Cinética de cristalização em vidros teluritos do sistema TLWN
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Data
2013-03-05
Autores
Sousa, Edi Carlos Pereira de [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Vidros preparados a partir de massa fundida podem nuclear ou cristalizar novas fases quando são submetidos a tratamentos térmicos acima da temperatura de transição vítrea. Neste traba- lho foram apresentados estudos sobre a cinética de cristalização de vidros teluritos do sistema 80TeO2 –10WO3 –(10–x)Li2 O–xNa2 O, x = 0, 2, 4, 6 e 10% mol, denominado sistema TLWN. As principais teorias sobre nucleação e cristalização de vidros foram detalhadas, tais como: Teoria Clássica de Nucleação, Teoria Clássica de Nucleação Modificada, Teoria de Nucleação Adiabática e Teoria JMAK. Classicamente, o estudo da cristalização de vidros pode ser realizado através da teoria formulada por Johnson–Mehl–Avrami–Kolmogorov (JMAK), a qual descreve os processos de nucleação e cristalização, por intermédio das curvas de calorimetria exploratória diferencial – DSC. Os vidros foram sintetizados pelo método de resfriamento rápido (melt–quenching ). Medidas de DSC foram realizadas a diferentes taxas de aquecimento e com diferentes tama- nhos de partículas para estudar a cinética de cristalização dos vidros. Foi evidenciado o caráter amorfo de alguns vidros e para o vidro TLWN6 foram encontradas diferentes fases cristalinas, tais como: Na2 (TeW2 O9 ), Li2 Te2 O5 , WO3 , α–TeO2 e γ–TeO2 , dispersas na matriz devido aos di- versos tratamentos térmicos realizados em torno das temperaturas correspondentes aos máximos dos picos de cristalização e evidenciadas por DRX. Deconvoluções foram realizadas utilizando funções gaussianas para separar os picos sobrepostos da amostra TLWN6. Ficou evidente, por intermédio da análise dos termogramas, que o número de picos de cristalização aumenta com o incremento do óxido de sódio e também que os vidros teluritos deste sistema não possuem boa estabilidade térmica, quando...
The glasses prepared from the melt mass may crystallize or nuclear new phases when subjected to heat treatment above the glass transition temperature. In this work were presented studies on the kinetics of nucleation and crystallization of glasses tellurite of the system 80TeO2 –10WO3 – (10–x)Li2 O–xNa2 O, x = 0, 2, 4, 6 e 10% mol called TLWN system. The main theories on nucleation and crystallization of glasses have been detailed, such as: Classical Theory of Nucle- ation, Modified Classical Theory of Nucleation, the Nucleation Adiabatic Theory and Theory JMAK. Classically, the study of crystallization of glasses can be performed by theory formu- lated by Johnson–Mehl–Avrami–Kolmogorov (JMAK) which describes processes of nucleation and crystallization through of differential scanning calorimetry curves – DSC. The glasses were synthesized by the method of melt - quenching. DSC measurements were made at different hea- ting rates and with different particle sizes to study the crystallization kinetics of glass. It became evident amorphous character of some glasses and glass TLWN6 different crystalline phases have been found, such as Na2 (TeW2 O9 ), Li2 Te2 O5 , WO3 , α–TeO2 e γ–TeO2 , dispersed in the matrix due to the different heat treatments performed in around the temperatures corresponding to the peak maximum crystallization and evidenced by XRD. Deconvolutions were performed using gaussian functions to separate overlapping peaks TLWN6 sample. It became evident through the examination of thermographs, that the number of peaks of crystallization increases with the increase of sodium oxide and also that this system tellurite glasses do not have good thermal stability when compared to traditional glasses. The activation energies of the crystalline pha- ses were obtained using the... (Complete abstract click electronic access below)
The glasses prepared from the melt mass may crystallize or nuclear new phases when subjected to heat treatment above the glass transition temperature. In this work were presented studies on the kinetics of nucleation and crystallization of glasses tellurite of the system 80TeO2 –10WO3 – (10–x)Li2 O–xNa2 O, x = 0, 2, 4, 6 e 10% mol called TLWN system. The main theories on nucleation and crystallization of glasses have been detailed, such as: Classical Theory of Nucle- ation, Modified Classical Theory of Nucleation, the Nucleation Adiabatic Theory and Theory JMAK. Classically, the study of crystallization of glasses can be performed by theory formu- lated by Johnson–Mehl–Avrami–Kolmogorov (JMAK) which describes processes of nucleation and crystallization through of differential scanning calorimetry curves – DSC. The glasses were synthesized by the method of melt - quenching. DSC measurements were made at different hea- ting rates and with different particle sizes to study the crystallization kinetics of glass. It became evident amorphous character of some glasses and glass TLWN6 different crystalline phases have been found, such as Na2 (TeW2 O9 ), Li2 Te2 O5 , WO3 , α–TeO2 e γ–TeO2 , dispersed in the matrix due to the different heat treatments performed in around the temperatures corresponding to the peak maximum crystallization and evidenced by XRD. Deconvolutions were performed using gaussian functions to separate overlapping peaks TLWN6 sample. It became evident through the examination of thermographs, that the number of peaks of crystallization increases with the increase of sodium oxide and also that this system tellurite glasses do not have good thermal stability when compared to traditional glasses. The activation energies of the crystalline pha- ses were obtained using the... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Vidro, Cristalização, Glass
Como citar
SOUSA, Edi Carlos Pereira de. Cinética de cristalização em vidros teluritos do sistema TLWN. 2013. 86f. Dissertação (mestrado) - Universidade Estadual Paulista Júlio de Mesquita Filho, Faculdade de Engenharia de Ilha Solteira, 2013.