Synthesis of ultrafine and ultrapure silicon nitride powder in an RF-plasma furnace

ABSTRACT Ultrafine and ultrapure Si3N4 powder with nitrogen content >37 wt%, particle size 40 m2/g has been synthesised successfully by injecting NH3, H2 and SiCI4 into an N2-plasma furnace. At the present time, a production rate of 1 Kg/h has been achieved which is limited by the powder collection system rather than the plasma capacity. The prepared powder is soft, fluffy, perfectly white, and completely amorphous. In order to evaluate the best conditions for carrying out the synthesis of Si3N4 powder, plasma process has been examined from a thermodynamic point of view. The thermodynamic equilibrium compositions of Si-N-H-Cl system have been calculated at different conditions using the SOLGASMIX-PV program. The effects of reaction temperature as well as the flow rates of N2, H2 and NH3 on the equilibrium compositions have been investigated theoretically. Some very useful conclusions have been obtained.