A novel thermal gradient chemical vapor infiltration process for carbon-carbon composites

Solid cylindrical carbon-carbon composites were processed using conventional thermal gradient chemical vapor infiltration. High thermal conductivity (55 W/m.degrees C) carbon fibers (48 k) were inserted in the center of a cylindrical low thermal conductivity (0.15W/m degrees C) needle punched carbon felt preform, to create a thermal gradient because of the difference in thermal conductivities. The hottest portion ( 900-1200 degrees C) was along the inserted carbon fibers, where the pyrolytic reaction of natural gas occurred. The densification radially moved outwards and ultimately a density of 1.778 g/cm(3) was obtained after 67 h. The process parameters such as the electric power of the furnace, electrical resistance of the sample, densification time, and the position of the deposition layer were studied. A densified sample having a volume fraction of carbon fibers of 10 % was tested for ablation and erosion. The microstructure of the pyrolytic carbon matrix of the as-prepared sample was investigated by polarized light microscopy and scanning electron microscopy.