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Effect of heat-treatment temperature of vapor-grown graphite fibers II. Stability of their bromine intercalation compounds

Synthetic Metals
Publication Date
DOI: 10.1016/0379-6779(89)90819-9


Abstract Portions of a batch of graphite fibers grown from benzene precursor are heat treated to 2000, 2200, 2400, 2600, 2800 and 3000 °C. The fibers are then subjected to about 165 Torr of bromine vapor for two days and subsequently allowed to outgas for at least two weeks. Fiber resistivities are monitored while they are subjected to ambient conditions, high vacuum (10 −4 Pa), high humidity (100% at 60 °C) and high temperature (up to 400 °C in air). Vapor-grown graphite fibers, when heat treated to high temperatures and brominated, have resistivities as low as 8 μω cm. After two-week outgassing, fiber resistivities are invariant at ambient and vacuum conditions. At high humidities they degrade only minimally over several weeks. When the fibers are exposed to high temperatures, degradation occurs at higher temperatures for fibers heat treated to lower temperatures. The onset of degradation ranges from 200 °C for fibers heat treated to 2800 °C and above, to 400 °C for 2000 °C heat treatment. A comparison of these results with similar studies on pitch-based fibers with radial graphene-plane orientation reveals that the stability of bromine intercalation compounds is more dependent upon the bromine-graphite interaction than on the orientation of the graphene planes. Unlike the rates of the bromination and debromination reactions, which are strongly dependent on the graphene-plane orientation the rates of degradation at high temperature in air for fibers of similar resistivity are comparable, independent of their graphene-plane orientation.

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