Preparation And Electromagnetic Characteristics Of Fe₃O₄and Its Composite Powders

Fe3O4particles with different reaction times were synthesized via hydrothermal process and reduction method with hydrazine hydrate as deoxidizer at ambient temperature and atmospheric pressure. Then, we have done some special handling and fabricated Fe3O4/Co and carbon fiber/Fe3O4core/shell particles. The phase structure, morphology, magnetic properties and electromagnetic characteristies in the frequeney range of2-18GHz were studied by means of X-ray diffraction (XRD), Transmission electron microscopy (TEM), Vibrating sample magnetometer (VSM), Vector network analyzer. And, the microwave absorption properties were evaluated by calculating the reflection loss.Both the hydrothermal process and reduction method with hydrazine hydrate as deoxidizer can be used to synthesize homogeneous Fe3O4sphere-shaped particles. But compared with hydrothermal process, the reduction method is much efficient. The microwave absorbing property of the Fe3O4particles fabricated by these two methods is both improved with increase of reaction times. Meanwhile, the microwave absorption curves exhibit enhanced absorption and the peaks shift to lower frequency with increase of layer thickness.Fe3O4/Co core/shell particles were prepared by an electroless plating technique using hydrazine hydrate as a reducing agent. It is found that the Co coating layer possesses a crystalline structure with layer thickness of63nm. Compared with pure Fe3O4particles, the Fe3O4/Co core/shell particles revealed better magnetic property and microwave absorption property. Especially, It is worth noting that the effective microwave absorbing frequency (RL<-10dB) of the Fe3O4/Co core/shell particles is in the range of6.1-8.9GHz with its minimum value of-20.1dB with a thickness of3.3mm.Carbon fiber/Fe3O4composite, which is well composed by dielectric and magnetic materials, was prepared. The carbon fiber/Fe3O4composite has great microwave absorption property for its good dielectric property of carbon fibers and excellent magnetic property of the Fe3O4particles. Especially when the simulated thicknesses are5mm and6mm, the effective microwave absorbing frequency (RL<-10dB) of the carbon fiber/Fe3O4composite are in the range of3.1-4.3、11.3-12.6GHz and2.7-3.5、9.8-10.5GHz.