Research On MnZn Ferrites With High Saturation Flux Density At High Temperature

With the miniaturization and energy saving of electronic products,it is required that the soft magnetic ferrite material for high frequency power electronics not only needs the lower loss,but also keeps higher saturation flux density under high temperature so as to maintain the miniaturization and high efficiency of magnetic components.Compared with soft magnetic metal materials,the low saturation flux density is the important deficiency of soft magnetic ferrite.This paper takes the traditional low-cost oxide process as the base to expect to develop a Mn-Zn soft magnetic ferrite material with higher saturation flux density under the high temperature through research on the composition,pre-burning and sintering process,additives and combinations of Mn-Zn ferrite,which will make ferrite component can be applied in high operating temperature range above 100℃ to realize the miniaturization and high temperature reliability of magnetic components.According to the research on the contents of Fe₂O₃ and ZnO in the trinary formulation（Fe₂O₃-MnO-ZnO）of Mn-Zn ferrite,the final determination of Mn-Zn ferrite formulation with high temperature and high Bs power is that:Fe₂O₃=65.0 mol%（Mole percentage）,ZnO=17.0 mol%（Mole percentage）,MnO=18.0 mol%（Mole percentage）.Proper pre-burning temperature can enhance the uniformity of grain distribution,improve microstructure and crystalline gain relatively higher saturation flux density（Bs）,initial permeability（μi）and lower power loss（Pcv）,and the pre-burning temperature experiment form 775 to 950℃ shows that the best material performance is obtained at 850℃.Sintering temperature is another important craft factors to influence the final properties of materials and the sintering experiment from 1300 to 1400℃ finds that with the increase of sintering temperature,the crystalline grain integrity continuously improves and the number of pores in crystal boundary decreases;the overhigh sintering temperature will trigger abnormal growth of crystalline grains,which will make material vortex loss increase and the best sintering temperature determined by experience is 1350℃.At that time,the initial permeability（μi）of material is 1085,the saturation flux density（Bs）under 100℃ is 496 mT and the power loss（Pcv）under 100℃ is 1138 kW/m3（100 kHz/200 mT）.Choose the two additives CuO and NiO and their mixture to carry out the experience and theoretical analysis,and determine the final dosage of additives.CuO has lower melting point and it is easy to form the liquid phase during the sintering process,which will promote the ion diffusion,so as to improve the sintering density of ferrite.Excessive addition will cause abnormal growth of crystalline grains so that it will have the impact on density and loss properties of materials.Moderate NiO can refinecrystalline grains an enhance resistivity of materials.When about 0.20 wt%CuO and about 1.0 wt%NiO are combined together to add,the best comprehensive properties of the material can be achieved.The initial permeability of material（μi）is 1286,the saturation flux density（Bs）under 100℃ is 502 mT and the power loss（Pcv）under 100℃ is 1058 kW/m3.