Preparation Of Mnzn Power Ferrites For Industrial Grade Sulfate

Conventional dry process, used in today's ferrite industry, has the disadvantages of strict requirements for raw materials, unsufficient mix, and low sintering activity which restricts the further development of high performance Mn-Zn ferrite. With the advantage of high purity, small particle size, uniform size distribution and high sintering activity, wet method can compensate the shortcomings of dry process. On the basis of this, this study adopted chemical coprecipitation method using ammonium bicarbonate as coprecipitator to prepare high purity Mn-Zn ferrite powders from cheap industrial grade sulfate. Then, these powders were made into Mn-Zn power ferrite magnetic cores after the processes of pre-sintering, doping, milling, granulating, forming and sintering. The main conclusions are as follows:Using three-stage purifying technology including hydrolytic purification,fluoride precipitation and pickling purification, fine-grained and high-purity Mn-Zn ferrite powders could be prepared by coprecipitation method using industrial grade sulfate as starting materials. The concentration of SiO2 and CaO in these powders with particle size less than 1μm is 0.0086% and 0.0102%, respectively, meeting the requirements for ferrite powders.Microstructure, initial permeability and power loss of Mn-Zn power ferrite are affected by factors such as composition, pre-sintering temperature, doping and sintering. The feasible composition is as follows:Fe2O3 68.33～69.33%, Mn3O4 23.25～23.75%, ZnO 7.32～7.82%(mass fraction). The suitable pre-sintering temperature is 950℃. The optimal doping combination is CaCO3 0.02%, ZrO2 0.02%, V2O5 0.02% and Nb2O5 0.02%. The appropriate sintering condition is:sintering at 1320℃for 4 h with 5.4% partial pressure of oxygen, with heating rate of 50℃·h-1 between 900℃and 1100℃using densification measures of controlling the partial pressure of oxygen to 5.4%.Using the optimal composition, the pre-sintering temperature, the dopants and the sintering parameters determined through the experiments, Mn-Zn power ferrite whose various performance indexes have reached or even exceeded the level of PC40 made by TDK was obtained. The performance indexes of the optimal Mn-Zn power ferrite magnetic core were:initial permeabilityμi=2015(25℃,10 kHz,50 mV), saturation flux density BS=503 mT (25℃,1194 A·m-1) and 398 mT(100℃,1194 A·m-1),curie temperature Tc=225℃and power loss per unit volume PCV=421 kW·m-3(100 kHz,200 mT,100℃). Furthermore,its PCV～T curve was more flat than the PC40's.