Localization of Potassium in Al2O3

Abstract

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.