Properties Of The Fesial Magnetic Powder And Powder Cores Coated With MnZn Powder

FeSiAl magnetic powder core is widely used in switching power supply transformer core, filter circuit, pulse flyback transformer,energy storage filter inductors, power factor corrector device, etc, because of its high saturation magnetic induction intensity and low cost. But FeSiAl magnetic powder core cannot be used in the high frequency field because it has higher high-frequency loss.Ferrites/FeSiAl composite magnetic powder and its magnetic powder core (CMC) are prepared in this paper, MnZn ferrites used as coating layer, so as to reduce the high-frequency loss and obtain high permeability.In this paper, ferrites/FeSiAl CMC were prepared by chemical co-precipitation method, hydrothermal method and milled mixing method, the effect of coating conditions on the properties of composite powder and its powder core are discussed. The influence of the weight ratio of MnZn ferrite/FeSiAl, co-precipitation reaction temperature, pH, the hydrothermal temperature and time, the milling time and annealing temperature were all studied. The crystal structures of the powders were analyzed by X-ray diffractometer and the saturation magnetization was measured by vibrating samples magnetometer, the power loss of the powder cores was measured by dynamic magnetic hysteresis loop apparatus, the inductance is measured by the precision magnetic element analyzer and then the permeability is calculated. The results showed that:(1) The ferrites/FeSiAl CMC were prepared by chemical co-precipitation method. The saturation magnetization of the powders coated by MnZn ferrite with the weight ratio 6% is 76.4 A·m2/kg, lower than original powder(114.6 A·m2/kg). As the weight ratio of MnZn ferrite/FeSiAl increased, the power loss and the permeability would be decreased. When the weight ratio was 6%, the power loss reached 46.9W/kg under the condition of 100 kHz and magnetic induction of 300 mT, and the permeability of the composite magnetic cores was lowered from 102.0(original powder) to 78.4 under the condition of 100kHz. When the weight ratio continued to increase, the permeability would further decreased, but the power loss would not change obviously.(2) Given a 6% weight ratio of MnZn ferrite/FeSiAl, when the chemical co-precipitation reaction temperature increased from 30℃ to 70℃, the magnetization and the permeability would both increase, and reach its Max 76.8 A·m2/kg and 70.4 respectively at 70℃, but both of them would be descreased when the reaction temperature was higher than 70℃. The power loss decreased at first and then remain unchanged as the increased of the reaction temperature, and reached its minimum 48.2 W/kg at 60℃.(3) The ferrites/FeSiAl CMC were prepared by hydrothermal method. When weight ratio of MnZn ferrite/FeSiAl was 6%, and the pH increased from 7 to 12, the permeability would increase first and then decrease, and reach its maximum 68.9 at pH=10. When the pH was between 9 and 11, the magnetization would reach 67.8 A-m2/kg and the powder loss reach its minimum 62.0W/kg.(4) The effects of hydrothermal temperature on the magnetic properties of the SMC were studied. When pH=10, and the temperature increased from 120℃～220℃, the change of the saturation magnetization was not obvious, but the power loss would decrease and reach its minimum 56.2 W/kg at 220℃. Meanwhile, the permeability would rise at first but decrease later, and reach its Max 73.0 at 180℃～220℃.(5)The effects of reaction time on the magnetic properties of the SMC were studied. When keeping pH=10 and the hydrothermal temperature 180℃, as the reaction time increased, the saturation magnetization and the permeability would increase. When the reaction time was 7h, the power loss would decrease and reach its minimum 57.0W/kg. And the saturation magnetization was 78.5A-m2/kg and the permeability was 75.4. However, both of them would change little when the reaction time longer than 7h.(6) The ferrites/FeSiAl SMC were prepared by milled mixing method. The effects of the weight ratio of ferrite/FeSiAl and the milling time on the properties of the magnetic powder core were studied. As the milling time increased from 10h to 30h, the power loss of the ferrites/FeSiAl with weight ratios of 2%,4%,6% respectively would all decrease. When the weight ratio was 6%, the power loss would reached 53.8W/kg.(7) The effects of annealing temperatureon on the magnetic properties of the ferrites/FeSiAl SMC were studied. As the annealing temperature increased from 600℃ to 720℃, the permeability would rise at first but decrease later, while the power loss decreased at first but rised later. The power loss would reach its minimum and the permeability reach its Max when annealled at 690℃.