| The selection and preparation of absorption materials were made a great progress in recently years. In particular, nano-thin films composites absorbing materials combine with nanotechnology have caused a hot research. It can be used promising new absorbing materials due to their small quality, thinner, absorbing properties and other advantages. Many treatments have been used to enhance the absorbing property of carbon fibers, including changing the cross-section shape and size of carbon fibers, modifying the carbon fiber surfaces such as coating the surface with a layer of metal or other oxide. So we coated magnetic films by chemical method to improve its electromagnetism properties. The excellent magnetic and microwave absorption properties of nano-absorbing composites were obtained.(1)Therefore, by modifying Izaki's method, a convenient way was presented in this paper, the pretreated CFs were immersed into aqueous solution at best temperature and time. The conclusions were found as follows:a. The best reaction condition is queous solution containing 10 mM iron nitrate 9-hydrate [Fe (NO3)3·9H2O] and 30 mM dimethylamin borane complex (DMAB) [(CH3)3NHBH3] treated at 90℃forl h.b. The magnetic properties of the Fe3O4/CFs composites were measured with VSM at room temperature. We found that the carbon fibers exhibited paramagnetism. But the Fe3O4/CFs composites exhibited ferromagnetism.c. The electromagnetic parameter of 50 wt.% Fe3O4/CFs composites is measured by the coaxial line method at 0-18 GHz.d. The lowest reflectivity of the Fe3O4/CFs composites is-35 dB at 6.37 GHz for a layer of 4.41 mm in thickness. The result shows that the strong absorption (RL<-20 dB) is broadened from the 5.49 to 7.75 GHz with the thickness varying from 5.12 to 2.90 mm.(2) Fe-Co films were prepared by the electroplating method. ITO glass and carbon fibers were used as the substrates, respectively. In this study, the structure and magnetic property of electrodeposited Fe-Co films were investigated. The conclusions were found as follows:a. By changing the molar ratio of Co2+/Fe2+ in the reaction electrolyte from 0.50/0.50 to 0.90/0.10, the Co content x in the films ranges from 40% to 85%. Mean- while, the Fe content in the films decreases from 60% to 15%. It can be seen that Ms increases with the Co content x increasing from 0.40 to 0.70, reaches a maximum value at x= 0.70, and then decreases with further increasing of x. Meanwhile, He decreases with the Co content x increasing from 0.40 to 0.70, reaches a minimum value at x= 0.7, and then increases with the further increasing of x. The change of the magnetic properties of the Fe-Co films can be attributed to the increase of Co content in the deposited films.b. The fixed electrolyte were fasted at room temperature as the pH values varying from 2.1 to 4.3. Ms increases with the pH values increasing from 2.1 to 2.9, reaches a maximum values at pH=2.9, and then decreases with further increasing of pH values. Meanwhile, Hc decreases with the pH values increasing from 2.1 to 2.9, reaches a minimum values at pH=2.9, and then increases with the pH values increasing from 3.9 to 3.7, reaches a maximum values at pH=3.7, and then decreasing with further increase of pH values.c. The magnetic performance of the FeCo films shows the best composition and pH values. We coated FeCo films on carbon fibers by electroplating method. We found the FeCo/CFs composites exhibited ferromagnetism.d. The electromagnetic parameter of 50 wt.% FeCo/CFs composites is measured by the coaxial line method at 2-18 GHz.e. The lowest reflectivity of the FeCo/CFs composites is-14.7 dB at 2.0 GHz for a layer of 3.3 mm in thickness. The results show that the reflectivity is less than-10 dB the reflection loss of microwave absorption materials achieves 90%. The reflectivity of Fe3O4/CFs composites is less than-10 dB over the range of 1.6-2.1 GHz.
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