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Master's Dissertation
DOI
10.11606/D.54.1978.tde-16032015-105640
Document
Author
Full name
Edgar Dutra Zanotto
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1978
Supervisor
Committee
Mascarenhas, Yvonne Primerano
Qualifik, Paul
Title in Portuguese
Separação de fases amorfas e nucleação de cristais em vidros do sistema Li2O-Si02
Keywords in Portuguese
Não disponível
Abstract in Portuguese
Foram estudados vidros do sistema Li2O - SiO2, com 29,0 31,0 e 33,3% mol de Li2O, em regiões adjacentes à fronteira de imiscibilidade metaestável. Amostras foram obtidas por meio da técnica de splat cooling. Caracterizou-se o desenvolvimento da separação de fases amorfas com o tratamento térmico, através da evolução da intensidade integrada do espalhamento de raios-X a baixos ângulos. Utilizando-se de microscopia ótica de reflexão e métodos estereológicos, definiu-se a cinética de nucleação de cristais, mostrando-se de maneira clara que a separação de fases acelera a nucleação cristalina em vidros desse sistema. Observou-se também, que esse efeito é mais acentuado durante o estágio de nucleação e crescimento da separação amorfa que na etapa de coarsening. Os resultados obtidos experimentalmente, sugerem que o gradiente de concentração existente na vizinhança das partículas vítreas separadas, contribui apreciavelmente à aceleração da nucleação de cristais. Um aumento significativo da mobilidade atômica, através das interfaces das fases amorfas, poderia ser uma explicação alternativa ou complementar para o efeito verificado. Adicionalmente, mostrou-se as razões pelas quais vários autores concluíram que a separação amorfa não influencia a nucleação cristalina
Title in English
Not available
Keywords in English
Not available
Abstract in English
Phase separation and its influence on crystal nucleation in Li2O - SiO2 glasses were studied. Samples having 29,0%, 31,0% and 33,3% mol Li2O were obtained by the splat cooling technique. The development of amorphous phase separation with heat treatment was characterized by determining the evolution of the integrated intensity of small angle x-rays scattering. Using the optical reflection microscopy and stereological techniques, the kinetics of crystal nucleation was defined, and it was proved that phase separation accelerates crystal nucleation in glasses belonging to this system. It was also observed that this effect is more pronounced during the nucleation and growth stage of amorphous separation than during the coarsening stage. The experimental results suggest that the depleted zone around the separated vitreous particles plays an important role on the acceleration of crystal nucleation. The increase in atomic mobility through the interfaces of the amorphous phases could be an alternative or complementary explanation to the observed effect. Additionally, arguments were given to explain why several authors found that that amorphous separation does not influence crystal nucleation
 
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Publishing Date
2015-03-16
 
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