Thermal shock resistance and oxidation behavior of in-situ synthesized MgAl2O4–Si3N4 composites used for solar heat absorber

Abstract MgAl 2 O 4 –Si 3 N 4 ceramics were fabricated via pressureless sintering by using α-Si 3 N 4 , α-Al 2 O 3 and MgO as starting materials. MgAl 2 O 4 was in-situ synthesized in the composite ceramics to improve the sintering process and high-temperature performance of Si 3 N 4 . Results show that the composite with approximately 30 wt% MgAl 2 O 4 sintered at 1620 °C exhibits the best physical properties, excellent thermal shock resistance, oxidation resistance and solar absorptance. No cracks were found after 30 thermal shock cycles (1100–25 °C, wind cooling). At the same time, the bending strength has experienced an improvement of 24.5%, which increases to 248 MPa. A dense oxide film is formed on the surface of the sample during oxidation at 1300 °C, which protects it from further oxidation. The oxidation kinetics of MgAl 2 O 4 –Si 3 N 4 ceramic transforms from passivation oxidation into activation oxidation with increasing MgAl 2 O 4 content. Only moderate amount of MgAl 2 O 4 (10–30 wt%) can provide the excellent oxidation resistance. These in-situ MgAl 2 O 4 –Si 3 N 4 composites could be a promising candidate for solar heat absorbing material.