| Fe nanoparticles (NPs) were prepared by the DC arc-discharge plasma method and characterized by TEM and XRD. The Fe NPs prepared were in sphere shapes and possessed a core/shell microstructure. TEM images revealed that Fe NPs were about 30-80 nm in diameter with the outer shells of about 2 nm in thickness. As shown in the XRD profile, Fe NPs had body centered cubic (bcc) structure.The Fe NPs prepared were modified by silane coupling agent KH550 to improve the dispersion stability in the epoxy resin (EP) matrix. FTIR spectra of unmodified Fe NPs, modified Fe NPs and KH550 were measured. For further verification of improving dispersion stability in EP matrix, the Fe NPs before and after modification were dispersed in ethanol by ultrasonic concussion separately. The experimental results show that KH550 was successfully grafted on the surface of Fe NPs and the dispersion stability has been improved effectively.The electromagnetic wave absorbing nanocomposites were fabricated by using the modified Fe NPs as the microwave absorber, carbon fibers (CFs) and glass fibers (GFs) as the reinforced phase and EP as the matrix. The cross section of the nanocomposite was characterized by SEM and elemental distribution was studied by EDS. The Fe NPs and CFs were combined well with EP matrix. The Fe NPs in each layer of EP matrix were in a gradient distribution.The bending properties of the nanocomposites were tested by three points bending test according to ASTM standard. The bending strength of the nanocomposite with 30 wt.% Fe NPs is lower than that with 0 wt.% Fe NPs by 5.8%. CFs can maintain the bending properties of nanocomposites effectively.Reflection losses (RL) in the frequency range of 2-18 GHz were measured by the vector network analyzer. For the 30 wt.% Fe NPs nanocomposite with one layer of CFs, when CFs are parallel with the electric field of electromagnetic wave the effective absorbing band of the top surface is from 4.7 to 7.2 GHz and the peak value is-19 dB at 6 GHz. When the 30 wt.% Fe NPs nanocomposite with two layers of CFs, its effective absorbing bandwith can reach 5.77 GHz and the RL peak value at low frequency is -26.8 dB. Carbon fibers can greatly improve multiple reflection and absorption of electromagnetic wave in the absorbing composite. Lower RL values and wider effective absorbing bandwidth can be achieved when the CFs arc parallel with the electric field of electromagnetic wave. Increasing the contents of Fe NPs can improve the absorption of nanocomposite but an optimum wt.% of Fe NPs are required. The higher contents of Fe NPs built up strong cross linked network to consume more microwave within the structure. For the gradient distribution of Fe NPs, when the microwave enters the surface with high concentration of Fe NPs more electromagnetic wave can be consumed. The Fe NPs can improve the selective absorption of electromagnetic wave for the unidirectional GFs. When using the layer of CFs as the electromagnetic wave incident layer, Fe NPs are in gradient distribution from low concentration to high concentration and the fibers are parallel with the electric field, the effective absorbing bands are 4.2-7.1 GHz and 15-18 GHz and the RL peak values are -23.3 dB and -15.6 dB, that means the lower RL values for electromagnetic wave can be achieved. |
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