Controllable Preparation Of Fe₃O₄ And Study Of Its Electromagnetic Wave Absorption Performanc

In recent decades,the use of electronic devices and the wireless devices has grown rapidly and the resulting electromagnetic pollution has adversely affected the functionality of electronic devices and human health in the surrounding environment.To overcome these problems,efforts have been devoted to developing outstanding microwave absorbing performances（EMA）materials with strong reflection loss（RL）,wide effective absorption bandwidth（EAB）,light weight and low cost.Magnetite（Fe₃O₄）has been widely studied as a microwave absorbing material due to its high compatibility,proper magnetism,and strong spin polarization.However,single magnetite has poor impedance matching and single magnetic loss mechanism.Strong RL with a wide absorption bandwidth（>4 GHz）under thinner thickness is rarely reported.Therefore,this thesis is aiming at Fe₃O₄ materials with excellent performance.Sphere-like Fe₃O₄ were first prepared,and then flower-like Fe₃O₄,Fe₃O₄&Fe and Fe were constructed through a component adjustment.On this basis,Fe₃O₄@SiO₂（TiO₂）was obtained by coating with a dielectric layer.The composite material realizes the development and utilization of excellent EMA performance.In this thesis,an efficient and simple solvothermal method was used to synthesize spherical Fe₃O₄ with a size about 300 nm in one step.The addition of an appropriate amount of H₂O to the solvent made Fe₃O₄ display nano-sized and uniformly distributed.A wide effective absorption bandwidth of 5.1 GHz（5.4-10.5 GHz）and a strong reflection loss of70.4 dB can be obtained.A series of flower-like Fe₃O₄,Fe₃O₄&Fe and Fe were constructed through rational design of hierarchical structure and component adjustment.The introduction of hierarchical structure increased many interfaces,the introduction of Fe element regulated the electromagnetic properties.Fe₃O₄@SiO₂（TiO₂）composites with core-shell structure were prepared by sol-gel method and coated with dielectric layer,and the thickness of the dielectric layer can be adjusted.The structural characterization and performance analysis of Fe₃O₄@SiO₂（TiO₂）composites show that the thickness of the dielectric layer SiO₂ and TiO₂ shell has little effect on the electromagnetic parameters of flower-like Fe₃O₄.But the introduction of the dielectric layer greatly improves the thermal stability and oxidation resistance of the composites in air.Analysis of microwave absorbing performances of flower-like Fe₃O₄,Fe₃O₄&Fe and Fe revealed that the hierarchical structure produces more interfaces,which further improves the efficient absorption of electromagnetic waves by effectively adjusting multiple losses such as interface polarization and eddy current loss.This hierarchical structure offers flower-like Fe₃O₄ an excellent effective absorption bandwidth performance from C to Ku band.Meanwhile,the multiple components offer Fe₃O₄&Fe a perfect impedance matching and providing an excellent EAB as wide as 5.7 GHz（9.0-14.7 GHz）at 1.88 mm and a RL as strong as 78.7 dB in 11.6 GHz,which covers 75%X and 45%Ku bands.With the coordination of hierarchical structure and multiple components,Fe₃O₄&Fe shows the overall outstanding EMA performances.