Composition And Process Optimization Of Magnetic Mn-Zn Ferrite Materials For Electromagnetic Heating

Induction cooker is a new type of kitchen cooker based on electromagnetic effect.Compared with the traditional cookers,induction cooker has the advantages of high thermal efficiency,fast heating,environmental friendliness,good safety and reliability,etc.With the increasing energy crisis and environmental problems,higher energy efficiency for induction cooker is requires.Mn-Zn ferrite has lowand excellent soft magnetic properties such as high permeability,high saturation induction density and low loss,which make it widely used in home appliances,communications,computers and other electronic industries.Currently,Mn-Zn ferrite is commonly used as the magnetic stripsl for electromagnetic heating coil plate in induction cooker.In this thesis work,Mn-Zn ferrite was prepared by ceramic technology.The influences of main compositions,calcining temperature,pressure,sintering atmosphere,and additives on the magenetic properties and the temperature range characteristics of Mn-Zn power ferrite have been investigated.The main content of this article is divided into the following six parts: In Chapter1 gives a brief introduction to the basic concept,the research status,fundamental theory and the important characteristic parameters of the Mn-Zn ferrites.The significance and objectives of the present work have also been described.Chapter 2 present the preparation and characterization methods employed in this work.In chapter 3,the effects of the main formula（Fe2O₃,ZnO and MnO）on the microstructure and properties of Mn-Zn ferrite are investigated.In chapter 4,based on the best main formula,the effects of presintering temperature,molding pressure,and sintering atmosphere on the microstructure and magnetic properties of Mn-Zn ferrite have been investigated.The optimized presintering process and sintering process are obtained.In chapter 5,based on the best main formula and optimized process,the effects of additives on the microstructure and magnetic properties of Mn-Zn ferrite have been investigated.The best doping amount for different additives have been obtained.In Chapter 6,some preliminary work on the rare earth addition effects on the Mn-Zn ferrite are presented.The main conclusions of this dissertation are summarized as follows:1.The best molar ratio of three oxides of raw materials for preparing Mn-Zn ferrite for magnetic strips is optimized as Fe2O₃:ZnO:MnO=52.5:12:35.5（mol.%）.With the increases of Fe2O₃ or ZnO content,the initial permeability and saturation magnetic induction increase while the power loss and coercivity decrease.2.Presintering temperature has a significant effect on the Mn-Zn ferrite.Appropriate presintering temperature can contribute to the good microstructure,so as to improving the initial permeability and saturation magnetic induction while decreasing the power loss and coercivity.The sample has the optimal magnetic properties after pre-sintered at 920 ℃ for 2h.3.When the forming pressure is low,the microstructure of sintered samples is relatively loose with poor uniformity and high porosity.If it is too high,it is also not beneficial for the the microstructure.When the forming pressure is controlled between 100-125 MPa,the sample show the best microstructure and performance.4.With the increase of sintering oxygen partial pressure,the saturation magnetic induction and the initial permeability of the sintered samples decrease slightly,while the power loss and coercivity first increase and then decrease.The magnetic properties of the sintered samples are optimized at the sintering oxygen partial pressure of 4%.The optimized processing parameter for Mn-Zn ferrite include the pre-sintering temperature of 920 ℃,forming pressure of 100-125 MPa,and sintering oxygen partial pressure of 4%.As a result,the obtained ferrite show the permeability,loss,and coercivity of 2904,81.18 W/kg,12.67 A/m,respectively,at 100 mT and 100 kHz.5.Doping is an important approach to optimize the magnetic properties of Mn-Zn ferrite.The addition of CaCO₃,V₂O₅ or TiO₂ can improve the microstructure and magnetic properties of Mn-Zn ferrite.For the best microstructure and magnetic properties,the optimized incorporations of Ca CO₃,V₂O₅ and TiO₂ are 0.05 wt.%,0.05 wt.% and 0.01 wt.%,repsectively.6.Rare earth ions can be employed as good additives,which enter into the crystal lattice of ferrite.A small amount of Ce2O₃ or Y2O₃ doping can effectively improve the magnetic porperties of Mn-Zn ferrite,and the optimized doping amounts are 0.03 wt.% for both oxides.