Investigation Of Insulation Coating Process Of Reduced Iron Powders And Soft Magnetic Properties Of Iron Powder Cores

The iron powder cores have good soft magnetic properties,widely used in electric motors,transformers,filters and other electronic power and communication fields.At present,electronic components are gradually developing towards high-frequency and energy-saving applications,which requires higher soft magnetic properties of iron powder cores,but due to the low resistivity of iron powders leads to a large soft magnetic loss of iron powder cores at middle and high frequency,which limits its application range.In order to develop iron powder cores with low cost and excellent soft magnetic properties,this paper selects high purity reduced iron powders as matrix powders and reduces soft magnetic loss of iron powder cores through discussing the insulation coating process of reduced iron powders.Firstly,the reaction mechanism of iron powders in Na H₂PO₄phosphating solution and the effect of oxidation accelerator on Na H₂PO₄phosphating and iron powder cores’structure and properties were investigated.Meanwhile,the structure and properties of iron powder cores coated by H₃PO₄and Zn（H₂PO₄）₂ phosphating processes were characterized,and the effect of different phosphating processes and heat treatment temperature on the soft magnetic properties of iron powder cores was investigated.On this basis,this paper designed the phosphate/silane composite insulation coating process,and explored the influence of process parameters such as alcohol/water ratio,silane content and heat treatment temperature on the structure and properties of phosphate/silane composite insulation coated iron powder cores.The obtain results are as follows:（1）Reduced iron powders in a single Na H₂PO₄ phosphating solution cann’t generate uniform and complete phosphate coating,through Na H₂PO₄ phosphating solution adding Na₂Mo O₄+Na NO₂ composite oxidation accelerator can promote the deposition of phosphate on the surface of iron powders,improve the phosphating reaction,the coating structure is composed of Fe PO₄ and Fe₂（Mo O₄）₃.When the mass concentration of Na H₂PO₄ in phosphating solution is 5wt.%,the uniformity and integrity of phosphate layer on the surface of iron powders are the best,the prepared iron powder cores have high density of 7.15 g/cm³,high resistivity of 194.2μΩ·m at 400℃;and high permeability of 92.5 and low soft magnetic loss of 142.0 W/kg at B_m=50 m T,f=100 k Hz.（2）H₃PO₄ and Zn（H₂PO₄）₂ phosphating processes can produce uniform and complete phosphate coating on the surface of iron powders.H₃PO₄ iron phosphide powders’coating is composed of Fe₃（PO₄）₂and Fe PO₄,and Zn（H₂PO₄）₂ iron phosphide powders’coating is composed of Zn₂Fe（PO₄）₂·4H₂O,Zn₃（PO₄）₂·2H₂O,Fe PO₄ and a small amount of Fe₂（Mo O₄）₃.The permeability and magnetic loss of iron powder cores prepared from H₃PO₄ and Zn（H₂PO₄）₂ iron phosphide powders at 450℃are 72.5 and 99.5,respectively,and 119.8 W/kg and 122.3 W/kg,respectively.The iron powder cores prepared by Na H₂PO₄ phosphating process with Na₂Mo O₄+Na NO₂ composite oxidation accelerator have a higher density of 7.26 g/cm³ and permeability of 108.3 after heat treatment at 450℃,the magnetic loss of 120.7 W/kg at B_m=50 m T,f=100 k Hz.（3）The silane film with composite network structure was prepared by the condensation of tetraethyl orthosilicate（TEOS）andγ-aminopropyl triethoxysilane（APTES）on the surface of iron phosphide powders.When V（C₂H₅OH）:V（H₂O）=2:1,the amount of silane is 5wt.%,and heat treatment temperature is 500℃,the phosphat/silane composite insulation coated iron powder cores have the best magnetic performance,with high density of 7.05 g/cm³ and relatively low hysteresis losses and eddy current losses.When B_m=50 m T and f=100 k Hz,the total soft magnetic loss of iron powder cores is 106.1W/kg,compared with the magnetic loss of iron powder cores prepared by iron phosphide powders after heat treatment at450℃is reduced by 13.2%.Based on the above results,the iron powder cores prepared by insulating the reduced iron powders with phosphate and silane coating has high permeability and low magnetic loss in this paper,which is of great significance to expand the application of iron powder cores at middle and high frequency.Compared with water atomized iron powders and carbonyl iron powders,the iron powder cores prepared reduced iron powders have lower cost,and have high application value in electric motor,energy storage inductor,filter and other electronic components.