Evaluation of Nitridation Catalyst of Silicon Powder by Activation Energy Measurements

The nitridation of silicon powder with or without 5 volume percent iron oxides, Al2O3 and AlN, was studied by thermogravimetry under constant heating rate from room temperature to 1350°C. The activation energy of nitridation at the initial stage was estimated at 670kJ/mol by using Jander's diffusion model, and the initial nitridation layer of silicon particles was about 200Å thick. The starting temperature of nitridation dropped and the activation energy decreased by adding a small amount of iron oxides into silicon powder. Thus, iron oxides were effective as a catalyst. On the other hand, addition of aluminum compounds increased the activation energy. The activation energy is closely related to the crystal structure of the material to be nitrified. The material was entirely composed of α-Si3N4 single-phase when the activation energy was less than 460kJ/mol. Both α-and β-Si3N4 phase were observed when the activation energy was greater than this value.