Simple methed of SiC coating on carbon/carbon composites and evaluations of oxidation resistance

SiC coatings for oxidation protection of Carbon-Carbon (C/C) composites were produced by the Si/Polymer (S/P) process and the SiC/C/Polymer (S/C/P) process; these processes are much simpler than the conventional CVD process. Oxidation tests were also carried out to evaluate effectiveness of the coatings. In the S/P process, C/C composites were coated with slurry of Si particle-polymer mixtures. The slurry coated composites were then heat treated to carbonize the polymer and form SiC by the liquid silicon-carbon reaction. Porous and dense two-layer SiC coatings were observed. As for the S/C/P process, a carbon layer containing SiC particle was first formed on C/C composite; this layer was then reacted with impregnated liquid silicon. A dense SiC layer was therefore formed through the S/C/P process. Although the oxidation rates of C/C composites were reduced in all the testing temperatures (900∼2000 K), the SiC coatings by the S/P process were less effective than those by the CVD process. This was explained by small and nonuniform thicknesses of the dense SiC layer in the coatings by the S/P process. On the other hand, C/C composites coated by the S/C/P process showed almost the same oxidation rates as those by the CVD process.