When sintered $Al_2O_3$ was in contact with a $CaO\cdotMgO\cdotSiO_2$ melt at 1600℃, $Al_2O_3$ dissolved and $MgAl_2O_4$ formed in a CMSA($CaO-MgO-SiO_2-Al_2O_3$) glass. The observed shape of $MgAl_2O_4$ grains was an octahedron with $\{111\}$ planes and it is believed to be the equilibrium shape of $MgAl_2O_4$ in CMSA liquid. When $MgAl_2O_4$ grains were etched by $H_3Po_4$, the dissolving shape of etch-pits on $MgAl_2O_4$ grains was octahedron, too. Each plane of etch-pit was parallel with a plane of the $MgAl_2O_4$ grain.
The chemically induced grain boundary migration(CIGM) was observed in $MgAl_2O_4$. $MgAl_2O_4$ sintered body was prepared by sintering of $MgO\cdot1.22Al_2O_3$ powder mixture at 1600℃ for 60h. When sintered specimen was heat-treated at 1500℃ in a ZnO atmosphere, the grain boundary area was increased and the grain boundaries migrated away from their center of curvature, producing corrugated or faceted ones. In the migrated region, ZnO content was higher than that in the other region. Therefore, the migration was accomplished by a solutioning of ZnO, as in the typical grain boundary migration induced by chemical potential difference between the specimen and the atmosphere.
