【作者】 王波；

【导师】 孙科；

【作者基本信息】 电子科技大学 ， 材料科学与工程， 2015， 硕士

【摘要】 各种小型轻量化、高可靠性的电子设备急需小型高效、高可靠性开关电源模块,而MnZn功率铁氧体磁心作为开关电源的“心脏”,完成功率的转换与传输,是开关电源体积和重量的主要占有者。磁心材料应具有较高起始磁导率μi、高饱和磁感应强度Bs和高温低损耗Pcv等特征。在当今的电路系统中,大部分电子器件在交变信号下正常工作的同时还需承载一定的直流信号。而应用于电路系统中的MnZn铁氧体磁心则是交直流信号的主要承载者,其对叠加直流的承载能力直接影响电源系统的效率及可靠性。基于课题组已有研究基础,本论文主要研究了主配方、添加剂及制备工艺对材料磁性能温度特性及直流叠加特性的影响。在主配方研究方面,对于分子式为Mn0.867-xZn0.133Fe2+xO4的铁氧体材料,适当的Fe2+离子取代量x有助于获得合适的起始磁导率(μi)二峰位置及损耗(Pcv)谷点温度,同时有助于直流叠加特性的提高。对于分子式为Mn0.9-xZnx Fe2.1O4的铁氧体材料,适当的Zn2+离子取代量x可以增大分子磁矩,有助于提高起始磁导率,并获得较优的直流叠加特性。在添加剂研究方面,Co2+离子对磁晶各向异性常数有正的贡献,从而使起始磁导率二峰及损耗谷点温度移向低温,在0~0.25wt%的范围内,随着Co2O3含量的增加,材料的ΔB(Bs-Br)增大,增量磁导率及磁心损耗的直流叠加特性均变好;Ni2+离子的加入会导致Fe2+离子浓度减小,从而使起始磁导率二峰及损耗谷点温度移向高温,同时会使Bs及ΔB先增大后减小,当添加量为0.02wt%时,材料磁导率及损耗的直流叠加特性达到最优;在0~0.06wt%的范围内,V2O5的添加会使磁导率二峰及损耗谷点温度移向低温,材料的烧结密度和Bs都先增大后减小,磁导率及损耗的直流叠加特性均先变好,当添加量超过0.02wt%后则变化不大,与ΔB的变化相一致;适量加入CaCO3可以细化晶粒,得到较为均匀致密的结构,提高磁导率μi和并降低损耗Pcv,并获得良好的直流叠加特性。在100kHz,200mT的测试条件下,随着叠加场的增大,各样品的动态磁滞回线都会发生明显的变化,剩磁Br和矫顽力Hc先缓慢减小后增大,而磁场强度的最大值Hm则迅速增大,磁滞回线的面积先略有减小后增大,并且有向横轴倾斜的趋势,由此引起了磁滞损耗先减小后增大,这是磁心总损耗变化的主要原因。当NiO、Co2O3、V2O5、CaCO3添加量分别为0.02 wt%、0.09 wt%、0.02 wt%、0.05 wt%时,可以获得最优的性能。制备工艺对材料的微结构及性能同样有着重要的影响,在870~930℃的范围内,提高预烧温度会导致粉体活性降低,使材料的饱和磁感应强度Bs和烧结体密度d1先增大后减小,较为适宜的预烧温度为910℃。在1280~1340℃的范围内,提高烧结温度会导致晶粒尺寸长大,μi先增大后减小,Pcv先减小后增大,较为适宜的烧结温度为1300℃,此时材料具有最好的显微结构和磁性能。更多还原

【Abstract】 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.更多还原