Gas leakage through C/C composite and its suppression technology

Carbon fiber reinforced carbon matrix composites(C/Cs)are porous materials including voids，cracks，and interfacial debonding between the fiber and matrix。Hence，in applications of C/Cs to airtight hot structures such as heat exchangers，the gas leakage becomes serious problem。However，within author‘s best knowledge，few studies has treated this problem，and essentially no discussion has been performed on gas leak mechanisms and measures to minimize gas leak rate.In the present study，the following discussion was performed；1.A test fixture capable of high temperature measurement of gas leak rates was designed，and fabricated.2..In order to fill the defects in C/Cs，molten Si was infiltrated，and filled Si was converted to SiC by chemical reaction with carbon in C/Cs.3。Cracks in C/Cs have tendency to be closing with temperature rise，so that additional measures which can be done under low temperature environment were attempted.The results obtained in the present research were as follows；1.A test fixture capable of high temperature gas leak rate measurements up to 800°C of gas leak rates was designed，and fabricated.2.The Si impregnation resulted in decreasing gas leak rate to1/10.3。As low temperature methods，carbon infiltration by HIP(Hot Isostatic Pressure)，glass formation by the sol-gel method，and glass coating by the sol-gel method were examined after the Si impregnation。The first method resulted in slight lowering of gas leak rate，the second and third treatments yielded less gas leak rates over 1/10 compared with Si impregnated C/Cs。Thus，this study established technology lowering gas leak rate through C/Cs less than1/1000compared with non-treated C/Cs。

Carbon fiber reinforced carbon matrix composites (C/Cs) are porous materials including voids, cracks, and interfacial debonding between the fiber and matrix. Hence, in applications of C/Cs to airtight hot structures such as heat exchangers, the gas leakage becomes serious problem. However, within author's best knowledge, few studies has treated this problem, and essentially no discussion has been performed on gas leak mechanisms and measures to minimize gas leak rate.In the present study, the following discussion was performed ;1. A test fixture capable of high temperature measurement of gas leak rates was designed, and fabricated.2. In order to fill the defects in C/Cs, molten Si was infiltrated, and filled Si was converted to SiC by chemical reaction with carbon in C/Cs.3. Cracks in C/Cs have tendency to be closing with temperature rise, so that additional measures which can be done under low temperature environment were attempted.The results obtained in the present research were as follows ;1. A test fixture capable of high temperature gas leak rate measurements up to 800゜C of gas leak rates was designed, and fabricated.2. The Si impregnation resulted in decreasing gas leak rate to 1/10.3. As low temperature methods, carbon infiltration by HIP (hot isostatic pressure), glass formation by the sol-gel method, and glass coating by the sol-gel method were examined after the Si impregnation. The first method resulted in slight lowering of gas leak rate, the second and third treatments yielded less gas leak rates over 1/10 compared with Si impregnated C/Cs. Thus, this study established technology lowering gas leak rate through C/Cs less than 1/1000 compared with non-treated C/Cs.