp(2)). and tribological properties of films deposited by pulsed-DC sputtering of Ti targets in Ar/C2H2 plasma were studied as a function of the substrate bias voltage, Ti-target current, C2H2 flow rate and pulse frequency by nanoindentation, Raman spectroscopy and ball-on-disc tribometry. The new findings in this study comprise: dense, column-free, smooth, and ultra-low friction TiC/a-C:H films are obtained at a lower substrate bias voltage by pulsed-DC sputtering at 200 and 350 kHz frequency. The change in chemical and phase composition influences the tribological performance where the TiC/a-C:H films perform better than the pure a-C:H films. In the case of TiC/a-C:H nanocomposite films, a higher sp(2) content and the presence of TiC nanocrystallites at the sliding surface promote formation of a transfer layer and yield lower friction. In the case of a-C:H films, a higher sp(3) content and higher stress promote formation of hard wear debris during sliding, which cause abrasive wear of the ball counterpart and yield higher friction.

Noviembre, 2010 | DOI: 10.1016/j.surfcoat.2010.10.020

Titulo: Segregation-induced grain boundary electrical potential in ionic oxide materials: A first principles model
Autores: D. Gómez-García, Juan J. Meléndez, Robert L. González-Romero, A. Domínguez-Rodríguez
Revista: Acta Materialia, 58 (2010) 6404-6410
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A first principles continuum analytical model for cationic segregation to the grain boundaries in complex ceramic oxides is presented. The model permits one to determine the electric charge density and the segregation-induced electric potential profiles through the grain and can be extrapolated to the range of nanostructured grain sizes. The theoretical predictions are compared with existing data for yttria-stabilized tetragonal zirconia polycrystals. The implications for physical properties (mainly high temperature plasticity and hardening behaviour) are then discussed.

Octubre, 2010 | DOI: 10.1016/j.actamat.2010.08.002

Titulo: Microstructural study of the LiBH4-MgH2 reactive hydride composite with and without Ti-isopropoxide additive
Autores: Deprez, E; Justo, A; Rojas, TC; Lopez-Cartes, C; Minella, CB; Bosenberg, U; Dornheim, M; Borrnann, R; Fernandez, A
Revista: Acta Materialia, 58 (2010) 5683-5694
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An exhaustive microstructural characterization is reported for the LiBH4-MgH2 reactive hydride composite (RHC) system with and without titanium isopropoxide additive. X-ray diffraction with Rietveld analysis, transmission electron microscopy coupled to energy dispersive X-ray analysis, selected-area electron diffraction and electron energy loss spectroscopy are presented in this paper for the first time for this system for all sorption steps. New data are reported regarding average crystallite and grain size, microstrain, phase formation and morphology; these results contribute to the understanding of the reaction mechanism and the influence of the additives on the kinetics. Microstructural effects, related to the high dispersion of titanium-based additives, result in a distinct grain refinement of MgB2 and an increase in the number of reaction sites, causing acceleration of desorption and absorption reactions. Considerations on the stability of phases under electron beam irradiation have also been reported.

Septiembre, 2010 | DOI: 10.1016/j.actamat.2010.06.043

Titulo: Si-doped multifunctional bioactive nanostructured films
Autores: Shtansky, DV; Gloushankova, NA; Sheveiko, AN; Kiryukhantsev-Korneev, PV; Bashkova, IA; Mavrin, BN; Ignatov, SG; Filippovich, SY; Rojas, C
Revista: Surface and Coatings Technology, 205 (2010) 728-739
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Si-doped multifunctional bioactive nanostructured films (MuBiNaFs) were deposited by DC magnetron sputtering of composite TiC0.5 + CaO + Si (A) and TiC0.5 + CaO + Si3N4 (B) targets produced by self-propagating high-temperature synthesis method. The films were characterized in terms of their structure, elemental and phase composition using X-ray diffraction, scanning and transmission electron microscopy, electron energy loss spectroscopy, glow discharge optical emission spectroscopy. Raman, and IR spectroscopy. The Ti-Si-Ca-P-C-O-(N) films consisted of TiC(N) as a main phase with a minor amount of TiOx, SiNx, SiOx, SiC, and CaO phases probably mainly in amorphous state at the grain boundaries and COO- groups on the film surface. The excess of carbon atoms in the Ti-Si-Ca-P-C-O-N film (target A) precipitated in a DLC form. The films showed hardness in the range of 26-31 GPa, reduced Young's modulus of 200-270 GPa, and high percentage of elastic recovery of 60-71%. The best Ti-Si-Ca-C-O-N films exhibited low friction coefficient both in physiological solution and Dulbecko modified Eagle medium with fetal calf serum, hydrophilic properties, improved electrochemical characteristics, and excellent impact resistance. Nevertheless, the wear resistance of the Ti-Si-Ca-C-O-N films against Al2O3 ball was lower compared with the best Si-free MuBiNaFs. In vitro studies showed that the Si-doped Ti-Ca-C-O-N films possess improved osteoconductive characteristics during early stage of cell/material interaction. The film surface was highly adhesive for IAR-2 epithelial and MC3T3-E1 osteoblastic cells. The films revealed a high level of biocompatibility and biostability in experiments in vivo. The Ti-Si-Ca-C-O-N film (target A) did not show any bactericidal activity during cultivation of bacterial strains both on solid and in liquid Luria Bertani mediums. The film did not reveal any bactericidal and toxic activity against macrophages and therefore did not change bacterial status and defence system of macro-organisms.

Septiembre, 2010 | DOI: 10.1016/j.surfcoat.2010.07.063

Titulo: Superplasticity in nanocrystalline ceramics: pure grain boundary phenomena or not?
Autores: Dominguez-Rodriguez, A; Gomez-Garcia, D; Castillo-Rodriguez, M; Zapata-Solvas, E; Chaim, R
Revista: International Journal of Materials Research, 101 (2010) 1215-1221
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Superplasticity in ceramics has been the subject of intense research activity for the last two decades. Quite recently, the fabrication of fully dense nanocrystalline oxides with grain size below 100 nm enabled examination of their superplastic behaviour. This work presents a critical analysis of the plasticity of two important nanostructured oxide systems: MgO and yttria tetragonal zirconia polycrystals. A thorough comparison of their plastic deformation reveals that nano-structuring may be a necessary, but not a sufficient condition for superplasticity in ceramics as commonly assumed. Instead, the changes in the chemical composition and the transport properties, through the bulk and at grain boundaries, versus temperature and grain size can induce a rich variety of mechanical responses.

Septiembre, 2010 | DOI: 10.3139/146.110401

Titulo: Aleuritic (9,10,16-trihydroxypalmitic) acid self-assembly on mica
Autores: Heredia-Guerrero, JA; San-Miguel, MA; Sansom, MSP; Heredia, A; Benitez, JJ
Revista: Physical Chemistry Chemical Physics, 12 (2010) 10423-10428
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Aleuritic (9,10,16-trihydroxypalmitic) acid self-assembly on mica from solution has been studied using AFM, ATR-FTIR and MD simulations. The goal of this study is to define the role of hydroxyl groups in the interaction between molecules as reference data to understand the mechanism of formation of synthetic and natural biopolyesters from polyhydroxylated long chain carboxylic acids. In a confined structure, such as the one imposed by a vertically self-assembled layer on mica, aleuritic acid has a tendency to adopt a monolayer configuration ruled by the lateral interactions between molecules via the two secondary hydroxyl groups. This (2D) growth competes with the multilayer formation (3D), which is conditioned by the terminal primary hydroxyl group. As the self-assembly spatial constraint is relaxed, MD has shown that the structure tends to become an amorphous and crosslinked phase that can be characterized by topographic and friction force AFM data.

Agosto, 2010 | DOI: 10.1039/c0cp00163e

Titulo: Characterization of Ti1-xAlxN coatings with selective IR reflectivity
Autores: Godinho, V; Philippon, D; Rojas, TC; Novikova, NN; Yakovlev, VA; Vinogradov, EA; Fernandez, A
Revista: Solar Energy, 84 (2010) 1397-1401
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Ti1-xAlxN thin films were deposited by reactive magnetron sputtering. The obtained different stoichiometries give rise to different optical properties as the films change from metallic to dielectric. In this work the IR reflectivity of these coatings is investigated taking into account different application fields for IR selective Ti1-xAlxN thin films. Low Al content coatings present high reflectivity, high absorptance and low thermal emittance. High Al compositions give raise to coatings with high absorptance and high thermal emittance. The composition of the coatings was evaluated combining electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy. Scanning electron microscopy (SEM) revealed a columnar structure. Reflectance spectra for the visible and infrared spectral ranges were used to obtain the solar absorptance and thermal emittance values, used to calculate the equilibrium temperature of the coatings. The thermal stability in air from 300 to 600 degrees C was also evaluated.

Julio, 2010 | DOI: 10.1016/j.solener.2010.04.021

Titulo: Tailored synthesis of nanostructured WC/a-C coatings by dual magnetron sputtering
Autores: Abad, MD; Munoz-Marquez, MA; El Mrabet, S; Justo, A; Sanchez-Lopez, JC
Revista: Surface and Coatings Technology, 204 (2010) 3490-3500
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Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED analysis shows that increasing the C incorporation. the WC nanocrystalline phases evolve from gamma-W2C to beta-WC1-x. Further C enrichment leads to a nanocomposite structure of small WC1-x crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36-40 GPa; mu=0.6-0.8) to moderate-hard/low friction (16-20 GPa; mu similar to 0.2) coatings depending on the film composition. The transition point is found for a-C content of 10 at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC1-x/a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.

Julio, 2010 | DOI: 10.1016/j.surfcoat.2010.04.019

Titulo: Steering the Self-Assembly of Octadecylamine Monolayers on Mica by Controlled Mechanical Energy Transfer from the AFM Tip
Autores: Benitez, JJ; Heredia-Guerrero, JA; Salmeron, M
Revista: Journal of Physical Chemistry C, 114 (2010) 12630-12634
resumen | texto completo


We have studied the effect of mechanical energy transfer from the tip of an atomic force microscope on the dynamics of self-assembly of monolayer films of octadecylamine on mica. The formation of the self-assembled film proceeds in two successive stages, the first being a fast adsorption from solution that follows a Langmuir isotherm. The second is a slower process of island growth by aggregation of the molecules dispersed on the surface. We found that the dynamics of aggregation can be altered substantially by the addition of mechanical energy into the system through controlled tip surface interactions. This leads to both the creation of pinholes in existing islands as a consequence of vacancy concentration and to the assembly of residual molecules into more compact islands.

Junio, 2010 | DOI: 10.1021/jp102813s

Titulo: Microstructural Effects on the Creep Deformation of Alumina/Single-Wall Carbon Nanotubes Composites
Autores: Gomez-Garcia, D; Poyato, R; Lee, Z; Castillo-Rodriguez, M; Dominguez-Rodriguez, A; Radmilovic, V; Padture, NP
Revista: Journal of the American Ceramic Society, 93 (2010) 2042-2047
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The enhanced high-temperature creep resistance in alumina/single-wall carbon nanotubes (SWNTs) composites has been attributed to the unprecedented grain-boundary structure of these composites, where the SWNTs bundles segregated at the alumina grain boundaries partially impede grain-boundary sliding. In this study, the effect of SWNTs distributions at alumina grain boundaries on the creep behavior of alumina/SWNTs composites has been investigated. Microstructures of two different alumina/10 vol% SWNTs composites, one with heterogeneous and the other with homogenous distributions of SWNTs at grain boundaries, have been characterized quantitatively. The steady-state creep rate (uniaxial compression) in the heterogeneous composite has been found to be over three times higher than that in the homogeneous composite at 1300° and 1350°C (argon atmosphere). It is argued that the less uniform distribution of SWNTs at the alumina grain boundaries in the heterogeneous composite results in less effective obstruction of grain-boundary sliding, and attendant higher creep rate. This also results in more efficient recovery in that composite.

Junio, 2010 | DOI: 10.1111/j.1551-2916.2010.03681.x

Titulo: Influence of carbon chemical bonding on the tribological behavior of sputtered nanocomposite TiBC/a-C coatings
Autores: Abad, MD; Sanchez-Lopez, JC; Brizuela, M; Garcia-Luis, A; Shtansky, DV
Revista: Thin Solid Films, 518 (2010) 5546-5552
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The tribological performance of nanocomposite coatings containing Ti-B-C phases and amorphous carbon (a-C) are studied. The coatings are deposited by a sputtering process from a sintered TiB2:TiC target and graphite, using pulsed direct current and radio frequency sources. By varying the sputtering power ratio, the amorphous carbon content of the coatings can be tuned, as observed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The crystalline component consists of very disordered crystals with a mixture of TiB2/TiC or TiBxCy phases. A slight increase in crystalline order is detected with the incorporation of carbon in the coatings that is attributed to the formation of a ternary TiBxCy phase. An estimation of the carbon present in the form of carbide (TiBxCy or TiC) and amorphous (a-C) is performed using fitting analysis of the C 1s XPS peak. The film hardness (22 to 31 GPa) correlates with the fraction of the TiBxCy phase that exists in the coatings. The tribological properties were measured by a pin-on-disk tribometer in ambient conditions, using 6 mm tungsten carbide balls at 1 N. The friction coefficients and the wear rates show similar behavior, exhibiting an optimum when the fraction of C atoms in the amorphous phase is near 50%. This composition enables significant improvement of the friction coefficients and wear rates (mu similar to 0.1; k < 1 x 10(-6) mm(3)/Nm), while maintaining a good value of hardness (24.6 GPa). Establishing the correlation between the lubricant properties and the fraction of a-C is very useful for purposes of tailoring the protective character of these nanocomposite coatings to engineering applications.

Junio, 2010 | DOI: 10.1016/j.tsf.2010.04.038

Titulo: Advances in Aerogels made by Sonocatalysis
Autores: Esquivias, L; Morales-Florez, V; de la Rosa-Fox, N
Revista: Transactions of the Indian Ceramic Society, 69 (2010) 125-130
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High power ultrasound applied to liquids produces cavities. When an alkoxide/water mixture is sonicated, the cavities, which attain very high temperatures and pressures, act as nanoreactors, where the hydrolysis reaction starts. When the resultant sonosol gels to produce a sonogel, it is denser, with finer and more homogeneous porosity than that of a classic counterpart. Thus, acoustic cavitation permits to obtain nanostructured materials. Sono-aerogels have a high surface/volume ratio and are built by small particles (similar to 1 nm radius) and a high cross-linked network with low -OH surface coverage radicals. Structural models based on randomly-packed spheres in several hierarchical levels that represent the real sono-aerogel are shown. Finally, these materials find application, between others, for CO2 sequestration, since the small size of the pore permits hosting silicate nanocrystals that carbonate easily in the presence of CO2 in aqueous solution.

Junio, 2010 | DOI: ---

Titulo: Self-assembly of supramolecular lipid nanoparticles in the formation of plant biopolyester cutin
Autores: Dominguez, E; Heredia-Guerrero, JA; Benitez, JJ; Heredia, A
Revista: Molecular Biosystems, 6 (2010) 948-950
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The implication of a self-assembly process in the early stages of cutin biosynthesis has been shown by means of antibodies raised against polyhydroxy fatty acid nanoparticles (cutinsomes).

Mayo, 2010 | DOI: 10.1039/b927186d

Titulo: Structural models of randomly packed Tobermorite-like spherical particles: A simple computational approach
Autores: Gonzalez-Teresa, R; Morales-Florez, V; Manzano, H; Dolado, JS
Revista: Materiales de Construcción, 60 (2010) 7-15
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In this work, and in order to bring together the atomistic and colloidal viewpoints, we will present a Monte Carlo computational scheme which reproduces the colloidal packing of nano-spherical crystalline tobermorite-like particles. Different Low Density (LD) C-S-H and High Density (HD) C-S-H structures will be developed just by varying the computational packing parameters. Finally, the structures resulting from our computational experiments will be analyzed in terms of their densities, surface areas and their mechanical properties.

Mayo, 2010 | DOI: 10.3989/mc.2010.57010

Titulo: Permanent magnetism in phosphine- and chlorine-capped gold: from clusters to nanoparticles
Autores: Munoz-Marquez, MA; Guerrero, E; Fernandez, A; Crespo, P; Hernando, A; Lucena, R; Conesa, JC
Revista: Journal of Nanoparticle Research, 12 (2010) 1307-1318
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Magnetometry results have shown that gold NPs (similar to 2 nm in size) protected with phosphine and chlorine ligands exhibit permanent magnetism. When the NPs size decreases down to the subnanometric size range, e.g. undecagold atom clusters, the permanent magnetism disappears. The near edge structure of the X-ray absorption spectroscopy data points out that charge transfer between gold and the capping system occurs in both cases. These results strongly suggest that nearly metallic Au bonds are also required for the induction of a magnetic response. Electron paramagnetic resonance observations indicate that the contribution to magnetism from eventual iron impurities can be disregarded.

Abril, 2010 | DOI: 10.1007/s11051-010-9862-0

Titulo: On the microstructure of single wall carbon nanotubes reinforced ceramic matrix composites
Autores: Zapata-Solvas, E; Gomez-Garcia, D; Dominguez-Rodriguez, A
Revista: Journal of Materials Science, 45 (2010) 2258-2263
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A microstructural modelling of the microstructure in single wall carbon nanotubes reinforced alumina ceramics has been developed. The model accounts for the main microstructural features, being quite useful to describe the carbon nanotube distribution along the ceramic matrix. The microstructural analysis derived from this model is found to give a deeper insight into the high-temperature creep of these composites.

Abril, 2010 | DOI: 10.1007/s10853-009-4126-z

Titulo: SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties
Autores: Godinho, V; de Haro, MCJ; Garcia-Lopez, J; Goossens, V; Terryn, H; Delplancke-Ogletree, MP; Fernandez, A
Revista: Applied Surface Science, 256 (2010) 4548-4553
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In this work amorphous silicon oxynitride films with similar composition (ca. Si0.40N0.45O0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N-2-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus. The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N-2 gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.

Abril, 2010 | DOI: 10.1016/j.apsusc.2010.02.045

Titulo: Structural characterization of polyhydroxy fatty acid nanoparticles related to plant lipid biopolyesters
Autores: Heredia-Guerrero, JA; Dominguez, E; Luna, M; Benitez, JJ; Heredia, A
Revista: Chemistry and Physics of Lipids, 163 (2010) 329-333
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In the present work, we report the physico-chemical properties and structural characteristics of special polyhydroxy fatty acid nanoparticles after their fusion by means of attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), atomic force microscopy (AFM), and light microscopy. All the characteristics and properties investigated have an important degree of similarity to the native plant cutin, the main biopolymer present in the plant cuticles. The supramolecular organization of these polymerized prime nanoparticles after their interaction on cellulose substrate and isolated cuticle samples, simulating the in vivo conditions in epidermal plant cells, strongly suggests a growth of these nanoparticles after a self-assembly process.

Febrero, 2010 | DOI: 10.1016/j.chemphyslip.2010.01.006

Titulo: Magnetometry and electron paramagnetic resonance studies of phosphine- and thiol-capped gold nanoparticles
Autores: Guerrero, E; Munoz-Marquez, MA; Fernandez, A; Crespo, P; Hernando, A; Lucena, R; Conesa, JC
Revista: Journal of Applied Physics, 107 (2010) 064303-064309
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In the last years, the number of studies performed by wholly independent research groups that confirm the permanent magnetism, first observed in our research lab, for thiol-capped Au nanoparticles (NPs) has rapidly increased. Throughout the years, the initial magnetometry studies have been completed with element-specific magnetization measurements based on, for example, the x-ray magnetic circular dichroism technique that have allowed the identification of gold as the magnetic moment carrier. In the research work here presented, we have focused our efforts in the evaluation of the magnetic behavior and iron impurities content in the synthesized samples by means of superconducting quantum interference device magnetometry and electron paramagnetic resonance spectrometry, respectively. As a result, hysteresis cycles typical of a ferromagnetic material have been measured from nominally iron-free gold NPs protected with thiol, phosphine, and chlorine ligands. It is also observed that for samples containing both, capped gold NPs and highly diluted iron concentrations, the magnetic behavior of the NPs is not affected by the presence of paramagnetic iron impurities. The hysteresis cycles reported for phosphine-chlorine-capped gold NPs confirm that the magnetic behavior is not exclusively for the metal-thiol system.

Febrero, 2010 | DOI: 10.1063/1.3327414

Titulo: Oxidation State and Local Structure of Ti-Based Additives in the Reactive Hydride Composite 2LiBH(4) + MgH2
Autores: Deprez, E; Muñoz-Marquez, MA; Roldan, MA; Prestipino, C; Palomares, FJ; Minella, CB; Bosenberg, U; Dornheim, M; Bormann, R; Fernandez, A
Revista: Journal of Physical Chemistry C, 114 (2010) 3309-3317
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Nowadays, the technological utilization of reactive hydride composites (RHC) Lis hydrogen storage materials is limited by their reaction kinetics. However, addition of transition-metal-based additives, for instance titanium isopropoxide (Ti-iso), to the 2LiBH(4)+MgH2 system, results in a significant improvement of sorption kinetics. In this work, the evolution of chemical state and local structure of the Ti-based additive has been investigated by means of X-ray absorption (XAS) and photoemission (XPS) spectroscopy. X-ray absorption near-edge Structure (XANES) its well as extended X-ray absorption fine structure (EXAFS) analysis have been Undertaken at the Ti K-edge. The measurements reveal the formation of a highly dispersed and disordered TiO2-like phase during ball milling. During first desorption reduced titanium oxide and titanium boride are formed and remain stable upon cycling. The Surface analysis performed by XPS shows that the reduction processes of the Ti-based additive during first desorption IS Coupled to the migration of the Ti species front the surface to the bulk of the material. Several factors, related to favoring heterogeneous nucleation of MgB2 and the increase of interfacial area through grain refinement are proposed as potential driving force, among other effects, for the observed kinetic improvement.

Enero, 2010 | DOI: 10.1021/jp910955r

Titulo: Behaviour of sonogels under isotropic pressure
Autores: Esquivias, L
Revista: Comptes Rendus Chimie, 13 (2010) 282-289
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The aim of this article is to present a method that simplifies the standard procedure to determine the yield point providing complementary information about changes in the behaviour of the materials under study. It is generally accepted that the yield point is determined by the inflection point of the curve of pressure versus apparent volume of the sample, P(V), from Hg porosimetry runs. Although compressible materials present an easily identifiable neat inflection point, in resilient materials, the inflection point is not easy to identify by simple visual inspection of the curve. A physical magnitude (K&#8217;) is introduced to characterise the evolution of the material's compliance under isotropic pressure. The physical meaning of K&#8217; is the variation in the resistance to uniform compression with the pressure applied, helping to identify the yield point and the plastic mechanism beyond the yield point in a single run.

Diciembre, 2009 | DOI: 10.1016/j.crci.2009.09.011

2009


Titulo: Metal carbide/amorphous C-based nanocomposite coatings for tribological applications
Autores: Sanchez-Lopez, JC; Martinez-Martinez, D; Abad, MD; Fernandez, A
Revista: Surface and Coatings Technology, 204 (2009) 947-954
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This paper tries to assess the factors governing the tribological behaviour of different nanocomposites films composed by metallic carbides (MeC) mixed with amorphous carbon (a-C). Different series of MeC/a-C coatings (with Me: Ti(B) and W) were prepared by magnetron sputtering technique varying the power applied to the graphite target in order to tailor the carbon content into the films. A deep investigation of the chemical and structural features at the nano-scale is carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS) and Raman spectroscopy techniques in order to establish correlations with the tribological properties measured by a pin-on-disk tribometer in ambient air. The analysis of the counterfaces by Raman confocal microscopy after the friction tests is used to follow the chemical phenomena occurring at the contact area responsible of the observed friction behaviour. The importance of determining the fraction of C atoms in the amorphous phase (xa-C) is highlighted as a key-parameter to control the tribological properties. A comparative analysis of the mechanical and tribological performance of the three systems (TiC/a-C, WC/a-C, TiBC/a-C) is done and conclusions are obtained concerning the friction and wear mechanism involved.

Noviembre, 2009 | DOI: 10.1016/j.surfcoat.2009.05.038

Titulo: Thermogravimetric and in situ SEM characterisation of the oxidation phenomena of protective nanocomposite nitride films deposited on steel
Autores: Mege-Revil, A; Steyer, P; Thollet, G; Chiriac, R; Sigala, C; Sanchez-Lopez, JC; Esnouf, C
Revista: Surface and Interface Analysis, 204 (2009) 893-901
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The lifetime of TiN coatings is often limited by its poor resistance to high temperatures. For an optimized addition of silicon, both mechanical and physico-chemical properties are enhanced, owing to the formation of a nanocomposite structure. In this study, pure Ti and TiSi (80/20) targets were arc-evaporated to produce hard, single-layered coatings. Magnetron sputtered SiNx films were also synthesized for a comparison purpose. The nanocomposite structure was determined by XRD and TEM, and its efficiency regarding the mechanical properties was confirmed by nanohardness measurements. Through thermogravimetric experiments it is shown that in isothermal and dynamic conditions, the chemical stability inherent to SiNx controls the oxidation behaviour of TiSiN. However, in thermal cycling conditions TiSiN withstand efficiently temperature variations whereas SiNx does not. The aim of this study is to understand the role of SiNx on the oxidation of the TiSiN nanocomposite film. For this purpose, an in situ approach of the oxidation phenomena is detailed, based on experiments performed in an environmental scanning electron microscope (ESEM) operating in controlled pressure mode up to 1000 °C. ESEM, used in real-time oxidative conditions, has been proved to be an efficient tool to characterise the mechanism of degradation. The successive steps of the attack throughout the in situ oxidation process are as follow: oxidation first initiates at coating defects (open pores and droplets), then spreads to the whole surface. The whole flaking of the film that is observed at the microscopic scale during the cooling step proves the poor thermal fatigue resistance of SiNx. This strong propensity to cracking is explained on the basis of thermo-mechanical considerations. The nanocomposite structure thus combines the chemical stability inherent to the SiNx matrix with the beneficial thermo-mechanical properties associated to TiN nanograins.

Noviembre, 2009 | DOI: 10.1016/j.surfcoat.2009.06.040

Titulo: Bonding Structure and Mechanical Properties of Ti-B-C Coatings
Autores: Abad, MD; Caceres, D; Pogozhev, YS; Shtansky, DV; Sanchez-Lopez, JC
Revista: Plasma Processes and Polymers, 6 (2009) S107-S112
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Nanocomposite coatings combining hard phases (TiB2, TiC) with an amorphous carbon (a-C) were developed to provide a good compromise between mechanical and tribological properties for M2 steels used in a wide variety of applications such as cutting tools, bearings and gear mechanisms. A combined d.c.-pulsed and r.f.-magnetron deposition process was used to deposit nanocomposite TiBC/a-C coatings with a variable content of carbon matrix phase. Chemical composition was determined by electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) revealed that the coatings microstructure is rather amorphous with small nanocrystals of TiC and/or TiB2 (not possible to differentiate by diffraction techniques). Investigation of the chemical bonding environment by XPS and EELS allows us to confirm the presence of titanium-boron and titanium-carbon bonds together with free a-C. Coatings exhibited hardness values (H) of 25–29 GPa, effective Young modulus (E*) of 310–350 GPa, H/E* ratios over 0.080 and resistance to plastic deformation (H3/E*2) from 0.15 to 0.20. Tribological properties of the coatings were characterized by a pin-on-disk tribometer using steel and WC balls at high contact stresses (1.1 and 1.4 GPa respectively). Friction coefficients were reduced from 0.6 to 0.2 by increasing the content of free carbon without reduction of the hardness (around 28 GPa), by self-lubricant effects. The tribo-mechanical data are revised according to the phase composition and chemical bonding inside the nanocomposites.

Octubre, 2009 | DOI: 10.1002/ppap.200930403

Titulo: Synthesis and characterization of a plant cutin mimetic polymer
Autores: Heredia-Guerrero, JA; Heredia, A; Garcia-Segura, R; Benitez, JJ
Revista: Polymer, 50 (2009) 5633-5637
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A mimetic polymer of plant cutin have been synthesized from 9,10,16-trihydroxyhexadecanoic (aleuritic) acid through a low temperature polycondensation reaction. Reaction conditions (solvent, catalyst, temperature, etc…) were studied and modified to optimize yield and product characteristics. The resulting polyaleurate polymer was characterized by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and solid state 13C-Cross Polarization/Magic Angle Spinning Nuclear Magnetic Resonance (13C-CP/MAS NMR). Mechanical and hydrodynamic properties were also investigated. In the average, the product obtained is physically and chemically very similar to plant cutin (a hydrophobic polyester). However, a more detailed analysis of results reveals that polyaleurate framework is more rigid than natural cutin and with additional larger short-range ordered domains. Also, the synthetic polymer displays slightly different mechanical properties with respect to natural cutin. Additional hydrogen bonding within the framework of polyaleurate is considered to be responsible for such experimental observations.

Octubre, 2009 | DOI: 10.1016/j.polymer.2009.10.018

Titulo: Vibrational spectroscopy characterization of magnetron sputtered silicon oxide and silicon oxynitride films
Autores: Godinho, V; Denisov, VN; Mavrin, BN; Novikova, NN; Vinogradov, EA; Yakovlev, VA; Fernandez-Ramos, C; de Haro, MCJ; Fernandez, A
Revista: Applied Surface Science
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Vibrational (infrared and Raman) spectroscopy has been used to characterize SiOxNy and SiOx films prepared by magnetron sputtering on steel and silicon substrates. Interference bands in the infrared reflectivity measurements provided the film thickness and the dielectric function of the films. Vibrational modes bands were obtained both from infrared and Raman spectra providing useful information on the bonding structure and the microstructure (formation of nano-voids in some coatings) for these amorphous (or nanocrystalline) coatings. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis have also been carried out to determine the composition and texture of the films, and to correlate these data with the vibrational spectroscopy studies. The angular dependence of the reflectivity spectra provides the dispersion of vibrational and interference polaritons modes, what allows to separate these two types of bands especially in the frequency regions where overlaps/resonances occurred. Finally the attenuated total reflection Fourier transform infrared measurements have been also carried out demonstrating the feasibility and high sensitivity of the technique. Comparison of the spectra of the SiOxNy films prepared in various conditions demonstrates how films can be prepared from pure silicon oxide to silicon oxynitride with reduced oxygen content.

Septiembre, 2009 | DOI: 10.1016/j.apsusc.2009.07.101

Titulo: Chemical and electronic interface structure of spray pyrolysis deposited undoped and Al-doped ZnO thin films on a commercial Cz-Si solar cell substrate
Autores: Gabas, M; Barrett, NT; Ramos-Barrado, JR; Gota, S; Rojas, TC; Lopez-Escalante, MC
Revista: Solar Energy Materials and Solar Cells, 93 (2009) 1356-1365
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We have studied differences in the interface between undoped and Al-doped ZnO thin films deposited on commercial Si solar cell substrates. The undoped ZnO film is significantly thicker than the Al-doped film for the same deposition time. An extended silicate-like interface is present in both samples. Transmission electron microscopy (TEM) and photoelectron spectroscopy (PES) probe the presence of a zinc silicate and several Si oxides in both cases. Although Al doping improves the conductivity of ZnO, we present evidence for Al segregation at the interface during deposition on the Si substrate and suggest the presence of considerable fixed charge near the oxidized Si interface layer. The induced distortion in the valence band, compared to that of undoped ZnO, could be responsible for considerable reduction in the solar cell performance.

Julio, 2009 | DOI: 10.1016/j.solmat.2009.02.018

Titulo: Comparative investigation of TiAlC(N), TiCrAlC(N), and CrAlC(N) coatings deposited by sputtering of МАХ-phase Ti2 − хCrхAlC targets
Autores: Shtansky, DV; Kiryukhantsev-Korneev, PV; Sheveyko, AN; Mavrin, BN; Rojas, C; Fernandez, A; Levashov, EA
Revista: Surface and Coatings Technology, 203 (2009) 3595-3609
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A comparative investigation of the structure and properties of TiAlC(N), TiCrAlC(N), and CrAlC(N) coatings deposited by sputtering of МАХ-phase Ti2 − хCrхAlC targets (where x = 0, 0.5, 1.5, and 2) in an Ar atmosphere or in a gaseous mixture of Ar + N2 is presented. The coatings were characterized in terms of their structure, elemental and phase composition, hardness, elastic modulus, elastic recovery, thermal stability, friction coefficient, wear rate, corrosion, and high-temperature oxidation resistance. The structure of the coatings was studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, glow discharge optical emission spectroscopy, electron energy loss spectroscopy, and Raman spectroscopy. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum or in air at temperatures 600–1200 °C. The results obtained show that the TiAlCN coatings possess high hardness of 32–35 GPa, low friction coefficient against WC–Co well below 0.25, high thermal stability up to 1200 °C, and superior performance in dry milling tests against high Cr steel. Meanwhile, the coatings with high Cr content demonstrated improved oxidation resistance up to 1000 °C and superior electrochemical behavior, but their mechanical and tribological properties were deteriorated.

Julio, 2009 | DOI: 10.1016/j.surfcoat.2009.05.036

Titulo: Thermal Evolution of WC/C Nanostructured Coatings by Raman and In Situ XRD Analysis
Autores: El Mrabet, S; Abad, MD; Lopez-Cartes, C; Martinez-Martinez, D; Sanchez-Lopez, JC
Revista: Plasma Processes and Polymers, 6 (2009) S444-S449
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In this work, a series of WC/C nanostructured films were deposited on silicon substrates by changing the ratio of sputtering power applied to graphite and WC magnetron sources (PC/PWC: 0, 0.1, 0.5, 1). The thermal stability of WC/C coatings was followed in situ by means of X-ray diffraction measurements up to 1 100 °C in vacuum (10−1 Pa). Initially, the film microstructure is composed of nanocrystalline WC1−x and W2C phases. As the PC/PWC ratio increases the crystallinity decreases, and WC1−x becomes the predominant phase from PC/PWC = 0.1. The results show that the structural evolution with temperature of all studied layers depends essentially on their initial phase and chemical composition (determined by the synthesis conditions: ratio PC/PWC). The coating deposited at PC/PWC = 0 reveals a transformation of W2C phase into W and W3C phases at 400 °C. However, the samples with PC/PWC greater than 0 exhibits an improved thermal stability up to 600–700 °C where the WC1−x begins to transform into W2C and WC phases. At 900 °C, WC is the predominant phase, especially for those coatings prepared with higher ratios. Further annealing above 1 000 °C yields W as the foremost phase. The thermal behaviour was later studied by means of Raman spectroscopy measurements at certain temperatures where the main changes in phase composition were observed. Particularly, a fitting analysis was carried out on the D and G bands typical of disordered and amorphous carbon. The changes induced during heating are discussed in terms of the positions of D and G lines, and full width at half maximum (FWHM).

Mayo, 2009 | DOI: 10.1002/ppap.200931004

Titulo: Chemical Reactions in 2D: Self-Assembly and Self-Esterification of 9(10),16-Dihydroxypalmitic Acid on Mica Surface
Autores: Heredia-Guerrero, JA; San-Miguel, MA; Sansom, MSP; Heredia, A; Benitez, JJ
Revista: Langmuir, 25 (2009) 6869-6874
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9(10),16-Dihydroxypalmitic acid (diHPA) is a particularly interesting polyhydroxylated fatty acid (1) because it is the main monomer of cutin, the most abundant biopolyester in nature, and (2) because the presence of a terminal and a secondary hydroxyl group in midchain positions provides an excellent model to study their intermolecular interactions in a confined phase such as self-assembled layers. In this study we have combined atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy, as well as molecular dynamics (MD) simulations to conclude that the self-assembling of diHPA molecules on mica is a layer by layer process following a Brunauer−Emmett−Teller (BET) type isotherm and with the first layer growing much faster than the rest. Interactions between secondary hydroxyls reinforce the cohesive energy of the monolayer, while the presence of the terminal hydroxyl group is necessary to trigger the multilayered growth. Besides, XPS and ATR-FT-IR spectroscopies clearly indicate that spontaneous self-esterification occurs upon self-assembling. The esterification reaction is a prerequisite to propose a self-assembly route for the biosynthesis of cutin in nature. Molecular dynamics simulations have shown that internal molecular reorganization within the self-assembled layers provides the appropriate intermolecular orientation to facilitate the nucleophilic attack and the release of a water molecule required by the esterification reaction.

Mayo, 2009 | DOI: 10.1021/la9001412

Titulo: Thermal Stability and Oxidation Resistance of Nanocomposite TiC/a-C Protective Coatings
Autores: Martinez-Martinez, D; Lopez-Cartes, C; Gago, R; Fernandez, A; Sanchez-Lopez, JC
Revista: Plasma Processes and Polymers, 6 (2009) S462-S467
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Nanocomposite films composed by small crystallites of hard phases embedded in an amorphous lubricant matrix have been extensively studied as protective coatings. These kinds of coatings have often to work in extreme environments, exposed to high temperatures (above 800–900 °C), and/or oxidizing/corrosive atmospheres, which may resist. As a result, it is important to study the behavior of such coatings at high temperatures (thermal stability) and in the presence of oxygen (oxidation resistance). In this sense, we have selected a TiC/a-C nanocomposite coating with good mechanical and tribological properties in order to do several thermal tests under three different environments: high vacuum (10−6 mbar), low vacuum (10−1 mbar), and air. Our observations allow us to establish that the film microstructure is stable at least up to 1 000 °C in high vacuum. When oxygen is present, the practical temperature of use is reduced at 700 °C (low partial pressure) and 300 °C (air) by formation of Ti oxides and C removal.

Abril, 2009 | DOI: 10.1002/ppap.200931002

Titulo: High deposition rates of uniform films in tetramethylsilane-based plasmas generated by elementary microwave sources in matrix configuration
Autores: Latrasse, L; Lacoste, A; Sanchez-Lopez, JC; Bes, A; Rayar, M; Pelletier, J
Revista: Surface and Coatings Technology, 203 (2009) 2343-2349
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Plasma scaling up can be achieved by distributing elementary microwave plasma sources on planar rectangular networks. These so-called matrix plasmas can generate uniform sheets of plasma over a wide argon pressure range, from 7.5 to 750 Pa, with densities between 1012 and 1013 cm− 3. In order to estimate the capabilities of matrix plasmas for PACVD processing in terms of deposition rate and uniformity, SiOCH and SiNCH films were deposited using TMS (tetramethylsilane), as the organic gas precursor of silicon, mixed with oxygen or nitrogen flows. Plasmas of O2 / TMS and N2 / TMS gas mixtures can be sustained between 5 and 25 Pa. Variations in the deposition rate as a function of microwave power and nitrogen partial pressure are reported. Thickness uniformity of SiOCH and SiNCH films was measured across a silicon wafer. The obtained deposition rates exceed 1.3 μm/min and the films present a uniformity better than 5% on 75 mm diameter silicon wafers. Composition of the films has also been analyzed by XPS as a function of process parameters: microwave input power, composition of gas mixture, and N2 partial pressure. In particular, these analyses have shown a very low yield of nitrogen incorporation when using N2 gas as nitrogen precursor and high Si and Si–Si bonding contents in the films, probably due to a strong fragmentation of the TMS precursor in the high density plasma.

Abril, 2009 | DOI: 10.1016/j.surfcoat.2009.02.121

Titulo: Tribological carbon-based coatings: An AFM and LFM study
Autores: Martinez-Martinez, D; Kolodziejczyk, L; Sanchez-Lopez, JC; Fernandez, A
Revista: Surface Science, 603 (2009) 973-979
resumen | texto completo


In this work some carbon-based coatings were studied by atomic force microscopy (AFM) and lateral force microscopy (LFM) techniques in order to evaluate their microstructure and friction properties at the micro and nanoscale. With this aim, four samples were prepared by magnetron sputtering: an amorphous carbon film (a–C), two nanocomposites TiC/a–C with different phase ratio (∼1:1 and ∼1:3) and a nanocrystalline TiC sample. Additionally, a highly oriented pyrolytic graphite (HOPG) and an amorphous hydrogenated carbon coating (a-C:H) were included to help in the evaluation of the influence of the roughness and the hydrogen presence respectively. The topography (roughness) of the samples was studied by AFM, whereas LFM was used to measure the friction properties at the nanoscale by two different approaches. Firstly, an evaluation of possible friction contrast on the samples was done. This task was performed by subtraction of forward and reverse images and lately confirmed by the study of lateral force profiles in both directions and the histograms of the subtraction images. Secondly, an estimation of the average friction coefficient over the analysed surface of each sample was carried out. To take into account the tip evolution/damaging, mica was used as a reference before and after each sample (hereafter called sandwich method), and samples-to-mica friction ratios were calculated. The LFM was shown to be a useful tool to characterise a mixture of phases with different friction coefficients. In general, the friction ratios seemed to be dominated by the amorphous carbon phase, as it was impossible to distinguish among samples with different proportions of the amorphous phase (friction ratios between 1.5 and 1.75). Nevertheless, it could be concluded that the differences in friction behaviour arose from the chemical aspects (nature of the phase and hydrogen content) rather than surface characteristics, since the roughness (Ra values up to 5.7 nm) does not follow the observed trend. Finally, the Ogletree method was employed in order to calibrate the lateral force and estimate the friction coefficient of our samples. A good agreement was found with macroscopic and literature values going from ∼0.3 for TiC to ∼0.1 for pure carbon.

Marzo, 2009 | DOI: 10.1016/j.susc.2009.01.043

Titulo: Cutin synthesis: A slippery paradigm
Autores: Heredia, A; Heredia-Guerrero, JA; Dominguez, E; Benitez, JJ
Revista: Biointerphases, 4 (2009) P1-P3
resumen | texto completo


Despite its biological importance, the mechanism of construction of cutin, the polymer matrix of plant cuticles, has not yet been elucidated. Recently, progress on lipid barrier formation of polymers such as cutin and suberin has been recently reviewed by Pollard et al. In their review the authors state that the ubiquitous cutin is the least understood of the plant extracellular polymers and that major questions about cutin structure and its macromolecular assembly remain to be resolved. At the time this paper was being published our research group has developed a new hypothesis on plant cutin synthesis.

Febrero, 2009 | DOI: 10.1116/1.3063816

Titulo: Duplex SiCN/DLC coating as a solution to improve fretting—Corrosion resistance of steel
Autores: Pech, D; Schupp, N; Steyer, P; Hack, T; Gachon, Y; Heau, C; Loir, AS; Sanchez-Lopez, JC
Revista: Wear, 266 (2009) 832-838
resumen | texto completo


Fretting corrosion damages are commonly observed when two metallic bodies, which are in contact with each other, are subjected to oscillatory motions of low amplitude. Such kind of degradation mode is often responsible for limited durability of aeronautical joints. In the present paper, a multifunctional duplex coating based on Si–C–N and diamond-like carbon (DLC) materials, combining corrosion resistance and good tribological properties is described. Amorphous hydrogenated SiC, SiCN, SiC/DLC and SiCN/DLC were deposited on steel substrates by a plasma assisted chemical vapour deposition (PACVD) technique, using tetramethylsilane (TMS), ammonia (NH3) or acetylene (C2H2) as gas precursors. Nitrogen incorporation has shown to improve the corrosion protection ability of SiC coatings. The corrosion behaviour and the tribological performance in aqueous media of SiCN/DLC coating have therefore been investigated. A test rig has been designed to validate the fretting resistance of this duplex coating for aeronautic applications. It was found that the combination of a SiCN-based PACVD sublayer with a DLC topcoat could provide an enhanced solution to withstand both fretting and corrosion.

Febrero, 2009 | DOI: 10.1016/j.wear.2008.12.007

Titulo: Self-lubricating Ti–C–N nanocomposite coatings prepared by double magnetron sputtering
Autores: Martinez-Martinez, D; Lopez-Cartes, C; Justo, A; Fernandez, A; Sanchez-Lopez, JC
Revista: Solid State Sciences, 11 (2009) 660-670
resumen | texto completo


This paper is devoted to the development of Ti(C,N)-based nanocomposite protective coatings consisting of nanocrystals of a hard phase (TiN or TiCxNy) embedded in an amorphous carbon-based matrix (a-C or a-CNx). The objective here is the achievement of a good compromise between the mechanical and tribological properties by the appropriate control of the hard/soft phase ratio and the microstructural characteristics of the film. To achieve this purpose, dual magnetron sputtering technique was employed following two different strategies. In the first one, we use Ti and graphite targets and Ar/N2 gas mixtures, while in the second case, TiN and graphite targets are sputtered in an Ar atmosphere. By changing the sputtering power applied to each magnetron, different sets of samples are prepared for each route. The effect of the bias voltage applied to the substrate is also studied in some selected cases. The mechanical and tribological properties of the films are characterized and correlated with the microstructure, crystallinity and phase composition. The establishment of correlations enables the development of advanced coatings with tailored mechanical and tribological properties for desired applications.

Febrero, 2009 | DOI: 10.1016/j.solidstatesciences.2008.10.017

Titulo: WC/a-C nanocomposite thin films: Optical and electrical properties
Autores: Abad, MD; Sanchez-Lopez, JC; Cusnir, N; Sanjines, R
Revista: Journal of Applied Physics, 105 (2009) 033510
resumen | texto completo


WC/amorphous carbon (a-C) thin films were deposited by dual magnetron sputtering from individual WC and graphite targets. The influence of film composition and microstructure on the optical and electrical properties was investigated. As evidenced by x-ray photoelectron spectroscopy and grazing angle x-ray diffraction measurements, the WC/a-C films are composite materials made of hexagonal W2C and/or cubic β-WC1−X nanocrystallites embedded in (a-C) matrix. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the van der Pauw method between 20 and 300 K. Both the optical and the electrical properties of the WC/a-C films are correlated with the chemical composition and microstructure evolution caused by a-C addition. The optical properties of W2C/a-C and β-WC1−x/a-C films with a-C content ≤ 10 at. % are explained by modeling their dielectric functions by a set of Drude–Lorentz oscillators. Further increase in a-C content leads only to the formation of β-WC1−x/a-C nanocomposite structures and their optical properties progressively evolve to those of a-C single phase. The electrical resistivity as a function of the temperature of all the films exhibits a negative temperature coefficient of resistivity. Theoretical fitting using the grain-boundary scattering model shows that the transport properties are mainly limited by the grain size and electron mean free path parameters.

Enero, 2009 | DOI: 10.1063/1.3060717

Titulo: Influence of the microstructure on the mechanical and tribological behavior of TiC/a-C nanocomposite coatings
Autores: Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A; Sanchez-Lopez, JC
Revista: Thin Solid Films, 517 (2009) 1662-1671
resumen | texto completo


The performance of protective thin films is clearly influenced by their microstructure. The objective of this work is to study the influence of the structure of TiC/a-C nanocomposite coatings with a-C contents ranging from ~ 0% to 100% on their mechanical and tribological properties measured by ultramicroindentation and pin-on-disks tests at ambient air, respectively. The microstructure evolves from a polycrystalline columnar structure consisting of TiC crystals to an amorphous and dense TiC/a-C nanocomposite structure when the amount of a-C is increased. The former samples show high hardness, moderate friction and high wear rates, while the latter ones show a decrease in hardness but an improvement in tribological performance. No apparent direct correlation is found between hardness and wear rate, which is controlled by the friction coefficient. These results are compared to the literature and explained according to the different film microstructures and chemical bonding nature. The film stress has also been measured at the macro and micro levels by the curvature and Williamson–Hall methods respectively. Other mechanical properties of the coating such as resilience and toughness were evaluated by estimating the H3/E⁎2 and H/E⁎ ratios and the percentage of elastic work (We). None of these parameters showed a tendency that could explain the observed tribological results, indicating that for self-lubricant nanocomposite systems this correlation is not so simple and that the assembly of different factors must be taken into account.

Diciembre, 2008 | DOI: 10.1016/j.tsf.2008.09.091



Santiago Domínguez Meister
Recubrimientos Protectores Nanoestructurados preparados por Magnetron Sputtering

Director/es: Juan Carlos Sánchez López y Cristina T. Rojas Ruiz
Universidad de Sevilla
Jueves, 17 Noviembre, 2016




Jaime Caballero Hernández
Control of Microstructure in Porous Silicon Coatings with Closed Porosity for Functional Applications

Director/es: Asunción Fernández Camacho y Vanda Cristina Fortio Godinho
Universidad de Sevilla
Miércoles, 20 Abril, 2016




Carlos Andrés García Negrete
Síntesis, Estructura y Caracterización en Entornos Biológicos de Nanopartículas de Au y Heterodímeros Pt-Au

Director/es: Asunción Fernández Camacho
Universidad de Sevilla
Jueves, 4 Febrero, 2016




Gisela Mariana Arzac Di Tomaso
Estudio de la reacción de hidrólisis del borohidruro sódico como medio de producción de hidrógeno para aplicaciones portátiles

Director/es: Asunción Fernández Camacho y Cristina Rojas Ruiz
Universidad de Sevilla
Martes, 2 Abril, 2013




José Alejandro Heredia Guerrero
Autoensamblaje molecular y síntesis de materiales biomiméticos a partir de hidroxiácidos derivados de cutinas vegetales

Director/es: José Jesús Benítez Jiménez y Antonio Heredia Bayona
Universidad de Málaga
Viernes, 28 Octubre, 2011




Emilie Deprez
Study of the reactive hydride composite 2LiBH4+MgH2 and its additives for hydrogen storage applications

Director/es: Asunción Fernández Camacho
Universidad de Sevilla
Viernes, 24 Junio, 2011




Vanda Godinho Fortio
Synthesis and Characterization of magnetron sputtered thin films of the Ti-Al-Si-N(O) system

Director/es: Asunción Fernández Camacho y Marie-Paule Delplancke Ogletree
Universidad de Sevilla
Viernes, 18 Febrero, 2011




Manuel David Abad Roldán
Nanostructured lubricant systems for tribological applications

Director/es: Juan Carlos Sánchez López
Universidad de Sevilla
Viernes, 10 Septiembre, 2010




Diego Martínez Martínez
Recubrimientos protectores autolubricantes con estructura "nanocomposite" TiC/a-C y derivados nitrogenados preparados por pulverización catódica

Director/es: Asunción Fdez. Camacho y Juan Carlos Sánchez-López
Universidad de Sevilla
Lunes, 16 Abril, 2007




Oliver Friedrichs
Hydrogen storage mechanisms in nanocrystalline materials based or Mg

Director/es: Asunción Fdez. Camacho y Juan Carlos Sánchez López
Universidad de Sevilla
Viernes, 16 Marzo, 2007




Cristina Fernández Ramos
Estudio de recubrimientos basados en el nitruro de carbono preparados por pulverización catódica reactiva

Director/es: Asunción Fernández Camacho y Juan Carlos Sánchez López
Universidad de Sevilla
Lunes, 24 Mayo, 2004


Eugenio Zapata Solvas Premio Real Maestranza de Caballería de Sevilla 2014


El día 27 de Mayo, a las 19:00 horas, se celebró en la Casa de esta Real Corporación, el acto de entrega de los Premios de Investigación de la Real Maestranza de Caballería de Sevilla y Real Academia Sevillana de Ciencias, correspondientes a la convocatoria de 2014. Dichos premios han sido concedidos a:

Premio Real Academia Sevillana de Ciencias

Al Doctor D. Juan Ramón Sánchez Valencia, Licenciado en Ciencias Físicas por la Universidad de Granada (2005) e Ingeniero de Materiales y Doctor (2010) por la Universidad de Sevilla. Buena parte de su carrera investigadora se ha desarrollado en el Instituto de Ciencias Materiales de Sevilla.

Su actividad como investigador se concentra en el estudio de nanomateriales funcionales con aplicaciones en fotónica, sensórica y electrónica. Se trata de materiales de alto interés técnico que se preparan mediante técnicas de laboratorio de vacío y de procesado de plasma, que pueden asimismo desarrollarse a escala industrial, y que son compatibles con los métodos actuales de fabricación de dispositivos microelectrónicos.

Premio Real Maestranza de Caballería de Sevilla

Al Doctor D. Alejandro Martín-Montalvo, investigador contratado Miguel Servet, que desarrolla actualamente su labor en el Departamento de Células Troncales del Centro Andaluz de Biología Molecular y Medicina Regenerativa de la Universidad Pablo de Olavide (UPO). Ha desarrollado una importante tarea investigadora, tanto en la UPO como en el National Institute on Aging, de los National Institutes of Health de los EE.UU., en Baltimore.

Como resultado de sus investigaciones, El Dr. Martín-Montalvo ha publicado un buen número de artículos en revistas científicas de alto impacto, con contribuciones destacadas en estrés oxidativo, resistencia a insulina y envejecimiento, así como el enlentecimiento de este último por la acción de distintos compuestos. Estos trabajos han recibido amplia atención por parte de la comunidad científica, con comentarios editoriales y abundantes citas.

Al Doctor D. Eugenio Zapata Solvas, investigador contratado por el Instituto de Ciencia de Materiales de Sevilla, dentro del grupo de investigación Diseño de Nanomateriales y Microestructuras. Formado en la Universidad de Sevilla y, después de diversas estancias en prestigiosos centros científicos extranjeros, el doctor Zapata ha dedicado su atención a las propiedades mecánicas y térmicas de compuestos cerámicos nanoestructurados y a “composites” con matriz cerámica. El resultado de su investigación ha sido difundido preferentemente mediante veintiún artículos científicos publicados en diversas e importantes revistas internacionales de la especialidad.

El jurado ha destacado, entre otras, sus importantes contribuciones al desarrollo de sensores fotónicos (por ejemplo de oxígeno o de dióxido de nitrógeno), al de fuentes portátiles de rayos X basadas en nanotubos de carbono, así como sus trabajos relacionados con la fabricación de nanotubos de carbono con precisión atómica.

Dicho acto que estuvo presidido por el Excmo. Sr. Marqués de Puebla de Cazalla, Teniente de Hermano Mayor de la Real Maestranza de Caballería, contó con la presencia del Ilmo. Sr. D. Juan Carlos Raffo Camarillo, Delegado del Gobierno de la Junta de Andalucía en Sevilla, el Excmo. Sr. D. Manuel García León, Vicerrector de Investigación de la Universidad de Sevilla, la Excma. Sra. Dña. Pilar Rodríguez Reina, Vicerrectora de Internacionalización y Comunicación de la Universidad Pablo de Olavide, el Excmo. Sr. D. Manuel Romero Carril, General Adjunto al Teniente General Jefe de la Fuerza Terrestre, el Excmo. Sr. D. Javier García Blázquez, Comandante Militar, el Excmo. Sr. D. Lucas Manuel Muñoz Bronchales, General Adjunto al Director de Enseñanza del Mando de Personal del Ejército del Aire, el Ilmo. Sr. D. Pedro Miguel Serrano Alférez, Delegado de Defensa en Andalucía, el Excmo. Sr. D. Jesús Castiñeiras Fernández, Presidente de la Real Academia de Medicina de Sevilla, el Excmo. Sr. D. Antonio A. Oropesa cáceres, Presidente de la Real Academia de Ciencias Veterinarias, el Ilmo. Sr. D. Luis Carlos Torcal Ortega, Coronel Jefe del RAAA, 74 y el Ilmo. Sr. D. Agustín Lobato Dabaña, Comandante Naval de Andalucía Occidental.


Alejandro Heredia Guerrero, Premio Extraordinario de Doctorado


Alejandro Heredia Guerrero acaba de recibir el Premio Extraordinario de Doctorado de la Facultad de Ciencias de la Universidad de Málaga. El premio ha sido concedido por la tesis titulada "Autoensamblaje Molecular y Síntesis de Materiales Biomiméticos a partir de Hidroxiácidos derivados de Cutinas Vegetales".

 

Alejandro llevó a cabo su trabajo doctoral en el Instituto de Ciencias Materiales de Sevilla con una beca JAE-Pre durante los años 2008-2011, bajo la dirección del Científico Titular José Jesús Benítez Jiménez.

En colaboración con el Catedrático Antonio Heredia Bayona del Departamento de Biología Molecular y Bioquímica de la Universidad de Málaga, en la tesis ha estudiado la reactividad a diferentes escalas del principal monómero de la cutina vegetal de los frutos de tomate. La cutina es el biopoliéster más abundante del reino vegetal que forma parte de la cutícula, la película protectora más externa de la epidermis vegetal.

La primera parte de la tesis, más académica, ha consistido en el estudio del autoensamblaje molecular de esta molécula y la comparación con otras similares. La fuerte inclinación a la ordenación bidimensional y a la autopolimerización en condiciones ambientales, hizo pensar que originarían una película de un material hidrófobo e inerte químicamente que actuaría de barrera con el entorno.

La segunda parte, con una orientación mucho más aplicada, ha consistido en la obtención de plásticos con propiedades a la carta a partir de estos monómeros, consiguiéndose nuevos materiales poliméricos completamente biodegradables y no tóxicos. Estos materiales han sido propuestos como envases para la industria alimentaria. Esta parte de la tesis ha recibido cierta notoriedad en algunos medios de comunicación.


Poliéster biomimético

CSIC y la Universidad de Málaga han patentado un nuevo procedimiento para la síntesis del poliéster de polialeurato, material idéntico al que conforma la cutícula vegetal, y al uso del mismo como material de envasado biodegradable de alimentos o principios activos. Se trata de un material polimérico plástico tipo, no tóxico, que se puede obtener a partir de materias primas procedentes de desechos de la industria conservera vegetal. El nuevo procedimiento no emplea disolventes ni catalizadores, lo que permite un ahorro en materias primas, una reducción de los residuos a eliminar y la obtención de un material de mayor pureza, y que se puede desechar sin peligro de contaminación pues es totalmente biodegradable. Adicionalmente, al partir de fases fundidas, al material se le puede dar cualquier forma deseada. El proceso de fabricación se puede implementar con facilidad a escala industrial, sin necesidad de un esfuerzo adicional.

Se buscan socios industriales para la licencia de la patente.

Icono PDF Poliéster_biomimético.pdf

Captura de CO2 y SO2 usando residuos industriales a temperatura y presión ambiente

El Instituto de Ciencia de Materiales de Sevilla (CSIC), junto con la Universidad de Sevilla y la Universidad de Cádiz, ha patentado un procedimiento que permite el secuestro mineral del CO2 y del SO2, gases provocantes del efecto invernadero y de la lluvia ácida respectivamente. El proceso se basa en la reutilización de residuos industriales ricos en calcio, producidos por multitud de tipos de industrias, y se realiza a temperatura ambiente y al aire libre, más fácil y barato por tanto que procesos similares.

Se buscan socios industriales para la licencia de la patente.

Icono PDF Captura_CO2.pdf

Recubrimientos nanoporosos con propiedades ópticas a medida

El Instituto de Ciencia de Materiales de Sevilla (CSIC) ha patentado un nuevo recubrimiento, y el procedimiento para fabricarlo, con la particularidad de que contiene nanoporos cerrados (nanoburbujas de 1-50 nm). El control de la microestructura del recubrimiento a través de las nanoburbujas determina las propiedades del mismo, tales como su índice de refracción, color, densidad y propiedades mecánicas. Esta posibilidad abre un amplio abanico de aplicaciones desde filtros y reflectores en la longitud de onda deseada, hasta recubrimientos del color deseado o acumuladores de calor, todo ello sin modificar significativamente la estabilidad química, térmica y mecánica.
El nuevo método de fabricación presenta la gran ventaja de basarse en una tecnología plenamente implantada a nivel industrial, con lo que el salto a la producción a gran escala del recubrimiento está garantizada sin el más mínimo esfuerzo de adaptación.

Se buscan socios industriales para la licencia de la patente

Icono PDF Nanoporosos.pdf

Captura de CO2 mediante la gestión inteligente de residuos industriales

El Instituto de Ciencia de Materiales de Sevilla (CSIC), la Universidad de Sevilla y la Universidad de Cádiz han desarrollado un método para capturar el CO2 presente en el ambiente usando para ello residuos industriales ricos en calcio. Supone una alternativa a los métodos vigentes para el secuestro de CO2, consiguiéndose importantes mejoras como la reducción de costos, baja complejidad y bajo consumo de energía. Adicionalmente el nuevo procedimiento permite la revalorización de residuos de diversas procedencias, sirviendo el mismo proceso para ambos fines, la
captura de CO2 y el reciclaje de residuos.

Se buscan socios industriales para la licencia de la patente

Icono PDF CapturaCO2.pdf

Método para fabricar materiales avanzados por concentración de corriente eléctrica

La US y el CSIC patentan un método para fabricar materiales avanzados por concentración de corriente eléctrica. Los investigadores han diseñado un molde que permite ahorrar hasta 100 veces la energía necesaria para la creación de este tipo de materiales, útiles principalmente en la industria aeroespacial, automovilística y biosanitaria.

Se buscan socios industriales para la licencia de la patente.

Icono PDF Metodo materiales.pdf

 

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