Design and reinforcement mechanisms of the binary alumina ceramics with improved density derived from industrial gibbsite and boehmite

The properties of starting aluminum hydroxide powder greatly determine the sintering activity and microstructure of final alumina ceramic. Combing the modified properties of industrial gibbsite and boehmite, binary alumina ceramics with high mechanical property were fabricated under ambient pressure without any additives. The enhanced sintering activity of binary alumina compacts is attributed to the high tetrahedral aluminum content stemmed from gibbsite due to pseudomorphic transition. The low α-Al 2 O 3 content and high microstrain in boehmite-derived α-Al 2 O 3 also facilitate the densification of binary alumina compacts. In addition, the sintering mechanism shifted from boundary diffusion to the combination of boundary and volume diffusion with the introduction of boehmite-derived alumina, leading to accelerated atoms migration and significant reduction of activation energy from 426   kJ/mol to 289   kJ/mol. The resultant rapid densification at low temperature prevented excessive grain growth at the late sintering and resulted in remarkable grains refining. Benefited from the collective effect of binary alumina packing, accelerated sintering kinetics and grain refinement strengthening, full dense in binary alumina ceramics with a 99.8% relative density, 0.02% apparent porosity, 25.88   GPa Vickers hardness and 4.41   MPa·m 1/2 fracture toughness was achieved at 1650℃ for 2   h. This study presented a facile efficient strategy to preparing high-quality binary alumina ceramics, also highlighting the differences in aluminum hydroxide precursor on the performance of alumina-bearing materials.