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Titulo: High-temperature thermal conductivity of biomorphic SiC/Si ceramics
Autores: Ramirez-Rico, J.; Singh, M.; Zhu, D.; Martinez-Fernandez, J.
Revista: Journal of Materials Science, 52 (2017) 10038-10046
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Thermal conductivity of biomorphic SiC/Si, a silicon carbide + silicon containing two phase material, was evaluated using the laser steady-state heat flux method. These materials were processed via silicon melt infiltration of wood-derived carbon scaffolds. In this approach, heat flux was measured through the thickness when one side of the specimen was heated with a 10.6-A mu m CO2 laser. A thin mullite layer was applied to the heated surface to ensure absorption and minimize reflection losses, as well as to ensure a consistent emissivity to facilitate radiative loss corrections. The influence of the mullite layer was accounted for in the thermal conductivity calculations. The effect of microstructure and composition (inherited from the wood carbonaceous performs) on measured conductivity was evaluated. To establish a baseline for comparison, a dense, commercially available sintered SiC ceramic was also evaluated. It was observed that at a given temperature, thermal conductivity falls between that of single-crystal silicon and fine-grained polycrystalline SiC and can be rationalized in terms of the SiC volume fraction in biomorphic SiC/Si material.

Septiembre, 2017 | DOI: 10.1007/s10853-017-1199-y

Titulo: Lead-Free Polycrystalline Ferroelectric Nanowires with Enhanced Curie Temperature
Autores: Datta, Anuja; Sanchez-Jimenez, Pedro E.; Al Orabi, Rabih Al Rahal; Calahorra, Yonatan; Ou, Canlin; Sahonta, Suman-Lata; Fornari, Marco; Kar-Narayan, Sohini
Revista: Advanced Functional Materials, 27 (2017) 1701169
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Ferroelectrics are important technological materials with wide-ranging applications in electronics, communication, health, and energy. While lead-based ferroelectrics have remained the predominant mainstay of industry for decades, environmentally friendly lead-free alternatives are limited due to relatively low Curie temperatures (T-C) and/or high cost in many cases. Efforts have been made to enhance T-C through strain engineering, often involving energy-intensive and expensive fabrication of thin epitaxial films on lattice-mismatched substrates. Here, a relatively simple and scalable sol-gel synthesis route to fabricate polycrystalline (Ba0.85Ca0.15)(Zr0.1Ti0.9)O-3 nanowires within porous templates is presented, with an observed enhancement of T-C up to similar to 300 degrees C as compared to similar to 90 degrees C in the bulk. By combining experiments and theoretical calculations, this effect is attributed to the volume reduction in the template-grown nanowires that modifies the balance between different structural instabilities. The results offer a cost-effective solution-based approach for strain-tuning in a promising lead-free ferroelectric system, thus widening their current applicability.

Agosto, 2017 | DOI: 10.1002/adfm.201701169

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: Biomorphic ceramics from wood-derived precursors
Autores: Ramirez-Rico, J.; Martinez-Fernandez, J.; Singh, M.
Revista: International Materials Reviews, 62 (2017) Issue 8
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Materials development is driven by microstructural complexity and, in many cases, inspired by biological systems such as bones, shells and wood. In one approach, one selects the main microstructural features responsible for improved properties and design processes to obtain materials with such microstructures (continuous-fibre-reinforced ceramics, porous ceramics, fibrous ceramic monoliths, etc.). In a different approach, it is possible to use natural materials directly as microstructural templates. Biomorphic ceramics are produced from natural and renewable resources (wood or wood-derived products). A wide variety of SiC-based ceramics can be fabricated by infiltration of silicon or silicon alloys into cellulose-derived carbonaceous templates, providing a low-cost route to advanced ceramic materials with near-net shape potential and amenable to rapid prototyping. These materials have tailorable microstructure and properties, and behave like ceramic materials manufactured by advanced ceramic processing approaches. This review aims to be a comprehensive description of the development of bioSiC ceramics: from wood templates and their microstructure to potential applications of bioSiC materials.

Agosto, 2017 | DOI: 10.1080/09506608.2017.1354429

Titulo: Large-scale high-temperature solar energy storage using natural minerals
Autores: Benitez-Guerrero, Monica; Sarrion, Beatriz; Perejon, Antonio; Sanchez-Jimenez, Pedro E.; Perez-Maqueda, Luis A.; Manuel Valverde, Jose
Revista: Solar Energy Materials and Solar Cells, 168 (2017) 14-21
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The present work is focused on thermochemical energy storage (TCES) in Concentrated Solar Power (CSP) plants by means of the Calcium-Looping (CaL) process using cheap, abundant and non-toxic natural carbonate minerals. CaL conditions for CSP storage involve calcination of CaCO3 in the solar receiver at relatively low temperature whereas carbonation of CaO is carried out at high temperature and high CO2 concentration to use the heat of reaction for power production by means of a CO2 closed power cycle. Under these conditions, large CaO particles derived from limestone to be used in industrial processes are rapidly deactivated due to pore plugging, which limits the extent of the reaction. This is favored by the relatively small pores of the CaO skeleton generated by low temperature calcination, the large thickness of the CaCO3 layer built upon the CaO surface and the very fast carbonation kinetics. On the other hand, at CaL conditions for CSP storage does not limit carbonation of CaO derived from dolomite (dolime). Dolime is shown to exhibit a high multicycle conversion regardless of particle size, which is explained by the presence of inert MgO grains that allow the reacting gas to percolate inside the porous particles.

Agosto, 2017 | DOI: 10.1016/j.solmat.2017.04.013

Titulo: New insights into surface-functionalized swelling high charged micas: Their adsorption performance for non-ionic organic pollutants
Autores: Pazos, MC; Castro, MA; Cota, A; Osuna, FJ; Pavon, E; Alba, MD
Revista: Journal of Industrial and Engineering Chemistry, 52 (2017) 179-186
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The major components of the wastewater from the petroleum refineries are benzene, toluene and phenol and one of the techniques applied to the treatment of effluents is sorption using organo-functionalized clay. The materials exploited in the present study are a family of surface-functionalized synthetic micas and their sorption capacities for non-ionic organic pollutants are analyzed. The organo-functionalization of their surface provides them the capacity to sorb effectively non-ionic pollutants in the interface. Their adsorption performance is a function of the alkylamonium properties such as the chain length, the mass fraction and the organization of the organic cation in the interlayer space of the micas.

Agosto, 2017 | DOI: 10.1016/j.jiec.2017.03.042

Titulo: One-reactor plasma assisted fabrication of ZnO@TiO2 multishell nanotubes: assessing the impact of a full coverage on the photovoltaic performance
Autores: Filippin, Alejandro Nicolas; Macias-Montero, Manuel; Saghi, Zineb; Idigoras, Jesus; Burdet, Pierre; Sanchez-Valencia, Juan R.; Barranco, Angel; Migdley, Paul A.; Anta, Juan A.; Borras, Ana
Revista: Scientific Reports, 7 (2017) art 9621
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This paper addresses the fabrication of vertically aligned ZnO@TiO2multishell nanotubes by a combined full vacuum-plasma approach at mild temperatures. The growth is carried out within the premises of a one-reactor approach, i.e. minimizing the number of vacuum chambers and sample transferences. In this way, the interface between ZnO and TiO2 is fully preserved from humidity thus increasing ZnO durability and stability. These nanostructures are studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy in STEM (EDX-STEM). High density one-dimensional arrays of these nanotubes formed on FTO substrates are applied as photoanode in a dye-sensitized solar cell (DSC). The evolution of the dye adsorption capacity and solar cells parameters are explored as a function of the crystallinity and thickness of the TiO2 shell. The results show the critical effect of a full coverage by TiO2 of ZnO core to explain the mixed results found in the literature.

Agosto, 2017 | DOI: 10.1038/s41598-017-09601-7

Titulo: Crystal structure, NIR luminescence and X-ray computed tomography of Nd3+:Ba0.3Lu0.7F2.7 nanospheres
Autores: Gonzalez-Mancebo, D; Becerro, AI; Cantelar, E; Cusso, F; Briat, A; Boyer, D; Ocana, M
Revista: Dalton Transactions, 46 (2017) 6580-6587
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Uniform, hydrophilic 50 nm diameter Nd3+-doped Ba0.3Lu0.7F2.7 nanospheres are synthesized at 120 degrees C using a singular one-pot method based on the use of ethylene glycol as solvent, in the absence of any additive. The composition and crystal structure of the undoped material are analyzed in detail using ICP and XRD, which reveals a BaF2 cubic crystal structure that is able to incorporate 70 mol% of Lu ions. This finding contrasts with the reported phase diagram of the system, where the maximum solubility is around 30 mol% Lu. XRD proves as well that the Ba0.3Lu0.7F2.7 structure is able to incorporate Nd3+ ions up to, at least 10 mol%, without altering the uniform particles morphology. The Nd-doped particles exhibit near-infrared luminescence when excited at 810 nm. The maximum emission intensity with the minimum concentration quenching effect is obtained at 1.5% Nd doping level. X-ray computed tomography experiments are carried out on powder samples of the latter composition. The sample significantly absorbs X-ray photons, thus demonstrating that the Nd3+-doped Ba0.3Lu0.7F2.7 nanospheres are good candidates as contrast agents in computed tomography.

Agosto, 2017 | DOI: 10.1039/c7dt00453b

Titulo: Flash sintering of highly insulating nanostructured phase-pure BiFeO3
Autores: Perez-Maqueda, LA; Gil-Gonzalez, E; Perejon, A; Lebrun, JM; Sanchez-Jimenez, PE; Raj, R
Revista: Journal of the American Ceramic Society, 100 (2017) 3365-3369
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We show that BiFeO3, that is electrically homogeneous, is a good insulator, and has a low dielectric constant (the properties desired in its applications), can be produced by flash sintering, which is nominally difficult to achieve by conventional and spark plasma sintering processes. The flash-sintered specimens had a uniform microstructure with a nanometric grain size of similar to 20 nm.

Agosto, 2017 | DOI: 10.1111/jace.14990

Titulo: Thermal study of residues from greenhouse crops plant biomass
Autores: Morales, Laura; Garzon, Eduardo; Maria Martinez-Blanes, Jose; Jose Sanchez-Soto, Pedro
Revista: Journal of Thermal Analysis and Calorimetry, 129 (2017) 1111-1120
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The principal aim of this work is to examine the effect of thermal treatments using a muffle furnace (static heating) and by simultaneous TG/DTA (dynamic heating) on selected greenhouse crops plant biomass investigated here as the first time. The effect of fractionation by sieving (<25 and <2.5 mm), preheating at 150 °C for 48 h and leaching with water on the thermal behavior has been studied. The observation of similar profiles of mass variation corresponding to several samples heated in air up to 1150 °C allows to conclude that particle size did not influence the thermal evolution, but the effect of heating cycle is evidenced. Thermal analysis in air of a representative sample showed the several mass variation steps and DTA exothermic effects produced by the complex thermal decomposition and pyrolysis of the organic matter. Elemental analysis (CHNS and O) of the starting samples and thermally treated revealed the effect of the temperature, with formation of ashes with lower C content from 44.37 to 0.70 mass% as a minimum after elimination of organic matter by heating. Leaching increased the thermal mass variation as an effect of elimination of water-soluble components. According to the present results, the size fractionation of the greenhouse crops biomass did not influence the results of elemental composition. The present study has provided results of interest concerning this biomass source of renewable energy originated by the remains of tomato (Solanum lycopersicum L.), being estimated the highest of all the biomass produced by the greenhouse crops agricultural industry in Almería (SE Spain).

Agosto, 2017 | DOI: 10.1007/s10973-017-6243-2