Oxidation resistant SiC coating for graphite materials

A dense functional gradient SiSiC coating with good oxidation resistance when applied to a graphite substrate has been developed using a novel process, in which large pores in the coating were eliminated by application of a primary coating, and pinholes were filled with free silicon. The mechanism for the formation of a continuous SIC coating on graphite was investigated experimentally and theoretically. Oxidation tests were conducted from 800 degrees C to 1600 degrees C for up to 1000 h. Samples of graphite with the SiSiC coating were found to be totally intact after oxidizing for 1000 h together with 100 thermal cycles at 1200 degrees C and 200 h with 20 thermal cycles at 1400 degrees C, indicating excellent oxidation resistance and thermal shock resistance of the coating. The good thermal shock resistance is attributed to the compositional gradient in the coating. (C) 1999 Elsevier Science Ltd. All rights reserved.