Structure and electrical conductivity of graphite fibers prepared by pyrolysis of cyanoacetylene

Highly electroconductive graphite fibers are prepared by the pyrolysis (CVD) of cyanoacetylene on the surface of carbon fibers, followed by heat treatment. Many thin graphite strata, cylindrically layered and scrolled around an axial core of the original carbon fiber, are observed. The lattice constant C₀ of the graphite fiber obtained from cyanoacetylene and heat-treated at 3000 °C is 6.712° (002), which is smaller than that of a graphite fiber from benzene. The magnetoresistance of graphite fibers obtained from cyanoacetylene is as high as 800% (4.2K, 15 kG) (HTT 3300 °C), while that of graphite fibers obtained from benzene is around 150%. Measurements of Raman scattering and X-ray diffraction also show that cyanoacetylene forms more highly graphitized fiber than benzene. Cyanoacetylene is a good starting material for synthesizing graphite. The room temperature conductivity is as high as 1.8 × 10⁴ S/cm for fiber heat treated at 3250 °C. Treatment of the graphite fiber by fuming nitric acid increases the conductivity up to 1.3 sx 10⁵ S/cm in less than 10 min. Upon exposure of the nitrated fiber to air at ambient temperature, the conductivity decreases slightly. After this slight decrease, the conductivity is stable for at least 90 days.