Thermal shock resistance and oxidation resistance of MgAl2O4-Si3N4 ceramics for solar thermal absorber: The effects of TiO2 additive content

TiO2 is employed to improve the performance of pressureless sintered MgAl2O4-Si3N4 ceramics in this study, aiming to make the ceramics more suitable for solar thermal absorbing materials in concentrating solar power. Effects of TiO2 content on the microstructure and properties of the composites were the focus, especially the thermal shock and oxidation resistance. The results show that composite with 2 wt% TiO2 sintered at 1620 degrees C has the highest bending strength exceed 320 MPa, which contributes to resist the thermal stress. Instead of being damaged after 30 thermal shock cycles (Delta T approximate to 1100 degrees C), the bending strength of the sample increases 12.03%. The weight gain rate is only 0.8964 mg/cm2 when finishing the oxidized process at 1300 degrees C for 100 h, and the oxidation kinetic obeys the parabolic low. Solar absorptance and thermal conductivity of the composite reach 93.5% and 13.27 W/(m.K) respectively. MgAl2O4-Si3N4 composite can be presureless sintered at lower temperature, and it has better high temperature stability than Si3N4 and SiC ceramics prepared via the same procedure, which makes it an ideal choice for solar thermal absorbing material.