Obtenção de niobato de chumbo e zinco (PZN) com fase e microestrutura controladas
Carregando...
Arquivos
Data
1997
Autores
Mazon, Talita [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
O método de Pechini bem como o uso da adição simultânea de partículas sementes (BaTiO3 ou PbTiO3) e de solução dopante contendo íons Ba2+ e Ti4+ ou Pb2+ e Ti4+ foram usados para preparar o niobato de zinco e chumbo (PZN). Com a finalidade de se estudar a influência do tamanho das partículas sementes na obtenção da fase PZN perovskita estável e na microestrutura da cerâmica, trabalhou-se com dois intervalos de tamanhos das partículas sementes: 1- entre 40 nm < φ < 100 nm, denominadas sementes de menor tamanho (frequência de 1015 partículas por cm3); 2- entre 100 nm< φ < 900 nm, denominadas sementes de maior tamanho (frequência de 1013 partículas por cm3). Os difratogramas de raios X obtidos para as amostras calcinadas a 800 oC ou a 900 oC permitiram identificar a formação das fases perovskita e pirocloro, sendo que a 900 oC predomina a fase perovskita. As amostras preparadas com as sementes de maior tamanho, menor frequência de núcleos cristalinos, apresentaram maior porcentagem de fase pirocloro que as preparadas com as sementes de menor tamanho após a calcinação. Os pós foram compactados isostaticamente e sinterizados entre 950 a 1100 oC. Para a sinterização utilizou-se um sistema fechado contendo atmosfera de pó de PbZnO3 + 5% PbO para controlar a evaporação do chumbo estequiométrico, durante a sinterização. A forma na qual os aditivos foram adicionados ao polímero (se como íons ou como sementes), assim como a frequência de núcleos cristalinos influeciaram no processo de sinterização e na microestrutura desenvolvida. As amostras preparadas com as sementes de maior tamanho exigiram uma temperatura mais elevada para a sinterização e apresentaram uma microestrutura mais heterogênea que as amostras preparadas com as sementes de menor tamanho. A microestrutura dos compactos obtidos a partir de pós contendo 50% dos aditivos na forma...
Pechini method as well as the simultaneous addition of seeds particles (BaTiO3 or PbTiO3) and dopant solutions containing Ba2+ and Ti4+ or Pb2+ and Ti4+ were used to prepare the perovskite phase of lead zinc niobate (PZN). To study the influence of seed particle size in the formation of stable PZN phase and in the ceramic microstructure, two range of seed particle size were considered: a) in the range of 30 to 100 nm, named small seed particles (frequency of 1015 particles/cm3); and b) in the range of 50 to 900 nm, named large seed particles (frequency of 1013 particles/cm3). The perovskite and pyroclore phases were identified for powder calcined at 800 oC and at 900 oC with predominance of perovskite phase for powder calcined at 900 oC. Powders prepared with large seed particles, smaller crystalline nuclei frequency, showed large amount of pyroclore phase after calcining, compared with the powder prepared with small size seeds. Calcined powders were isostaticaly pressed and sintered at temperatures ranging from 900 to 1100 oC. A close system containing powder with PbZnO3 + 5 PbO, to control the lead evaporation from the compacted samples, was used during sintering. Both, the way in which the additives were added to the polymer (seeds or ions) as well as the crystalline nuclei frequency influenced in the sintering process and in the microstructure. Samples prepared with large seeds need higher temperatures for sintering and showed a more heterogeneous microstructure compared with samples prepared with small seed particles. The microstructure of ceramics prepared for powder containing 50% of additives as seed and 50% of additives as ions is more homogeneous. The microstructure of ceramics obtained from powders containing 80% of additives as seeds and 20% as ions showed grains with well-defined crystalline planes. All the sintered samples showed a second phase segregated to the grain boundary...(Complete abstract click electronic access below)
Pechini method as well as the simultaneous addition of seeds particles (BaTiO3 or PbTiO3) and dopant solutions containing Ba2+ and Ti4+ or Pb2+ and Ti4+ were used to prepare the perovskite phase of lead zinc niobate (PZN). To study the influence of seed particle size in the formation of stable PZN phase and in the ceramic microstructure, two range of seed particle size were considered: a) in the range of 30 to 100 nm, named small seed particles (frequency of 1015 particles/cm3); and b) in the range of 50 to 900 nm, named large seed particles (frequency of 1013 particles/cm3). The perovskite and pyroclore phases were identified for powder calcined at 800 oC and at 900 oC with predominance of perovskite phase for powder calcined at 900 oC. Powders prepared with large seed particles, smaller crystalline nuclei frequency, showed large amount of pyroclore phase after calcining, compared with the powder prepared with small size seeds. Calcined powders were isostaticaly pressed and sintered at temperatures ranging from 900 to 1100 oC. A close system containing powder with PbZnO3 + 5 PbO, to control the lead evaporation from the compacted samples, was used during sintering. Both, the way in which the additives were added to the polymer (seeds or ions) as well as the crystalline nuclei frequency influenced in the sintering process and in the microstructure. Samples prepared with large seeds need higher temperatures for sintering and showed a more heterogeneous microstructure compared with samples prepared with small seed particles. The microstructure of ceramics prepared for powder containing 50% of additives as seed and 50% of additives as ions is more homogeneous. The microstructure of ceramics obtained from powders containing 80% of additives as seeds and 20% as ions showed grains with well-defined crystalline planes. All the sintered samples showed a second phase segregated to the grain boundary...(Complete abstract click electronic access below)
Descrição
Palavras-chave
Chumbo, Niobatos, Zinco, Lead
Como citar
MAZON, Talita. Obtenção de niobato de chumbo e zinco (PZN) com fase e microestrutura controladas. 1997. 141 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Química, 1997.