Study On The Insulating Coating Treatment Of Iron Powder And The Magnetoelectric Properties After Molding

In recent years,soft magnetic composites have been widely used in communication engineering,electronic information,automobile industry and other fields due to their good comprehensive performance.In the process of preparation and design of soft magnetic composites,the matrix particles were uniformly coated with a material with high electrical resistivity,and the final products are obtained after molding and stress relief annealing heat treatment.Excellent magnetic properties,low core loss and low internal stress are the research emphases of soft magnetic composites.In this paper,iron/sodium silicate/ferric oxide soft magnetic composites were prepared by mechanical ball milling.Subsequently,four kinds of iron phosphide powder were prepared by optimizing the composition of phosphating solution in the phosphating process.The obtained soft magnetic composite materials were characterized and analyzed by XRD,SEM,EDX,etc.,and their magnetic properties and core loss were tested using soft magnetic DC test device and silicon steel material measuring instrument.At last,the curve fitting analysis of the loss results was carried out.The following conclusions were drawn:1.Sodium silicate water glass with similar coefficient of thermal expansion to iron and magnetic nano-iron tetroxide are used as double-layer insulating materials.The prepared Fe/Na2SiO3/Fe3O4 soft magnetic composites combines the advantages of the two coating components in strength,magnetism,electrical resistivity,etc.Firstly,during the preparation process,the presence of sodium silicate water glass can increase the surface electrical resistivity of iron powder,reduce the core loss,and at the same time act as a binder.Adding sodium silicate water glass can obviously improve the agglomeration of Fe3O4 on the surface of iron powder during ball milling,and the interface between particles after pressing is more smooth.Secondly,in the double insulation layer,the sodium silicate water glass layer can hinder the redox reaction of Fe and Fe3O4 at high temperature,and can retain the excellent magnetic properties and high electrical resistivity of the material after annealing.2.The optimized passivation solution has better thermal stability than the soft magnetic composite insulating layer prepared by phosphoric acid passivation solution.Firstly,the coated iron powder prepared by H3PO4+Mn(NO3)2 passivation solution containing Mn2+ has high resistivity and the lowest core loss after annealing at 500?.However,the Mn-P insulation layer on the surface of iron powder is relatively thick,so the magnetic properties of soft magnetic composites decrease obviously.Secondly,the soft magnetic composite prepared by H3POa+Na2MoO4 passivation solution can form a magnetic ferrous molybdate insulating layer on the surface of iron powder particles.Compared with the sample prepared by H3PO4 passivation solution,the soft magnetic composite prepared by H3PO4+Na2MoOa passivation solution has high resistivity and good thermal stability.Compared with H3POa+Mn(NO3)2 passivation solution,the magnetic properties of coated iron powder increased obviously,but the resistivity decreased.Thirdly,the iron-based soft magnetic composite prepared by H3POa+Na2MoO4+Mn(NO3)2 passivating solution combines the advantages of two kinds of additive ions,forming a magnetic molybdate in the coating layer on the surface of the iron powder,which has excellent resistivity and magnetic properties.3.The eddy current loss coefficient a and hysteresis loss coefficient b are obtained by fitting the core loss of insulating coated iron powder,and the critical frequency when the eddy current loss is equal to the hysteresis loss is calculated.Firstly,as the annealing temperature increases,the resistivity of soft magnetic composites decreases and the eddy current loss coefficient increases.The hysteresis loss coefficient does not always decrease with the increase of annealing temperature.During annealing,the thermal residual stress caused by the large difference in thermal expansion coefficient between coated material and iron powder particles will lead to the increase of hysteresis loss coefficient.2.When the insulation layer fails,the critical frequency of the iron-based soft magnetic composite prepared in this paper is 245Hz?462Hz when the hysteresis loss is equal to the eddy current loss,which means that the hysteresis loss still occupies a high proportion below 500Hz.