Abstract
Ferrites with a typical AB2O4 structure are excellent soft magnetic material precursors. One progress for preparation of manganese ferrite is to use the minerals as raw materials. However, the inclusive impurities, such as Ca and Si, may dope in the AB2O4 structure and have an adverse effect on the magnetism of ferrites. In this work, the effects of CaO and SiO2 on the crystalline structure transformation, interfacial elements distribution, and magnetism change of the MnO2-Fe2O3-CaO-SiO2 system for preparation of high-performance ferrite materials were systematically investigated. It's found that Ca ions can readily be doped in the sit A of spinel-type structure to form CaaMnbFe2O4, and the magnetism of manganese ferrite was observably declined due to the Ca doping. A diffusion couple of synthetic CaaMnbFe2O4 and SiO2 was designed to determine the Ca migration. Results demonstrated that regulation of Ca out of sit A from the spinel-type structure can be successfully realized via adjusting the CaO/(CaO + SiO2) mass ratio below 0.55, and the magnetism of ferrite after Ca migration was obviously enhanced. The migrated CaO combined with SiO2 to form calcium silicate which was distributed at the boundaries of ferrite particles. Eventually, the verification test of low-grade manganese ores with CaO and SiO2 impurities was conducted to validate the Ca migration effect.
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