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 C3H6 were employed as carbon sources. The deposition temperatures were in the range of 800 1000 degrees C, 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 x 60 mm x 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 C3H6. The deposition rate for LPG under optimized conditions was more rapid than for C3H6. 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.