The XYZ 3-dimensional thermal conductivities of the C/C up to 2000 °C were measured by a laser flash method. Carbon fiberreinforced carbon composites (C/C) were generally developed for aerospace missions due to their excellent thermal resistivity at ultrahigh temperature. C/C must endure harsh environments such as thousands of degrees Celsius without degradation of its mechanical properties. To solve this problem, among the passive thermal protection system, we suggest a method of conducting more heat through the mono-axial direction, which resulted in ease of the thermal rise in the heat receiving part. For example, the X-43A flight applied unbalanced C/C (UCC) with different carbon fiber orientation ratios according to the XY direction in the leading edge part. To investigate the difference in thermal conductivity between unbalanced C/C (UCC) and balanced C/C (BCC), unbalanced and balanced preforms were prepared by a needle punching process, and then they were densified by pitch infiltration and a carbonization process. We compared and analyzed the effects of unbalanced C/C(UCC) and balanced C/C (BCC) structures on the thermal conductivity. We also designed the “rule of mixtures” equation for calculating thermal conductivities of each C/C using reported data of carbon fiber and graphite matrix. Our calculations of thermal conductivity ratio match the ratio of real data.

Carbon/Carbon composite was been manufactured by the technology of warmer-molding process of clutter chopped carbon fiber, using phenolic resin as an adhesive. The degree of graphitization, the microstructure and the friction properties were studied. The results show that the clutter chopped carbon fiber fully scatter in the Carbon/Carbon composite and the degree of graphitization of phenolic resin can reach up to 86.2%, this matrix carbon can form the continuous and stable graphitic thin film on the friction surface during braking process so that the composite has fine friction properties and low wear rate.

Modification of C/C composite bipolar plate for improving electrical conductivity was carried out by addition of electroconductive carbon black (EC-CB). Carbon black was carefully mixed to methanol-containing phenolic resin, impregnated into 2D-carbon fabrics, hot pressed and then carbonized to obtain composite plate. Inclusion of electro-conductive carbon black enhanced the electrical conductivity of the C/C composites by increasing the conduction path. Addition of 10 vol% carbon black increased the electrical conductivity from 5.5/Ωcm to 32/Ωcm and reduced the crack formation by filling effect, resulting in the increase of flexural properties of composite plate. However, at carbon black content over 10 vol%, flexural properties decreased by delaminating role of excess carbon black at the interface in C/C composites.