Study On Carbon-based Absorbent For Light And High-efficiency Wave Absorbing Structural Materials

Light and efficient absorbing structural materials are of great significance in various fields of national economy and national defense construction.At present,the selection of absorbent is the primary requirement of the design of lightweight and efficient absorbing structural materials.Carbon materials have high conductivity,large specific surface area and extremely low density,making it one of the most potential absorbers in the field of electromagnetic wave absorption.However,the high conductivity of carbon materials will make the electromagnetic parameters of the material unbalance,resulting in the mismatch between the electromagnetic wave incident interface and the impedance of free space,and the electromagnetic wave will be fully reflected at the incident surface.Therefore,it is necessary to improve the impedance matching characteristics of carbon-based absorbing materials by modifying them.Firstly,using conductive carbon black（CB）,carbon nanotubes（CNT）and reduced graphene oxide（rGO）as dielectric loss absorbers,the electromagnetic parameters and absorbing mechanism of carbon materials with different morphological characteristics were analyzed.On this basis,rGO was selected as the modified object to prepare two kinds of graphene-based composite absorbers,and their electromagnetic and wave-absorbing properties at 0.5-18 GHz were analyzed.The microstructure,phase composition,chemical state,thermal stability and electromagnetic parameters of the composite absorbent were studied by means of SEM,TEM,XRD,Raman,XPS,TGA and VNA,and the absorbing mechanism was analyzed.Specific research contents are as follows:（1）Based on the phase composition and microstructure,the electromagnetic properties of three carbon based absorbers with different mass fractions were studied,and the absorbing loss mechanism was analyzed.The results show that rGO has more abundant defect characteristics and high dielectric loss,which makes rGO more suitable as a modified absorber compared with CB and CNT.（2）Reduced graphene oxide-NiZn ferrite（rGO-NZF）composite absorbent was prepared by hydrothermal method.The morphology,structure and electromagnetic properties of the composite absorbent varied with the proportion of components,and the absorbing mechanism was analyzed.The results show that the absorption properties of the composite absorbers vary greatly with the content of rGO.The 10rGO-NZF sample showed excellent absorbing performance,and the minimum reflection loss was-41.3d B at the frequency of 10.8 GHz when the thickness was 2.5 mm,and the effective bandwidth was 5.68 GHz（11.7-17.38 GHz）when the thickness was 2 mm.（3）Reduced graphene oxide-NiZn ferrite@Si O₂ composite absorbent（rGO-NZF@Si O₂）was prepared by a one-pot method.The effects of coating structure on the microstructure,phase structure,thermal stability and wave absorption performance of the composite absorbent were investigated.The results showed that the core-shell NZF@Si O₂ nanoparticles modified the multilayer rGO to form a three-dimensional heterogeneous structure,which alleviated the strong reflection of electromagnetic wave caused by rGO and improved the impedance matching characteristics of the composite absorber.Through the synergistic interaction of NZF@Si O₂ and rGO,the minimum reflection loss of-49 d B is achieved at a frequency of 10.7 GHz at a thickness of 2.9 mm,and the effective absorption bandwidth reaches 5.7 GHz（12.3-18 GHz）at a thickness of2.2 mm.Moreover,the introduction of Si O₂ temperature resistant layer can effectively reduce the decomposition rate of the sample,thus prolongating the thermal stability time of the sample and expanding the application field of graphene-based composite absorbent.