Porous Al2O3-Spinel Based Polycrystals That Resist Free-Sintering

We show that increasing MgO content in Al2O3 from 0.25 to 10 wt% has a remarkable effect on the sintering behavior. While 0.25 wt% specimens sinter to near full density, the higher weight percent sample could be sintered to a maximum of 92% relative density even when held for 24 h at 1673 K. The resistance of the pores to sintering is ascribed to a reduction in the driving force for sintering (rather than to kinetics). The volume fraction of the pores increases with the fraction of the spinel phase, which forms by a reaction between magnesia and alumina. These findings raise the promise of membranes that can be tailored for pore size and pore volume, for high temperature applications.