Preparation And Microwave Absorbing Properties Of Modified Carbonyl Iron Powder-Polychloroprene Composite Films

Carbonyl iron powder was superficially modified by silane coupling agent. Microwave absorbing composite films, containing polychloroprene and carbonyl iron powder, were prepared by direct co-blending. According to impedance matching principle and electromagnetic spreading regulation, a three-layer composite film was designed. The structure and performance of the prepared materials were characterized by X-Ray Diffraction, Scanning Electron Microscope, Transmission Electron Microscope, Vibrating Sample Magnetometer and Vector Network Analyzer etc, and the microwave absorbing mechanism of the composite films was simply discussed.The surface modification of carbonyl iron powder was carried out by wet pretreatment with vinyltrimethoxysilane. The agglomeration of powders was reduced by the oligomer of silane coupling agent, which improved the wettability between polychloroprene and carbonyl iron powder. After modification, the coercivity and residual magnetization of carbonyl iron powder were slightly increased, and the saturation magnetization was slightly reduced. Magnetic properties of carbonyl iron powder were not enormously changed after modified by vinyltrimethoxysilane. However, the complex permittivity of the carbonyl iron powder was reduced, which improved the impedance matching properties with the free space and the dissipation of the electromagnetic wave.The dispersibility of carbonyl iron powder in polychloroprene was improved by adding an anti-setting agent of organobentonite during the formation of films, which made the both sides of the single-layer film have the similar microwave absorbing properties, and the homogeneity of the composite film was improved.With a thickness of 0.68 mm, areal density of 1.3 kg·m-2, the maximum reflection loss of the single-layer composite film was -22.67 dB, and the frequency width with reflectivity larger than -8 dB reached 4.55 GHz of the whole frequency range. A three-layer composite film of transparent layer, transition absorption layer and significant magnetic absorption layer was designed. The transparent layer containing proper amount of graphite reduced the direct reflection of the electromagnetic wave, which improved the impedance matching properties of the film. A structure of gradually increased magnetic loss was composed of transition absorption layer whose electromagnetic parameter was adjusted through the mixture of graphite and carbonyl iron powder and significant magnetic absorption layer, which increased the dissipation of the electromagnetic wave. With a thickness of 0.64 mm and areal density of 0.71 kg·m-2, the maximum reflectivity of the three-layer film was -13.45 dB,and the frequency width with reflectivity above -8 dB reached 5.51GHz of the whole frequency range. It's an effective method for absorbing electromagnetic wave through designing a three-layer film made up of transparent layer, transition absorption layer and significant magnetic absorption layer.The magnetic anisotropic properties of the single-layer composite film was increased by the magnetic field, and the magnetic moment of the particles was regularly arranged. The dissipation of the electromagnetic wave can be enhanced by vertical magnetization. Some further study needs to do to find out of the principle of the dependence between the magnetic field and the dissipation of the electromagnetic wave of the composite film.