Preparation of Si3N4and AlN Powders from Alkoxide-Derived Oxides by Carbothermal Reduction and Nitridation

The preparation of Si{sub 3}N{sub 4} and AlN powder was performed by carbothermal reduction and nitridation of silica gel and aluminum hydroxide, respectively. Very fine (<0.1 {mu}m) silica gel or aluminum hydroxide powder was precipitated by the hydrolysis of tetraethyl silicate or aluminum isopropoxide solution, respectively. The precipitate was formed on fine carbon powder dispersed in alkoxide or alkoxide solution. The process gave uniformly mixed starting powders (in situ mixing). The stoichiometric mixtures were heated in flowing nitrogen at 1,430{degree} or 1,500{degree}C. The carbothermal reduction and nitridation reaction was investigated by measuring the weight loss and chemical compositions of powders at intermediate stage of heating. About 8% of the SiO{sub 2} was evaporated as SiO during the preparation of Si{sub 3}N{sub 4}. There was no appreciable evaporation of Al species during the preparation of AlN. Submicrometer Si{sub 3}N{sub 4} and AlN powders were prepared by the present process.