Study on in-situ reaction synthesis and mechanical properties of Si ₂N₂O ceramic

Si₂N₂O ceramics were fabricated using an in-situ reaction synthesis method by nitriding powder mixture of Si and SiO₂. The reaction mechanism in the SiSiO₂N₂ system was discussed by analyzing the variation of Gibbs free energy with temperature. As the sintering temperature rises from 1450 to 1700 °C, the Si ₂N₂O phase increases with the Si₃N₄ phase decreasing and there is only Si₂N₂O with hardly any Si₃N₄ after sintering at 1700 °C, the volume shrinkage and mean pore size decrease respectively from 26.1% to 18.0% and from 0.4 to 0.04 μm, the porosity increases from 20.8% to 29.1%, and the Vickers hardness decreases from 5.6 to 4.5 GPa. After sintering at 1600 °C, Si ₂N₂O ceramic possesses the highest flexural strength of 229 MPa and fracture toughness of 2.3 MPa m^1/2.