Synthesis of near‐spherical α‐Si ₃ N ₄ powder via carbon‐assisted crystallization of amorphous Si ₃ N ₄ powder

Abstract This study presents a scalable method for fabricating near‐spherical silicon nitride (Si ₃ N ₄ ) particles with a high α phase content. Amorphous Si ₃ N ₄ powder was synthesized using the diimide synthesis method, mixed with graphite powder as a carbon source, and calcined at 1550°C to produce α‐Si ₃ N ₄ powder. The effects of varying carbon contents on the phase composition and microstructure of the resulting products were investigated. In the presence of carbon, the Si ₃ N ₄ particles exhibit a near‐spherical morphology, with a reduction in the fraction of whisker‐like structures. The products show a complex, nonuniform structure with a broad particle size distribution and varying structural characteristics when excessive powder is added. Graphite powder not only provides nucleation sites but also plays a critical role in the phase transition from amorphous Si ₃ N ₄ to the α phase. The nucleation and growth of α‐Si ₃ N ₄ are facilitated by the presence of SiO(g), which is reduced through interactions with C(s) or CO(g). It indicates that carbon accelerates the Si ₃ N ₄ phase transition through the vapor‐solid mechanism, which is the key to inhibiting the whisker growth and controlling the particle size of α‐Si ₃ N ₄ powder.