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Titulo: High temperature compressive strength and creep behavior of Si-Ti-C-O fiber-bonded ceramics
Autores: Vera, MC; Martinez-Fernandez, J; Singh, M; Ramirez-Rico, J
Revista: Journal of the European Ceramic Society, 37 (2017) 4442-4448
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Fiber bonded silicon carbide ceramic materials provide cost-advantage over traditional ceramic matrix composites and require fewer processing steps. Despite their interest in extreme environment thermostructural applications no data on long term mechanical reliability other than static fatigue is available for them. We studied the high temperature compressive strength and creep behavior of a fiber bonded SiC material obtained by hot-pressing of Si Ti-C-O fibers. The deformation mechanism and onset of plasticity was evaluated and compared with other commercial SiC materials. Up to 1400 degrees C, plasticity is very limited and any macroscopic deformation proceeds by crack formation and damage propagation. A transient viscous creep stage is observed due to flow in the silica matrix and once steady state is established, a stress exponent n similar to 4 and an activation energy Q similar to 700 kJ mol(-1) are found. These results are consistent with previous data on creep of polymer derived SiC fibers and polycrystals.

Diciembre, 2017 | DOI: 10.1016/j.jeurceramsoc.2017.06.037

Titulo: Effect of the crystal chemistry on the hydration mechanism of swelling micas
Autores: Pavon, E; Alba, MD; Castro, MA; Cota, A; Osuna, FJ; Pazos, MC
Revista: Geochimica et Cosmochimica Acta, 217 (2017) 231-239
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Swelling and dehydration under minor changes in temperature and water vapor pressure is an important property that clays and clay minerals exhibit. In particular, their interlayer space, the solid-water interface and the layers' collapse and re-expansion have received much attention because it affects to the dynamical properties of interlayer cations and thus the transfer and fate of water and pollutants. In this contribution, the dehydration and rehydration mechanism of a swelling high-charge mica family is examined by in situ X-ray Diffraction. The effect of the aluminosilicate layer charge and the physicochemical properties of the interlayer cations on these processes are analyzed. The results showed that the dehydration temperature and the number of steps involved in this process are related to the layer charge of the silicate and the physicochemical properties of the interlayer cations. Moreover, the ability to adsorb water molecules in a confined space with high electric field by the interlayer cations does not only depend on their hydration enthalpy but also on the electrostatic parameters of these cations.

Noviembre, 2017 | DOI: 10.1016/j.gca.2017.08.028

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
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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: Cellulose-polyhydroxylated fatty acid ester-based bioplastics with tuning properties: Acylation via a mixed anhydride system
Autores: Heredia-Guerrero, JA; Goldoni, L; Benitez, JJ; Davis, A; Ceseracciu, L; Cingolani, R; Bayer, IS; Heinze, T; Koschella, A; Heredia, A; Athanassiou, A
Revista: Carbohydrate Polymers, 173 (2017) 312-320
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The synthesis of microcrystalline cellulose (MCC) and 9,10,16-hydroxyhexadecanoic (aleuritic) acid ester-based bioplastics was investigated through acylation in a mixed anhydride (trifluoroacetic acid (TFA)/trifluoroacetic acid anhydride (TFAA)), chloroform co-solvent system. The effects of chemical interactions and the molar ratio of aleuritic acid to the anhydroglucose unit (AGU) of cellulose were investigated. The degree of substitution (DS) of new polymers were characterized by two-dimensional solution-state NMR and ranged from 0.51 to 2.60. The chemical analysis by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the presence of aleuritate groups in the structure induces the formation of new H-bond networks. The tensile analysis and the contact angle measurement confirmed the ductile behavior and the hydrophobicity of the prepared bioplastics. By increasing the aleuritate amounts, the glass transition temperature decreased and the solubility of bioplastic films in most common solvents was improved. Furthermore, this new polymer exhibits similar properties compared to commercial cellulose derivatives.

Octubre, 2017 | DOI: 10.1016/j.carbpol.2017.05.068

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: Synthesis and characterization of Rh/MnO2-CeO2/Al2O3 catalysts for CO-PrOx reaction
Autores: Martinez, TLM; Laguna, OH; Lopez-Cartes, C; Centeno, MA
Revista: Molecular Catalysis, 440 (2017) 9-18
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Rh/MnO2-CeO2/Al2O3 catalysts with different manganese-to-ceria ratios have been synthesized, characterized and tested in CO-PrOx reaction. The physicochemical properties of the solids were studied by XRD, Raman spectroscopy, BET surface area, H-2-TPR, TGA-DTG and TEM. The differences observed in the textural, structural and redox properties were related to the Mn-to-ceria ratio of the samples. The segregation of Mn species was observed at high Mn-to-Ce ratios. In opposite way, MnO2-CeO2 solid solutions were obtained at low Mn to Ce ones. In this last case, the physicochemical properties of the solids were favored by the intimate Rh-Ce-Mn contact. The effect of the Mn-Ce presence on Rh catalysts which promotes the catalytic behavior towards selective CO oxidation was observed to be better at low temperatures. At higher temperatures, Mn species promote the Reverse Water Gas Shift reaction, whilst ceria promotes the H-2 oxidation in the whole range of working temperatures.

Octubre, 2017 | DOI: 10.1016/j.mcat.2017.06.018

Titulo: Europium-doped NaGd(WO4)(2) nanophosphors: synthesis, luminescence and their coating with fluorescein for pH sensing
Autores: Laguna, M; Escudero, A; Nunez, NO; Becerro, AI; Ocana, M
Revista: Dalton Transactions, 46 (2017) 11575-11583
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Uniform Eu-doped NaGd(WO4)(2) nanophosphors with a spherical shape have been synthesized for the first time by using a wet chemistry method based on a homogeneous precipitation process at low temperature (120 degrees C) in ethylene glycol/water mixtures. The obtained nanoparticles crystallized into the tetragonal structure and presented polycrystalline character. The europium content in such phosphors has been optimized through the analysis of the luminescence dynamics (lifetime measurements). By coating the Eu3+-doped wolframate based nanoparticles with fluorescein through a layer-by-layer (LbL) approach, a wide range (4-10) ratiometric pH-sensitive sensor has been developed, which uses the pH insensitive emission of Eu3+ as a reference.

Septiembre, 2017 | DOI: 10.1039/c7dt01986f

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: Enhanced green fluorescent protein in optofluidic Fabry-Perot microcavity to detect laser induced temperature changes in a bacterial culture
Autores: Lahoz, F; Martin, IR; Walo, D; Freire, R; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Revista: Applied Physics Letters, 111 (2017) 111103
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Thermal therapy using laser sources can be used in combination with other cancer therapies to eliminate tumors. However, high precision temperature control is required to avoid damage in healthy surrounding tissues. Therefore, in order to detect laser induced temperature changes, we have used the fluorescence signal of the enhanced Green Fluorescent Protein (eGFP) over-expressed in an E. coli bacterial culture. For that purpose, the bacteria expressing eGFP are injected in a Fabry-Perot (FP) optofluidic planar microcavity. In order to locally heat the bacterial culture, external infrared or ultraviolet lasers were used. Shifts in the wavelengths of the resonant FP modes are used to determine the temperature increase as a function of the heating laser pump power. Laser induced local temperature increments up to 6-7 degrees C were measured. These results show a relatively easy way to measure laser induced local temperature changes using a FP microcavity and using eGFP as a molecular probe instead of external nanoparticles, which could damage/alter the cell. Therefore, we believe that this approach can be of interest for the study of thermal effects in laser induced thermal therapies. 

Septiembre, 2017 | DOI: 10.1063/1.4990870

Titulo: Rare earth based nanostructured materials: synthesis, functionalization, properties and bioimaging and biosensing applications
Autores: Escudero, Alberto; Becerro, Ana I.; Carrillo-Carrion, Carolina; Nunez, Nuria O.; Zyuzin, Mikhail V.; Laguna, Mariano; Gonzalez-Mancebo, Daniel; Ocana, Manuel; Parak, Wolfgang J.
Revista: Nanophotonics, 6 (2017) 881-921
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Rare earth based nanostructures constitute a type of functional materials widely used and studied in the recent literature. The purpose of this review is to provide a general and comprehensive overview of the current state of the art, with special focus on the commonly employed synthesis methods and functionalization strategies of rare earth based nanoparticles and on their different bioimaging and biosensing applications. The luminescent (including downconversion, upconversion and permanent luminescence) and magnetic properties of rare earth based nanoparticles, as well as their ability to absorb X-rays, will also be explained and connected with their luminescent, magnetic resonance and X-ray computed tomography bioimaging applications, respectively. This review is not only restricted to nanoparticles, and recent advances reported for in other nanostructures containing rare earths, such as metal organic frameworks and lanthanide complexes conjugated with biological structures, will also be commented on.

Septiembre, 2017 | DOI: 10.1515/nanoph-2017-0007