Active oxidation of silicon carbide

The active oxidation of SiC has been studied at 1390 and 1490°C, paying particular attention to the active-to-passive and passive-to-active transition points. First the active-to-passive transition for pure silicon was studied at 1290°C. The beginning of passivity is characterized by micron-sized SiO2 rod formation on the surface due to the oxidation of SiO(g), consistent with other investigators. These rods were not observed in the active-to-passive transition for SiC; but they were observed in the passive-to-active transition for SiC. This type of microstructure yields information about the breakdown of the passive film. Unlike pure silicon, at a fixed temperature a substantial difference in the transition oxygen pressure for the active-to-passive and passive-to-active transitions was not observed for SiC. This is due to the fact that both processes are controlled by SiCySiO2 interfacial reactions. Studies were also conducted on active oxidation of SiC with a pre-formed SiO2 scale in order to understand the breakdown of the passive film.