Synthesis of spherical-like β-Si3N4 powder by direct nitridation of silicon saw dust

Spherical-like β-phase silicon nitride (β-Si3N4) powder has been synthesized by direct nitridation of silicon saw dust recovered from the photovoltaic industry in ammonia gas (NH3) at 1300°C with calcium fluoride (CaF2) as additive. The X-ray diffraction (XRD) analysis indicates that the formation of β-Si3N4 is enhanced and accelerated in NH3 compared to nitrogen (N2). The scanning electron microscope (SEM) examination shows that, compared with N2, NH3 contributes to the formation of spherical-like particles, and all irregular silicon particles are transformed into spherical-like β-Si3N4 particles in the NH3 atmosphere. These results indicate that the NH3 atmosphere is conducive to the formation of submicron spherical-like β-Si3N4 particles. A complete submicron spherical-like Si3N4 powder with 93.12 wt% β phase has been synthesized by direct nitridation of silicon saw dust assisted with 5 wt% CaF2 additives in NH3. The mechanism for the formation of the spherical-like β-Si3N4 powder has also been discussed.