Study on in-situ reaction synthesis and mechanical properties of Si2N2O 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 SiSiO2N2 system was discussed by analyzing the variation of Gibbs free energy with temperature. As the sintering temperature rises from 1450 to 1700 °C, the Si2N2O 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, Si2N2O ceramic possesses the highest flexural strength of 229 MPa and fracture toughness of 2.3 MPa m1/2.