Kinetics of Silicon Nitridation and the Formation Mechanism of α/β-Si3N4 at Atmospheric Pressure and 1410 °C

The formation of alpha/beta-Si3N4 relates to the reaction process in the direct nitridation method, which can produce cheap ultrafine Si3N4 powder on a large scale in a fluidized bed. Complete nitridation of silicon powder was conducted in a 1 atm nitrogen atmosphere at 1410 degrees C, which is slightly lower than the silicon melting point of 1414 degrees C. Comprehensive analyses with thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy show several-stage nitridation kinetics of silicon powder. Compared with previous research projects, more reaction details can be observed. The reaction undergoes evaporation and multiple melting-freezing processes, causing the deviation of the actual reaction curve from the theoretical logarithm curve in a solid-gas reaction. According to heat flow curves and their derivative to time curves, the reaction can be divided into 4 main stages. The repeated melting-freezing phenomenon and the produced alpha/beta-Si3N4 phase were investigated. The increase of particle size increases the liquid-gas and liquid-solid-gas reaction time which causes beta-Si3N4 to increase rapidly.

Automated summary

This study investigates the formation process and reaction kinetics of α/β-Si3N4, revealing a multi-stage nitridation process for silicon powder involving complex phenomena like evaporation, melting, and freezing.