Grain growth suppression in alumina via doping and two-step sintering

Efficiency of two-step sintering on grain growth elimination in the final stage of sintering of polycrystalline alumina has long been considered questionable. The published works failed either to suppress the grain growth entirely or to achieve the relative densities above 99% where the grain growth is the most severe. This paper reports on successful grain growth elimination in the final stage of sintering of a sub-micron alumina ceramics by a combination of the two-stage sintering and doping with metal oxides (MgO, ZrO2 or Y2O3). Relative densities up to 99.7% were achieved. Neither doping of aluminas sintered under conventional conditions nor the two-step sintering of pure alumina alone resulted in entire grain growth suppression in the final stage of sintering. A combination of the two-step heating regime with suitable doping (500 ppm MgO added as MgAl2O4 nanopowder) led to complete grain growth suppression at relative densities above 99%.