PREPARATION OF MONODISPERSED SPHERICAL SILICON-CARBIDE BY THE SOL-GEL METHOD

Monodispersed spherical SiC gel powders were synthesized by hydrolysis and condensation of phenyltrimethoxysilane (PTMS) or a mixture of PTMS and tetraethylorthosilicate (TEOS) from a system of silane-H2O-catalyst to which no co-solvent such as alcohol was added. The experiments were conducted through two routes; base catalysed and acid base catalysed routes. In each process, excess water was used as a dispersing medium in addition to a hydrolysing agent. In the base-catalysed route, monodispersed spherical gel powders were obtained regardless of NH4OH content used in this experiment when the concentration of silane and the molar ratio of TEOS to PTMS were less than 0.5 mol l-1 and 0.5, respectively. In the acid base catalysed route, polydispersed powders were produced when the concentration of silane exceeded 0.25 mol l-1. When heated above 1400-degrees-C, the initially monodispersed powders sustained their shape in the PTMS TEOS system, but bulk and fibre phase were produced in the PTMS system.