Effect of Fe2O3–TiO2-Sm2O3 Composite Additive on Sintering Behavior and Thermal Properties of Al2O3 Ceramics for Thermal Storage

Al2O3 ceramics were prepared by introducing Fe2O3-TiO2-Sm2O3 composite additive, in which the content and ratios of Fe2O3 and TiO2 remained constant, but Sm2O3 was variable. The phase transformation, micromorphology, physical properties and thermal properties were investigated. The results showed that Fe2O3 and TiO2 made the grains high sintering activity through a solid solution mechanism, which promoted grain growth, but Sm2O3 preferred to form SmFe4Al8O19 at the grain boundaries, which slowed grain growth and refined the grains. With the increase in Sm2O3, the grain refinement of SmFe4Al8O19 became outstanding, and the grain diameter gradually decreased, which is favorable for denser sintering. However, only a proper amount of Sm2O3 in the Fe2O3-TiO2-Sm2O3 composite additive resulted in better thermal shock resistance. The Al2O3 ceramics with 9 wt% Fe2O3-1 wt% TiO2-5 wt% Sm2O3 sintered at 1520 degrees C exhibited the optimum properties, yielding an increase in the bending strength by 6.60% after 30 thermal shocks, a thermal conductivity of 13.33-5.64 W/(m.K) (25-800 degrees C) and a specific heat capacity of 0.94-1.25 J/(g.K) (25-800 degrees C), all of which demonstrate the potential for thermal storage.