| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 87 === The monolithic SiC bulks and hot pressed SiC/zirconia/mullite composites were exposed in air isothermally at 950-1050℃ for up to 500hrs. This study aims at the effect of SiC particle size and content on this oxidation behavior. The oxidation rate was impliedly the weight change divided by the surface area of SiC powders in the composite for SiC-containing composites. The sequence of oxidation rate were SiC bulk ﹥SiC powder ﹥SiC-containing composites. In the composites, these containing coarser SiC particles were oxidized faster than these containing finer SiC particles. The oxidation rate decreased with SiC content in the composites containing 50 vol% zirconia, while the oxidation rate remained constant in the composites containing 10 vol% zirconia. The activation energy was 135-141kJ/mol for SiC powders, 94-97kJ/mol for SiC bulks, 174 kJ/mol for coarser SiC particles in the composites containing 50 vol% zirconia and 194 kJ/mol for finer SiC particles in the composites containing 50 vol% zirconia. The oxidation behavior of the composites containing 50 vol% zirconia with a lower SiC content and coarser SiC particle were characterized by a large oxidation depth as well as a relatively small gradient, which exhibited oxidation behavior of Mode II, while higher SiC content and finer SiC particles tend to demonstrate the oxidation behavior of Mode I.
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