The Development Of The High Temperature And Ultra-high B_smnzn Power Ferrite

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 （B_s） 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 B_sat high temperature are widelyused in starting system of cars or other big electronic devices. In this dissertation, thefour oxide compositions power ferrites with ultrahigh B_sat 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（μ_i） is1500±25%, the losses(P_cv) are lower than1350kW/m³within wide temperature ranging from25℃to120℃, and the B_sreaches580mT,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 μ_i～T curve moves to highertemperature, when the amount of the NiO and Li₂O is1mol%, both of the specimenshave largest μ_i, and the lowest P_cv, residual magnetic induction intensity（B_r） andcoercivity（H_c）. 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 μ_iand P_cvrespectively, the B_sof 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 μ_iand the lowest P_cvand B_rat room temperature, the P_cvdecreasemore than800kW/m³and the B_sincreases 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 P_cv, μ_iincreases first and decreases subsequently with increasingTa₂O₅amount, when the amount reaches0.025wt%, the ferrite presents the besttemperature property of B_s.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 μ_iand B_sreaches the largest while the P_cvisthe 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 μ_iand B_sincreases while the P_cvdecreases.Finally, the ferrite whose B_sreaches578mT,495mT and469mT at roomtemperature,100℃,120℃respectively has been prepared, and the goal of preparingfor the power ferrites with ultrahigh B_sat high temperarture has been achieved,meanwhile the losses are not high at temperature ranging from25℃to120℃.