Navegando por Autor "Santos, Maria Rita de Cássia"
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Artigo Influence of doping on the preferential growth of α-MoO3(Elsevier, 2008-07-14) Pereira, Luiza G.; Soledade, Luiz Edmundo Bastos; Ferreira, Jailson M.; Lima, Severino Jackson Guedes; Fernandes Júnior, Valter José; Araújo, Antônio Souza de; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Santos, Maria Rita de Cássia; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dosMoO3 is a lamellar material with applications in different areas, as solid lubricants, catalysis, solar cells, etc. In the present work, MoO3 powders, synthesized by the polymeric precursor method, were doped with nickel or cobalt. The powder precursors were characterized by TG/DTA. After calcination between 500 and 700 ◦C, the samples were characterized by X-ray diffraction, infrared and Raman spectroscopy and scanning electron microscopy. -MoO3 was obtained after calcination at low temperatures. With the temperature increase, -MoO3 is observed, with a preferential growth of the (0 2k 0) planes, when the material is doped and calcined at 700 ◦C. Doping with nickel increases five times the preferential growth. As a consequence, plate-like particles are observedArtigo Influence of the network former on the properties of magnesium spinels(Springer, 2007-03-07) Silva, Márcia R. S.; Miranda, Lydianne C. de O.; Santos, Maria Rita de Cássia; Lima, Severino Jackson Guedes; Soledade, Luiz Edmundo Bastos; Silva, Elson Longo da; Paskocimas, Carlos Alberto; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dosUndoped and/or doped with 1 mol% of Co2+ Mg2TiO4 andMg2SnO4 powders were synthesized by the polymeric precursor method. The influence of the network former (Sn4+ or Ti4+) on the thermal, structural and optical properties was investigated. The recorded mass losses are due to the escape of water and adsorbed gases and to the elimination of the organic matter. Mg2TiO4 crystallizes at lower temperatures and also presents more ordered structure with a smaller unit call and having more intense green color than Mg2SnO4 hasArtigo Photoluminescence in the CaxSr1 xWO4 system at room temperature(Elsevier, 2008-08) Pôrto, S. L.; Silva, Elson Longo da; Pizani, Paulo Sérgio; Boschi, Tania M.; Simões, Luis Gustavo Pagotto; Lima, Severino Jackson Guedes; Ferreira, Jailson M.; Soledade, Luiz Edmundo Bastos; Espinoza, J. W. M.; Santos, Maria Rita de Cássia; Maurera, Maria Aldeiza M. A.; Paskocimas, Carlos Alberto; Santos, Ieda Maria Garcia dos; Souza, Antônio Gouveia deIn this work, a study was undertaken about the structural and photoluminescent properties, at room temperature, of powder samples from the CaxSr1 xWO4 (x ¼ 0–1.0) system, synthesized by a soft chemical method and heat treated between 400 and 700 1C. The material was characterized using Infrared, UV–vis and Raman spectroscopy and XRD. The most intense PL emission was obtained for the sample calcined at 600 1C, which is neither highly disordered (400–500 1C), nor completely ordered (700 1C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO4 or SrWO4, but for Ca0.6Sr0.4WO4. The PL emission spectra could be separated into two Gaussian curves. The lower wavelength peak is placed around 530 nm, and the higher wavelength peak at about 690 nm. Similar results were reported in the literature for both CaWO4 and SrWO4Artigo Planejamento experimental aplicado à otimização de massas cerâmicas contendo matérias-primas naturais(ABCERAM, 2007) Albuquerque, F. R.; Santos, Ieda Maria Garcia dos; Lima, Severino Jackson Guedes; Santos, Maria Rita de Cássia; Soledade, Luiz Edmundo Bastos; Souza, Antônio Gouveia de; Martinelli, Antonio EduardoA otimização da composição é uma etapa de fundamental importância no processamento cerâmico. Neste trabalho, planejamento experimental foi aplicado a fim de se avaliar a relação entre propriedade e a composição de um sistema obtido a partir de matérias-primas naturais extraídas no Pegmatito do Seridó, na região fronteiriça RN-PB. Para o estudo do sistema ternário foram combinadas variáveis de processo (temperatura: 1100 e 1200 oC; patamar de calcinação: 0 e 2 h), com a utilização de planejamento de misturas, de acordo com o planejamento simplex centróide. Os percentuais mínimos de cada componente na mistura foram de 10% v/v. Foram avaliadas as propriedades reológicas de suspensões aquosas das misturas com 50% v/v, otimizadas com PAA-Na. Determinou-se a porosidade aparente e massa específica aparente, além da retração de queima. A composição mineralógica das peças cerâmicas obtidas a 1200oC foi basicamente mulita e quartzo. O estudo permitiu especificar a região de composição que leva à maior densidade após sinterização, com um número relativamente pequeno de amostras