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

MgAl2O4-Si3N4 ceramics were fabricated via pressureless sintering by using alpha-Si3N4, alpha-Al2O3 and MgO as starting materials. MgAl2O4 was in-situ synthesized in the composite ceramics to improve the sintering process and high-temperature performance of Si3N4. Results show that the composite with approximately 30 wt% MgAl2O4 sintered at 1620 degrees 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 degrees 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 degrees C, which protects it from further oxidation. The oxidation kinetics of MgAl2O4-Si3N4 ceramic transforms from passivation oxidation into activation oxidation with increasing MgAl2O4 content. Only moderate amount of MgAl2O4 (10-30 wt%) can provide the excellent oxidation resistance. These in-situ MgAl2O4-Si3N4 composites could be a promising candidate for solar heat absorbing material. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.