High-temperature oxidation of non-oxide ceramics

The oxidation behavior of nonoxide silicon-based ceramics was investigated. Various Si3N4 and SiC ceramics were examined after long term oxidation tests (.ltoreq.10,000 h) at 1500.degree. in ambient air. The oxidation of the materials obeyed a nearly parabolic mechanism. However, different characteristic oxidation processes at the surface and the microstructure were observed dependent on the chemical components of the ceramic materials. The diffusion of oxygen into the material and its further reaction in the bulk of the material were found to be the most critical factors during long term oxidation.