ELECTRICAL-RESISTIVITY, MAGNETORESISTANCE, AND MORPHOLOGY OF VAPOR-GROWN CARBON-FIBERS PREPARED IN A MIXTURE OF BENZENE AND LINZ-DONAWITZ CONVERTER GAS BY FLOATING CATALYST METHOD

Vapor-grown carbon fibers (VGCF's) were prepared in a mixture of benzene and Linz-Donawitz converter gas using floating catalytic seeds derived from ferrocene, cobalt acetylacetonate, and thiophene. The diameters of the fibers thus grown were in the range of 2-7 mum. The fibers were heat-treated in argon atmosphere at temperatures between 1700 and 3000-degrees-C. The electrical resistivity at room temperature and magnetoresistance at liquid nitrogen temperature were measured for the as-grown and heat-treated fibers, and morphology of the heat-treated fibers was observed with a scanning electron microscope. The electrical resistivity was nearly similar to that obtained for VGCF's prepared on a substrate in a mixture of benzene and hydrogen. The size effects on the resistivity and magnetoresistance were observed. The magnetoresistance was also found to depend on the heat-treatment time. The magnetoresistance results showed that a transition heat-treatment temperature for the magnetoresistance change from negative to positive was between 2200 and 2300-degrees-C, indicating the graphitizable nature of the present fiber. A characteristic polygonal appearance was observed for the fibers heat-treated above 2500-degrees-C.