Study On Insulation Coating Process And Electromagnetic Properties Of FeNiMo Soft Magnetic Particle Core

The metal soft magnetic material FeNiMo has the advantages of high permeability,high saturation magnetization,low coercivity and low residual magnetization.It has been widely used in electronic power,communication,radar and other fields.The low resistivity of metal soft magnetic materials will produce large eddy current loss in the application process,resulting in serious heating of powder core,which is not conducive to high-frequency application.In this paper,FeNiMo/SiO₂ magnetic powder core was prepared by sol-gel method.The high-temperature pretreatment process,SiO₂ insulation coating and forming process were adjusted respectively to reveal their effects on the structure and properties of magnetic powder core.(1)The FeNiMo raw powder was pretreated by high temperature pretreatment process in H₂/Ar mixed gas,and the effect of pretreatment temperature on its soft magnetic properties was revealed.It is confirmed that reducing atmosphere high temperature treatment can effectively remove metal oxides on the surface of the material,increase the content of simple matter,and significantly improve the effective permeability of fenimo raw powder.On this basis,the pretreated FeNiMo powder was further coated with SiO₂ insulation,and the change process of magnetic properties of soft magnetic powder core at different annealing temperatures was explored.The obtained FeNiMo/SiO₂ soft magnetic powder core is coated evenly.After annealing at a temperature below 600?,it has a very stable effective permeability in the frequency range of 10 k Hz-1 MHz.The soft magnetic powder core annealed at 600?has the highest effective permeability(46.8)and the lowest loss(1087.3k W/m~3,100 m T/100 k Hz).Compared with soft magnetic powder cores such as Fe/Al₂O₃,Fe/Ni Zn ferrite and FeSiCr/SiO₂,the prepared FeNiMo/SiO₂ powder core has higher effective permeability and lower loss than most soft magnetic powder cores through H₂/Ar mixed gas high-temperature pretreatment process and insulation coating process.Therefore,the insulation coating after high temperature pretreatment in reducing atmosphere can greatly improve the soft magnetic properties of soft magnetic powder core.(2)The thickness of SiO₂ coating was controlled by adjusting the amount of tetraethyl orthosilicate(TEOS)and silane coupling agent(APTES).The effects of the addition of TEOS and APTES on the soft magnetic properties of FeNiMo/SiO₂ powder core were studied.With the increase of TEOS content,the thickness of SiO₂ coating increases gradually,and the effective permeability and eddy current loss of powder core decrease.However,too much TEOS will lead to the increase of hysteresis loss.Under different TEOS additions,hysteresis loss plays a major role,and the increase of hysteresis loss increases the total loss.APTES is used as modifier in the reaction,and the change of its addition has little effect on the magnetic properties of the powder core.When 5 ml APTES and 1 ml TEOS are added,the SiO₂ coating is the thinnest.At this time,the FeNiMo/SiO₂ magnetic powder core has higher effective permeability(48.6)and lower total loss of 926.9 k W/m~3(100 m T/100 k Hz).Compared with other SiO₂ coated Fe or FeSiCr powder cores,FeNiMo/SiO₂ in this paper has better soft magnetic properties under the same test conditions.Therefore,the control of SiO₂ insulation coating process based on high temperature pretreatment can significantly improve the soft magnetic properties of powder core.(3)The FeNiMo/SiO₂ soft magnetic material was prepared by sol-gel method.The influence of the amount of release agent and molding pressure on the magnetic properties of FeNiMo/SiO₂ soft magnetic powder core was studied.The influence mechanism of forming process on hysteresis loss and eddy current loss is revealed.The results show that the addition of zinc stearate mainly affects the effective permeability and eddy current loss of the powder core.Increasing the amount of zinc stearate release agent can improve the density and resistivity of the powder core,improve the effective permeability and reduce the eddy current loss.Excessive zinc stearate reduces the density and resistivity of the powder core,reduces the effective permeability and increases the eddy current loss.Increasing the molding pressure increases the sample density and increases the eddy current loss while reducing the hysteresis loss.Through the optimization of molding process,the optimal magnetic properties can be obtained by adding 0.25 wt%zinc stearate and 10 MPa molding pressure.The permeability and total loss are 56.8 and 709.7 k W/m~3(100 m T/100 k Hz)respectively.Compared with other SiO₂ coated powder cores,FeNiMo/SiO₂ powder core has higher effective permeability and lower total loss.Therefore,the molding process regulation based on the insulation coating process can significantly improve the magnetic properties of the powder core.