The influence of hydrocarbon gas on the density and microstructure of C/C composites formed by chemical vapor infiltration

Chemical vapor infiltration (CVI) of carbon felts to fabricate C/C composites was carried out by implanting a special electrically conductive layer in the carbon felts, which resulted in rapid densification by a coupling effect of temperature gradient, reaction intermediate gradient, and magnetic field. Liquefied petroleum gas (LPG) and C_3H_6 were employed as carbon sources. The deposition temperatures were in the range of 800-1000℃, and the deposition pressure was in the range of 0.1-15.0kPa. The textures of the pyrolytic carbons were observed by polarized light microscopy, and the crystallite size of these C/C composites was analyzed by XRD. Results show that infiltration of the porous C/C performs, 260mm×60mm×20mm, for 20h leads to C/C composites with density of more than 1.7g/cm3 from LPG, and of more than 1.6g/cm3 from C_3H_6. The deposition rate for LPG under optimized conditions was more rapid than for C_3H_6. It is shown that LPG mixed with hydrocarbon gas, whose activation energy is different, can cooperate with other physical fields to improve the deposition rate and texture of the pyrolytic carbons.