Preparation Of Silicon Nitride Powder By Combustion Synthesis Process And Study Of The Phases Influencing Factor

Silicon nitride is a new high-temperature structural ceramics. It is researched, exploited and used for its excellent performance. The silicon nitride power is a raw material and severely effects the performance of the ceramics. At the present time, some shortage including long-time, wasting-power and high-cost exist in the four preparation methods. In the several years, one new preparation-Combustion Synthesis causes the interesting of some scholars. The matheod is that reaction mass is lighted by external heater, maintains it's own synthetic reaction through releasing reactive heating. It has some essential features,such as simple procedure convenient operation high productivity, short-time reaction product of high-purity low cost and so on. So it is very significant in studying preparing silicon nitride power by Combustion Synthesis.By the mean of X-ray experiment results, the article calculated quantitatively the phase composition of silicon nitride power by normalized matheod. The phase composition's effect of addition diluent, initial particle size and nitrogen pressure was discussed.The oxygen and water vapor in NH4Cl may improve the formation of α phase, and NH4CI can lower reaction temperature, slow up speed of phase change. With increasing percengtage composition of addition (NH4CI), the content of α phase increases. When the diluents (Si3N4) is between 30wt% and 60wt%, the reaction happens, the diluents not only improve the formation of β phase, but also slow up speed of phase change,so With increasing percengtage composition of diluents (SiaN4), the composition of phase in Combustion Synthesis has different changes. The initial size of silicon affects the reaction mechanism of Combustion Synthesis. Initial size is more thin ,evaporating capacity is more large, the reaction rate more fast, temperature is more high,and phase change is more fast, the content of α phase is less. Combustion Synthesis of Si and N2 depends on permeatingof N₂ If the pressure of nitrogen is larger ,the capacity of permeating is stronger; But it the pressure of nitrogea is too larger, the solubility of α -Si3N4 in the liquid phase will be smaller.In the end, the article discusses that the diluent and the initial size of silicon influence on the size of crystal article of Si3N4. With increasing percengtage compos lion of diluent in materials, the size of crystal article of Si3N4 increases. With decreasing initial size of siliciun, the size of crystals article of Si3N4 decreases.