Microstructure and performances of corundum−mullite composite ceramics for heat transmission pipelines: Effects of Ho2O3 additive content

Abstract Ho2O3 was employed to improve the microstructural densification and performances of pressureless sintered corundum–mullite ceramic composites. This study investigated the influences of Ho2O3 addition on the microstructure, physical properties and thermal shock resistances of the composites. The results indicated that sample AH5 (80 wt% Al2O3, 20 wt% coal series kaolin, and 5 wt% additional Ho2O3), which was sintered at 1550 °C, showed the best comprehensive properties. In this Al2O3-rich and SiO2-poor system, a reaction between the Ho2O3 and Al2O3–SiO2 system produced an Ho2O3–Al2O3–SiO2 liquid phase. This liquid phase increased the microstructural densification and resulted in a lower sintering temperature. The generation of mullite and holmium disilicate during thermal shocks improved the thermal shock resistance. The high bending strength and satisfactory thermal shock resistance of the as-prepared corundum–mullite ceramic composites showed their potential for use in heat transmission pipelines.