Simple fabrication of highly dispersive β-Si3N4 seeds with moderate aspect ratio

A powder mixture was prepared using a-phase-rich silicon nitride (Si3N4) as the major raw material, with 0.5 wt % Yb2O3 as the additive. These powders were fired at 1650-1800 degrees C for 0.5-2 h at a nitrogen pressure of 0.1 MPa. The effects of firing temperature and holding time on the crystalline phase and microstructure evolution of beta-Si3N4 seeds were investigated in detail. The particle size distribution of the beta-Si3N4 seeds before and after acid treatment was also evaluated using laser diffraction/scattering. The results show that, even with a low mass fraction of sintering additive, rod-like beta-Si3N4 seeds with an average aspect ratio of 4 could be successfully obtained after firing at 1750 degrees C for 2 h. Furthermore, the use of a dilute HF soak for a short period, the resultant powder showed a single peak frequency distribution with a narrow particle size range (D-50 approximate to 2.5 mu m). This suggests that the residual crystalline/glassy phase contained in the as-prepared powder is readily attacked by acid rinse, resulting in the subsequent easy separation of the beta-Si3N4 seed grains. The present method is therefore a simple and promising procedure for the preparation of highly dispersive rod-like beta-Si3N4 seeds for use in the mechanical properties improvement of Si3N4 ceramics.