High B_s High T_cnicuzn Ferrite Developed

In this dissertation, NiCuZn ferrites were prepared by a solid-state reaction method. In order to achieve the target of high initial permeability, high saturation magnetic induction and high Curie temperature, the influences of the composition, the calcining technics, the additives, the first ball-milling process, the second ball-milling process and the sintering technics on NiCuZn ferrites were investigated. And some innovative improvements on technics were taken. To show the effect of the microstructures on the magnetic properties, the XRD patterns and the SEM micrograghs of NiCuZn ferrites were taken. At the same time, we worked deeply on the extent of solid-state reaction by DSC-TGA.As the results shown: when the molar percentage of Fe2O3 varied from 47.0% to 54.0%, initial permeability and saturation magnetic induction raise initially and then decline, while power loss and coercive force changes contrarily. With the raise of calcining temperature from 830℃to 980℃, activity of ferrite decline, then the magnetic properties, grain size and lattice parameter raise initially and then decline. In addition, the reactive ability of calcined powders can be enhanced by optimizing some preparation parameters, such as the first-milling time and the second-milling time, etc, which promotes the solid-state reaction during sintering and results in the improvement of magnetic properties. It is found that V2O5 induces liquid phase during sintering, leading to the decrease in sintering temperature. Although Nb2O5 can restrain the growth of grain to decrease the initial permeability, high saturation magnetic induction will be obtained because of high density. With the raise of sintering temperature from 1100℃to 1180℃, the magnetic properties raise initially and then decline. The optimum process is followed: NiCuZn ferrites with the compositions of 49.0 mol% Fe2O3,29.0mol% ZnO,6.3 mol% CuO,15.7 mol% NiO are milled for 3 h and calcined at 930℃in air for 2 h. After adding CaCO3(0.01 wt%), V2O5(0.01 wt%), Nb2O5(0.01 wt%), and MoO3(0.01 wt%) , the resulting powder is second milled for 6 h. The pressed toroidals are sintered at 1120℃in air for 3 h. In according to the optimum process, NiCuZn ferrites with high high saturation magnetic induction (360mT) and high Curie temperature (160℃) can achieveμi =1200, Br=170mT and Q=60.