Self-diffusion coefficients of oxygen ion in single crystals of MgO · n Al2O3 spinels

Abstract

Oxygen self‐diffusion coefficients in single crystal spinels were determined for three compositions of MgO · Al₂O₃, MgO · 1.2Al₂O₃, and MgO · 2.2Al₂O₃ by a gas‐solid exchange technique utilizing ¹⁸O as a tracer. The temperature dependence of the self‐diffusion coefficient for MgO · Al₂O₃ was expressed as D = 0.89 exp(− 105 × 10³/RT) cm²/sec. The self‐diffusion coefficients for MgO · 1.2Al₂O₃ and MgO · 2.2Al₂O₃ were close to that for MgO · Al₂O₃, which was interpreted as being due to intrinsic diffusion. The determined self‐diffusion coefficient of oxygen ion was smaller by several orders of magnitude than that of magnesium ion and was closer to the apparent diffusion coefficients calculated from the sintering rates. The influence of surface exchange reaction was noticed in determining the self‐diffusion coefficient.