Effects of Sulfates on the Properties of Strontium Ferrite Magnets

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Abstract
Up to 6.0 wt % SrSO4, CaSO4, and BaSO4 were added to strontium ferrite magnets consisting of the magnetoplumbite phase SrO·6 Fe2O3. The hysteresis loop, density, saturation moment per gram, and the degree of orientation were measured. The magnets were analyzed by standard chemical methods and by x‐ray diffraction techniques. The microstructures of the magnets were examined with a light microscope and with an electron‐beam microanalyzer. It was found that approximately 0.1 to 2.0 wt % SrSO4, CaSO4, or BaSO4 are extremely beneficial in activating the ferrite magnet formation and in improving the magnet properties. SrSO4 is particularly effective. With only 0.22 wt % SrSO4 and at a sintering temperature of 2250°F, the remanence is increased from 3425 to 4150 G, the saturation moment from 65.2 to 69.1 G·cm3/g, the density from 4.21 to 4.86 g/cm3, and the degree of orientation from 81% to 87%. X‐ray scanning micrographs show that the solubility of SrSO4 in SrO·6 Fe2O3 is greater than 0.22 and less than 1.1 wt % at 2250°F.

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