Property And Preparation Of High-frequency And High-tension NiCuZn Ferrite

In this paper, NiCuZn ferrites have been prepared using the traditional solid-state mixing method. The analytical reagent-grade powders of Iron oxide (Fe₂O₃), nickel oxide (NiO), copper oxide (CuO) and zinc oxide (ZnO) were chosen as the precursor materials to prepare the ferrites. The toroidal samples were obtained after being ball-milled, calcinated, granulated, formed and sintered. The impact between properties and microstructure of the ferrite was assessed by checking phase purity and composition using X-ray diffraction (XRD) with Cu K_α radiation and obtaining micrographs using scanning electron microscopy (SEM).At first, the relation between properties and prescription of NiCuZn ferrites was studied, the experimentation of Fe₂O₃, ZnO, and CuO replacing NiO were discussed. It was found that a NiCuZn ferrite with maximum sintering density as high as 5.184g/cm³ and minimum power loss as lower as 264.8 kw/m³ were obtained with 50mol% Fe₂O₃ at 1200℃ in air for 3h. The relatively higher initial permeability was obtained with 10mol%～12mol% NiO and the equimolar compositions for NiCuZn ferrites, the maximum initial permeability with 1925 was obtained with 28mol% ZnO and 10mol% NiO. The result was propitious to exploit ferrite material with high relative initial permeability. Besides, additions of CuO contributed to the grain growth, densification of matrix and sintering temperature lower in the sintering process, which were favorable for increase in relative initial permeability, decrease in power loss. The sintering temperature was lowered to 1160℃ with 6mol% CuO at initial permeability(μ_i)was more than 1000,saturated flux density(B_s) was more than 360mT, power loss (P_cv) was less than 350kw/m³. The maximum μ_i with 1426 was obtained with 8mol% CuO, 12.5mol% NiO at 1190℃, and the minimum P_cv, as low as 275kw/m³ with 6mol% CuO, 14.5mol% NiO at 1220℃.But with further increasing CuO, porosity also becomes the predominant factor to determine the magnetic properties, and consequently, the magnetic properties could be deteriorated by more porosity and abnormal grain growth.Second, the effect of calcinations temperature, after presintering quenching, heating rate on properties of NiCuZn ferrite was studied. The results showed that the shrinkage ratio is big when the calcinated temperature was less than 900℃ abnormal grain growth appears when the calcinated temperature was more than 1020℃ which could deteriorate d, μ_i, and P_cv. To raise the sintering temperature properly is favorable to the grain growth and densification of the ferrites so as to the improvement of magnetic properties of the NiCuZn ferrites. But the magnetic properties such as μ_i, d could be deteriorated by more porosity and abnormal grain growth and with bad crack in samples when sintering temperature is more than 1250℃.The result indicated that better microstructure, higher μ_i with 1249, higher density with 5.05g/cm³ and lower loss with 255kw/m³ can be obtained when calcinations power was quenched in copper container. The initial permeability and grain size had a very sharp decrease, so does sintering density when heating rate was more than 2.5℃/min. 2℃/min was the critical heating rate value to obtain high performance NiCuZn ferrites.Finally, the effect of additions on magnetic properties of low-temperature sintering NiCuZn ferrites was studied. The optimal content addition of Bi₂O₃,V₂O₅, MoO3 and Nb₂O₅ was different with optimal integrated properties respectively. The maximum initial permeability with 901, relative higher saturated flux density with 391mT, lower power loss with 358kw/m³ and higher sintering density with 5.15g/cm³ was obtained with 0.5wt% Bi₂O₃ at 925℃. The optimal value of μ_i,, B_s, P_cv and d were 794, 343mT, 422kw/m³ and 5.10g/cm³ with 0.5wt% V₂O₅ at 910℃, respectively. The optimal value of μ_i, B_S, P_cv and d were 793,335mT, 318kw/m³ and 5.13g/cm³ with 0.2wt% MoO₃ at 900℃, respectively. The optimal value of μ_i, B₅, P_cv and d were 604, 408kw/m³ and 5.00g/cm³ with 0.4wt% Nb₂O₅ at 920℃, respectively. The result showed that the optimal properties were obtained with addition of Bi₂O₃. Though Nb₂O₅ with high-milting point (1520) could lower sintering temperature, decelerated grain growth and increased density, μ_i, and P_cv were deteriorated.