95/05973 Microstructural aspects of zeolite formation in alkali activated cements containing high levels of fly ash

Abstract

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 Fe3(CO)12. Addition to the substrate of small amounts of phosphorus from a solution of H3PO4 in ethanol, followed by impregnation with Fe3(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/Fe ∼0.25 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.