Experiment research and numerical simulation of thermal process in a suspended bed for Si₃N₄ synthesis

Aiming to a method for the synthesis of silicon nitride powder by direct nitridation process based on fluidization technology, a two-dimensional mathematical model of thermal process in a suspended bed was established, the thermal process was simulated based on the commercial CFD software FLUENT, and the effects of the flow velocity of nitrogen gas, the ratio of particle to gas and nitridation temperature on the temperature of the bed and the conversion rate of silicon were analyzed. The results show that the errors between simulation and experimental values are less than 5% and the model can be used to predict the thermal process in the suspended bed. Under the experimental conditions in this study, when the silicon powder with a particle size of 2.7 μm is used as raw materials, with a nitridation temperature of 1380℃ and nitridation time of 54.5 s, the conversion rate of silicon is 22.5%. Theoretical predictions suggest that if the nitridation temperature is increased to 1450℃ and the nitridation time is extended to 7.1 min, the conversion rate of silicon and the purity of silicon nitride should reach 98.6% and 98%, respectively.