Effect of MgO and NiO on the sintering of slip cast alumina

Similar to pressed compacts, slip cast alumina can be sintered to near theoretical density if minor additions of MgO or NiO are made. Sintering kinetics of alumina were analyzed in terms of the Wong and Pask model which was shown to give the more realistic representation of powder compacts. The rate controlling step with and without additions is the migration from the neck along the pore surface rather than diffusion along the grain boundaries to the neck. Both MgO and NiO retard mass transport probably due to changes in surface energy. However, they allow sintering to near complete densification. Although grain growth limitation via second phase inclusions or solute segregation is expected, the final density improvement was shown to result from modifying pore kinetics such that the pores remain attached to the grain boundaries during grain growth until complete densification.