A novel in-situ β-Sialon/Si3N4 ceramic used for solar heat absorber

β-Sialon/Si3N4 composites were fabricated via pressureless sintering method at 1580 °C using α-Si3N4, calcined bauxite, AlN as the main raw materials, Y2O3 and La2O3 as the sintering additives. Mechanical properties, phase composition, microstructure, thermal shock resistance, oxidation resistance, thermophysical properties and solar absorptance were investigated. The results show that the sample with 3 wt% Y2O3 and 3 wt% La2O3 as additives exhibits the best mechanical properties, which also has high thermal conductivity and solar absorptance: 7.96 W/(m K) and 91.10%, respectively. The sample has intact morphology after 30 thermal shock cycles (wind cooling from 1100 °C to 25 °C), and the bending strength remains as high as 138.36 MPa. Its weight gain rate after oxidation at 1100 °C for 100 h is just 0.9331 mg/cm2, which shows the excellent oxidation resistance. A dense oxide layer is found to be formed on the surface during the process which protects the sample from further oxidation. It is believed that this in-situ β-Sialon/Si3N4 ceramic could be a promising candidate for solar heat absorbing material.