Effect of dual liquid phase sintering aids on the densification and microstructure of low temperature sintered alumina ceramics

Abstract Alumina ceramics was prepared by pressureless sintering technology in which a CuO–TiO2–Bi2O3 mixture (0–4.0 wt.% Bi2O3 and 4.0 wt.% CuO and TiO2) was added as dual liquid phase sintering aids. The phase compositions, microstructural feature, and sintering behaviour of the alumina ceramics were analysed. The results showed that adding 2.5 wt.% Bi2O3 to alumina ceramics can increase the contribution rate of initial stage of sintering to the sintering process. The relative density of the sample reached 97.63% after sintering at 1200 °C for 90 min. Measurements from differential scanning calorimetry, with the addition of CuO–TiO2–Bi2O3, demonstrated the formation of two liquid phase points, 827.4 and 936.8 °C. Notably, the solid solution temperature of TiO2 and Al2O3 ceramics diminished thanks to the dual liquid phase sintering aids, and at the same time the activation energy required also dropped from 368.96 to 137.31 kJ/mol. Research indicates that the combined action of dual liquid phase sintering and solid-state reaction sintering has promoted the densification of alumina ceramics during the sintering process while at the same time inhibiting the growth of abnormal grains so that a homogeneous microstructure can be formed.