Surface modification and oxidation kinetics of hot-pressed AlN-SiC-MOSi2 electroconductive ceramic composite

The effects of oxidation on the microstructural modification and on the electrical resistivity and mechanical strength of a hot-pressed AlN-SiC-MOSi2 electroconductive ceramic composite were studied. The kinetic of the oxidation was also evaluated. After the oxidation at temperatures below 1000 degreesC samples do not gain weight, due to simultaneous formation of SiO2 and evaporation of MoO3 formed by the oxidation of MoSi2. However, the AlN/SiC matrix disables the "pesting" phenomena and strength degradation, despite the fact that at these temperatures MoSi2 oxidizes rapidly. At temperatures above 1000 degreesC, the composite gains weight due to protective mullite layer formation on the surface, that provides a good oxidation resistance for use at higher temperatures. The kinetics of the oxidation follows the parabolic law. The possible rate-controlling mechanism is the diffusion of oxygen through the mullite-rich surface oxide scale. (C) 2003 Elsevier Science B.V. All rights reserved.