Thermodynamic analysis and kinetics mechanism for direct nitridation reaction

The mechanism and chemical kinetics of nitridation reaction at different heating rates was investigated by thermogravimetry. It is found that there is an exothermic peak and an endothermic peak in the differential scanning calorimetry curve at 1 000~1 300 ℃ centigrade, which indicates that the mechanism has changed. The conversion rate of silicon nitride is significantly increased within 1 000 to 1 100 ℃, and it indicates temperature is the dominant factor affecting the conversion rate. Experiments results show that the restrictive step of nitridation reaction is composed of chemical reaction in early stage of reaction and the mixed-control of chemical reaction and intraparticle diffusion in the subsequent reaction; the apparent activation energy is kinetically calculated to be 404.5 kJ/mol, the frequency factor A=9.57×10¹⁵ min/s, the reaction order n=0.95, and mathematical expression of reaction rate equation is finally obtained.