Oxidation behavior of three dimensional C/SiC composites in air and combustion gas environments

A three dimensional C/SiC composite was prepared and flexural strengths during combustion atmosphere and weight changes in air were investigated. When oxidized in air, the C/SiC composite gained weight above the cracking temperature, and lost weight below the cracking temperature. The weight loss reached its maxumum value at about 700 °C. When oxidized during combustion atmosphere, the composite always lost weight due to the large temperature gradient along the specimen. The strengths were lowest at the area close to the nozzle wall where the flame temperature was about 700 °C. There were four oxidation zones along the specimens. There was an unoxidized zone (I) at the supporting end. Close to this was the cracking-oxidation zone (II). At the high-temperature end was the coating-oxidation zone (IV). Between the coating-oxidation and cracking-oxidation zones was the transition zone (III). Uniform, non-uniform and superficial oxidation regimes were observed which were considered to be responsible for the weight changes in air and strength changes during combustion atmosphere.