Synthesis of ultrafine silicon nitride powders
by H.R. Orthner, R. Brink, P. Roth
International Journal of Materials and Product Technology (IJMPT), Vol. 15, No. 6, 2000

Abstract: Silicon nitride powders were synthesised during vapour phase reaction of silicon tetrachloride (SiCl₄) and ammonia (NH₃) in a hot wall flow reactor. The effect of process variables on powder composition was investigated by means of thermogravimetric analysis (TGA), specific surface area measurements (BET) and elementary analysis. The powders obtained consist of amorphous silicon nitride (Si₃N₄) and contain various amounts of volatile ammonium chloride (NH₄Cl). The amount of by-products is strongly dependent on reactor temperature. At high temperatures (T = 1200°C), the amount of volatile compounds is less than 35%, chloride is less than 19% and the specific surface area is around 40m²g^-1. The initial NH₃/SiCl₄ ratio used does not significantly affect the ammonium chloride formation, indicating that temperature and flow rate rather than concentration of ammonia determine the formation of NH₄Cl. At temperatures 900°C and lower all chloride originating from SiCl₄ was converted to ammonium chloride.

Online publication date: Tue, 01-Jul-2003

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