Electrical resistivity as a tool for the characterisation of carbonaceous phases in vapour-grown carbon fibres

By making electrical resistivity measurements as a function of diameter, ir has been possible to prove that the kind of carbon fibres grown from a gas eous stage (VGCF), possess a duplex structure. We have found that these fib res present a catalytic phase or core, which shows a higher level of crysta lline perfection than the pyrolytic or cortical phase. This is clearly reve aled by the high electrical conductivity observed for thin fibres, when com pared to thick VGCF. Estimations of electrical resistivity have allowed us to establish that this physical property, for different sorts of VGCF, can be accurately expressed by the rule of mixtures. In the same way, we have n oticed that fibres fabricated from acetylene-containing precursor atmospher es show better electrical properties than VGCF grown from standard reactant gases. We have also observed that over-hydrogenation of VGCF, which gives rise to an improvement in mechanical properties, involves a decrease in ele ctrical conductivity. (C) 1999 Elsevier Science Ltd. All rights reserved.