Abstract: An apparatus and a method of producing a vapor-grown carbon structure capable of obtaining a vapor-grown carbon structure with a markedly low production cost are provided. A vapor-grown carbon structure producing apparatus 1 has a screw feeder 4 for supplying a biomass raw material into a furnace 2, a thermal decomposition zone 5 having a first high-temperature air introducing nozzle 6 for thermally decomposing the supplied raw material at a thermal decomposition temperature of 500 to 900° C., a combustion zone 7 having a second high-temperature air introducing nozzle 8 for combusting a thermal decomposition product at a reaction temperature of 900 to 1300° C., and a charbed zone 9 for holding a combustion residue having passed through the combustion zone 7 and generating a carbon radical in a decomposition gas, to generate a vapor-grown carbon structure.

Abstract: A method is proposed for the preparation of pitch-based carbon fibers having excellent mechanical properties or , in particular, a surprisingly high knot strength much higher than that of PAN-based carbon fibers. The method comprises the steps of melt-spinning of starting pitch material, infusibilization of the pitch fibers by oxidation and carbonization of the infusibilized pitch fibers in an inert atmosphere. The improvement of the inventive method consists in the infusibilization treatment of pitch fibers under controlled conditions so as to effect preferential oxidation of the surface layer to such an extent that the value m=(O.sub.1s /C.sub.1s)/(O/C) is at least 2, in which O.sub.1S /C.sub.1S is the molar ratio of the oxygen content to the carbon content in the surface layer as determined by the ESCA method and O/C is the molar ratio or the oxygen content to the carbon content for the infusibilized pitch fiber as a whole.