| High-performance electromagnetic shielding materials are widely used in communication technology,stealth technology and electronic devices.In recent years,the spongy three-dimensional graphene aerogel(GA)assembled from graphene oxide(GO)has attracted extensive attention in electromagnetic shielding due to its ultra-high specific surface area and ultra-light density.In the process of GO assembly into GA,the strong interaction between the lamellas and the physical crosslinking between adjacent lamellas will seriously reduce the effective surface area of graphene sheets,resulting in the attenuation of the electromagnetic shielding performance.To solve the above problems,this paper proposed to introduce carbon fiber(CF)with structural support into GA to increase the assembled surface of graphene microplates,improve the electrical conductivity of GA and reduce the shrinkage and cracking of GA.Then,hafnium carbide nanowires(HfCnw)with high aspect ratio were composite to enhance the interface polarization loss,multiple reflection loss and conductivity loss,and finally the HfCnw-CF/GA composites with excellent electromagnetic shielding performance was obtained.In this paper,the hydrothermal self-assembly process of GA and CF/GA hybrid aerogels was studied.pyrolytic carbon(PyC)protective layer was deposited on the hybrid aerogels by chemical vapor osmosis(CVI).Finally,HfCnw was grown in situ on the hybrid aerogels by chemical vapor deposition(CVD).On this basis,the effects of the composition and structure of the material on the conductivity and electromagnetic shielding performance were studied,and the regulation mechanism and electromagnetic shielding mechanism of HfCnw-CF/GA composites were revealed.The main research contents and conclusions of this paper are as follows:(1)The effects of ethylenediamine(EDA):GO mass ratio,hydrothermal reaction time,hydrothermal reaction temperature and GO solution concentration on the preparation of GA were studied.With the increase of EDA content,hydrothermal reaction time and temperature,the interaction between graphene sheets is enhanced.With the increase of GO solution concentration,the shrinkage degree of GA decreased,the density increased,and the electrical conductivity increased.The SE_T of the prepared GA in the X-band is 23 d B to 25 d B,and the SE_R is low(2.3 d B).(2)The effects of CF ratio,CF length and GO concentration on CF/GA hybrid aerogels were studied.Shorter CF has better dispersion.With the increase of CF:GO mass ratio and GO concentration,the shrinkage degree of hybrid aerogels decreases,while the density and conductivity increase.CF has the function of supporting skeleton,which can prevent the coiling and stacking of graphene,thus reducing the shrinkage and cracking of GA,and improving the conductivity of GA.The conductivity of CF/GA hybrid aerogel can be increased to 7.78 S/cm,and the maximum SE_T of CF/GA hybrid aerogel prepared is 46 d B.(3)The effects of PyC deposition time and CVD time on HfCnw-CF/GA composites were studied.When PyC deposition time was 4 h,more HfCnw grew in HfCnw-CF/GA composites.The higher the HfCnw content in HfCnw-CF/GA composites,the higher the SE_T.The electrical conductivity of HfCnw-CF/GA composites can reach 93.95 S/cm,and the maximum SE_T is 65 d B.(4)The electromagnetic shielding mechanism of HfCnw-CF/GA composites was studied.The loss mechanism of HfCnw-CF/GA composites for electromagnetic wave includes:multiple reflection loss of electromagnetic wave in the cavity structure inside the sample;Graphene,CF,PyC and HfCnw interfaces are interfacial polarization loss caused by abundant interfaces;Dielectric loss of graphene and polarization loss caused by its own defects;Conductance loss of electron migration and transition,etc.By controlling the ratio of graphene,CF,HfCnw and PyC,the SE_Tof porous carbon matrix composites can be adjusted between 23 d B and 65 d B. |
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