The present paper addresses a possible route for the manufacturing of silicon nitride (Si3N4) powder under rather a low pressure of nitrogen using a combustion synthesis (CS) method. Reactant mixtures were diluted by 30-50 wt% of Si3N4 to avoid the melting of silicon during combustion. Si3N4 powders with α/(α + β) ratios were prepared in a loose powder mixture state in the temperature range of 1500-2200 oC with dwell times from 10 to 60 minutes. The influence of the amount of ammonium fluoride (NH4F) in the mixture with silicon, the silicon particle size distribution, and the nitrogen pressure on the extent of silicon conversion into silicon nitride was experimentally studied. It was revealed that a small ammonium fluoride addition to silicon powder allowed the production of silicon nitride powder with a good output for industrialization. Because of the existence of the NH4F, the reaction involves not only the silicon nitriding mechanism, the growth of α-Si3N4 occurred partially by a vapor-crystal growth mechanism, and a vapor-liquid-solid (VLS) mechanism works during the rod-like β-Si3N4 growth. The as-synthesized samples were characterized using X-ray diffraction and scanning electron microscopy analyses. Possible mechanisms of CS Si3N4 particle growth are discussed. CS technology has the advantage over traditional technology in simple equipments, low cost, high quality and relative good sintering activity.

Keywords: Combustion Synthesis, α-Si3N4, β-Si3N4.