Estudos estruturais em vidros e vitrocerâmicas contendo 'PBF IND.2'-'CDF IND.2
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Data
2000-12-01
Autores
Silva, Maurício Antonio Pereira da [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Vidros e vitrocerâmicas foram obtidos dos sistemas oxifluoretos envolvendo os fluoretos de chumbo e cádmio e um óxido conhecido como formador de vidros: SiO2, B2O3, P2O5, e TeO2. Os domínios vítreos foram estabelecidos e um grande número de composições incluindo alta concentração de metais pesados leva à formação de vidros estáveis. A estrutura amorfa foi estudada por técnicas espectroscópicas de determinação de estruturas a curtas distânicas (Espalhamento Raman e Absorção de Raios X). Além dos óxidos, o papel de formador desempenhado pelos átomos de cádmio foi também identificado. Atenção especial foi direcionada aos processos de cristalização. Fluoreto de chumbo cúbico β-PbF2, telurito de chumbo PbTe3O7 (fase cristalina de uma vitrocerâmica transparente), óxido de telúrio tetragonal α-TeO2 e soluções sólidas do tipo Pb1-xCdxF2 foram obtidos como produtos da cristalização, dependendo da composição e do tratamento térmico. A adição de íons terras-raras leva ao controle do processo de cristalização. Na presença do íon nucleante apenas a forma β-PbF2 foi identificada. Os íons terras raras apresentamse concentrados na fase cristalina e as propriedades espectroscópicas são aquelas apresentadas em um meio cristalino, sugerindo interessantes aplicações destes materiais na indústria tecnológica.
Glasses and glass-ceramics have been obtained in oxyfluoride systems involving lead and cadmium fluorides and one of the well-known glass former oxides SiO2, B2O3, P2O5, GeO2 and TeO2. Vitreous domain were established and a wide range of compositions including high heavy metal contents lead to stable glasses. Amorphous structures have been studied by short-range order spectroscopy techniques (Raman scattering and x-ray absorption) and molecular basic structures have been identified. Besides the usual oxides, the role of glass former could also be proposed for cadmium ions. Special attention has been paid for crystallization process. Cubic lead fluoride, cubic lead tellurite, tetragonal tellurium oxide and a solid solution of the type Pb1-xCdxF2 are obtained as crystallization products depending on the composition and temperature of heat treatments. Pb1-xCdxF2 solid solutions are well known superionic materials and obtaining this solid solution as a crystal phase could be very interesting for applications concerning ionic electrical conduction properties. The addition of rare earth ions led to the control of the crystallization process. In the presence of the nucleating ion only the cubic form β-PbF2 was identified. Rare earth ions are concentrate in the crystal phase and crystal like spectroscopic properties were observed suggesting interesting applications for these perfectly transparent glass ceramics in photonics.
Glasses and glass-ceramics have been obtained in oxyfluoride systems involving lead and cadmium fluorides and one of the well-known glass former oxides SiO2, B2O3, P2O5, GeO2 and TeO2. Vitreous domain were established and a wide range of compositions including high heavy metal contents lead to stable glasses. Amorphous structures have been studied by short-range order spectroscopy techniques (Raman scattering and x-ray absorption) and molecular basic structures have been identified. Besides the usual oxides, the role of glass former could also be proposed for cadmium ions. Special attention has been paid for crystallization process. Cubic lead fluoride, cubic lead tellurite, tetragonal tellurium oxide and a solid solution of the type Pb1-xCdxF2 are obtained as crystallization products depending on the composition and temperature of heat treatments. Pb1-xCdxF2 solid solutions are well known superionic materials and obtaining this solid solution as a crystal phase could be very interesting for applications concerning ionic electrical conduction properties. The addition of rare earth ions led to the control of the crystallization process. In the presence of the nucleating ion only the cubic form β-PbF2 was identified. Rare earth ions are concentrate in the crystal phase and crystal like spectroscopic properties were observed suggesting interesting applications for these perfectly transparent glass ceramics in photonics.
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Fluoretos, Chumbo, Cadmio, Vidro, Lead
Como citar
SILVA, Maurício Antonio Pereira da. Estudos estruturais em vidros e vitrocerâmicas contendo 'PBF IND.2'-'CDF IND.2. 2000. 156 f. Tese (doutorado) - Universidade Estadual Paulista, Instituto de Química, 2000.