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Tungsten oxide (WO3) powders were obtained in this work by both wet chemical synthesis and homogeneous precipitation with ultrasound-assisted radiation methods. Experimental and theoretical investigations were performed to study the effect of the synthesis method and molarity concentration on the structural, optical, electric, and gas sensing properties of WO3. X-ray powder diffraction and Raman spectroscopy confirmed the presence of the monoclinic γ-phase. Rietveld refinement and size/strain calculations were done to perform a complete powder diffraction data analysis. The bandgap was calculated based on UV–Visible Diffuse Reflectance Spectroscopy data, resulting in 2.55 and 2.58 eV for the prepared samples by wet chemical and homogeneous precipitation methods, respectively. These experimental measurements were explained by first-principles total energy calculations, and the structural and electric properties of WO3 (002) surface were determined. Five atomic models were built with the purpose of determining the most stable structure of this surface with different oxygen terminations. Sensing tests were carried out for all the WO3 samples when interacting with carbon dioxide (CO2) molecules to analyze their performance as gas detecting devices. Parameters such as the sensing response, surface resistance behavior and response/recovery times were investigated in detail. Experimental tests confirmed that the maximum sensing response is obtained at 500 ppm of CO2, when operated at 300 °C. Based on the characterizations and gas sensing results, a CO2 gas sensing mechanism of WO3 was proposed and discussed in this work. Finally, the competitive properties of WO3 as a semiconductor-based gas sensor for CO2 detection were confirmed.

A simple method has been used to synthesize nanostructured La0.5Ba0.5CoO3 (LBCO) powders, by confining chemical precursors into the pores of polycarbonate filters. The proposed method allows us to obtain powders formed by crystallites of different sizes, it is scalable and does not involve the use of sophisticated deposition techniques. The area specific polarization resistance of symmetrical cells was studied to analyze the electrochemical behavior of the LBCO nanostructures as cathodes for Solid-Oxide Fuel Cells. We show that the performance is improved by reducing the size of the crystallites, obtaining area specific resistance values of 0.2 Wcm2 at 700C, comparable with newly developed cathodes using novel deposition techniques., 11 pages, 6 figures

In this work, we study the influence of the average crystallite size and dopant oxide on the reducibility of CeO2-based nanomaterials. Samples were prepared from commercial Gd2O3-, Sm2O3- and Y2O3-doped CeO2 powders by calcination at different temperatures ranging between 400°C and 900°C and characterized by X-ray powder diffraction, transmission electron microscopy and BET specific surface area. The reducibility of the samples was analyzed by temperature-programmed reduction and in situ dispersive X-ray absorption spectroscopy techniques. Our results clearly demonstrate that samples treated at lower temperatures, of smallest average crystallite size and highest specific surface areas, exhibit the best performance, while Gd2O3-doped ceria materials display higher reducibility than Sm2O3- and Y2O3-doped CeO2.

In this work we outline the mechanisms contributing to the oxygen reduction reaction in nanostructured cathodes of La0.8Sr0.2MnO3 (LSM) for Solid Oxide Fuel Cells (SOFC). These cathodes, developed from LSM nanostructured tubes, can be used at lower temperatures compared to microstructured ones, and this is a crucial fact to avoid the degradation of the fuel cell components. This reduction of the operating temperatures stems mainly from two factors: (i) the appearance of significant oxide ion diffusion through the cathode material in which the nanostructure plays a key role and (ii) an optimized gas phase diffusion of oxygen through the porous structure of the cathode, which becomes negligible. A detailed analysis of our Electrochemical Impedance Spectroscopy supported by first-principles calculations point toward an improved overall cathodic performance driven by a fast transport of oxide ions through the cathode surface. (Figure Presented). Fil: Sacanell, Joaquin Gonzalo. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Hernández Sánchez, Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Rubio Lopez, Adrian Ezequiel. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Martinelli, Hernan. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Siepe, Jimena Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Leyva de Guglielmino, Ana Gabriela. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Ferrari, Valeria Paola. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Juan, Dilson. Universidad Nacional de San Martín; Argentina Fil: Alonso Pruneda, José Miguel. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Mejía Gómez, Augusto Enrique. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina

Vivimos en una época en la que se demonizan las fuentes de “energías convencionales” debido a los efectos negativos que las misma tienen sobre el “medioambiente” o los accidentes sufridos en su explotación,y abrazamos sin ningún tipo de prejuicio y rápidamente las “energías renovables” sin hacernos muchas preguntas. La búsqueda de soluciones o alternativas rápidas y socialmente aceptables a los problemas expuestos, nos llevan a no exigir traer a la superficie aquellas cosas no tan buenas que pueden tener las nuevas tecnologías, que tienen un gran abanico de puntos positivos frente a sus competidoras convencionales; y que deben desarrollarse sin ocultar o esconder sus puntos negativos. En este trabajo se ponen en evidencia esas debilidades que presenta la energía solar fotovoltaica para que desde la visión mpliada nos permita exigir, interesados e involucrados en el futuro, que se profundicen los análisis en este tipo de tecnología y sus proyectos; para no vernos sorprendido por un impacto negativo que hoy sabemos o intuimos puede tener.

In this work we analyze the effect of adding CuO to a NiO/Ce0.9Zr0.1O2 oxide by in situ X-ray absorption near-edge structure XANES technique in Ce L3, Ni K and Cu K absorption edges in terms of sample reducibility and catalytic activity. The oxidation states of Ce, Ni and Cu cations are followed up during temperature programmed reduction (TPR) experiments in diluted hydrogen and during catalytic tests for partial oxidation of methane (POM) reaction. Redox behavior was correlated to conventional fixed bed reactor results. The effect of firing temperature, crystallite size, CeO2-ZrO2 support and the presence of Cu and/or Ni as an active phase is also analyzed. Results showed a beneficial effect of CuO addition in terms of Ce and Ni reduction. A stronger interaction of NiO species with the support was revealed upon analysis of XANES reduction profiles in sample NiO/ZDC in contrast to bimetallic CuO-NiO/ZDC sample. Reduction onset temperature was found to depend on Ni crystallite size, being markedly promoted when samples exhibited low values of crystallite size both in supported and non-supported CuO-NiO species. In situ catalytic experiments for partial oxidation of methane showed a clear interplay between the redox behavior from the Ce in the CeO2-ZrO2 support and the Ni from the active phase. Sample NiO/ZDC exhibited a continuous reduction of Ce cations in CH4:O2 feed flow, carbon formation was detected in X-ray Powder Diffraction (XPD) patterns and Ni re-oxidation was found to take place, clear indications of catalyst deactivation. In contrast, sample CuO-NiO/Ce0.9Zr0.1O2 displayed a slight re-oxidation of Ce and no re-oxidation of Ni altogether with the suppression of carbon formation. Fil: Toscani, Lucía María. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; Argentina Fil: Zimicz, Maria Genoveva. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Martins, Tereza S.. Universidade de Sao Paulo; Brasil Fil: Lamas, Diego Germán. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Larrondo, Susana Adelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; Argentina

In this work, we analyze Sm2O3-doped CeO2 (SDC) nanopowders and NiO/SDC nanocomposites in terms of sample reducibility and catalytic activity for partial oxidation of methane. We assess the role of the average crystallite size and specific surface area in Ni and Ce reduction kinetics by in-situ X-ray absorption spectroscopy experiments in diluted H2 and CH4/O2 mixtures. Our results indicate that crystallite size and surface area play a key role in CH4 activation through modification of the sample redox behavior. The oxidation of the metallic phase is the main cause of sample deactivation. A clear relationship is established between the temperature of maximum Ni oxidation rate and grain size. An interplay between Ce atoms from the support and Ni from the active phase was observed during the experiments, evidencing a complex relationship between oxygen vacancy concentration and catalytic activity. A high Ce3+ content in catalyst support was detrimental to catalytic activity

The aim of this paper is to study the oxidation states of metal cations and the changes in the crystalline phases in NiO/Ce0.9Zr0.1O2 nanocatalysts under typical conditions of methane catalytic partial oxidation reaction by in-situ X ray absorption near edge spectroscopy (XANES) and X-ray powder diffraction (XPD) studies. The Ce0.9Zr0.1O2 mixed oxide was obtained by glycine-nitrate-combustion method, being the nickel incorporated by incipient wetness impregnation. The evolution of the crystalline structure with temperature and operating conditions was followed by in-situ XPD experiments and the oxidation states of Ce and Ni cations by in-situ XANES experiments at the Ce-LIII and Ni-K absorption edges. It was observed that NiO is completely reduced to Ni° at temperatures above 650 °C while Ce0.9Zr0.1O2 fluorite-like phase showed changes in lattice parameter due to cerium reduction and crystallite growth, but no phase transformations or segregations were observed. It was confirmed that Ni° is the active centre to activate methane molecule while Ce4+/Ce3+ ratio is strongly related with CO/CO2 concentration in the exhaust gas flow. Fil: Zimicz, Maria Genoveva. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Prado, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Lamas, Diego Germán. Universidad Nacional de San Martín; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Larrondo, Susana Adelina. Universidad Nacional de San Martín; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina

Porous ceria-zirconia (Zr0·1Ce0·9O2−δ δ delete) powders were synthesized by a sol-gel route using inorganic chlorides (ZrCl4 and CeCl3·7H2O) as precursors, block copolymer P123 (PEO20PPO70PEO20) as the template and tri-isopropyl-benzene (TIPB) as the swelling agent. These porous materials show high surface area and gas permeability, important properties for Intermediate Temperature-Solid Oxide Fuel Cell (IT-SOFC) and catalytic applications. The samples were prepared with different P123:TIPB (w/w) % ratios (1:0, 1:1, 1:2 and 1:4), as a strategy to increase porosity. The samples were calcined at 400 °C in air to remove the template. Post-synthesis nickel impregnation was planned to obtain 3 and 10 (w/w) % of NiO after calcination. The structure and morphology of the samples were determined by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), nitrogen adsorption isotherms (NAI) and transmission and scanning electron microscopies (TEM and SEM). The resulting materials have high specific surface area (≈110 m2. g-1) and a wide pore size distribution of mesopores (3–50 nm). They are formed by nanocrystals (≈15 nm) of the predominant (≈90%) F m 3 ¯ m cubic phase and by the P 4 2 / n m c tetragonal phase. The micrographs revealed that the nanocrystalline oxides have mesopores with slit shape and a secondary smaller mesoporosity with a narrow size distribution (≈4 nm). An increase of micropore volume (sizes

Single-phased La0.6Sr0.4Co1-yFeyO3-d (y = 0.2, 0.5, 0.8) nanorods exhibiting the rhombohedral perovskite-type phase were synthesized by a pore-wetting technique. We studied their chemical composition, crystal and electronic structures, morphology and hyperfine properties as a function of the Co/Fe content of the samples. Our results demonstrate that Co cations exhibit a slightly lower oxidation state than Fe ones, resulting in a higher oxygen non-stoichiometry d for Co-rich samples. In addition, the values of d determined in this work for nanostructured samples are much higher than those reported in the literature for bulk materials. This can be attributed to the high degree of defects in nanomaterials and is probably one important factor in the high electrochemical performance for the oxygen reduction reaction of nanostructured La0.6Sr0.4Co1-yFeyO3-d IT-SOFC cathodes, which have been reported in a previous work. Keywords: electrode materials; nanostructured materials; X-ray diffraction; NEXAFS; M\"ossbauer spectroscopy, Comment: 18 pages, 8 figures, accepted for publication

In this work we studied the influence of particle size and agglomeration in the performance of solid oxide fuel cell cathodes made with nanoparticles of La0.8Sr0.2MnO3. We followed two synthesis routes based on the Liquid Mix method. In both procedures we introduced additional reagents in order to separated the manganite particles. We evaluated cathodic performance by Electrochemical Impedance Spectroscopy in symmetrical (CATHODE/ELECTROLYTE/CATHODE) cells. Particle size was tuned by the temperature used for cathode sintering. Our results show that deagglomeration of the particles, serves to improve the cathodes performance. However, the dependence of the performance with the size of the particles is not clear, as different trends were obtained for each synthesis route. As a common feature, the cathodes with the lowest area specific resistance are the ones sintered at the largest temperature. This result indicates that an additional factor related with the quality of the cathode/electrolyte sintering, is superimposed with the influence of particle size, however further work is needed to clarify this issue. The enhancement obtained by deagglomeration suggest that the use of this kind of methods deserved to be considered to develop high performance electrodes for solid oxide fuel cells., 20 pages, 17 figures

The aim of this work is to take further insight into the structural stability of cerium-zirconium catalysts under reducing, oxidizing and reaction conditions. In situ synchrotron based techniques (XANES and XPD) were used in order to determine the stability of crystal structure and the oxidation state of cerium cations in the reaction conditions prevailing in the catalytic studies. In situ XPD studies in 5 mol % H2 atmosphere revealed that no structural changes occur until 870 °C. At this temperature, the sample synthesized with glycine, which presents lower crystallite agglomeration, segregated a small quantity of a reduced phase. On the contrary, the solid synthesized with lysine, with more agglomerated crystallites, does not show structural changes in all the temperature range. Reoxidation treatments in 5 mol % O2 revealed that at 750 °C the segregated phase disappears and that the original cubic structure is restored. In situ XANES studies in the Ce LIII absorption edge indicate that under catalytic reaction conditions, the degree of reduction of Ce4+ is low, allowing the occurrence of methane oxidation. The solid is capable to deliver the oxygen of its structure when no oxygen is fed into the reactor until the 50% of cerium cations become reduced, triggering the deactivation process. Therefore, it is clear for these studies that the Ce4+ to Ce3+ ratio in the lattice is governing the catalytic behavior of the solid. The catalytic results collected during in situ XANES experiments are in excellent agreement with our previous catalytic studies performed with a laboratory fixed bed reactor. Fil: Zimicz, Maria Genoveva. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Prado, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina Fil: Larrondo, Susana Adelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; Argentina

Magnesium complex hydrides are attractive for hydrogen storage applications, mainly due to their high volumetric capacities and to their relatively low cost. In this work, nanocrystalline Mg2CoH5 was synthesized with very high yields (97%) by reactive milling cobalt and magnesium under relatively mild processing conditions (30 bar of H2 pressure and 12 h of milling). The behavior of the milled Mg2CoH5 during heating was studied by a combination of several techniques including DSC, QMS, TGA and in-situ synchrotron XRD. It is shown for the first time that two different mechanisms of hydrogen desorption take place. At low temperatures (up to 325°C), some hydrogen is released by a diffusional mechanism with no change in the crystalline structure of the high temperature γ-Mg2CoH5 phase. At higher temperatures, above 325°C, the γ-Mg2CoH5 phase becomes unstable and the complex hydride decomposes into Mg, Co and H2. This is the first work to report the diffusional hydrogen desorption mechanism for the Mg2CoH5 or any other complex hydride. Furthermore, a complete description of the allotropic β-Mg2CoH5 to γ-Mg2CoH5 phase transition is provided. Fil: Zepon, G.. Universidade Federal do São Carlos; Brasil Fil: Leiva, D. R.. Universidade Federal do São Carlos; Brasil Fil: Kaufman, M. J.. Colorado School of Mines; Estados Unidos Fil: Figueroa, Santiago Jose Alejandro. Centro Nacional de Pesquisa em Energia e Materiais Rua Giuseppe Máximo Scolfaro; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Floriano, R.. Universidade Estadual de Campinas; Brasil Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina Fil: Asselli, A. A. C.. Universidade Federal do São Carlos; Brasil Fil: Botta, W. J.. Universidade Federal do São Carlos; Brasil

This work reports the synthesis and characterization of mesoporous NiO/ZrO2-CeO2 composites. These materials are still being developed due to their excellent morphological and structural properties, especially for solid oxide fuel cells (SOFCs) anodes. A soft chemical route using a polymeric template was utilized to synthesize the samples. The structure after two different calcination processes at 400 °C and 540 °C was studied by X-ray diffraction and Rietveld refinement, before and after NiO loading. Nitrogen adsorption, scanning/transmission electron microscopy and small angle X-ray scattering revealed a nanocrystalline bi-phasic porous material. Temperature programmed reduction experiments showed higher Ni and Ce reduction values for samples calcined at 400 °C and 540 °C, respectively. Methane conversion values in the temperature range studied were similar for both calcination temperatures, showing 50% CH4 conversion around 550 °C and 80% around 650 °C. However, a sample calcined at 400 °C exhibited better morphological and textural properties leading to an enhancement in NiO and CeO2 reducibility that might be responsible for an improvement in oxygen surface exchange and gasification of carbon species in catalytic experiments. Fil: Bacani, R.. Universidade de Sao Paulo; Brasil Fil: Toscani, Lucía María. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina Fil: Martins, T. S.. Universidade Federal de Sao Paulo; Brasil Fil: Fantini, M. C. A.. Universidade de Sao Paulo; Brasil Fil: Lamas, Diego Germán. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Larrondo, Susana Adelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental; Argentina

Plasma nitriding of austenitic stainless steel is of high technological importance due to its ability to improve the surface hardness, wear and corrosion resistance. Therefore, such process presents a significant potential as a treatment of materials for biomedical applications. The resulting properties obtained on the nitrided layer depend on the nitriding parameters used, such as temperature, gases partial pressures, process time, among others. In this work, austenitic stainless steel AISI 316L was nitrided in a DC plasma using two different N2-H2 atmospheres: 25% N2 and 20% N2. A detailed analysis of surface microstructure has been carried out and related to corrosion behaviour in two saline solutions. The results were compared with the 316L unnitrided (UN). The chemical composition of the nitrided layer was determined by GDOES. The phases present in the nitrided layer were analysed by X-ray diffraction (XRD) and the phases in the surface of nitrided layer were analysed by grazing incidence X-ray diffraction mode (GIXRD). The corrosion behaviour of the samples was studied by an electrochemical corrosion test in 3 wt% NaCl and Ringer's solutions. The GDOES (Glow Discharge Optical Emission Spectroscopy) analysis shows a higher N concentration of in the surface of 25% N2 samples, named HN. The phases observed, by GIXRD, in HN samples were expanded austenite γN, CrN, Fe3N and Fe4N and, in the 20% N2 samples, named LN, only peaks of expanded austenite and Fe4N were observed. The corrosion results showed that LN present better corrosion resistance than HN, this could be due to the absence of chromium nitrides in the surface of LN as a consequence of lower N percentage in the nitriding atmosphere. Fil: de Las Heras, Maria Evangelina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Ybarra, Gabriel Omar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina Fil: Cabo, Amado. IONAR S.A.; Argentina Fil: Dalibon, Eugenia Laura. Universidad Tecnológica Nacional; Argentina Fil: Brühl, Sonia Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; Argentina

This chapter contains basic concepts and applications of wide-angle X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) to studies of nanostructured materials. The first part includes an introduction to the technique of X-ray powder diffraction (XPD), which is commonly applied to phase identification of powdered materials, characterization of unit cells, determinations of lattice parameters and, in some cases, also coordinates of atoms inside the unit cells. The main aspect described here is the analysis of the shape of X-ray diffraction peak profiles, which allows one to determine additional and also valuable structural information of nanomaterials, such as average crystallite sizes and crystallite microstrains. Detailed deductions of the equations used for different applications of X-ray diffraction and basic concepts of crystallography (such as those related to symmetries, Bravais and reciprocal lattices, etc.) are not described. The second part presents the basic equations related to the SAXS method and their applications to several biological systems (proteins in solution). Classical SAXS is an experimental procedure that is employed in transmission mode and is also applied to the study of many nanostructured inorganic materials. The third part includes two variants of the classical SAXS procedure, namely grazing incidence small-angle X-ray scattering (GISAXS) and anomalous small-angle X-ray scattering (ASAXS). The basic concepts of the GISAXS method and several applications to studies of nanostructured materials deposited on flat substrates and buried nanostructures are presented. The basic concepts of the ASAXS method are described, together with its applications to complex materials that cannot be properly studied using the classical SAXS technique, such as, for example, materials modeled by three phases with different electron densities. Most of the experiments described in this chapter were performed by the authors using X-ray beam lines of the National Synchrotron Light Laboratory (LNLS), Campinas, Brazil.

La0.8Sr0.2MnO3 (LSM) is one of the most commonly used cathodes in Solid Oxide Fuel Cells (SOFC). In spite of the fact that nanostructured cathodes are expected to display improved performance, the high operating temperature (∼ 1000°C) of LSM-based SOFCs hinders their stability. In the present work, we have developed nanostructured cathodes prepared from LSM nanotubes of enhanced performance, allowing its use at lower temperatures (∼ 800°C). We observed that our cathodes have qualitative improvements compared with microstructured materials: firstly, the diffusion in the gas phase is optimized to a negligible level and secondly, evidence of ionic conduction is found, which is extremely rare in LSM cathodes. We propose that this important change in the electrochemical properties is due to the nanostructuration of the cathode and deserves further attention, including the exploration of other materials. Fil: Sacanell, Joaquin Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Hernández Sánchez, Joaquin. Comisión Nacional de Energía Atómica; Argentina Fil: Rubio Lopez, Adrian Ezequiel. Comisión Nacional de Energía Atómica; Argentina Fil: Martinelli, Hernan. Comisión Nacional de Energía Atómica; Argentina Fil: Siepe, Jimena. Comisión Nacional de Energía Atómica; Argentina Fil: Leyva de Guglielmino, Ana Gabriela. Comisión Nacional de Energía Atómica; Argentina Fil: Ferrari, Valeria Paola. Comisión Nacional de Energía Atómica; Argentina Fil: Pruneda, Miguel. Institut Català de Nanociència i Nanotecnologia; España Fil: Juan, Dilson. Comisión Nacional de Energía Atómica; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

In this work nanostructured CeO2-ZrO2-Sc2O3 mixed oxides prepared by citrate complexation method are studied. The effects of the co-substitution of ZrO2 and Sc2O3 in the CeO2 lattice are assessed in terms of the reducibility of the samples and their catalytic activity towards oxidation of methane. In situ X-ray absorption near edge structure (XANES) and X-ray powder diffraction (XPD) experiments with synchrotron light were performed to study the oxygen exchange capacity of these ternary oxides in reaction conditions and their structure stability. Catalytic experiments for complete methane combustion indicated a superior performance of samples containing Sc2O3 compared to the CeO2-ZrO2 one in terms of reaction onset temperature, conversion values and activation energy. Samples with 4 at% and 6 at% Sc doping exhibited a stable behavior at 800 °C during 7.5 h on-stream experiments. Structural stability was confirmed by in-situ XPD experiments with no secondary phase segregation or carbon deposition in reaction conditions. Fil: Toscani, Lucía María. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Curyk, Pablo Andrés. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química; Argentina Fil: Zimicz, Maria Genoveva. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Halac, Emilia Beatriz. Comisión Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones No Nucleares. Gerencia Física (CAC). Departamento de Física de la Materia Condensada; Argentina Fil: Saleta, Martin Eduardo. Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia.; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina Fil: Larrondo, Susana Adelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentina

SrCo0.90M0.10O3-δ (M = Nb, Ta) perovskite powders were synthesized by sol-gel, using tartrate-precursor decomposition. The crystal structure of these materials was analyzed by x-ray powder diffraction. Rietveld refinements showed that both samples achieved the cubic crystal structure (Pm-3m), which was stabilized by the incorporation of highly-charged transition-metal cations at the octahedral sites. This synthesis method successfully lowered the calcination temperature relative to other methods mentioned in literature. The concentration of oxygen vacancies (δ value) was determined by thermogravimetric analysis. Microstructural analysis revealed micrometric scale particles with a superficial nanometric dendritic array with an average grain size less than 100 nm. The present work provides a new strategy to synthesize nanostructured perovskite materials that could have better electrical and electrochemical properties. Fil: Fuertes, Valeria Cintia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Eroles, Franco Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Menzaque, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Peláez, Walter José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Lamas, Diego Germán. Universidad Nacional de San Martín; Argentina

The Cu-In-Sn system is one of the Pb-free options to replace conventional Pb-Sn alloys in electronic industry. However, controversies still exist regarding some regions of the equilibrium phase diagram of the Cu-In-Sn ternary and also of the Cu-In and Cu-Sn binary systems. One of the most controversial fields of the Cu-In binary phase diagram lies between ~33 and 38 at.% In and temperatures ranging from 100 up to 500 °C. In this work, binary Cu-In alloys, with 30-37 at.% In nominal compositions and annealed at two different temperatures (i.e. 300°C and 500°C) for a long period (i.e. 7 months) were characterized by scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD). Three phases exist over the 33-38 at.% In composition range, namely the phase A at high temperatures and the B and C phases at low temperatures. These three phases can be described as superstructures of the hexagonal phase h (Cu2In) and differ, although slightly, from those previously reported in the literature. In addition, it has been demonstrated that even conventional XRD allows to unequivocally distinguishing between these phases despite their similar crystal structure. Fil: Baque, Laura Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Torrado, D.. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina Fil: Aricó, Sergio Fabián. Comisión Nacional de Energía Atómica; Argentina Fil: Craievich, A.F.. Universidade de Sao Paulo; Brasil Fil: Sommadossi, Silvana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina

In this work, a combined synchrotron X-ray diffraction (XPD), X-ray absorption near edge spectroscopy (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) study of La0.4Sr0.6Ti1-yCoyO3±δ (0 ≤ y ≤ 0.5), intended as symmetric solid oxide fuel cells electrode, is presented. Charge compensation mechanisms were characterized by room temperature measurements; LSTC has a perovskite pseudocubic structure with an A-site vacancy concentration related with Co doping level. This result seems to be triggered by the fact that Ti remains in a higher formal valence (around 4+) independent of the Co concentrations. On the contrary, Co K-edge XANES spectra show a dependency with the doping level but this seems to be related to structural changes. In-situ measurements simulating a symmetric SOFC working environment show that LSTC undergoes a rhombohedral to cubic perovskite phase transition with critical temperature dependent of the structural distortion level. Fil: Napolitano, Federico Ricardo. Comisión Nacional de Energía Atómica. Gerencia de Area de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Soldati, Analía Leticia. Comisión Nacional de Energía Atómica. Gerencia de Area de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Geck, Jochen. Leibniz Institute for Solid State and Materials Research IFW; Alemania Fil: Suescun, Leopoldo. Universidad de la Republica. Facultad de Química; Uruguay Fil: Acuña, Leandro Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Fernandez Zuvich, Afra. Comisión Nacional de Energía Atómica. Gerencia de Area de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina Fil: Lamas, Diego German. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina Fil: Serquis, Adriana Cristina. Comisión Nacional de Energía Atómica. Gerencia de Area de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina

We present combined Synchrotron X-ray Absorption Near Edge Spectroscopy (XANES) andExtended X-ray Absorption Fine Structure (EXAFS) study of La0.4Sr0.6Ti1yCoyO3d(0 The measurements were performed at room temperature at the Ti and the Co K-edges inorder to determine the local structural and electronic changes around the two transitionmetals. We find that Ti remains in a higher formal valence (around 4þ) independent of theCo concentration. In contrast to this, dramatic and systematic changes are observed for theCo as a function of y.We conclude that the stability of the Ti4þ triggers the A-site deficiencyin our samples and predicts that oxygen vacancies are much more easily formed at largeCo content, which in turn will greatly enhance the performance as electrode material. Fil: Napolitano, Federico Ricardo. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Soldati, Analía Leticia. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Geck, Jochen. Leibinz. Institute for Solid State and Materials Research; Alemania Fil: Lamas, Diego German. Universidad Nacional del Comahue; Argentina Fil: Serquis, Adriana Cristina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

We present a crystallographic, morphologic and redox dynamic study on (60:40) NiO/Ce0.9Gd0.1O1.95 (NiO/GDC) cermets simulating Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) anodes in situ conditions. We tested micro- and nanometer sized materials at 700ºC in three different atmospheres (5% H2, 5% O2 and 20% CH4). We used Dispersive X-ray Absorption Spectroscopy (DXAS) analysisat the Ce L3-edge and at the Ni K-edge to follow the metal´s oxidation states. A correlation between the catalytic/redox properties and the sample´s characteristics (microstructure, Ni distribution, etc.) was found, indicating that nanometric sized particles showed faster and higher reduction extents than micrometric particles of the same composition. Fil: Fernandez Zuvich, Afra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Larrondo, Susana Adelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química. Laboratorio de Procesos Catalíticos; Argentina Fil: Saleta, Martin. Laboratório Nacional de Luz Síncrotron; Brasil Fil: Napolitano, Federico Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Caneiro, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Arce, Mauricio Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Serquis, Adriana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

We investigated the electrochemical properties of Co?Fe perovskites, which can be used as cathodes for intermediate-temperaturesolid-oxide fuel cells (IT-SOFCs). We studied the electrochemical properties of nanostructured mixed ionic-electronic conductors for IT-SOFC cathodes with compositions of La0.6Sr0.4Co1-yFeyO3 (y = 0.2, 0.5 and 0.8). We analyzed the performance of two types of nanostructures: nanorods and nanotubes. Our results show that the electrochemical performance is highly influenced by the form of nanostructure, whereas the effect of composition is less significant. Fil: Mejía Gómez, Augusto Enrique. Comision Nacional de Energia Atomica. Gerencia del Area Investicaciones y Aplicaciones No Nucleares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martin. Escuela de Ciencia y Tecnología. Centro Internacional de Estudios Avanzados.; Argentina Fil: Sacanell, Joaquin Gonzalo. Comision Nacional de Energia Atomica. Gerencia del Area Investicaciones y Aplicaciones No Nucleares; Argentina Fil: Leyva, Ana Gabriela. Comision Nacional de Energia Atomica. Gerencia del Area Investicaciones y Aplicaciones No Nucleares; Argentina Fil: Lamas, Diego German. Universidad Nacional de San Martin. Escuela de Ciencia y Tecnología. Centro Internacional de Estudios Avanzados.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Polycrystalline Sr3MnMo2O9 (I) and Ba3MnMo2O9 (II) double perovskites with Mo5+ valence states are prepared by thermal treatment of gels produced from stoichiometric amounts of Sr(NO3)2 or Ba(NO3)2, MnCO3, and (NH4)6Mo7O24 dissolved in citric acid (5% H2/N2 reducing atmosphere, 1200 °C, 12 h).

Nanostructured CeO2-rich samples cosubstituted with ZrO2 and Sc2O3 are studied. The effects of the combined additions of both oxides on structural, morphological, and, especially, redox properties of the substituted lattice are assessed. In situ near edge X-ray absorption (XANES) experiments with synchrotron light were performed to study oxygen exchange capacity in a reducing environment for these ternary oxides. Structural characterization revealed that up to 8 at. % Sc was successfully incorporated into the CeO2–ZrO2 lattice without phase segregation. Increased scandia solubility was achieved through a soft chemical route synthesis involving citrate complexation which gave rise to porous powders with crystallite sizes in the nanometer range. In situ XANES experiments in 5 mol % H2/He atmosphere demonstrated that adding Sc3+ to the CeO2–ZrO2 mixed oxide leads to a ternary system (Ce0.9ScxZr0.1–xO2−δ) with faster reduction kinetics and enhanced reducibility in the whole temperature range analyzed (25–800 ...

Sr3MnMo2O9 and Ba3MnMo2O9 double perovskites with Mo5+ valence states have been prepared in polycrystalline form by thermal treatment, in reducing atmosphere (H2/N2 flow), of previously decomposed citrate precursors. These materials have been studied by X-ray and neutron powder diffraction (XRPD, NPD), magnetic and transport measurements. At room temperature, the crystal structure of Sr3MnMo2O9 is monoclinic, space group P21/n, with a = 5.6564(1) Å, b = 5.6383(1) Å, c = 7.9765(2) Å, β = 89.994(7)º; whereas Ba3MnMo2O9 presents a cubic lattice, space group Fm m, with a = 8.14900(8) Å. These samples present a frustrated magnetic interaction below to 12 and 9 K for Sr3MnMo2O9 and Ba3MnMo2O9, respectively. Semiconductor behaviour, observed either from d.c. or a.c. measurements, was modelled by a variable-range hopping mechanism. This transport behaviour is in accord with the electronic configurations Mn2+(3 d5)–Mo5+(4 d1) and supports the absence of mixed valence states in both double perovkites., J.C.P. thanks CONICET (Project PIP 112-200801-01360), SECyT-UNSL (Project PROICO 2-7707- 22/Q823) and ANPCYT (Project PICT 6/25459). R.D.S. thanks UN Cuyo, CONICET and ANPCyT (Argentina) under grants 06/C389, PIP-490 and PICT2007-0832/PICT2011-0752. J.A.A. acknowledges the financial support of the Spanish Please provide the grant number for: 1) Ministry of Education, 2) Brazilian Synchrotron Light Laboratory, if any.Ministry of Education to the project MAT2013-41099-R.

Lanthanum strontium titanates based oxides, materials with perovskite-type crystal structure, are good candidates for symmetrical fuel cell electrodes. They can become good mixed conductors (electronic and ionic) and reach adequate electrocatalytic activity for both oxygen reduction and fuel oxidation reactions if the right doping or structural modification of the (La,Sr)TiO3 compound is performed. However, the crystallographic information reported in the literature indicates a noticeable lack of reproducibility, since it is strongly dependent on synthesis conditions. In this work, La0.4Sr0.6Ti1−yCoyO3+δ (0.0 ≤ y ≤ 0.5) synthesis by a low-temperature chemical route and its structural characterization by X-ray powder diffraction and transmission electron microscopy are reported. From Rietveld refinements results, charge compensation mechanisms are studied and their correlation with synthesis parameters is discussed. We show that the creation of Sr vacancies at the A-site of the perovskite-type structure is the main compensation mechanism and their concentration decreases with the incorporation of Co in the crystal structure.

The aim of this paper is to gain further insight in the reduction and reoxidation processes taking place when Ce0.9Zr0.1O2 mixed oxides are in reducing or oxidizing atmospheres, respectively. The reduction process of these mixed oxides synthesized by two stoichiometric nitrate-aminoacid gel-combustion routes using glycine and lysine as fuels is studied by conventional H2-Temperature Programmed Reduction experiments. The results are compared with those obtained by time-resolved in situ X-ray absorption near-edge spectroscopy (XANES) in the energy level corresponding to the Ce LIII absorption edge. The reoxidation process by this last technique is also studied. Even though the identical composition and crystal structure of both samples, the redox processes resulted very different for each solid, suggesting the influence of specific surface area, pore volume and particle size on them. Fil: Zimicz, Maria Genoveva. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina Fil: Larrondo, Susana Adelina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química. Laboratorio de Procesos Catalíticos; Argentina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Prado, R.J.. Universidade Federal do Mato Grosso do Sul; Brasil Fil: Lamas, Diego Germán. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina

Gel-combustion syntheses (GCPs) employing different fuels are widely recognized in the literature because of their versatility, low cost and experimental flexibility. Besides, they allow to obtain a large amount of a pure, homogeneous nanopowder in a single batch process.In a previous work the authors reported new GCPs for zirconia-ceria nanopowders, syntheses based on nitrates-EDTA and nitrates-TRIS and preliminary results of morphology and structures of the different, obtained powders calcined at selected temperatures. In this article, new results about morphological and structural characterization of nanopowders obtained by fuel-rich and stoichiometric, nitrates-EDTA and nitrates-TRIS GCPs, mainly calcined at 600°C/2 h, are informed. The characterizations were performed by SEM, TEM, DRX and SBET techniques.By XRD, the expected retention of the metastable, tetragonal phase was established in ZrO2-rich, calcined nanopowders (ZrO2-15mol%CeO2), meanwhile, in CeO2-rich, calcined nanopowders (ZrO2-90mol%CeO2) the usually expected, thermodynamically stable, cubic phase was obtained.By SEM, typical agglomerates of variable morphology were observed, depending on the GCP/composition choice. By TEM the detailed nanostructure of the nanocrystallites aggregation was observed.In all cases, single-phased, homogeneous in composition, nanostructured powders were obtained. Some of them exhibit excellent properties, such as medium-high range specific surface area, for potential application in catalysis and SOFC technology. Fil: Lassa, Maria Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Tecnológicas. Laboratorio de Investigaciones y Servicios Ambientales Mendoza; Argentina Fil: Vazquez, Patricia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina Fil: Martínez, J.M. Martín. Universidad de Alicante; España Fil: Lascalea, Gustavo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Tecnológicas. Laboratorio de Investigaciones y Servicios Ambientales Mendoza; Argentina

This paper analyzes the influence of synthesis conditions on the reducibility and catalytic behavior of Ce0.9Zr0.1O2 mixed oxide synthesized by α-amino acid/metallic nitrate combustion processes, through stoichiometric and non-stoichiometric routes. We concluded that the α-amino acid selected and the α-amino acid/nitrate molar ratio strongly influence the reducibility and catalytic activity in the total combustion of methane. Thus, the Ce0.9Zr0.1O2 catalyst synthesized by the stoichiometric route with glycine showed the higher catalytic activity, which, in conjunction with the well-known ionic and electronic conductivities of ceria-based oxides under reducing conditions, positions this solid as an appropriate anode material for methane-fuelled solid oxide fuel cells.

The electrochemical performance of nanostructured cathodes for IT-SOFCs based on perovskite-type mixed ionic/electronic conductors (MIECs) is investigated. Different compounds (La 0.6 Sr 0.4 CoO 3− δ and Sm 0.5 Sr 0.5 CoO 3− δ ) and synthesis methods (freeze-drying and citrate complexation) were evaluated. These materials exhibited excellent performance (area-specific resistance values in the range of 0.05–0.20 Ω cm 2 for an operating temperature of 700 °C), which improved with decreasing grain size. This performance can be attributed to the high specific surface area of these nanostructured cathodes, thus dramatically increasing the number of active sites for the oxygen reduction reaction. Under these conditions, the electrochemical properties are mainly controlled by oxide ion diffusion through the MIEC cathode, which becomes faster with decreasing grain size.

In this work, the synthesis of nanocrystalline Ce0.9Zr 0.1O2 powders via the gel-combustion method, using different fuels, and following either stoichiometric or non-stoichiometric pH-controlled routes is investigated. The objective is to evaluate the effect of synthesis conditions on the textural and morphological properties, and the crystal structure of the synthesized materials. The solids were characterized by nitrogen physisorption, Scanning Electron Microscopy (SEM), X-ray powder diffraction (XPD), and Carbon-Hydrogen-Nitrogen Elemental Analysis (CHN). All the powders exhibited nanometric crystallite size, fluorite-type structure and negligible carbon content. Synthesis conditions strongly affect the average crystallite size, the degree of agglomeration, the specific surface area and the pore volume. Our results indicate that, by controlling the synthesis conditions it is possible to obtain solids with custom-made morphological properties. Fil: Zimicz, Maria Genoveva. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Fabregas, Ismael Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Larrondo, Susana Adelina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química. Laboratorio de Procesos Catalíticos; Argentina

We studied the electrochemical performance and microstructural characteristics of La0.5Sr0.5CoO3-d (LSCO) cathodes prepared by pulse laser deposition (PLD). This technique allows the growth of nanostructured cathode layers with vertically-aligned nanopores (VANP). In some samples, a vertically aligned nanocomposite (VAN) LSCO/CGO layer was introduced between the cathode and the Ce0.9Gd0.1O1.95 (CGO) electrolyte. The structure and morphology of several film configurations were characterized by X-ray diffraction, transmission and scanning electron microscopy, and synchrotron X-ray reflectometry, while the electrochemical properties were evaluated by means of impedance spectroscopy. We found that cathode area specific resistances (ASR) for VANP LSCO samples are almost independent of film thickness and are within the lowest reported values. A significant decrease in the ASR values was observed while heating the sample, but after this first heating, the ASR values were reproducible, indicating that these nanostructures are stable in the used temperatures and oxygen partial pressure ranges.

Plasma nitriding is a well established technology to improve wear and corrosion properties of austenitic stainless steels. Nevertheless, in the case of martensitic stainless steels, it continues being a problem mainly from the corrosion resistance viewpoint.In this work, three high chromium stainless steels (M340, N695 and Corrax) were hardened by ion nitriding at low temperature, intending to preserve their corrosion resistance.Corrosion behavior was evaluated by CuSO4 spot, salt spray fog and potentiodynamic polarization in NaCl solution. Microstructure was analyzed by optical microscopy, SEM (EDS) and glancing angle X-ray diffraction. All the samples showed an acceptable corrosion resistance in experiments with CuSO4, but in salt spray fog and electrochemical tests, only Corrax showed good behavior. The poor corrosion performance could be explained by chromium carbides formed in thermal treatment stage in martensitic steels and chromium nitrides formed during nitriding, even though the process was carried out at low temperature. Fil: Brühl, Sonia Patricia. Universidad Tecnológica Nacional. Facultad Regional Concepción del Uruguay; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Charadia, R.. Universidad Tecnológica Nacional. Facultad Regional Concepción del Uruguay; Argentina Fil: Simison, Silvia Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Lamas, Diego Germán. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Cabo, A.. IONAR; Argentina

In this work, the transport properties of fine-grained scandia-stabilized zirconia ceramics with low Si content have been investigated. These materials were prepared from ZrO2–6 mol% Sc2O3 nanopowders synthesized by a nitrate-lysine gel-combustion route. High relative densities and excellent electrical properties were obtained, even for sintering temperatures as low as 1350 °C. Our electrochemical impedance spectroscopy study showed that both the volume fraction of grain boundaries and the specific grain-boundary conductivity are significantly enhanced with decreasing grain size, resulting in a higher total ionic conductivity.

In this work we studied the electrochemical properties of cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) prepared with nanotubes of La 0.6 Sr 0.4 CoO 3 (LSCO). Their nanostructures consist of agglomerated nanoparticles in tubular structures of sub-micrometric diameter. The resulting cathodes are highly porous both at the micro- and the nanoscale. This fact increases significantly the access to active sites for the oxygen reduction. We investigated the influence of the diameter of the precursor nanotubes on the polarization resistance of the LSCO cathodes on CeO 2 –10 mol.% Sm 2 O 3 (SDC) electrolytes under air atmosphere, evaluated in symmetrical [LSCO/SDC/LSCO] cells. Our results indicate an optimized performance when the diameter of precursor nanotubes is sufficiently small to become dense nanorods after cathode sintering. We present a phenomenological model that successfully explains the behavior observed and considers that a small starting diameter acts as a barrier that prevents grains growth. This is directly related with the lack of contact points between nanotubes in the precursor, which are the only path for the growth of ceramic grains. We also observed that a conventional sintering process (of 1 h at 1000 °C with heating and cooling rates of 10 °C min −1 ) has to be preferred against a fast firing one (1 or 2 min at 1100 °C with heating and cooling rates of 100 °C min −1 ) in order to reach a higher performance. However, a good adhesion of the cathode can be achieved with both methods. Our results suggest that oxygen vacancy diffusion is enhanced while decreasing LSCO particle size. This indicates that the high performance of our nanostructured cathodes is not only related with the increase of the number of active sites for oxygen reduction but also to the fact that the nanotubes are formed by nanoparticles.

Synchrotron X-ray powder diffraction was applied to the study of the effect of crystallite size on the crystal structure of ZrO 2 –10 mol% Sc 2 O 3 nanopowders synthesized by a nitrate-lysine gel-combustion route. Nanopowders with different average crystallite sizes were obtained by calcination at several temperatures, ranging from 650 to 1200 °C. The metastable t″-form of the tetragonal phase, exhibiting a cubic unit cell and tetragonal P 4 2 / nmc spatial symmetry, was retained at room temperature in fine nanocrystalline powders, completely avoiding the presence of the stable rhombohedral β phase. Differently, this phase was identified in samples calcined at high temperatures and its content increased with increasing crystallite size. The critical maximum crystallite size for the retention of the mestastable t″-form resulted of about 35 nm.

In this work, two new gel-combustion routes for the synthesis of Al2O3 nanopowders with aspartic acid as fuel are presented. The first route is a conventional stoichiometric process, while the second one is a non-stoichiometric, pH-controlled process. These routes were compared with similar synthesis procedures using glycine as fuel, which are well-known in the literature. The samples were calcined in air at different temperatures, in a range of 600-1200 °C. They were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and BET specific surface area. Different phases were obtained depending on the calcination temperature: amorphous, γ (metastable) or α (stable). The amorphous-to-γ transition was found for calcination temperatures in the range of 700-900 °C, while the γ-to-α one was observed for calcination temperatures of 1100-1200 °C. The retention of the metastable γ phase is probably due to a crystallite size effect. It transforms to the α phase after the crystallite size increases over a critical size during the calcination process at 1200 °C. The highest BET specific surface areas were obtained for both nitrate-aspartic acid routes proposed in this work, reaching values of about 50 m2/g. © 2009 Elsevier B.V. All rights reserved. Fil: Gardey Merino, María Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Tecnológicas. Laboratorio de Investigaciones y Servicios Ambientales Mendoza; Argentina. Universidad Tecnológica Nacional; Argentina Fil: Lascalea, Gustavo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Tecnológicas. Laboratorio de Investigaciones y Servicios Ambientales Mendoza; Argentina Fil: Sánchez, Laura M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Vazquez, Patricia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina Fil: Cabanillas, Edgardo Domingo. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina

The local atomic structures around the Zr atom of pure (undoped) ZrO 2 nanopowders with different average crystallite sizes, ranging from 7 to 40 nm, have been investigated. The nanopowders were synthesized by different wet-chemical routes, but all exhibit the high-temperature tetragonal phase stabilized at room temperature, as established by synchrotron radiation X-ray diffraction. The extended X-ray absorption fine structure (EXAFS) technique was applied to analyze the local structure around the Zr atoms. Several authors have studied this system using the EXAFS technique without obtaining a good agreement between crystallographic and EXAFS data. In this work, it is shown that the local structure of ZrO2 nanopowders can be described by a model consisting of two oxygen subshells (4 + 4 atoms) with different Zr-O distances, in agreement with those independently determined by X-ray diffraction. However, the EXAFS study shows that the second oxygen subshell exhibits a Debye-Waller (DW) parameter much higher than that of the first oxygen subshell, a result that cannot be explained by the crystallographic model accepted for the tetragonal phase of zirconia-based materials. However, as proposed by other authors, the difference in the DW parameters between the two oxygen subshells around the Zr atoms can be explained by the existence of oxygen displacements perpendicular to the z direction; these mainly affect the second oxygen subshell because of the directional character of the EXAFS DW parameter, in contradiction to the crystallographic value. It is also established that this model is similar to another model having three oxygen subshells, with a 4 + 2 + 2 distribution of atoms, with only one DW parameter for all oxygen subshells. Both models are in good agreement with the crystal structure determined by X-ray diffraction experiments. Fil: Acuña, Leandro Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Lamas, Diego Germán. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Fuentes, Rodolfo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Fabregas, Ismael Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina Fil: Fantini, Márcia C. A.. Universidade de Sao Paulo; Brasil Fil: Craievich, Aldo F.. Universidade de Sao Paulo; Brasil Fil: Prado, Rogério J.. Universidade Federal do Mato Grosso do Sul; Brasil

Iron–cobalt-based perovskite oxides with general formula Ln0.7Sr0.3Fe0.8Co0.2O3−δ (where Ln = La, Pr and Gd) have been investigated for their application as intermediate-temperature cathodes in solid oxide fuel cells (SOFCs). Powdered samples of these materials were synthesized by a novel gel combustion process and then characterized by X-ray powder diffraction (XPD) and scanning electron microscopy (SEM). XPD patterns were satisfactorily indexed with an orthorhombic GdFeO3-type structure and, for all samples, a mean particle size of less than 1 μm was estimated from the SEM data. Experimental single-chamber SOFCs using with these materials as cathodes and NiO–SDC (samaria-doped ceria) and SDC as anode and electrolyte, respectively, were evaluated at 600 °C in a methane/oxygen mixtures. Peak power densities of 65.4, 48.7 and 46.2 mW cm−2 were obtained for Ag|Ln0.7Sr0.3Fe0.8Co0.2O3−δ|SDC|NiO–SDC|Pt cells with Ln = Pr, La and Gd, respectively. The relatively high power density obtained for the Pr compound shows that it could be an interesting material for cathode of single-chamber SOFCs.

The development of active and selective catalysts for methane partial oxidation is one of today's challenges, because these catalysts could be used either for hydrogen production purposes or as anode materials in single-chamber solid oxide fuel cells (SOFCs). In this work, the synthesis of ceria–zirconia solid solutions of nominal composition Ce 0.9 Zr 0.1 O 2 through the gel-combustion route is presented. The solids obtained were impregnated with nickel solutions to achieve contents of 9% and 50% (m/m), characterized texturally and structurally, and their catalytic behavior in the methane partial oxidation reaction was assessed. The synthesis method was effective, leading to solids with good morphological properties. Likewise, the Ni/Ce 0.9 Zr 0.1 O 2 catalysts proved to be active and showed a stable behavior during the working period, with methane conversion levels of 90% at temperatures above 550 °C, being hydrogen and carbon monoxide the main products.

The crystal structure and the local atomic order of a series of nanocrystalline ZrO2–CaO solid solutions with varying CaO content were studied by synchrotron radiation X-ray powder diffraction and extended X-ray absorption fine structure (EXAFS) spectroscopy. These samples were synthesized by a pH-controlled nitrate–glycine gel-combustion process. For CaO contents up to 8 mol%, the t′ form of the tetragonal phase (c/a> 1) was identified, whereas for 10 and 12 mol% CaO, the t′′ form (c/a= 1; oxygen anions displaced from their ideal positions in the cubic phase) was detected. Finally, the cubic phase was observed for solid solutions with CaO content of 14 mol% CaO or higher. The t′/t′′ and t′′/cubic compositional boundaries were determined to be at 9 (1) and 13 (1) mol% CaO, respectively. The EXAFS study demonstrated that this transition is related to a tetragonal-to-cubic symmetry change of the first oxygen coordination shell around the Zr atoms.

Crystal and local structures (long- and short-range order, respectively) of four nanocrystalline zirconia-based solid solutions—ZrO2-6 and 16 mol % CaO and ZrO2-2.8 and 12 mol % Y2O3—synthesized by a pH-controlled nitrate-glycine gel-combustion process were studied. These materials were characterized by synchrotron X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Our XRD results indicate that the solid solution with low CaO and Y2O3 contents (6 and 2.8 mol %, respectively) exhibit a tetragonal crystallographic lattice, and those with higher CaO and Y2O3 contents (16 and 12 mol %, respectively) have a cubic lattice. Moreover, our EXAFS study demonstrates that the tetragonal-to-cubic phase transitions, for increasing CaO and Y2O3 contents, are both related to variations in the local symmetry of the Zr–O first neighbor coordination sphere.

Crystal structure of compositionally homogeneous, nanocrystalline ZrO2–CeO2 solutions was investigated by X-ray powder diffraction as a function of temperature for compositions between 50 and 65 mol % CeO2. ZrO2-50 and 60 mol % CeO2 solid solutions, which exhibit the t′-form of the tetragonal phase at room temperature, transform into the cubic phase in two steps: t′-to-t″ followed by t″-to-cubic. But the ZrO2-65 mol % CeO2, which exhibits the t″-form, transforms directly to the cubic phase. The results suggest that t′-to-t″ transition is of first order, but t″-to-cubic seems to be of second order.

The transition between tetragonal and cubic phases in nanostructured ZrO2-Sc2O3 solid solutions by high-temperature X-ray powder diffraction using synchrotron radiation is presented. ZrO2-8 and 11 mol% Sc2O3 nanopowders that exhibit the t′- and t″-forms of the tetragonal phase, respectively, were synthesized by a stoichiometric nitrate-lysine gel-combustion route. The average crystallite size treated at 900°C was about 25 nm for both compositions. Our results showed that t′-t″ and t″-cubic transitions take place for the 8 and 11 mol% Sc2O3 samples, respectively.