A Test of the Second‐Phase and Impurity‐Segregation Models for MgO‐Enhanced Densification of Sintered Alumina

Abstract

To determine if MgO added within the solubility limit in Al 2 O 3 is sufficient to suppress discontinuous grain growth, an undoped alumina pellet was sintered next to a preequilibrated, two‐phase mixture of spinel (MgAl 2 O 1 ) and alumina. The MgO‐doped outer surface of the undoped pellet did sinter to full density; metallography confirmed that the sample was free of second phase. Grain boundaries were analyzed with a scanning Auger microprobe, which showed that the grain boundaries of the inner porous region had approximately the same Ca segregation as those in the dense outer shell region. Therefore, it was concluded that the beneficial effect of magnesium is due neither to second‐phase pinning nor to Ca impurity segregation.