Prevention of Gas Leakage through C/C Composites by Si Impregnation

摘要

Carbon/Carbon composites (C/Cs) have excellent high-temperature properties. However, C/Cs generally include many cracks, and thus gas easily leaks through these cracks. Hence it is an important subject to reduce gas flow through C/Cs for the applications of C/Cs especially to air tight structures, for example, a combustion chamber in an engine system for a space-plane. In the present paper, in order to suppress the gas permeability, Si was impregnated into defects in a C/C, and was converted to SiC. The gas leak rate through the Si-impregnated C/Cs was measured as a function of pressure, and was confirmed to decrease substantially by the SiC formation into cracks in C/Cs. By repeated Si impregnation, gas leakage was reduced to one thousandth compared with non-treated material. The gas leak paths were identified through micro-observations of cross-sections of C/Cs. Based on this observation, a laminar flow model through these cracks assumed narrow slits was constructed to roughly predict the gas leak rates. It was found that this model gave excellent predictions especially for 3-dimensionally reinforced C/C.