碳化矽顆粒大小及含量對碳化矽/氧化鋯/莫來石複合材料氧化行為的影響

Abstract

本研究是以熱壓法製備碳化矽╱氧化鋯╱莫來石之複合材料（MZY10/SiC和MZY50/SiC分別表示基地中氧化鋯體積百分比10 vol% 和50 vol% 的複合材料）及碳化矽塊體，將兩者和碳化矽粉體，暴露於950-1050℃的空氣中進行1到500小時的氧化實驗，探討碳化矽顆粒大小及含量對碳化矽塊體、粉體及碳化矽╱氧化鋯╱莫來石複合材料氧化行為的影響。本實驗將碳化矽粉體及塊體的氧化速率以氧化後的重量增量除以粉體、塊體的表面積來表示，複合材料的氧化速率以氧化後的重量增量除以複合材料內碳化矽顆粒的表面積來表示，得到碳化矽塊體的氧化速率高於粉體，粉體的氧化速率高於複合材料，且顆粒較大的碳化矽複合材料氧化速率高於顆粒較小的碳化矽複合材料，而在碳化矽體積百分比10 vol% 至40 vol% 之間，MZY50/SiC複合材料的氧化速率隨著碳化矽體積百分比的增加而降低，MZY10/SiC複合材料的氧化速率並未隨著碳化矽體積百分比的增加而呈現明顯的變化。本實驗並求得碳化矽粉體的活化能為135~141 kJ/mol，塊體的活化能為94~97 kJ/mol，碳化矽顆粒較大的MZY50/SiC複合材料活化能為174 kJ/mol，碳化矽顆粒較小的MZY50/SiC複合材料活化能為194 kJ/mol。此外，碳化矽顆粒較大和碳化矽含量較少的MZY50/SiC複合材料，具有一較深的氧化深度但較平緩的氧化層厚度變化梯度，氧化行為為模式II，而碳化矽顆粒較小和碳化矽含量較高的MZY50/SiC複合材料，具有一較淺的氧化深度但較陡的氧化層厚度變化梯度，氧化行為偏向於模式I。

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.