Grain Boundary Precipitation in Oxide Systems

Abstract

The spatial distribution of precipitate in several polycrystalline oxide systems after annealing of the crystalline solutions was investigated by using an electron probe microanalyzer. Preferential grain boundary and intergranular voids precipitation of the minor component was found in the majority of systems with limited crystalline solubility, e.g., MgO–Al₂O₃, MgO–CaO, UO₂–CaO, CaO–Yb₂O₃, as well as with the ZrO₂–MgO system which has an eutectoid. The formation of an intermediate phase during the precipitation may have a varied effect on the contribution of the surface free energy to the activation energy for nucleation. The intermediate phase appears in both MgAl₂O₄–Al₂O₃ and CaO–Yb₂O₃ systems, although complete phase separation occurs in the former and grain boundary precipitation in the latter.