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Doctoral Thesis
DOI
10.11606/T.97.2009.tde-22082013-092313
Document
Author
Full name
Roseli Marins Balestra
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Lorena, 2009
Supervisor
Committee
Ribeiro, Sebastiao (President)
Cairo, Carlos Alberto Alves
Rodrigues, José de Anchieta
Santos, Claudinei dos
Strecker, Kurt
Title in Portuguese
Sinterização de SiC via fase líquida usando mistura de La2O3 e Al2O3 - microestrutura e propriedades mecânicas
Keywords in Portuguese
Alumina
Lantânia
Microestrutura
Propriedades Mecânicas
SiC
Abstract in Portuguese
As cerâmicas de carbeto de silício, SiC, possuem excelentes propriedades físicas, químicas e mecânicas, fazendo com que as mesmas tenham um vasto campo de aplicações. Devido à natureza altamente covalente do SiC, este possui baixo coeficiente de autodifusão, dificultando sua sinterização via fase sólida. Por esse motivo as cerâmicas de SiC devem ser sinterizadas via fase líquida, usando aditivos. A dificuldade para a expansão das aplicações das cerâmicas de SiC é a baixa tenacidade à fratura, 3-4 MPa√m . Neste trabalho foi estudada a sinterização de cerâmicas de SiC aditivadas com o sistema La2O3 - Al2O3, obtido por mistura mecânica e mistura química. Foram preparadas misturas de SiC com 10% em volume de aditivos. As amostras foram prensadas e sinterizadas; e as que apresentaram melhores resultados de densificação foram tratadas termicamente com o objetivo de reforçar in situ essas cerâmicas. Tanto as amostras somente sinterizadas quanto as sinterizadas e tratadas termicamente foram submetidas as análises de microscopia eletrônica de varredura, difração de raios X, tenacidade à fratura e energia de fratura. Foram correlacionados os resultados de microestrutura e resistência à propagação de trincas. Além do aprofundamento científico na sinterização e caracterização das cerâmicas de SiC, foram também obtidas resultados de tenacidade à fratura da ordem de 6 MPa√m.
Title in English
SiC liquid phase sintered with the La2O3 and Al2O3 additive - microstructure and mechanical properties
Keywords in English
Alumina
Latania
Mechanical properties
Microstructure
SiC
Abstract in English
Silicon carbide, SiC, ceramics have excellent physical, chemical and mechanical properties, allowing them to be used in a vast range of applications. However, due to the highly covalent nature of SiC, its self-diffusion coefficient is low, making its solid phase difficult to sinter without additives. SiC ceramics should therefore be sintered via liquid phase using densifying additives. The expansion of SiC ceramic applications, however, is hampered by its low fracture toughness of 3-4 MPa √m . The purpose of this work was to study SiC ceramics sintered with La2O3 - Al2O3 as additive system produced by mechanical and chemical mixing. To this end, SiC mixtures were prepared containing 10% in volume of additives. The samples were pressed and sintered. The samples displaying the highest densification were heat-treated to improve their properties. All the samples, both sintered and sintered followed by heat-treatment, were subjected to analyses by scanning electron microscopy, X-ray diffraction, fracture toughness and fracture energy. The result of microstructure, fracture energy and fracture toughness among them selves were then correlated. In addition to contributing to the body of scientific knowledge on the sintering and characterization of SiC ceramics, the goal of reaching fracture toughness in the order of 6 MPa √m was also achieved.
 
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Publishing Date
2013-08-22
 
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