OXIDATION-KINETICS OF CHEMICALLY VAPOR-DEPOSITED SILICON-CARBIDE IN WET OXYGEN

The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen (P(H2O) = 0.1 atm) at temperatures between 1200-degree s and 1400-degrees-C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal a nd Grove model for oxidation of silicon. It was found that in an envir onment containing even small amounts of impurities, such as high-purit y Al2O3 reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rate s increased under these conditions presumably because of the formation of less protective sodium alumino-silicate scales.