PROPERTIES OF HYBRID CVD/PAN GRAPHITE FIBERS AND THEIR BROMINE INTERCALATION COMPOUNDS

A hybrid fiber with a PAN core surrounded by a vapor-grown carbon-fiber (VGCF) sheath has been fabricated using a proprietary process. The density, ultimate tensile strength, Young's modulus, and resistivity of pristine and bromine-intercalated fibers made by this technique, having diameters varying from 5 to 50-mu-m, were compared with the values predicted from the rule-of-mixtures model. For both the pristine and intercalated fibers, the density, ultimate tensile strength, and Young's modulus of the fibers were lower than predicted, but resistivity was measured to be consistent with predictions. Intercalation had little, if any, effect on ultimate tensile strength and Young's modulus, but raised the density by about 11 percent, and lowered resistivity by an order of magnitude. The diameter dependence of the resistivity showed evidence of a depletion layer of the type found in VGCF.