Grain Boundary Precipitation in Oxide Systems

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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.