Powder chemistry effects on the sintering of MgO-doped specialty Al₂O₃

In this work, we investigate the effects of powder chemistry on the sintering of MgO-doped specialty alumina. The stages at which MgO influences densification of Al₂O₃ were identified by comparing dilatometry measurements and the sintering kinetics of MgO-free and MgO-doped specialty alumina powders. MgO is observed to reduce the grain boundary thickness during densification using TEM. We show that MgO increases the solubility of SiO₂ in alumina grains near the boundaries using EDS. First-principles DFT calculations demonstrate that the co-dissolution of MgO and SiO₂ in alumina is thermodynamically favored over the dissolution of MgO or SiO₂ individually in alumina. This study experimentally demonstrates for the first time that removal of SiO₂ from the grain boundaries is a key process by which MgO enhances the sintering of alumina.