Synthesis of Sub-micron Spherical α-Si3N4 Powder by Direct Nitridation of Silicon Saw Dust

Sub-micron spherical alpha-Si3N4 powder has been synthesized by direct nitridation of silicon saw dust recovered from photovoltaic industry in nitrogen at 1300 degrees C with halogen salts as additives. XRD analysis indicates that the formation of alpha-Si3N4 is enhanced and accelerated, as compared to the direct nitridation without the additive. SEM examination shows that a complete transformation of morphology from irregular flake-like of the silicon powder to spherical-like of the silicon nitride powder takes place. These effects have been found to increase with increase of the percentage of the halogen salt additives in silicon powder. A complete sub-micron spherical alpha-Si3N4 powder has been achieved with 7 wt% halogen salt additives. A liquid phase induced by the additives, and cycling of alternative dissolving and subsequent nitridation of silicon in this liquid phase, are suggested to be responsible for the great changes.