The control of morphology in silicon nitride powder prepared from rice husk

Abstract

Abstract α-Silicon nitride powder of high purity has been prepared by nitriding pyrolysed rice husk at temperatures between 1260 and 1450°C under 95% nitrogen-5% hydrogen. Hydrogen addition is beneficial in accelerating the rate of nitride formation. The addition of iron (III) oxide and nickel (II) oxide to the rice husk promotes the competitive formation of silicon carbide at temperature as low as 1300°C. Other transition metal oxides are without catalytic effect on the nitridation reaction, though vanadium (V) oxide favours formation of β-phase silicon nitride. The silicon nitride particle morphology is determined in part by the particle dimension of the milled rice husk. Silicon nitride crystals of hexagonal symmetry are obtained from starting powder of dimension ≤ 53 μm, whereas greater particle dimensions, and lower packing densities, yield silicon nitride of a whiskery morphology. Addition of pre-formed silicon nitride powder results in the formation of fine, equiaxed, silicon nitride particles.