Effects of MgO doping concentration on densification and microstructure of flash sintered α-Al2O3 ceramics

The effects of MgO doping concentration on the sintering behavior of Al2O3 ceramics in flash sintering were studied. The relative density, grain size and oxygen vacancies of the flash sintered samples doped with different amounts of MgO were characterized. The results showed that the relative density and grain size increased with MgO concentration up to 0.25 wt.%, and then decreased with further increasing MgO content. These were coincident with the changes in oxygen vacancies in the flash-sintered samples. Flash sintering behaviors of 0.25 wt.% MgO doped Al2O3 disc were different from those in conventional sintering, where the grain growth was inhibited when the MgO content is 0.25 wt.%. The results can be explained by the fact that the higher oxygen vacancies in the flash sintered sample than that in the conventional sintered one, due to the applied electric field/current in flash sintering enhancing the solubility of MgO in Al2O3.