Effects of carrier gas on densification of porous carbon-carbon composites during chemical vapor infiltration

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Effects of carrier gas on densification of porous carbon-carbon composites during chemical vapor infiltration

The densification rate of C/C composites fabricated by directional flow thermal gradient chemical vapor infiltration process from C 3H 6, C 3H 6 N 2 and C 3H 6 H 2 was investigated respectively. The mechanism on the role of carrier gas in chemical vapor infiltration was also discussed. The results shows that whether or not adding N 2 as carrier gas has little influences on the densification behavior of C/C composites with the controlled temperature, the partial pressure of hydrocarbon and the effective residence time of the gas phase remain constant. When the controlled temperature is not less than 1 173 K,using N 2 or H 2 as carrier gas makes pronounced differences in densifying of C/C composites. The average bulk density of C/C composites from C 3H 6 H 2 is eight to ten percent higher than that from C 3H 6 N 2. However, when the controlled temperature is not higher than 1 123 K,the densification rate of C/C composites from C 3H 6 H 2 is much lower than that from C 3H 6 N 2, which implies that effects of carrier gas on densification of C/C composites are closely related to the type of carrier gas and infiltration temperature. At higher temperature, using H 2 as carrier gas is favorable to the densification of C/C composites, while at lower temperature, hydrogen, acting as reactive gas, can inhibit the formation of pyrolytic carbon.