An Attempt to Improve Mechanical Strength of Carbon Fiber / Carbon Composites by Whiskerizing

Carbon/Carbon (C/C) composites are of importance in the field of aerospace engineering. Two methods have so far been proposed for the production of the C/C composites: impregnation of carbon fiber (CF) fillers with pitch or resin followed by carbonization, and infiltration of the fillers with pyrolytic carbon. But, linkage between the fillers and the matrices is not satisfactory. To improve the linkage, in the present work the effect of whiskerization of the fillers with carbon micro fibers has been examined. Ptch-based commercial CF paper was used as a filler. Carbon microfibers of 0.1 -0.5 μm diameter and 20-60 μm length were grown on the CF paper by thermal decomposition of benzene at 1100℃ in the presence of iron and hydrogen sulfide as catalysts. The resulting whiskerized CF paper was then infiltrated with pyrolytic carbon (PC) under various conditions. Benzene diluted with nitrogen was also used as the source materials of PC. Infiltration with PC was most effective under the conditions of CsHs concentration 4-5%, reactant flow rate 450-600cm3/min, and pyrolysis temperature 1100℃. However, it was extremely difficult to fill up the inner space of the CF paper with PC. Thus, many voids were left behind even under the optimum conditions. The three point bending strength of the whiskerized CF paper was only 0.2-0.4 kg/mm2, which was lower than that of the as-recieved CF paper because of deterioration of the CF paper itself. On the other hand, the bending strength of the C/C composite based on the whiskerized CF paper increased to 2-3 kg/mm2, but it was approximately the same as that for the composite based on the non-whiskerized CF paper. Only a slight increase in the Young's modulus was attained by the whiskerization treatment