Effect of Heat-Treatment Temperature of Vapor-Grown Graphite Fibers I. Properties of Their Bromine Intercalation Compounds

Vapor-grown graphite fibers, which have been heat treated to 2000, 2200, 2400 2600, 2800 or 3000 ^oC, are treated with bromine vapor at room temperature for two days. The fibers are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), density and resistivity measurements. Fibers heat treated at any single temperature exhibit a wide range of properties. Bromination products of fibers that have been heat treated to 2600 ^oC and above exhibit a DSC peak near 100 ^oC, which is used as a signature of intercalation. The XRD, density and temperature dependence of the resistivity suggest fibers with regions of pristine graphite and regions of stage-two intercalation compounds. Fiber diameter is found to be an important variable, with fibers having a diameter greater than about 13 μm exhibiting low resistivities (50 μω cm or less) independent of their heat-treatment temperature. The temperature dependence of the resistivity suggests that 6 μω cm is the minimum resistivity of this system unless more uniform intercalation can be achieved