Abstract
Oxidation of fine powders of Mn-Zn Ferrites prepared by the ‘co-precipitation’ method has been presented.Differential thermal analysis showed a sharp exothermic peak corresponding to ‘hematite’ precipitation. A temperature of the peak, Tp, depends upon a heating rate φ and a crystallite size, ε, expressed by a simple relation:φ⋅ε∝exp(-Q/kTp), where Q=2.1±0.2eV. The relation indicates that the specific reaction rate is inversely proportional to crystallite size and that its temperature dependence is expressed by an activation process of 2.1eV. The size dependence could be explained by the oxidation of the total surface area and the temperature dependence by cation diffusion in Fe-poor Mn-Zn ferrite. Isothermal oxidation processes were studied by X-ray diffraction analysis and explained qualitatively by the same mechanism as the above relation.
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