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

Abstract

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 μm. The fibers were heat-treated in argon atmosphere at temperatures between 1700 and 3000 °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 °C, indicating the graphitizable nature of the present fiber. A characteristic polygonal appearance was observed for the fibers heat-treated above 2500 °C.