Thermodynamic study on the carbothermal nitridation synthesis of silicon nitride using silicon kerf loss

Abstract

A novel way to produce the silicon nitride using cheaper silicon kerf loss instead of expensive pure silicon as a raw material has been studied through thermodynamic analysis and Gibbs free energy minimization method. The mass fraction of Si3N4 in products increases with increasing the temperature at atmospheric pressure with mole ratio of carbon to oxygen of 1:1. More content of carbon added in silicon kerf loss, the less content of Si2N2O and the more content of SiC formed in the product. In addition, the pressure parameter obviously influences the composition of nitridation products, which can be attributed to lots of gas-phase reactions existing in the nitridation process. With the pressure increased, the mass fraction of Si3N4 decreases below 1500 °C, while it increases above 1500 °C. In conclusion, the optimal products contain Si3N4 of 95.6 mass%, Si2N2O of 1.7 mass% and SiC of 2.7 mass%, which formed at 1032 °C and 1 × 10−5 bar with mole ratio of carbon to oxygen of 1:3.