The C/C composites co-deposited with SiC were prepared by thermal gradient chemical vapor deposition(CVD) technique using propane as a source gas of carbon, methyltrichlorosilane as a source of Si, and ex-PAN carbon fibers. The oxidation behavior of these composites has been studied in the temperature range 600 to 1350℃ in air. The oxidation rates were calculated from the weight loss measured by thermogravimetric analyser. The corrosion figures were followed by SEM.
There are two rate-controlling steps for the oxidation of C/C composites in this temperature range. One is surface reaction with oxygen below 800℃, the other is gas phase diffusion above 800℃. The oxidation rates of C/C composites contained SiC are one order lower than those of pure C/C composites in the surface reaction-controlled region. The difference of the oxidation rates of both composites results from the change in total surface areas due to the difference of the surface morphology of both composites during the oxidation. In the gas phase diffusion-controlled region, however, there are no significant difference of the oxidation rates of both composites.
From these results, it is suggested that SiC particles prevent the oxidized pits from growing below 800℃, but do not play an important role of prevention against oxidation of C/C composites above 800℃.
