Power Loss, Permeability And Impedance Characteristics And Preparation Technology Of Manganese Zinc Ferrites

Manganese zinc (MnZn) ferrites are known as the basic materials of modern electronic industry and information industry. According to application characteristics, they can be divided into three types: power ferrites, high permeability ferrites and anti electro magnetic interference (EMI) ferrites. With the rapid development of telecommunication and computer technology, and the demand for more compact, lighter, thinner, and higher frequency electronic devices and equipments is more urgent. And MnZn ferrites are required for better performances in many targets more than for one best characteristic. For this reason, this dissertation presents a deep study on the mechanism and technology of high properties power MnZn ferrites, high permeability MnZn ferrites and high impedance MnZn ferrites with Fe-poor composition in broad band width.Firstly,this dissertation introduced the domestic and overseas research development status of high properties MnZn ferrites and basic ferrimagnetism theory. The molecular magnetic moment and Curie temperature were calculated by using the theory of Neer molecular field of ferrimagnetism theoretically. The relationship of the electromagnetic characteristics with composition and technology parameters was analyzed. The mechanism of MnZn ferrites magnetic characteristics, such as loss and initial permeability was discussed. MnZn ferrites samples were prepared by conventional ceramic processing techniques and the preparation process were studied. The measurement methods of common physic, electric, and magnetic parameters of MnZn ferrites were summarized.Secondly, we studied the mechanism and separation of power loss, DC-bias mechanism and preparation technology of power MnZn ferrites. The hysteresis loss, eddy current loss and residual loss were separated from the total power loss of MnZn ferrites by extrapolating the PL/f^f plots. This separation found that: 1) at 100 kHz, 200 mT, the total power loss is made up of hysteresis loss and eddy current loss, and the residual loss can be ignored; 2) at 500 kHz, 50 mT, the residual loss becomes important, and the total power loss is made up of hysteresis loss, eddy current loss and the residual loss. The power loss composition of JPP-44 material with low loss at middle frequency is very different from that of JPP-5 material with low loss at higher frequency. JPP-44 material with low loss at middle frequency can be prepared by adopting appropriate raw materials, composition, pre-sinter temperature, rate of bowl and powder and milling time of second milling, and sintering technology. The basic differences between JPP-5 material and JPP-44 material lie in that JPP-5 material has more Fe₂O₃, more MnO and less ZnO content in composition, more additions, lower sinter temperature as 1160℃, smaller grain size, higher resistivity and lower eddy current loss. The permeability observed when an alternating magnetic field is superimposed on a DC-bias field, is called incremental permeability. The incremental permeability of MnZn ferrites increases with a DC-bias field slightly and then decreases. Regulating composition and additions properly can improve DC-bias property of MnZn ferrites. LargerΔB=Bs-Br is better for DC-bias property of MnZn ferrites.Thirdly, we investigated the mechanism of initial permeability, stability of temperature and frequency of permeability, DC-bias property, total harmonic distortion (THD) and preparation technology of high permeability MnZn ferrites. MnZn ferrites with initial permeability above 15,000 can be obtained by adding appropriate MoO3, Bi₂O₃ and SnO₂, low temperature long time sintering technology (1365℃×9 h) and right mode of blank arranging. The temperature property of initial permeability can be improved by regulating composition, adding Co2O3 and optimizing sintering technology. The frequency dispersion properties of initial permeability include eddy current loss, dimension resonance, magnetic force resonance, magnetic domain resonance and nature resonance. Appropriate Nb₂O₅ addition can improve the permeability frequency dispersion properties of MnZn ferrites. The variation of incremental permeability with DC-bias field of high permeability MnZn ferrites is the same with that of power MnZn ferrites. The incremental permeability increases with ZnO content decreasing as x(Fe₂O₃) = 52.8 %, or a few Co₂O₃ or V₂O₅ additions. The THD of transformer is related to hysteresis constant, core distortion factor, and distortion transformer coefficient. Where, hysteresis constant is the intrinsical property of core ferrites to be decreased for low harmonic distortion MnZn ferrites. The effect of composition and addition (TiO₂, V₂O₅, Co₂O₃, Bi₂O₃ and Nb₂O₅) on hysteresis constant was studied.Finally, we investigated Curie temperature, resistivity, initial permeability and its frequency dispersion property, impedance property and preparation technology of MnZn ferrites with Fe-poor composition (less than 50 mol% of Fe₂O₃). The effects of Fe₂O₃ and ZnO content on Curie temperature of Fe-poor MnZn ferrites are slower than those of MnZn ferrites with Fe-rich composition. The experience formula of Curie temperature for Fe-poor MnZn ferrites was advanced on the basis of experience formula of Curie temperature for Fe-rich MnZn ferrites. The resistivity of Fe-poor MnZn ferrites is as large as 10⁴Ω·m, much higher than that of Fe-rich MnZn ferrites. The effect of composition and addition (TiO₂, SiO₂ and CaCO₃) on resistivity was studied. Tri-segment frequency dispersion model which consists of domain wall motion, magnetization rotation and gyro-magnetic spin rotation was used to simulate the permeability spectra of Fe-poor MnZn ferrites. The permeability and impedance of Fe-poor MnZn ferrites are comparable with those of Fe-rich ferrites in low frequency region, and those of NiZn ferrites in high frequency region. The impedance of ferrite core can be calculated from the real and imaginary parts of permeability, core dimension, winding number and frequency. For the same core and winding, the frequency dependence of impedance is only related to the permeability spectra.