Desenvolvimento de cerâmicas multicamadas de carbeto de silício destinadas a aplicações térmicas
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Data
2010-04-28
Autores
Santana, Jerusa Góes Aragão [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Cerâmicas multicamadas de carbeto de silício foram obtidas por conformação por consolidação ou prensagem e utilizando diferentes técnicas de adesão das camadas. Produzidas com duas ou três camadas e apresentando gradientes de porosidades, a sistemática para obtenção destas cerâmicas teve início com o estudo individual das amostras. Para atender a níveis de porosidades previamente estabelecidos (15, 30 e 50%), foram conformadas amostras com diferentes composições e percentuais de sólidos. Na prensagem uniaxial utilizou-se um aditivo de sinterização (YAG) para controle do nível de porosidade das amostras. Por meio da realização de ensaios físicos, mecânicos, microscópicos e termomecânicos, foi possível conhecer as particularidades e características inerentes ao método de conformação empregado. As cerâmicas conformadas por prensagem apresentaram melhores acabamentos superficiais, poros pequenos, menores incidências de defeitos, porosidade e resistência mecânica influenciada pelo teor de aditivo empregado. Nas cerâmicas conformadas por consolidação, a existência de uma elevada porosidade associada a defeitos como trincas e fissuras, deterioraram a resistência mecânica das amostras. Baseando-se nos resultados obtidos, partiu-se então, para confecção das cerâmicas multicamadas. Na conformação por consolidação foram produzidas cerâmicas com duas ou três camadas, utilizando-se dois métodos: sobreposição direta e sobreposição por meio de sulcos. Na sobreposição direta a constituição das camadas ocorreu por entorno da dispersão sobre uma camada anteriormente processada. Entretanto, as tensões originadas durante as etapas de secagem conduziram a formação de abaulamento no ponto de adesão das camadas, comprometendo a sua resistência. A utilização de um defloculante polietilenimina...
Multilayer ceramics of silicon carbide were obtained by consolidation or pressing by using different techniques for layers adhesion. Produced with two or three layers and showing porosity gradients, the method for obtaining these ceramics began with the individual study of the samples. In order to achieve the porosity levels previously established (15, 30 and 50%), the samples were conformed with different compositions and percentages of solids. A sintering additive (YAG) was used in the uniaxial pressing in order to control the porosity of the samples. Through physical, mechanical, microscopic and thermomechanical tests, it was possible to know the peculiarities and characteristics related to the conforming method that was used. The obtained ceramics by pressing showed better superficial finish, small pores, lower incidence of defects, porosity and mechanical strength, influenced by the percentage of additive employed in the samples. The ceramic samples by consolidation had their mechanical strength damaged due to the high porosity associated with defects such as cracks and fissures. Multilayer ceramics were produced from the obtained results. Ceramic samples were produced by consolidation with two or three layers, by using two methods: direct overlap and overlap through grooves. In the direct overlap, the layer forming was performed by pouring the dispersion over another layer previously processed. However, the arisen tensions during the drying steps, made the interface between the layers become convex, compromising their strength. The use of the dispersant polyethylenimine (Lupasol SK), with high molecular weight, formed a thick film on the sample surface, allowing the production of grooves between the layers. The reduction of tensions on sample layers enabled the ceramic forming without defects on the interface. Samples produced... (Complete abstract click electronic access below)
Multilayer ceramics of silicon carbide were obtained by consolidation or pressing by using different techniques for layers adhesion. Produced with two or three layers and showing porosity gradients, the method for obtaining these ceramics began with the individual study of the samples. In order to achieve the porosity levels previously established (15, 30 and 50%), the samples were conformed with different compositions and percentages of solids. A sintering additive (YAG) was used in the uniaxial pressing in order to control the porosity of the samples. Through physical, mechanical, microscopic and thermomechanical tests, it was possible to know the peculiarities and characteristics related to the conforming method that was used. The obtained ceramics by pressing showed better superficial finish, small pores, lower incidence of defects, porosity and mechanical strength, influenced by the percentage of additive employed in the samples. The ceramic samples by consolidation had their mechanical strength damaged due to the high porosity associated with defects such as cracks and fissures. Multilayer ceramics were produced from the obtained results. Ceramic samples were produced by consolidation with two or three layers, by using two methods: direct overlap and overlap through grooves. In the direct overlap, the layer forming was performed by pouring the dispersion over another layer previously processed. However, the arisen tensions during the drying steps, made the interface between the layers become convex, compromising their strength. The use of the dispersant polyethylenimine (Lupasol SK), with high molecular weight, formed a thick film on the sample surface, allowing the production of grooves between the layers. The reduction of tensions on sample layers enabled the ceramic forming without defects on the interface. Samples produced... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Ceramica - Propriedades mecânicas, Ceramics
Como citar
SANTANA, Jerusa Góes Aragão. Desenvolvimento de cerâmicas multicamadas de carbeto de silício destinadas a aplicações térmicas. 2010. 202 f. Tese (doutorado) - Universidade Estadual Paulista, Faculdade de Engenharia de Guaratinguetá, 2010.