The role of phosphorus in the growth of vapour-grown carbon fibres obtained by catalytic decomposition of hydrocarbons

Production of VGCF fibres from the decomposition of a methane-hydrogen mixture over metal particles is influenced by the support on which the particles have been laid. It was found that different as-received commercial graphite supports, according to their impurity content, could promote or inhibit the VGCF growth. Good yields of vapour-grown carbon fibres with a length up to 6 cm have been fabricated by catalytic decomposition of methane over particles obtained from Fe-3(CO)(12). Addition to the substrate of small amounts of phosphorus from a solution of H3PO4 in ethanol, followed by impregnation with Fe-3(CO)(12), was found to be effective in promoting the growth of VGCFs and increasing the yield. But increasing the amount of phosphorus over P/Fesimilar to0.25 had an inhibiting effect on the growth of VGCFs. So the yield of VGCFs was optimized for a given phosphorus concentration. These phenomena are interpreted by the formation of Fe-P compounds which, depending on their formulae, lower or increase the melting point of the catalyst particles. According to the VLS theory, catalytic growth up to a macroscopic scale results from the liquid state of the catalyst. (C) 2004 Elsevier Ltd. All rights reserved.