Oxidation Rate and Phase Diagram of Mu-Zn Ferrite Determined from the Cation Diffusion Coefficient

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Abstract
Oxidation rate of Mn-Zn ferrite, which means the rate of change in oxygen content in spinel phase, was determined from the diffusion coefficient of 59Fe, by assuming that the diffusion coefficient was proportional to the cation vacancy density, i.e., the excess oxygen content. Volume oxidation rate and grain boundary oxidation rate are expressed by coefficients having the same dimension as the diffusion coefficient, and measured respectively from the experiments on a single-crystal and a polycrystal. The oxidation process is well expressed by the familiar “parabolic law.” The parabolic law constant obtained by the latest investigation corresponded to that by the weight gain technique. Phase diagram of Mn-Zn ferrite–hematite–oxygen system was also determined by the behavior of the diffusion coefficient of 59Fe. This method of determining phase boundaries seems easier and more accurate than any other method utilized.

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