RIBBON-SHAPE CARBON-FIBERS FOR THERMAL MANAGEMENT

Their high thermal conductivity and low density make pitch-based carbo n fibers an attractive alternative to conventional metals in heat tran sfer applications. Already, thermal conductivities of up to 1100 W/m-d egrees-K, about three times that of copper, have been reported. These high conductivities are possible because of the excellent phonon condu ction in the two-dimensional graphite layer plane. Thus, the perfectio n of the graphitic structure to a large extent determines the thermal conductivity of a carbon fiber. In this study, circular fibers exhibit ing radial transverse texture and ribbon-shape fibers of linear textur e were melt spun from a mesophase pitch precursor. After equivalent ox idation and carbonization treatments, the fibers were characterized by single filament tensile and electrical resistivity tests. The strong inverse correlation of electrical resistivity and thermal conductivity allows the use of electrical resistivity measurement as a reliable pr edictor of thermal properties. In addition, differential scanning calo rimetry (DSC) and wide angle X-ray diffraction techniques were used to determine whether fiber texture can influence graphitization kinetics . The results indicated that linear textures of the ribbon-shaped fibe rs allow them to exhibit a lower electrical resistivity than circular fibers of equivalent tensile moduli. The electrical resistivity of the ribbon-shape fibers decreased with increasing aspect ratio, carboniza tion temperature, and dwell time during carbonization. Thus, ribbon-sh ape fibers with a linear texture should exhibit higher thermal conduct ivities than circular fibers, and their thermal conductivities may inc rease further with higher aspect ratios.