Synthesis of spherical Si₃N₄ powders by liquid-phase modified carbothermal reduction and nitridation

ss-Si3N4 powder with well-dispersed spherical particles was synthesized by liquid-phase modified carbothermal reduction and nitridation. The influence of the type and content of additives on the particle morphology was investigated. The liquid phase formed at the reaction temperaturemodifies the morphology of the Si3N4 powder. The Si3N4 products precipitated along the liquid-solid interface, thus forming a spherical morphology and promoting the transformation from alpha-Si3N4 to ss-Si3N4. The type of additives has a strong influence on the formation temperature and viscosity of the liquid phase and hence affects the productmorphology. In the samples with CaF2 and CaO additives, sufficient liquid phase occurred and spherical particles were obtained. In the sample with Y2O3, however, the liquid phase was insufficient due to the higher formation temperature, thus resulting in an irregular particle morphology.