硅粉常压直接氮化合成氮化硅粉的动力学研究

Kinetics of Direct Nitridation of Silicon Powders at Ambient Pressure

以平均粒径为2.8μm的硅粉为原料,添加氮化硅粉作为稀释剂,对常压氮气下直接氮化制备Si_3N_4粉的工艺进行了研究,氮化温度范围为1623～1823 K,氮化时间范围为0～20 min。借助XRD、SEM等检测方法,分析了氮化温度和氮化时间等因素对氮化过程的影响。基于不同氮化温度下硅的转化率与氮化时间的关系,利用粒径不变的缩芯模型,建立了一种简化的硅氮反应模型,该模型显示出硅的转化率随时间呈渐近线指数趋势。并利用该模型计算得出了硅粉常压直接氮化合成氮化硅粉的一些反应动力学参数:Arrhenius公式中指前因子为5.56×10^(12) cm/s;活化能为534 kJ/mol;有效扩散系数为6.2×10^(-8)cm^2/s;以及反应速率常数的计算公式。

Silicon nitride powders were prepared via direct nitridation of silicon powders diluted with α-Si3N4 at ambient pressure. Silicon powders with averaged particle size of 2.8μm were used as the starting materials. The nitridation temperature was ranged from 1623 K to 1823 K and the nitridation time was set as 0 minute to 20 minutes. The effects of nitridation temperature and time on the conversion rate of silicon were characterized. Based on the relations between the conversion rate of silicon and the time at different temperatures, and using shrinking core model, a simple model for the reaction between silicon and nitrogen was derived. The model had shown that the relations between the conversion rate of silicon and the time displayed asymptotic exponential conversion trend. Using this model, the kinetics parameters of nitridation of silicon powder at ambient pressure were calculated, including pre-exponential factor in Arrhenius equation was 5.56×10^12 cm/s, activation energy was 534 kJ/mol, effective diffusion coefficient was 6.2×10^-8 cm2/s, and the formula of the reaction rate constant was derived.