Research On Preparation And Magnetic Properties Of Low Power Loss Mn-Zn Ferrites

Low power loss Mn-Zn ferrites were prepared by the conventional ceramic process. Thecommercially pure raw materials were used, and the preparation process was optimized. The effects ofcompositions, pre-sintering temperature, second milling time, sintering temperature, sinteringatmosphere and additions on the microstructure and magnetic properties of Mn-Zn power ferriteswere systematically investigated.The effects of compositions, pre-sintering temperature, second milling time, sinteringtemperature and atmosphere on the microstructure and magnetic properties of Mn-Zn power ferriteswere investigated. The results indicate that the optimum molar ratio of compositions is Fe2O3: ZnO:MnO=52.75:10.45:36.8(mol%). The secondary maximum peak of μi-T curve and the minimumtotal power loss of sintered samples move to lower temperature when the Fe2O3or ZnO contentincreases. The mean grain size, grain size peak value, specific area and activity of powders areinfluenced by the second milling time. Therefore, the second milling time has an effect on thesolid-state reaction, which leads to the different microstructures and magnetic properties of samples.When the second milling time increases, the Fe2+generated by the steel ball abrasion makes acompensation to magnetocrystalline anisotropy constant (K1). Hence, the secondary maximum peakof μi-T curve and the minimum total power loss of sintered samples move to lower temperature whenthe second milling time increases. Besides that, the sintered sample shows optimal microstructure andmagnetic properties when the pre-sintering temperature and second milling time are920℃and2h,respectively. Moreover, when the sintering temperature is low (1320℃), the crystal grains of Mn-Znpower ferrites are small and inhomogeneous. And when the sintering temperature is high (1400℃),partial grain boundaries deform obviously, and molten inclusions happen. Therefore, the magneticproperties of samples which sintered at a high or low temperature are bad. However, the sampleswhich sintered with the temperature ranging from1340℃to1380℃show a similar magneticproperty. And the sample sintered at1360℃in twice deoxidizing atmosphere shows optimalmagnetic properties.Then, a direct comparison was made between the nano-TiO2and normal size TiO2additions inMn-Zn power ferrites by using the above composition, ball-milling, pre-sintering and sinteringtechnology. It is found that the magnetic properties of Mn-Zn power ferrites can be improved with asuitable amount of nano-TiO2or normal size TiO2addition. An obvious shift of peak positions occurs in the XRD pattern of sample when the nano-TiO2concentration is0.05wt%. The shrinkage of crystallattice leads to the increase of internal stress, which thus results in the decrease of magnetic properties.Moreover, a small amount of nano-TiO2addition into Mn-Zn ferrites helps to push the impurities andpores onto the grain boundaries, which thus makes sample show a more uniform grain structures.Besides that, at100℃, the PLof sample shows a monotonous decrease to315kW/m3when thenormal size TiO2concentration increases gradually to0.07wt%. In the temperature range of90-120℃, the PLof the sample with0.07wt%normal size TiO2addition are lower than330kW/m3. It isindicated that the optimal content of normal size TiO2is higher than0.07wt%. The thermal stabilityof Mn-Zn power ferrites is fluctuant with the nano-TiO2or normal size TiO2concentration, and bothof them can be considerably improved with a suitable amount of TiO2addition.Finally, the effect of ZrO2addition on the microstructure and magnetic properties of Mn-Znpower ferrites was investigated. The results indicate that Mn-Zn power ferrites with0.02wt%ZrO2concentration possesses superior microstructure and magnetic properties. A number of small crevassesare well dispersed on the surfaces of grains when the ZrO2concentration exceeds0.02wt%. Theprecipitation and agglomeration process of ZrO2particles from these crevasses are observed. And thepores along with agglomerated ZrO2particles on the surfaces of grains have a large pinning effect onthe domain wall, which thus causes the decrease of magnetic properties.