Oxidation Mechanisms of Si-Ti-C-O Fiber-Bonded Ceramics.

Abstract

The oxidation mechanisms of Si-Ti-C-O fiber-bonded ceramics had been investigated through thermogravimetric analysis, electron microscopy and X-ray diffraction. The influence of temperatures ranging from 773 to 1773K in air is discussed. The materials showed mass loss due to oxidation of the carbon interface and free carbon in the fibers at the beginning of the oxidation tests. Then, mass gain due to the formation of silica on the surface of the fibers was observed. When heat-treated below 1023K, most of the free carbon was oxidized and flexural strength decreased to almost zero. The free carbon contained in the materials was about 7.7mass% and oxidized along the fiber direction. On the other hand, upon heat treatment above 1073K, the oxidation of carbon was strongly inhibited due to a cristobalite coat formed on the surface of the specimen which maintained its initial strength even after oxidized for 100h. After the formation of the cristobalite coating, the materials showed an excellent oxidation resistance even if oxidized at 973K