The effect of heating rate on the microstructure and properties of high magnetic permeability MnZn-ferrites

In this paper the effect of the heating rate, during the final firing step, on the microstructure and initial magnetic permeability of high permeability MnZn-ferrites is reported. Increased heating rates result in higher density, coarser microstructure and higher magnetic permeability, independent of the particularly chosen process conditions such as prefiring temperature or compaction pressure. As also found, increased heating rates retard densification and grain growth, thus sintering, during the heating stage. This has the consequence that more powder sintering activity is being preserved within the microstructure of the compact. Subsequently, during the dwell time at the top temperature, densification and grain growth take place at higher rates resulting finally to increased density, coarser microstructure and higher magnetic permeability. The results indicate that shortening of the duration of the firing curves in high permeability MnZn-ferrites, without deteriorating the magnetic properties is possible through the heating rate.