Beschreibung:
Potassium‐containing plate‐like precipitates having the βm‐alumina structure were identified within intergranular spinel inclusions in MgO‐doped sintered aluminum oxide ceramics. Transmission electron microscopy revealed the corresponding epitaxial relation: (0001) βm{111} spinel and 1120 βm110 spinel. Chemical analyses and quantitative metallography suggested that in α‐Al2O3 the 1800°C solubility limits of magnesium and potassium do not exceed 300 to 400 ppm and 5 to 10 ppm by weight, respectively.