Abstract
Diffusion kinetics and mechanisms were studied in the FexO‐MgO (vacuum), NiO‐MgO (vacuum and air), and Fe203‐MgO (air) systems. In the FexO‐MgO system, Fe entered MgO by a redox reaction; the diffusivity and activation energy depended on concentration. In the NiO‐MgO system in air the diffusivity depended on concentration and the activation energy did not; in vacuum both the diffusivity and activation energy were concentration‐independent. In the Fe2O3‐MgO system in the MgO phase the activation energy and diffusivity did not depend on concentration. Because of impurities, the diffusion results were for the extrinsic region. Formation of trivalent ions and consequent chemically created vacancies in the FexO‐MgO and NiO‐MgO (air) systems resulted in the concentration dependence of diffusivity. Concentration dependence of activation energy in the FexO‐MgO system is associated with structural changes due to a change with concentration of the Fe3+ octahedraI/Fe3+ tetrahedral ratio. In the Fe2O3‐MgO system structural changes do not occur during diffusion because this ratio remains constant.
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