Alumina ceramics fabricated from bimodal alumina with additives

Superfine alpha-Al2O3 synthesized by a precipitation method and commercial alpha-Al2O3 were used to prepare bimodal alumina. Densification of bimodal alumina with MgO, SiO2 as additives was investigated from 1400 to 1550 degrees C. The addition of superfine alpha-Al2O3 is not effective to enhance the densification at the sintering temperature of 1400 degrees C. With further increase of the sintering temperature, the densities of alumina ceramics from bimodal alumina with different contents of superfine alpha-Al2O3 are similar in values. The microstructure evolution, as well as mechanical properties of the alumina ceramics was also studied. For the 1450 degrees C sintered Al2O3 ceramics, fine grains located in the skeletal structure of the coarse grains and the increasing fine alpha-Al2O3 led to fine-grain structure. Spinel and mullite were observed in the fine-grain regions. For the 1500 degrees C sintered Al2O3 ceramic, there was significant grain growth. Mullite, spinel and MAS glass formed in the triple-grain junctions. Both 1450 and 1500 degrees C sintered Al2O3 ceramics have no liquid phase in grain boundaries. The addition of superfine alpha-Al2O3 can distinctly enhance the bending strength of alumina ceramics. The best mechanical properties were gained when the temperature was 1450 degrees C and then deteriorated with further increase of sintering temperature. (c) 2006 Elsevier B.V. All rights reserved.