Mixing homogeneity and its influence on the manufacturing process and properties of soft magnetic ceramics

The homogeneity of the mixture of raw materials for the solid state reaction synthesis of MnZn-ferrites is quantified and investigated on its influence on the subsequent steps of the synthesis process and on the magnetic properties of the final products. A methodology is proposed according to which a homogeneity index can be defined from the determination of the compositional variance as a function of the sample size, with the scanning electron microscope. It appears that there is a good quantitative agreement between the so defined homogeneity index and basic characteristics of the synthesis process such as reaction during prefiring, densification after sintering and indicative magnetic properties of the sintered specimens such as permeability or power losses. It appears that homogeneity is proportional to the reaction progress during prefiring, as it affects the concentration of the reaction interfaces. It is further proportional to the densification during final firing by depressing the pore growth that is generated by reactive sintering. Finally, the homogeneity is proportional to the magnetic quality of the sintered specimens. The mechanism through which the raw materials mixture homogeneity influences the final magnetic properties is also discussed.