| In recent years,with the continuous upgrading of military detection technology,the higher requirements for stealth absorbing materials have been put forward,which not only require absorbing materials to have good oxidation resistance and chemical stability,but also to meet the wide bandwidth,thin thickness,light weight and strong absorption characteristics.Graphene has the advantages of good dielectric property,special microstructure,low specific gravity and excellent chemical stability,so it has a broad application prospect in the field of radar wave absorption.However,the high dielectric constant of single graphene absorbing material is not conducive to impedance matching,resulting in its poor microwave absorbing performance.Fortunately,combining it with magnetic loss material can effectively improve the electromagnetic matching characteristics and enhance the microwave absorbing performance.Hence,how to effectively couple graphene with other loss mechanism materials and optimize the structure and properties of multifunctional graphene-based composites with specific composition,structure as well as performance is still a great challenge.Nowadays,graphene-based microwave absorption materials(MAMs)mainly focus on two-dimensional structure.Three-dimensional graphene materials with complex porous network structure in which could generate multiple reflection and scattering is conducive to enhance the loss capacity.Compared to the typical two-dimensional graphene-based absorbing materials,the graphene foams with special three-dimensional structure show more excellent electromagnetic absorption characteristics.Combining the magnetic metal particles with graphene foams can realize ultra wide-band electromagnetic response,improving the microwave absorbing properties of the graphene foams composites.Therefore,in this paper,three-dimensional magnetic graphene foam composites and three-dimensional magnetic graphene aerogel composites have been designed and prepared to meet the requirements of light weight,wide band and high strength absorption performance of stealth wave absorbing materials.Inspired by the material structural design,various magnetic nanoparticles were deposited on the graphene sheets by hydrothermal reaction and in situ chemical reduction self-assembly process.A variety of magnetic graphene foam composites(MGF@Co?MGF@Ni?MGF@Fe3O4)with excellent microwave absorption capabilities and strong corrosion-resistant performance were successfully constructed.The effects of the kinds and contents of metal particles on the microwave absorption properties of composites were investigated.The experiments results revealed that the as-prepared MGF@Co?MGF@Ni and MGF@Fe3O4 composites with high porosity,high specific surface area and light weight are consist of highly wrinkled reduced graphene oxide sheets,and show three-dimensional architecture.The minimal reflection loss value of the MGF@Co composite could reach-65.8 dB at the absorber thickness of 1.9 mm,and its effective absorption bandwidth(RL?10 dB,EAB)was 5.2 GHz under 27wt.%filling content.After being immersed in 0.1 mol/L hydrochloric acid solution,the saturation magnetization of the MGF@Co composite only decreased by 8%.When the matching thickness was 3.2 mm,the minimal reflection loss value was-47.1 dB,and the effective absorption bandwidth was 5.4 GHz.The minimal reflection loss value of the MGF@Ni composite could reach-58.7 dB at the absorber thickness of 2.3 mm,and the effective absorption bandwidth was 5.8 GHz under 23wt.%filling content.After being immersed in 0.1 mol/L hydrochloric acid solution,the saturation magnetization of the MGF@Ni composite slightly decreased.When the matching thickness was 2.1 mm,the minimal reflection loss value was-45.4 dB,and the effective absorption bandwidth was 5.2 GHz.The minimal reflection loss value of the MGF@Fe3O4 composite could reach-64.4 dB at the absorber thickness of 3.1 mm,and the effective absorption bandwidth was up to 6.0 GHz under 23wt.%filling content After being immersed in 0.1 mol/L hydrochloric acid solution,the saturation magnetization of the MGF@Fe3O4 composite only decreased by 3%.When the matching thickness was 2.3 mm,the minimal reflection loss value was-49.4 dB,and the effective absorption bandwidth was 6.2 GHz.With the increase of the contents of metal particles,the microwave absorption properties of the three kinds of composites were firstly enhanced and then decreased,and the minimum reflection loss values shifted to the low frequency with the increase of the matching thickness.The comprehensive performance of the as-obtained three-dimensional composites were greatly superior to the most magnetic graphene-based absorbing materials reported recently in the literature.Starting from the material structural design and performance optimization,various magnetic nanoparticles were anchored on the graphene sheets by chemical reduction selfassembly process and in situ pyrolysis.A variety of magnetic graphene aerogels composites(SHGA@Fe3O4?SHGA@Co?HGA@Ni)with excellent microwave absorption capabilities and(super-)hydrophobic property were successfully constructed.The effects of the kinds,contents of metal particles and calcination temperature on the microwave absorption properties of composites were investigated.The experiments results revealed that the minimal reflection loss value of the SHGA@Fe3O4 composite could reach-57.94 dB at the absorber thickness of 3.0 mm,and the effective absorption bandwidth was 5.7 GHz under only 5wt.%filling content.The minimal reflection loss value of the SHGA@Co composite could reach-51.6 dB at the absorber thickness of 2.4 mm,and the effective absorption bandwidth was 6.2 GHz under only 4.25wt.%filling content.The minimal reflection loss value of the HGA@Ni composite could reach-52.3 dB at the absorber thickness of 3.0 mm,and the effective absorption bandwidth was up to 6.5 GHz under only 4.25wt.%filling content.With the increase of the filling amount and calcination temperatures,the microwave absorption properties of the three kinds of magnetic graphene aerogel composites were firstly enhanced and then decreased,and the minimum reflection loss values moved to the low frequency with the increase of the matching thickness.The microwave absorption performance of magnetic graphene aerogel composites is better than that of the corresponding magnetic graphene foam composites,and the filling content is only about 5wt.%,which has great advantages for practical application.The contact angles of SHGA@Fe3O4,SHGA@Co and HGA@Ni composites increases with the increase of calcination temperatures,and the maximum contact angles reaches 151.8°,152.0° and 137.9°respectively.Importantly,SHGA@Fe3O4 and SHGA@Co composites show super-hydrophobic properties,which endow them specific applications of waterproof,anti-icing and corrosion resistance.Meanwhile,the environmental water droplets could roll on the super-hydrophobic surface,which can remove the adsorbed dust and contaminants,achieving the self-cleaning function.The excellent microwave absorption ability of magnetic graphene foam/aerogel composites mainly benefits from the following reasons.First,the unique 3D porous structure can not only enhance the impedance matching,but also induce multiple scattering and reflection.Second,the improved conduction loss,dielectric loss(interface polarization/dipole polarization)and magnetic loss(natural resonance/exchange resonance)are another factor.Third,the synergistic effect between different loss mechanisms further improves the microwave absorption performance. |
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