| The electronic devices of small lightweight and high reliability are badly in need of miniaturized switching power supply modules with high efficiency and reliability. As the cores of the switching power supplies, Mn Zn power ferrite cores are the major component of the volume and weight, play the role of power transmission and transformation, and must have high initial permeability(μi), high saturation induction density(Bs) and low core loss(Pcv) under high temperature. In the circuit system currently, most electronic devices work properly under alternating signal, at the same time need to carry a certain DC signal. The Mn Zn ferrite cores which applied to the circuit system are the main carrier of AC/DC signal, the carrying capacity of DC superposition characteristics directly affect the efficiency and reliability of the power system. Based on the existing researches, the influences of compositions, addtives, and processes on the temperature dependence of magnetic properties and DC superposition characteristics were studied.In the study of main formula, for the composition of Mn0.867-x Zn0.133Fe2+x O4, the appropriate concentration of Fe2+ ions can help to obtain the appropriate secondary maximum peak temperature of permeability μi and the point of the minimum Pcv, and can also help to improve the DC superposition characteristic. For the composition of Mn0.9-x Znx Fe2.1O4, the appropriate Zn2+ ions concentration can help to improve the initial permeability and obtain more excellent DC superposition characteristics.In the study of additives, Co2+ ions have a positive contribution to the magnetocrystalline anisotropy constant, make the second peak of permeability and valley point of temperature move to low temperature. With the increase of Co2O3 from 0 wt% to 0.25wt%, the ΔB(Bs-Br) increase and the DC superposition characteristics of μΔ and Pcv are improved. The additive of Ni O can lead to a decrease of Fe2+ ions concentration, make the second peak of permeability and valley point of temperature move to high temperature, the ΔB increases first and then decreases, the DC superposition characteristics obtain the optimal when the appropriate amount is 0.02wt%. With the increase of V2O5 from 0wt% to 0.25wt%, the sintering density(d1) and Bs increases first and then decreases, the DC superposition characteristics are improved at first, but have not obvious change when the adding amount is over 0.02wt%, consistent with the changes of ΔB. Proper amount of Ca CO3 additive can promote grain growth, improve the initial permeability, decrease Pcv, and obtain high DC superposition characteristic. In the test condition at 100 k Hz,200 m T. With the increase of DC bias field, the dynamic hysteresis loops of all the samples have obvious change, the Br and Hc decrease slightly and then increase, while Hm is rapidly increasing. The hysteresis loop area decreases first and then increases, and has a tendency to tilt to the horizontal axis, the hysteresis loss decreases first and then increases, which is the main reason for the core total loss changes. The proper adding contents for Ni O, Co2O3, V2O5 and Ca CO3 were 0.02wt%, 0.09wt%, 0.02wt% and 0.05wt%, respectively.The preparation processes also have an important influence on the microstructure and properties of the material. In the range of 870~930℃, with the increase of calcination temperature, the density(d1), Bs, and μi increase first and then decrease. The Pcv reduces at first and then increases. The best microstructure and magnetic properties can be obtained at the suitable calcination temperature of 910℃. In the range of 1280~1340℃, the increase of sintering temperature will lead to a larger grain size. μi increases first and then decreases, which shows the opposite variation trends in the Pcv. Finally, when the sintering temperature is 1300 ℃, the sample have the best microstructure and magnetic properties. |
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