Effect of rare-earth oxides on microstructure and thermal shock resistance of Al2O3-SiCw composite ceramics for solar thermal storage

Abstract

Rare-earth oxides (i.e. Y2O3 and Sm2O3) were introduced to improve the thermal shock resistance of Al2O3-SiCw composite ceramics for solar thermal storage by aluminum-assisted carbothermal reduction. The effects of rare-earth oxides on the densification, microstructure, bending strength, phase composition and thermal shock resistance of the composites were studied. Results showed that Y2O3 could improve the aspect ratio of SiC whiskers and the bending strength of the composites by enhancing the carbothermal reduction and synthesizing yttrium aluminum garnet (YAG), respectively. The added Sm2O3 was capable of lowering the aspect ratio of SiC whiskers by forming Sm2Si2O7 and was superior in terms of grain refinement of Al2O3 matrix and microstructural densification of the composites. The rare-earth oxides contributed greatly to improve the thermal shock resistance (air cooling, room temperature-1100 °C) of the composites by densifying the microstructure, synthesizing YAG and forming tabular alumina with an interlocking texture. Al2O3-SiCw composites doped with 7 wt% Y2O3 and 7 wt% Sm2O3 exhibited the optimum thermal shock resistance and the bending strength had been improved to 92.6 MPa with an increasing rate of 19.6% after 30 thermal shock cycles. Tabular alumina was found to be in-situ formed using flake-like kaolin as templates with the assistance of rare-earth oxides during thermal shock.