Thermogravimetric study of the solid-gas interaction of a MnZn ferrite and the effect on its magnetic properties

An experimental technique has been used to explore the physicochemical interactions between a MnZn ferrite and the atmosphere in which it is fired. The technique uses a thermo-balance and an oxygen analyzer. A decrease of the atmospheric oxygen content or an increase of the sintering temperature results in an increase in weight loss of a sample during sintering. This weight loss was attributed primarily to the sublimation of zinc oxide. From cooling studies, the amount of oxidation was found to be dependent on the oxygen content of the atmosphere and the density of the specimen. The results are interpreted in light of the availability and diffusivity of oxygen through the sample. The disaccommodation was found to increase with the atmospheric oxygen content during sintering and to be dependent on the amount of oxidation during cooling. The data are in agreement with models which indicate the influence of cation vacancies on disaccommodation. The temperature dependence of the permeability was studied and found to be related to a shift in the secondary peak that is caused by compositional changes during sintering and cooling. An example is given illustrating the use of the experimental technique as a diagnostic tool to determine the relative oxygen content of ferrites fired under commercial conditions.