Microstructure And Magnetic Properties Of Mn_xZn_1-xFe₂ferritomers Prepared By Microwave Sintering Can

Polycrystalline MnZn soft ferrite with chemical formula MnxZn1-xFe2O4 was prepared by microwave sintering method.The Microstructure evolution of MnZn ferrite prepared by microwave sintering,and the effect of temperature on the microstructure of the material were studied systematically,using X-ray diffraction(XRD),scanning electron microscope(SEM).The magnetic properties and the effect of temperature on magnetic properties were studied.On this basis,the properties of microwave sintered MnZn ferrite material and conventional sintered material were compared and analyzed.The solid state reaction of microwave sintering of MnZn ferrite and the characteristics of microwave heating of MnZn ferrite powder compacts were discussed,The densification and grain growth of MnZn ferrite were discussed from the point of view of coupling between microwave and molecular vibration.Our results indicate that the microwave sintering method can be a potential technique used for MnZn ferrite sintering.The microstructure of MnZn ferrite sintered by microwave experienced typical formation and evolution process of MnZn ferrite,In other words,the early stage of particle contact,aggregation,the medium-stage nucleation,crystallization and grain growth,the later stage of grain cracking,and finally the formation of polycrystalline structure.Samples can be obtained by microwave sintering within the temperature range of 1350? to 1400?,within which,uniform structure,proper crystallization,flat grain boundary and good grain growth can be achieved.Though the micro morphology of microwave sintered sample is similar with conventional sintered sample(i.e.no essential difference between in microstructure),microwave sintering offers a quicker access to obtain the same morphology.The main phases sintered within the temperature range of 1200? to 1500? for the MnZn ferrite materials include the MnZnFe2O solid solution with typical spinel structure,accompanied by ZnFe2O4 phase and The ZnFe2O4 phase decreases with the increase of sintering temperature,at the temperature range from 1300? to about 1400?,the ZnFe2O4 phase almost disappeared,pure MnZnFe2O4 can be obtained.Avery small amount Fe2O3 phase and Fe304 phase were observed in all samples between 1200? and 1500?.Zn 2P presences in the form of Zn2+ iron,Mn 2P presences in the form of Mn2-iron and Mn3-iron,Fe2P are mainly in the presence of Fe3+ ions,there may be a small amount of Fe2+ ions exists in the samples of microwave sintering MnZn ferrite with spinel structure.The phase structure of the conventional samples sintered at 1400?,are close to the microwave sintered MnZn ferrite samples.The characteristics of microwave heating for MnZn ferrite powder compacts presents non uniform heating properties,the sample is heated up by microwave at a relatively fast rate at low temperature,and the main reason may be the influence of the dielectric constant and density of the sample on heating rate.At about 1450?,a phenomenon named "thermal runaway" occurres in the microwave heated MnZn ferrite powder compact,and the temperature of the sample increased from 1400? to about 1500? in three minutes.Microwave sintering has a strong effect on the densification and grain growth of MnZn ferrite,Coupling molecular microwave MnZn ferrite and the internal ionic groups vibration energy,or is the moment when the dipolar coupling vibration of ionic groups changed,the group valence ddbond rupture,ion rapid migration to form a new bond,promote the sintering process.The density of samples microwave sintered within the temperature range of 1200? to 1400?,without holding time,yielding a density range of 4.35 g/cm3 to 5.18 g/cm3.In comparison,those conventional sintered samples that heat preservation for 4 hours yield a density range of 3.95 g/cm3 to 4.85 g/cm3.Thus microwave sintering has a promoting effect on the growth of grain,and the grain size of microwave sintered samples is in the range of 48nm to 55mn,while the grain size of the conventional sintered samples is in the range of 52nm to 62nm.The solid state reaction of MnZn ferrite synthesized by Fe2O3,MnCO3 and ZnO,is mainly divided into three steps:1)the a-Fe2O3 with the hexagonal crystal system is transformed into FCC?-Fe2o3,which is formed by the reaction between ?-Fe2O3 and ZnO with the hexagonal wurtzite structure of ZnFe2O4.2)FCC-Mn3O4 is generated by multistage decomposition of MnCO3,and?-Mn3O4 reacts with FCC-Fe2O3 to generate MnFe2O4.3)ZnFe2O4 and MnFe2O4 react in the form of solid solution to form MnZnFe2O4 with spinel structure at higher temperature(generally higher than 950 ?).The magnetization curves of microwave sintered samples share the same characteristic of long and narrow with the conventional sintered samples,which suggests the typical characteristics of soft magnetic materials.Microwave sintering temperature has obvious impact on the coercive force Hc,and He drops with increasing sintering temperature,the material densifying,the improve of the new phase lattice correction,the defect elimination of microstructure.However,the He increases again when temperature is too high.The samples of MnZn ferrite of precursor(I)microwave sintered at 1300? have lower He value of 450.0 A.m-1,The samples of precursor(II)microwave sintered at 1350? have a lower He value of 270.4 A.m-1,while the samples(additive)have a minimum He value of 246 A.m-1 conventional sintered at 1400? for 4 hours.The microwave sintering temperature has little effect on the specific saturation magnetization of the material,but it has some influence on the remanence.The maximum specific saturation magnetization value of precursor(I)microwave sintered samples at a temperature about 1200? is 61.60 A.m2.kg-1,while the minimum remanence value of 2.50 A.m2.kg-1of the microwave sintered samples at about 1300? can be obtained.The maximum specific saturation magnetization value of precursor(II)microwave sintered samples is 72.35A-m2.kg-1,while the minimum remanence value of 2.40 A.m2.kg-1 of the microwave sintered samples at a temperature about 1400? can be obtained.The maximum specific saturation magnetization is 66.40A.m2.kg-1 for conventional samples(sintered at1400? for 4h),and the corresponding minimum remanence value is 2.81A.m2.kg-1.