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Author: search.filters.author.Gardey Merino, MaríaEnd date: 2009

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    Síntesis y caracterización de pinturas selectivas de Co3O4 para superficies selectivas en colectores solares de baja temperatura
    (2009-01-01) Gardey Merino, María
    Para aumentar el rendimiento energético de los calefones solares se recubre su colector con superficies selectivas siendo las pinturas selectivas una alternativa económica, empleandose como pigmento para fabricarlas Co3O4 obtenido por diferentes métodos. Como se encuentran pocas referencias sobre su síntesis por combustión, se han obtenido para este trabajo micropartículas de Co3O4 empleando una ruta de combustión. Luego, por Difracción de Rayos X se constató la estructura cúbica del Co3O4 obtenido. Además, por Microscopía Electrónica de Barrido, se observó una morfología compacta y aglomeración de las micropartículas y mediante Microscopía Electrónica de Transmisión se apreciaron tamaños de partícula de 1 µm aprox. La absorbancia espectral en un rango de 500 a 1100 nm de longitud de onda de las películas formadas a partir de este pigmento sobre vidrio y aluminio resultó entre 0.92 y 0.96, valor menor al obtenido para una pintura comercial que resultó entre 0.95 y 0.97.
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    Nanostructured aluminium oxide powders obtained by aspartic acid–nitrate gel-combustion routes
    (2009-10-01) Gardey Merino, María
    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, (metastable) or (stable). The amorphous-to- transition was found for calcination temperatures in the range of 700–900 ◦C, while the -to- one was observed for calcination temperatures of 1100–1200 ◦C. The retention of the metastable phase is probably due to a crystallite size effect. It transforms to the 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.