Síntese e caracterização do sistema ZrO2-SiO2 com adição de cobalto para uso como pigmentos cerâmicos

Pós de ZrSiO4 dopado com cobalto foram sintetizados por meio do método dos precursores poliméricos para obtenção de pigmentos cerâmicos. O efeito de diferentes concentrações de Co2+ na transição de fase t-ZrO2 para ZrSiO4 foi estudado por meio de difração de raios X e análise térmica diferencial. Resultados de espectroscopia na região do UV-visível permitiram comparar o deslocamento de bandas em função da transição de fase. Além disso, foi realizado um estudo de estabilidade térmica e intensidade da alteração de cor do azul ao vermelho dos pós sintetizados em função da presença de cobalto e temperatura de calcinação, sendo estes parâmetros comparados com a transição de fase. Os resultados obtidos permitem identificar a transição de fase t-ZrO2 para ZrSiO4.Co-doped ZrSiO4 powders were synthesized by the polymeric precursor method to obtain ceramic pigments. The effect of different Co2+ contents on the t-ZrO2 to ZrSiO4 phase transition was studied by X-ray diffraction and differential thermal analysis. UV-Vis spectroscopy of the samples allowed comparing the band shift with the phase transition. Moreover, a study of the thermal stability and intensity of the blue to red color change of the synthesized powders with the presence of cobalt in relation to the calcination temperature was accomplished and compared to the phase transition. The results allowed to identify the t-ZrO2 to ZrSiO4 phase transition.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Effect of temperature on glass-ceramic films prepared by impregnation of commercial float glass surfaces with oxide powders under pressure

SnO(2) samples were prepared as ultrafine powder by a chemical synthesis method and deposited on the surface of commercial float glass substrates The glass surface was impregnated with these powders under high gas pressure (1.6-1.8 MPa) and heating to below the glass transition temperature in a designed pressurized chamber, forming SnO(2) films on glass surface Phases were analyzed by X-ray diffraction and the results confirmed the SnO(2) powders as a single-phase tetragonal structure. Analysis of the chemical composition of glass substrates before and after powder impregnation revealed an ion exchange process caused by the substitution of sodium ions by tin ions on the glass surface. Differences in the surface morphology of SnO(2) films on glass surface were related to the morphology of synthesized powders for deposition and impregnation. The mechanism of SnO(2) films on glass surface was based on mass transfer between the glass substrates and SnO(2) powders as a function of the treatment temperature. (C) 2010 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

PII: S0040-6090(02)00269-9

concentration of organic materials on the phase formation has been studied. For this purpose, PMN solutions were prepared with different precursors and were characterized by thermogravimetric and differential thermal analysis. The obtained solutions were deposited onto a Si (100) substrate by dip coating and pre-treated in a hot plate at 300 8C for 1 h. The films were annealed at 600, 700, 800 and 900 8C for 1 h and characterized by X-ray diffraction. The perovskite phase was formed after annealing at 600 and 700 8C when the solution of PMN was prepared with a lower amount of organic material and starting with niobium oxide. By increasing the temperature to 800 or 900 8C, only the formation of pyrochlore phase was observed. With the solution prepared from niobium ethoxide, only the presence of pyrochlore phase was observed independently of the annealing temperature.

Investigação da cinética de sinterização para o estágio inicial no sistema SnO2: ZnO Investigation of the sintering kinetics for initial stage in SnO2: ZnO system

A sinterização do sistema SnO2:0,6 mol% ZnO, obtido via mistura de pós, foi investigada por dilatometria sob taxa de aquecimento constante de 2,5, 5,0 e 10,0 ºC.min-1. Os modelos clássicos de sinterização de Woolfrey-Bannister e Johnson foram utilizados para analisar o estágio inicial da sinterização e calcular a energia de ativação. Os valores de energia de ativação determinados por esses modelos são de 547 kJ.mol-1 e 511 kJ.mol-1 para Woolfrey-Bannister e Johnson, respectivamente. Verificou-se a coexistência de dois mecanismos de sinterização, difusão na rede e difusão por contorno de grão, para o estágio inicial da sinterização do sistema SnO2:0,6 mol% ZnO.The sintering of SnO2:0.6 mol% ZnO obtained by powder mixtures was investigated by dilatometry at constant heating rates 2.5, 5.0 and 10.0 ºC.min-1. Using classical sintering models of Woolfrey-Bannister and Johnson to analyze the initial stage sintering, the calculated activation energy was 547 kJ.mol-1 and 511 kJ.mol-1, respectively. The coexistence of the two sintering mechanisms, volume diffusion and grain boundary diffusion, was found to control the initial stage sintering of the SnO2:0.6 mol % ZnO system