Alumina ceramics fabricated from bimodal alumina with additives

Superfine α-Al2O3 synthesized by a precipitation method and commercial α-Al2O3 were used to prepare bimodal alumina. Densification of bimodal alumina with MgO, SiO2 as additives was investigated from 1400 to 1550 °C. The addition of superfine α-Al2O3 is not effective to enhance the densification at the sintering temperature of 1400 °C. With further increase of the sintering temperature, the densities of alumina ceramics from bimodal alumina with different contents of superfine α-Al2O3 are similar in values. The microstructure evolution, as well as mechanical properties of the alumina ceramics was also studied. For the 1450 °C sintered Al2O3 ceramics, fine grains located in the skeletal structure of the coarse grains and the increasing fine α-Al2O3 led to fine-grain structure. Spinel and mullite were observed in the fine-grain regions. For the 1500 °C sintered Al2O3 ceramic, there was significant grain growth. Mullite, spinel and MAS glass formed in the triple-grain junctions. Both 1450 and 1500 °C sintered Al2O3 ceramics have no liquid phase in grain boundaries. The addition of superfine α-Al2O3 can distinctly enhance the bending strength of alumina ceramics. The best mechanical properties were gained when the temperature was 1450 °C and then deteriorated with further increase of sintering temperature.