Iron Diffusion in Iron-Aluminate Spinels

The diffusion coefficient of ⁵⁹Fe in iron-aluminate spinels (Fe₃O₄-FeAl₂O₄) was measured by serial sectioning. The results were analyzed with a defect model, assuming that the predominant defects were cation vacancies and interstitials. At 1380°C, diffusion occurs in Fe₃O₄ and Fe(Fe_1.51Al_0.49))O₄ by an interstitial mechanism at low P_O2 and a vacancy mechanism at high P_O2* Diffusion of iron is by the vacancy mechanism for higher hercynite concentrations, except that the results for the end-member, FeAl₂O₄, suggest an interstitial mechanism. At 10⁻⁶ atm O₂, an Arrhenius plot of D _Fe exhibits a minimum for Fe₃O₄ and Fe(Fe_1.51 A1_0.49)O₄. This effect is explained in terms of a mechanism change. The D _Fe is essentially independent of temperature in Fe(Fe_1.03Al_0.97)O₄ and Fe(Fe_0.54Al_1.46)O₄.