Preparation And Microwave Absorbing Properties Of 3D Graphene,and 3D Graphene/Ni Composite

Microwave absorbing materials have been widely applied in military and civil fields.On the one hand,it provides stealth protection for military operations.On the other hand,it ensures human health and the normal operation of electronic components.However,since the traditional material failed to fulfill the increasing demand in various industries,new absorbing materials are in urgent need of research and development.Graphene,a promising material with low density,excellent thermal stability,good chemical stability,good mechanical properties,good conductivity and so on,is expected to be a new materials with excellent performance,which can meet the increasingly harsh demand in various fields.In this thesis,the three dimensional graphene（3DGN）is successfully prepared by the self-assembly of graphene oxide（GO）in the reduction process of L-ascorbic acid（L-AA）,in which the concentration of GO and the concentration of L-AA have great influence on the microstructure and absorption properties of 3DGN.The greater the concentration of GO,the more the graphene sheets in 3DGN change from disorder to stacking.The greater the concentration of L-AA,the faster the 3DGN is formed.With the increase of the concentration of GO and L-AA,the microwave absorbing properties of 3DGN first increase and then decrease.When GO concentration is 2mg/mL and L-AA concentration is 16mg/mL,3DGN possesses the best microwave absorbing properties.Based on the study of 3DGN mentioned above,3DGN/Ni composite has been prepared by hydrothermal method with Ni（NO₃）₂ as Ni source.The influence of the concentration of Ni（NO₃）₂ and NaOH on the microstructure and microwave absorbing properties of 3DGNs have been studied.The higher the concentration of Ni（NO₃）₂ is,the more Ni particles will be loaded on graphene sheets.With the increase of NaOH concentration,the morphology of Ni particles in 3DGN/Ni changes from sphere to prickle sphere,while the size and distribution of particles become more and more uneven.With the increase of Ni（NO₃）₂ and NaOH concentration,the absorbing properties of 3DGN/Ni first increase and then decrease.Compared with 3DGN,3DGN/Ni consumes more microwave energy.Though Ni decreases the maximum reflection loss,the bandwidth（<-5dB）of 3DGN/Ni is broadened to 10.7GHz of3DGN/Ni-0.1,while that of 3DGN1 is 5.4GHz.With statistics gained in chapter 3rd and chapter 4th,3DGNs are used as the main body to simulate the design of multilayer absorbing materials.The simulation results show that the absorbing properties and effective bandwidth of the microwave absorbing materials with different proportions of 3DGN2 and paraffin are better than that of3DGN2 and paraffin with a single concentration.Adding appropriate thickness of graphite and NiO is beneficial to improve the reflection loss of microwave absorbing materials.The addition of graphite enhances the absorption of the material at low frequency band,while NiO plays an important role in improving the impedance matching and wave penetration,and it also serve as microwave absorbing material in the middle and high frequency bands.In conclusion,the simulation results provide a reference for the design and preparation of high-performance graphene absorbing materials with concentraition gradient.