Preparation and electrical properties of bromine intercalated vapor-grown carbon fibers

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Abstract
Vapor-grown carbon fibers possessing a high degree of preferential orientation have been prepared using either a catalyzed substrate or a fluidized catalytic method, yielding fibers with diameters of about 10 and 1 μm, respectively. After heat treatment at 2600–2960 °C, the fibers were used as a host material for bromine intercalation to yield highly conductive filaments. Intercalation was carried out at room temperature by direct immersion into liquid bromine. Through bromination, the room-temperature electrical conductivity of these fibers measured under ambient conditions increased by a factor of about 6 relative to their pristine state. Typical values for the resistivity of the brominated fibers are ∼10 μΩ cm. Of particular importance is the stability of these brominated fibers under ambient conditions; the fibers showed less than a 3% increase in resistivity after 1 month of exposure to air. The fibers also displayed a high degree of thermal stability up to 500 °C, which was established by measuring the change in resistivity and the weight loss with increasing temperature. Whereas the thick fibers prepared by the substrate method showed a high degree of staging structure, the thin fibers prepared by the fluidized seeding method did not show significant staging fidelity, based on x-ray, Raman, and TEM observations. Nevertheless, the increase in conductivity observed for the thin fibers is almost as large as for the thick fibers. The fiber preparation and intercalation method used in this work, as well as the chemical and thermal stability that has been achieved, offer attractive possibilities for practical applications of these materials in light weight, highly conducting composites.