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Most of electronic devices are required to operate normally at complex conditions,high temperature for example, and their stable working temperature ishigh（100℃120℃）, meanwhile, most of electronic devices start with large pulsecurrent, under this circumstance, the higher of saturation magnetic induction （Bs） offerrite, the stronger of anti-saturation ability, and the smaller of inductancedisaccommodation（if the inductance disaccommodation is large, the electronic devicescan not work normally）. So the ferrites with high Bsat high temperature are widelyused in starting system of cars or other big electronic devices. In this dissertation, thefour oxide compositions power ferrites with ultrahigh Bsat high temperarture wereprepared by conventional oxide ceramic process. The effects of main compositions,additives, preparing processes on the microstructure, phase and magnetic properties ofthe power ferrite were studied. The results indicate that:In the aspect of main composition studying: the Fe2O3of Baosteel IV is moresuitable for the main compositions. As to the four compositions power ferrites whoseinitial permeability（μi） is1500±25%, the losses(Pcv) are lower than1350kW/m3within wide temperature ranging from25℃to120℃, and the Bsreaches580mT,490mT,460mT at room temperature,100℃,120℃respectively, the optimum molarratio of four compositions is Fe2O3: MnO: ZnO: NiO=60:24:11:5（mol%）. Thestudy of MnO substituted by NiO and Li2O respectively shows that both the Ni2+ionsand Li+ions can make the Fe3+ions shift from B to A site, resulting in the increase ofthe number of Fe3+-O-Fe3+pairs, which leads to an increase in the A-B interaction, andthe Curie temperature increases, meanwhile, with the increasing amount of the NiOand Li2O sbustitution, the secondary maximum peak of μi～T curve moves to highertemperature, when the amount of the NiO and Li2O is1mol%, both of the specimenshave largest μi, and the lowest Pcv, residual magnetic induction intensity（Br） andcoercivity（Hc）. In the aspect of additives doping studying: the Bi2O3can promote the solid-statereaction, resulting in the growth of grains, when the doped amount is more than0.05wt%, the grains become abnormal, the porosity increases, resulting in the decreaseand increase of μiand Pcvrespectively, the Bsof the samples increases first anddecreases subsequently with increasing Bi2O3amount. The Sn4+ions can decrease thedistribution of cation cacancy, leading to the growth of the grains of ferrite, thedenstity increases apparently after the SnO2doping. The grains grow with theincreasing doping amount of Nb2O5, when the amount reaches0.05wt%, the sampleshave the largest μiand the lowest Pcvand Brat room temperature, the Pcvdecreasemore than800kW/m3and the Bsincreases after the Nb2O5doping. Part of Fe3+willreduce to Fe2+after doping certain amount of Ta2O5, which results in the increase ofthe cation vacancy flux, and the mobility of grain boundaries increases, the grainsgrow. Contrary to the Pcv, μiincreases first and decreases subsequently with increasingTa2O5amount, when the amount reaches0.025wt%, the ferrite presents the besttemperature property of Bs.In the aspect of preparation process studying: the particle size of the secondmilled powder decreases with the increasing scond-milling time, making the powdermore active which accelerates the velocity of the solid-phase reaction, the grains growwith the increasing scond-milling time. When second milled for3h, the ferrite takes ongood magnetic properties and microstructure. The particle size and the activity ofpower increases and decreases respectively with the increasing calcining temperatureduring the solid-phase reaction, causing the decrease of velocity of the solid-phasereaction during sintering which decreases the grain size of the ferrite. When thesintering temperature reaches1350℃, the grains of the ferrite are uniform and are intheir integrity, the porosity decreases, the μiand Bsreaches the largest while the Pcvisthe lowest. Sintering in twice deoxidizing atmosphere can promote the solid-statereaction, making the grain tend to be intact, the the porosity decreases, themicrostructure of the ferrite is uniform, the μiand Bsincreases while the Pcvdecreases.Finally, the ferrite whose Bsreaches578mT,495mT and469mT at roomtemperature,100℃,120℃respectively has been prepared, and the goal of preparingfor the power ferrites with ultrahigh Bsat high temperarture has been achieved,meanwhile the losses are not high at temperature ranging from25℃to120℃.
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