High-frequency Low-power Aerosol FeSiAl Magnetic Powder Core Insulation Coating Process And Formulation Development

As key materials for power conversion and information transmission,soft magnetic composite materials have comprehensive advantages of zero magnetostrictive coefficient,high saturation magnetization and relatively low core loss,which have been widely used in magnetic coils,inductors,sensors,electromagnetic interference filters and other electronic communication equipment.Nowadays,there is a growing demand for soft magnetic materials in the field of electronics and power.But the high core loss（especially eddy current loss）caused by the excessive thickness and discontinuity of the coating seriously limits their application in high frequency.In order to solve this problem,a new type of magnetic powder core with multi-coating structure was prepared by phosphoric acid,sodium silicate and resin.In addition,another low loss magnetic powder core was prepared by in situ coating of molybdenum oxide.The results are as follows:（1）Using phosphoric acid,sodium silicate and resin to prepare a new magnetic core with multi-coating structure.Phosphate insulating layer can be formed on the surface of FeSiAl powder through phosphoric acid.Sodium silicate coating layer is prepared on the basis of phosphate coating layer.After the two layers of coating layer,silicone resin is added as the final insulation layer.SEM and XPS curves were used to characterize the surface morphology of the coated magnetic powder,the internal chemical composition was analyzed and the change of magnetic properties after high temperature annealing process was investigated in detail.The results show that the total loss(P_cv)of the core with 3 wt.%phosphoric acid is the lowest at 100 kHz and 50 mT,the total loss(P_cv)is 53.45 mW/cm³ at 50 kHz and 50 mT,and the average effective permeability（μ_e）is the highest at 50.91.（2）Molybdenum oxide in situ coating process is used to prepare low-loss magnetic powder core.Ammonium molybdate is decomposed once to form molybdenum oxide,and then bonded and pressed into shape.Finally,after secondary heat treatment,molybdenum oxide is fused in situ and uniformly coated on the surface of magnetic powder core.Coating MoO₃ on FeSiAl powder can effectively inhibit the core loss of soft magnetic composites.At 50 mT/100 kHz,400℃,and 700℃,FeSiAl/MoO₃ core containing 15 wt.%ammonium molybdate has the lowest core loss(P_cv)of 128.8 mW/cm³,which is lower than most of the literature on soft magnetic composites.The results of loss separation show that the eddy current loss is less than 1/3 of the hysteresis loss,which confirms that a complete insulation layer is formed on the surface of FeSiAl particles.（3）Based on the in-situ coating process of low-loss magnetic powder core molybdenum oxide,in order to improve the effective permeability of soft magnetic composite,the effective permeability of soft magnetic composite was adjusted and the performance of magnetic core was improved by changing the amount of ammonium molybdate and the particle size of magnetic powder.The results showed that by adjusting the dosage of ammonium molybdate,2 wt.%ammonium molybdate was completely coated on the FeSiAl particles,and the excellent permeability（μ_e=61.5）,the lowest coercivity（H_c=3.3A/m）and the lowest core loss(P_cv=60.9 mW/cm3)were obtained at 1800 MPa.