Ribbon-shape carbon fibers for thermal management

Abstract

Their high thermal conductivity and low density make pitch-based carbon fibers an attractive alternative to conventional metals in heat transfer applications. Already, thermal conductivities of up to 1100 W/m-°K, about three times that of copper, have been reported. These high conductivities are possible because of the excellent phonon conduction in the two-dimensional graphite layer plane. Thus, the perfection of the graphitic structure to a large extent determines the thermal conductivity of a carbon fiber. In this study, circular fibers exhibiting radial transverse texture and ribbon-shape fibers of linear texture were melt spun from a mesophase pitch precursor. After equivalent oxidation 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 predictor of thermal properties. In addition, differential scanning calorimetry (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 fibers 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, carbonization temperature, and dwell time during carbonization. Thus, ribbonshape fibers with a linear texture should exhibit higher thermal conductivities than circular fibers, and their thermal conductivities may increase further with higher aspect ratios.