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 gaseous stage (VGCF), possess a duplex structure. We have found that these fibres present a catalytic phase or core, which shows a higher level of crystalline perfection than the pyrolytic or cortical phase. This is clearly revealed by the high electrical conductivity observed for thin fibres, when compared 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 noticed that fibres fabricated from acetylene-containing precursor atmospheres 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 electrical conductivity. (C) 1999 Elsevier Science Ltd. All rights reserved.