Preparation And Study On Magnetic Properties Of Fe-based Soft Magnetic Composites By Inorganic Insulation Coating

As a new type of soft magnetic material,soft magnetic composites have high permeability,good frequency characteristics and DC-bias performance,and they are widely used in inductors,transformers etc.However,with the development of electronic information technology,soft magnetic composites face serious magnetic loss problem at high frequency.In order to reduce the high frequency magnetic loss of soft magnetic composites.In this paper,Fe/SiO₂、Fe/Mg O and Fe/Al₂O₃composite powders were prepared by chemical precipitation coating technology using Fe powder as magnetic matrix,and three kinds of soft magnetic composites were obtained by pressing and heat treatment.The microstructure and properties of three composite powders and soft magnetic composites were investigated.On this basis,Fe Ni Si/SiO₂composite powders and soft magnetic composites were prepared by optimized process using Fe Ni Si alloy powder with higher resistivity as matrix,and the microstructure and properties of composite powders and soft magnetic composites were investigated.Finally,in order to further improve the soft magnetic properties of Fe Ni Si/SiO₂soft magnetic composites,a layer of magnetic（Ni Zn）Fe₂O₄ was coated on the SiO₂insulating layer,thereby Fe Ni Si/SiO₂/（Ni Zn）Fe₂O₄composite powders and soft magnetic composites were prepared with double insulating layers structure,and the related microstructure and properties were investigated.The results are as follows:（1）The surface of Fe powder was successfully coated with SiO₂,Mg O and Al₂O₃ respectively,and found the SiO₂ insulating layer was more uniform and denser,and the composite powder had high resistivity,good corrosion resistance and excellent soft magnetic properties.It was found that the effective permeability₀)of Fe/SiO₂ soft magnetic composites is48,the DC-bias performance（1 MHz/100 Oe）is 76%,the quality factor Q is 41,the maximum permeability₈)is 68,and the magnetic loss（50m T/100 k Hz）is 82.0 W/kg.（2）The first-principles calculations showed that the Fe-O and Fe-Si covalent bonds stabilize the Fe/SiO₂ interface in the Fe/SiO₂ system,and the interface adhesion energy(2₍(6（9） is about 1.18 J/m².Meanwhile,the covalent bonds of Fe-O and Fe-Si can effectively bind conduction electrons,improve surface resistivity,and play an important role in reducing the magnetic loss of Fe/SiO₂ soft magnetic composites.（3）When the coating amount of SiO₂ is 4.0 wt.%,the Fe Ni Si/SiO₂composite powders had a relatively complete insulating layer.With the continuous increase of SiO₂ coating amount,the magnetic permeability of the Fe Ni Si/SiO₂soft magnetic composites decreased,and the magnetic loss increased.When the SiO₂ coating amount is 4.0 wt.%,the pressing pressure is 1500 MPa,and the heat treatment temperature is 400℃,the prepared Fe Ni Si/SiO₂ soft magnetic composites had the best comprehensive magnetic properties:the effective permeability₀)is 37,the DC-bias performance（1 MHz/100 Oe）is 91%,the quality factor Q is 83,the maximum permeability₈)is 48,and the magnetic loss（50 m T/100k Hz）is 46.5 W/kg.（4）The magnetic（Ni Zn）Fe₂O₄ coating improved the soft magnetic properties of Fe Ni Si/SiO₂ soft magnetic composites.When the（Ni Zn）Fe₂O₄ coating amount is 1.5 wt.%and the heat treatment temperature is 400℃,the prepared Fe Ni Si/SiO₂/（Ni Zn）Fe₂O₄ soft magnetic composites had the best comprehensive magnetic properties:the effective permeability₀)is 46,the DC-bias performance（1 MHz/100 Oe）is 87%,the quality factor Q is 96,the maximum permeability₈)is 60,and the magnetic loss（50 m T/100 k Hz）is 35.4 W/kg.