Effect of magnesium oxide addition on surface roughening of alumina grains in anorthite liquid

Abstract

Alumina sintered with 5 wt% anorthite at 1620degreesC for 48 It has grains with flat boundaries and a size distribution representing abnormal grain growth. TEM observations of the grain triple junctions show flat grain surfaces, some of which are the (0001), ((1) over bar 012), and (1 (1) over bar 01) planes. HRTEM observations confirm these surfaces to be atomically flat and hence singular. When sintered further after embedding in MgO powder, the {0001} and {01 (1) over bar2} planes remain flat, but curved surface segments also appear. These curved surface segments are confirmed to be atomically rough by HRTEM. They are connected to the flat segments with discontinuously changing slopes. Thus, when MgO is added, the singular and rough surface phases coexist.