Effects of Sm2O3 and TiO2 on the performance of MgAl2O4-Si3N4 ceramics for solar thermal absorber in concentrating solar power

Aiming to further improve the properties of novel MgAl2O4-Si3N4 ceramic used as solar thermal absorbing material in concentrating solar power, effects of Sm2O3 and TiO2 on performance of the composites were investigated especially the mechanisms of different additives on microstructure and high temperature stability. The results show that both additives can accelerate sintering, reduce sintering temperature, improve the density and high temperature stability via liquid phase sintering mechanism. Besides, TiO2 can form displacement solid solution with Al2O3 to promote the sintering process. Sm2O3 is more conducive to improving the bending strength due to its function of increasing the length diameter ratio of beta-Si3N4. TiO2 is more favorable for improving solar absorption owing to the distinctive absorption spectrum and large number of cation vacancy caused by substitution of Al3+ by Ti4+. MgAl2O4-Si3N4 composites with Sm2O3 and TiO2 additives have better performance than MgAl2O4-Si3N4, Si3N4 and SiC ceramics prepared via the same procedure, which makes it a certain choice for solar thermal absorbing material.