Modern investigation methods for the optimization of high-quality soft-ferrite manufacture

The various stages for the manufacture of manganese-zinc ferrite have been studied using the most powerful available techniques of physicochemical analysis. The selection of the starting oxides has been achieved by studying their reactivity; the formation mechanism of the ferrite was first determined by X-ray diffractometry and Mössbauer spectrometry. For iron oxide the index of reactivity is correlated with the temperature of the spinel phase appearance, while for manganese oxide the rate of dissolution in zinc ferrite may be used. The electrical properties of the finished material depend very closely on the level of homogeneity reached during the various manufacturing steps of the process and, in particular, during the mixing of the starting oxides. In order to measure the homogeneity of the mixed oxides, the local concentration of the various elements are determined using an electron-probe microanalyser. The efficiency of mixing is then measured by the ratio of the calculated theoretical standard deviation to the experimental standard deviation of composition. Various methods of mixing have been compared, and an optimum mixing duration can be defined leading to improved magnetic properties of the finished product. X-ray spectrometry, electron-probe microanalysis, and Mössbauer spectrometry have been proved very fruitful for the understanding of the sintering phenomena. The magnetic structure of the sublattices as well as the inversion degree of the ferrite were determined by neutron diffraction experiments which gave quantitative results on the stoichiometry. By using modern methods for optimum seeking, the various parameters defining the sintering schedule can be adjusted to maximize the μQ quality factor of low losses ferrites.