Synthesis of α-Si3N4 from carbon coated silica by carbothermal reduction and nitridation

The production of alpha-Si3N4 powder was performed by carbothermal reduction and nitridation of carbon coated fumed silica precursor. The precursor is derived from a fumed silica and a hydrocarbon gas (C3H6) and provides intimate contact between the reactants. This yields a better distribution of carbon within the silica and inhibits the agglomeration among the oxides of silicon during the reactions, resulting in a more complete reaction and purer product at a comparatively low temperature. The Si3N4 powders produced at 1500 degrees C for 5 h in flowing nitrogen gas have low oxygen content (1.2 wt%), submicrometer particles (0.3-0.7 mu m), high a phase content and no agglomeration. (C) 1998 Published by Elsevier Science Limited. All rights reserved.