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Master's Dissertation
DOI
10.11606/D.54.1980.tde-03062015-112954
Document
Author
Full name
Johnny Rizzieri Olivieri
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1980
Supervisor
Title in Portuguese
Decomposição espinodal durante o resfriamento contínuo no sistema B2O3-PbO-Al2O3
Keywords in Portuguese
Não disponível
Abstract in Portuguese
Através da técnica de espalhamento de raio-X a baixos ângulos, forem estudadas misturas vítreas resfriadas até temperaturas interiores a um "gap" de miscibilidade, quando se produz a segregação dos seus componentes. As curvas de intensidade de espalhamento foram obtidas em função do módulo do vetor do espaço recíproco, h, que está associado com o comprimento das "ondas de composição" do sistema por h = 2π / ∧. A partir de amostras com diferentes velocidades médias de resfriamento, Q, determinou-se o valor de hm, correspondente a amplificação máxima, e também as intensidades Im correspondentes aos respectivos Hm. Com esses valores, foi possível obter a dependência entre hm-Q e Im-Q. Por outro lado, observou-se também a variação do ponto de cruzamento entre as diferentes curvas. Estes resultados foram comparados com as diversas teorias existentes, apresentando um bom acordo qualitativo. As diferenças quantitativas foram explicadas levando-se em conta que o sistema estudado não se encontra nos primeiros estágios de desenvolvimento da segregação
Title in English
Not available
Keywords in English
Not availabel
Abstract in English
The decomposition of vitreous mixtures cooled continuously inside the miscibility gap were studied by means of small angle X-ray scattering techniques. The Fourier spectrum associated to the composition distribution is directly recorded by measuring the scattered intensity I as a function of the magnitude of the reciprocal vector h = 2π / ∧, where ∧ is the length of the concentration waves. The maximum in the scattered intensity Im (associated with waves receiving maximum amplification rate) and its position in reciprocal space hm were determined for samples subject to different average cooling rates Q. Thus, is was possible to establish experimentally the dependence of hm vs. Q and of Im vs. Q. Furthermore, a variation of the crossover point between intensity curves for different cooling rates was observed. The experimental observation were found to be in good qualitative agreement with existing theories. Some quantitative discrepancies with theoretical predictions can be traced to the fact that the system under study does not conform to the requirement of early stages of decomposition imposed by the theories
 
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Publishing Date
2015-06-12
 
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