Oxidation behaviour and protection of carbon/carbon composites

The oxidation behaviour of carbon/carbon composite materials and graphite (in cube form), in flowing air, has been studied in the temperature range 500 to 1100 °C. Gasification for unprotected samples occurred at temperatures around 500 °C. SiC coatings offered only limited protection below their intrinsic protection range due to the diffusion of oxygen along microcracks. Diffusional control was more significant for thicker coatings. However, the use of boron oxide applied on an underlayer of SiC, gave good protection for extended periods at temperatures up to 1000 °C, due to microcrack sealing. The use of borate coatings, both with and without an SiC underlayer, was limited by the volatility of the borate.