Research Of Low Loss MnZn Power Ferrite In Wide Temperature

With the development of electronic information technology, the electronic equipment arerequired to be smaller, lighter and more reliable, which puts forwards a higher request to theelectronic elements with ferrite materials.In this dissertation, low lossMnZnpower ferrite with awide temperature are fabricated by solid state reaction method. The influences of maincompositions, additives, second-milling time, calcining temperature and sintering temperature onthe magenetic properties and the temperature range characteristics ofMnZnpower ferrites areinvestigated.In the first chapter the dissertation summarized the development history and recentachievements ofMnZnferrite, which are the backgrounds of this research. Then in the secondchapter, the structure, origin of magnetic properties and magnetization technique theoryofMnZnferrite are introduced, based on which possible method for fabricatingMnZnferrite withhigh permittivity is proposed. In chapter 3, the process of fabrication technology ofMnZnferrite areintroduced. The influences of main compositions, additives, second-milling time, calciningtemperature and sintering temperature on the magenetic properties and the temperature rangecharacteristics ofMnZnpower ferrites are analyzed according to the results of the experiments inchapter 4. At last conclusions and insufficiencies of this dissertation are summarized at chapter 5.Though the experiment study, this dissertation has used oxide ceramic process to fabricate losspowerMnZnferrites with a wide temperature successfully and got following conclusions:The main compositions are choosen Fe2O3-52.5mol%, MnO-35.5molï¼…, ZnO-12molï¼…, accordingto the relation chart between initial permeability and Mn-Zn ferrites components and the relationchart between Mn-Zn ferrites K1、λs.Doping is an important way to optimize the magenetic properties of MnZn ferrites. AddingTiO₂,Co₂O₃and Nb₂O₅can improve the microstructure and magnetic properties of Mn-Zn ferrites;Milling technics affect powder diameter directly. Powder diameter will decrease as millingtime increases. The smaller size and larger specific surface area, the higher activity they willperform in sintered process, and it is easier to emerge grain secondary growth, so some unusual biggrains will appear in microstructure making the grain size nonuniform. So the milling time must becontrolled strictly, the optimum time got in the experiment is 2 hours;Calcining temperature affects the performance of high permeabilityMnZnferrites greatly. If it’stoo low, size of sintered grain will be too big and very nonuniform, it may occur grain secondary growth phenomenon, so the permeability will be low; if it’s too high, for the powders will lose theiractivity、size of sintered grain will decrease but the grain boundary will increase, so do the blocks ofmovement of domain wall, then, the initial permeability will also be low. So calcining temperaturemust be selected appropriately, and the optimum calcining temperature got in the experiment is930℃;Sintering is the important process deciding MnZn ferrites properties. Designing a suitablesintering technology and controlling it are the keys to fabricate ferrites material with wellperformance. For this reason , this dissertation studied sintering temperature、sintering time andsintering atmosphere. In sintering process, sintering temperature must be increased properly tomake ferrites solid state reaction completely, make ferrites grains grow evenly, but controlled nottoo high to avoid the discontinuously growing, which lead to ferrites material magnetic performancedegradation. Because of equipment limits, the sintering equipment used in this dissertation isvacuum resistance furnace, which control the air in resistance furnace to regulate sinteringatmosphere, that is to control the pressure in vacuum resistance furnace. The proper sinteringtemperature、sintering time、the beginning pressure in vacuum resistance furnace studied outseparately is 1320℃、3 hours、0.05MPa.