Sepiolite-PAN intercalation used as Si3N4 forming precursor

Abstract

Silicon nitride (Si3N4) formation was investigated using sepiolite and polyacrylonitrile as silicon and carbon source, respectively. It was found that purified sepiolite could readily adsorb a sufficient amount of acrylonitrile (AN) reagent without pre-treatment. Polymerisation of sepiolite-AN mixtures and subsequent cyclization of the polymerised complex yielded a precursor, which was found ideal as a starting material in carbothermal reduction-nitridation (CRN) for the formation of silicon nitride powders. The quantity of silicon nitride, grain size and morphology were found to be dependent on the reaction conditions and starting reagent. Fine grain size, high surface area (up to approx. 12.4 m(2)/g) powders of mainly beta -Si3N4 were obtained via pyrolysis of sepiolite-PAN complex after 4 h heating at 1400 degreesC in 1000 ml/min nitrogen flow with a heating rate of 300 degreesC/h. Mg retained in the molecular structure of the mineral must have promoted the formation of beta -grains in CRN process. (C) 2001 Kluwer Academic Publishers.