Pyrolytic conversion of spherical organo-silica powder to silicon nitride under nitrogen

Abstract

Monodisperse, spherical Si3N4 powder composed of fine particulates was synthesized by pyrolyzing spherical organo-silica powder under nitrogen. The organo-silica powder was prepared by hydrolyzing a mixture of phenyltrimethoxysilane (PTMS) and tetraethoxysilane (TEOS) in a methanol solution of mater and ammonia, The organo-silica powder consisted of 81.3 at.% silicon units derived from PTMS and 18.7 at.% silicon units derived from TEOS, During the pyrolysis under nitrogen, the organo-silica powder decomposed to a mixture of free carbon and silica, with an increase of the surface area, at 500 degrees-600 degrees C, followed by the formation of alpha-Si3N4, with beta-Si3N4 as a minor phase, ai: 1450 degrees and 1500 degrees C and beta-SiC at 1550 degrees C. The pyrolyzed powders, which retained the spherical shape and monodispersity of the organo-silica powders, with a reduction in mean particle diameter, were composed of fine particulates that were similar to 40 mm in size.