| In recent years,the rapid development of wireless communication and electronic equipment has brought convenience to life.At the same time,the problem of electromagnetic interference and pollution have become increasingly serious.Electromagnetic pollution not only affects the normal operation of instruments and equipment,but also poses a great threat to human health.Therefore,developing electromagnetic wave absorbing materials is an urgent task at present.Carbon/magnetic composite absorbing materials circumvent the problem of high density and poor impedance matching of magnetic materials.Besides,they also add magnetic loss to the single dielectric loss mechanism of pure carbon materials,which can achieve the attenuation of electromagnetic waves through a double loss mechanism.In this paper,we prepared carbon-based composite absorbing materials with multiscale structures by optimizing the structural design of carbon/magnetic composites.The multi-scale material is synthesized by a simple one-step calcination method using economical and environmentally friendly petroleum asphalt as the carbon source,melamine as the inducer and iron nitrate as the catalyst.The zero-dimensional iron carbide particles are uniformly embedded inside the porous carbon nanosheets and melamine-induced carbon nanotubes.The one-dimensional carbon nanotubes spread out from the surface of the two-dimensional porous carbon nanosheets,which interleaving with each other to form the multi-level network.The network can provide a large number of interfaces and abundant defects and contributing to the attenuation of electromagnetic waves.By adjusting the experimental parameters,we prepared multiscale structured composites at the quantity of 0.4 g of iron nitrate and 5 g of melamine.The material has favorable multiscale structure,impedance matching and strong attenuation at a filling rate of 10 wt.%,with an absorption rate of-59.76 d B and an effective absorption bandwidth of 5.2 GHz at a thickness of 1.63 mm.Combining the characterization of the material structure,the variation of the electromagnetic parameters and the calculation of the radar scattering cross-sectional area by the simulation software,it can be assumed that the conductive network and the double loss mechanism of dielectric loss due to the large number of interfaces and dipoles and magnetic coupling formed by the uniformly dispersed magnetic particles lead to the excellent absorption performance.The structural advantages of the multi-scale structure not only lead to excellent wave absorption but also excellent protection of the sample against acid,alkali,and salt corrosion and high-temperature oxidation due to the iron carbide particles encased in a thin carbon layer.In addition,the intertwined and cross-linked internal structure enables the formation of NC/N-CNT@Fe-0.4 hybrid paper as well as NC/N-CNT@Fe-0.4/WPU flexible films in combination with nanocellulose and aqueous polyurethane.In summary,this paper has prepared multi-scale structural composites by a simple synthesis method.We optimize the structure and absorbing properties of the materials through a series of comparative experiments.Then,the reasons for the formation of multi-scale structures and the mechanisms for the enhancement of absorbing properties is summarized.Finally,this work provides new ideas for the design development and application of future absorbing materials by exploring the multi-functionality of multiscale structural materials and the prospect of intelligent applications. |
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