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Preparation And Research Of Alumina Matrix Ceramic Composite Reinforced By Mullite And Silicon Carbide Particle

Posted on:2002-09-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q S ZhouFull Text:PDF
GTID:1101360062480344Subject:Non-ferrous metallurgy
Abstract/Summary:PDF Full Text Request
Improving the fracture strength and fracture toughness of ceramic materials is always the key problem in the research of advanced ceramic materials. Especially with the rapid development of modern science and technology, materials with higher and higher properties, for example, wear-resistance, thermal-resistance, erosion-resistance, etc, are required in many special applications, such as machinery, electronic industry, aviation and energy etc, where the traditional metal or high polymer materials are not qualified completely. However, as the advanced ceramic materials have a series of excellent properties, more and more attention was put on the field.In this case, it was attempted to research and explore an advanced alumina matrix ceramic composite with high fracture strength and fracture toughness using nano-sized silicon carbide powder and in-stiu formed mullite phase as reinforcements by combining the excellent properties of monolithic alumina, mullite and SiC ceramic. In detail, the following aspects have been explored and studied systematically in this dissertation:The oxidation behavior of sub-micrometer sized silicon carbide powder in air, oxygen and H2O2 medium was studied systematically for the first time in this paper. Much work has been done on the oxidation behavior of macroscopical silicon carbide materials. But no work has been reported on the oxidation of sub-micrometer sized silicon carbide powder in the literature. In this paper, its oxidation behavior was firstly studied. It was found that the sub-micrometer sized silicon carbide powder had good oxidation resistance at temperature lower than 800癈 in the natural flowing air because a density SiO2 oxidation layer was formed on its surface to prevent the inside of silicon carbide from being further oxidized. And then it was very easily to be oxidized at the temperature range 900-1200 癈 in the oxygen, and the relationship between oxidation rate andoxidation time followed the parabolic equation with the average activation energy 143.40 kJ/mol, and the inward diffusion of oxygen molecules across the growing silicon dioxide oxidation layer was the controlling step. And it was also found that adopting the fluidization oxidation apparatus to substitute the traditional method might alleviate the agglomeration phenomenon of silicon carbide powder during the oxidation process in air or oxygen.It was indicated that sub-micrometer silicon carbide powder might be easily oxidized in the t^Oa medium according to the thermodynamic calculation and analysis. And experiments proved that the sub-micrometer silicon carbide powder could be easily oxidized in the H2O2 medium. Furthermore, the agglomeration deficiency can almost be avoided which happened in air or oxygen atmosphere during the oxidation process of ultrafine silicon carbide powder.Systematical studies were also done in the hydrothermal synthesis of boehmite and diaspore powder in this dissertation. And homogeneous composite ceramic powder boehmite/SiC/SiO2 was prepared successfully. It was investigated systematically that the influence of hydrothermal temperature and isothermal holding time on the crystallization and particle size of synthesized boehmite powder. Under suitable hydrothermal condition, equiaxial boehmite nano-powder with well crystallization and little agglomeration was synthesized successfully with the mean particle size about 30nm. Besides preparing nano-sized boehmite powder by hydrothermal method, diaspore powder with the average particle size about lOOnm was also successfully prepared at 35CTC for holding time 240 hours without adding any seeds for the first time. In order to obtain homogeneous mixture ceramic powder, pre-oxidized silicon carbide powder was added to the precursor of preparing boehmite powder or adding sub-micrometer sized silicon carbide powder to H2O2 medium directly and through the hydrothermal process homogeneous ceramic powder mixture can be prepared. This is a good solution to the heterogeneous problem of mechanical mixture of several powders.
Keywords/Search Tags:hydrothermal synthesis, nano-composite, ceramic, alumia matrix, mechanical properties, HP sintering, pressureless sintering, mechanism
PDF Full Text Request
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