Preparation Of Core-shell Iron-based Nanocrystalline Material And Study On Its Magnetic Property

Iron-based nanocrystalline materials is a typical kind of soft-magnetic materialwith great application in high-tech industry because of its advantages such like highsaturation low coercivity as well as great frequency stability,In the current thesis, highvolume fraction iron-based nanocrystalline materials(iron volume fraction is as high as95%) is prepared to investigate the soft magnetic properties.The as-prepared sampleshave been investigated characterized by means of X-ray diffraction (XRD), FT-IRanalysis, scanning electronmicroscope (SEM) and vibrating sample magnetometerVSM). The influence of mechanical ball milling parameters, chemical graft parameters,sintering temperature and Y volume fraction added in the materials are investigated inthis thesis. The optimized technological parameter is explored to prepare iron-basednanocrystalline composite.In the process of mechanical ball milling to prepare nanocrystalline materials, thegrain size is getting smaller with milling time increasing. Grain size is close to nealy10nm, when milling time reaches20h. Grain size has very little change if milling timecontinues increasing. Grain size will decrease with the increasing milling speed, thegrain size will be less than10nm when milling speed reaches450r/min. The millingball volume ratio is settled0.3, powder percentage has litter difference to the grain sizeof prepared material. The optimal technological parameter to prepare iron-basednanocrystalline materials is as follows: milling time20h,milling speed450r/min,milling ball/powder ratio10:1.Nanocrystalline iron powder morphology can be modified and materialagglomeration can be improved by surfactant. The core-shell structure can improve thethermal stability and oxidation resistance of materials. The optimal chemical coatingmethod parameters are as follows: TEOS6ml, ammonia water5ml, ratio ofethanol/water3:1. the saturation magnetization of as-prepared materials reached275.7emu/g, the coercive force is36.59Oe, residual magnetism is13.5emu/g.Iron-based soft magnetic composite is prepared by pressing sintering method, grainsize of materials increases with sintering temperature raising from800to1000℃. Thesaturation magnetization increases and the coercivity first increases and then decreaseswith the temperature changing.The magnetic property changes with Y atom added inmaterials, when the weight content of Y increases from2%to6%, the grain size of materials decreases. The saturation magnetization decreases obviously and coercivitytends to increase instead.