Localization of Potassium in Al2O3

The accommodation of small amounts of intentionally added potassium in sintered and hot–pressed polycrystalline α-alumina was studied. In sintered specimens, potassium was pushed out by, and accumulated along, the grain boundaries enclosing abnormally large α-alumina grains. Potassium was also localized in hot-pressed specimens and formed large (up to 1-mm diameter), randomly dispersed precipitates of polycrystalline potassium β-alumina. Each precipitate was enclosed within a thin shell (0.5– to 1.5-mm radius) of potassium–rich material. The experimental observations of this precipitation are compared to the formation of Liesegang rings.