Noncatalytic gas-solid reaction model for directly nitridizing silicon powder under atmospheric pressure

In order to study the nitridation kinetics of silicon powder under atmospheric pressure, a set of nitrida- tion experiments were performed at 1350 and 1400 ℃ for 10 to 30 rain. Silicon powder of 2.2 ~m in average diameter and 99.99% in purity was adopted as the experimental materials, and nitrogen of 99.993% in purity was used as the reaction gas. At different temperatures, the conversion rate of silicon is obtained as a function of reaction time. Based on the noncatalytic gas-solid reaction model, a dynamic model of silicon nitridation under atmospheric pressure is introduced, which includes two key model parameters: reaction rate constant of silicon nitridation and diffusion coefficient of nitro- gen in silicon nitride, These model parameters are obtained by fitting the experimental data under different conditions. Assuming that reaction rate constant and the diffusion coefficient can both be expressed as the Arrhenius style, the activation energy and pre-exponential factor of the reaction are calculated as 2.71× 10⁴ J·mol^-1 and 3.07× 10^-5 m·s^-1, and the activation energy and pre-exponential factor of diffusion are calculated as 1.06×10⁵ J·mol^-1 and 1.12×10^-9 m²·s^-1, respectively. Then a series of conversion curves are predicted at different temperatures and powder sizes. On the trend, the predicted curves are in good agreement with experimental data in literatures.