Preparation And Properties Of Fe-Si/Fe₃O₄ Soft Magnetic Composites With Core-shell Structure

Soft magnetic materials are one of the key materials in electronic devices.With the development of miniaturization,high-frequency and high-power of modern electronic technology,magnetic components meet the needs of its development.Therefore,soft magnetic materials with high saturation magnetization,high permeability and low magnetic loss are required,so the development of high performance soft magnetic composite materials(SMCs)has been widely concerned.At present,the soft magnetic composites have two shortcomings:low magnetic properties and high loss.In this paper,ferrous magnetic insulating layer with high resistivity is formed on the surface of Fe-Si powder by in-situ reaction method,the soft magnetic composite with core-shell structure was prepared.The effects of reaction conditions and technological parameters on the microstructure of the coating and the properties of the magnetic powder core were studied.The Fe-Si/Fe₃O₄composite particles with core-shell structure were synthesized by in-situ reaction method,and magnetic powder cores with excellent comprehensive magnetic properties were prepared.The Fe-Si is reacted in situ in KNO₃solution,and the microstructure of the shell layer is controlled by controlling the concentration of KNO_3.And then the magnetic properties of the magnetic powder core are adjusted.The growth process and the growth process of the coating layer under different potassium nitrate concentrations are discussed.The law of influence on magnetic properties.When the potassium nitrate concentration is 0.1 mol/L and the reaction time is 1 h,the magnetic powder core has the best comprehensive soft magnetic properties,and its permeability and saturation magnetization are 34 and 175.3 emu/g,respectively.The core loss is only 13.6 w/kg under the condition of at 20 m T and 150k Hz.Adding the surfactant PEG during the in-situ reaction makes the coating layer more uniform and dense,achieving better coating effect and reducing magnetic loss.Based on the previous study of the in-situ reaction process,the influence of process parameters such as molding pressure and heat treatment temperature on the microstructure and magnetic properties of soft magnetic composites was systematically studied.The increase of the molding pressure makes the magnetic permeability and magnetic loss of the magnetic powder core show a change law of first rising and then falling and first falling and then rising.When the molding pressure up to 1200 MPa,the magnetic powder core has a higher density and better comprehensive magnetic properties.Low molding pressure will result in lower magnetic powder core density and poor magnetic properties.Excessive molding pressure will damage the coating layer and greatly increase the internal stress.A suitable molding pressure will help optimize the magnetic powder.The magnetic powder core needs to be heat treated to reduce or eliminate the internal stress after compression molding,and lower heat treatment temperature is difficult to eliminate the internal stress in the magnetic powder core,and if the heat treatment temperature is too high,the Fe₃O₄coating layer will decompose and produce non-magnetic.The impurity phase deteriorates the performance of the magnetic powder core.When the heat treatment temperature is 500°C,the overall magnetic performance of the magnetic powder core is the best.A suitable annealing temperature is beneficial to the removal of internal stress and improves the performance of the magnetic powder core.