Oxidation of SiC-Whisker/Mullite Composites in Dry Air

Abstract

Oxidation behavior of mullite composites containing 10 to 30vol% of SiC-whisker (SiC-w) has been studied at 1300°C in dry air. As the volume fraction of SiC-w increased, the weight gain increased. The weight gain curve obeyed the parabolic law for the SiC-w content of 10vol% and at the oxidation time shorter than 200h. However, the weight gain of the specimen containing more than 20vol% SiC-w was accelerated when the oxidation time exceeded 200h. It was found that impurities such as Na₂O, K₂O and CaO, originally contained in the SiC-w, were concentrated near the surface of the specimen. The acceleration of the weight gain for longer oxidation duration is explained in terms of corrosion of mullite and SiC-w by the liquid phase formed through the reaction between oxidized SiC-w and the impurities.