| Due to low density,corrosion resistance,large specific surface area and excellent conductivity,the 3D porous structure graphene composite aerogel has shown great application prospects which in the fields of electromagnetic shielding and wave absorbing materials.In this paper,the combination of freeze drying and high temperature reduction treatment is used to prepare graphene composite aerogels.By adding different material compositions and microstructure design,the synergy between the dielectric loss/magnetic loss and electrical/dielectric properties of the sample is adjusted.The correlations between the sample performance,composition and structure are analyzed,and the absorbing performance and corresponding absorbing mechanism of the composite aerogel are studied.First,we use the advantages of CNTs which have superior electrochemical performance,heat and oxidation resistance,controllable dielectric properties,and good stability to prepare CNTs/rGO composite aerogels by high-temperature reduction method.And the three-dimensional porous structure of different CNTs effect of microwave absorption characteristics of CNTs/rGO composite aerogel are studied.Experimental data shows that the composite aerogel containing 33.3% CNTs / rGO at21.7 GHz has a minimum reflection loss of-50.1 dB.The good microwave absorption performance is due to the good impedance matching produced by the three-dimensional porous structure,which can not only adjust the dielectric constant but also cause reflection and scattering,thus consuming more energy.Next,we use the advantages of CoNi which the high temperature resistance,corrosion resistance,high permeability and saturation magnetization to prepare CoNi/rGO composite aerogel with porous structure.Among them,w en the absorbent layer thickness is 3.2mm,the minimum RL value of the composite aerogel with 50% CoNi/rGO can reach-22.5db at 18.3 GHz.We can know that CoNi/rGO composite has good dielectric loss and magnetic loss which can effectively convert electromagnetic energy into thermal energy and attenuate microwave;at the same time,the impedance matching of the sample can be adjusted by the introduction of CoNi alloy,thus This results in more microwave absorption and less reflection;in addition,the porous structure of CoNi/rGO aerogel also helps interface polarization and scattering to enhance microwave absorption.Finally,a three-dimensional porous CoNi/CNTs/rGO composite aerogel are prepareed to combined the excellent properties of magnetic metal CoNi and conductivefiller CNTs.Experiment show that the obtained three-dimensional porous structure helps to enhance the microwave absorption ability,and at the same time,between dielectric loss and magnetic loss between three phases were played the synergy makes the CoNi/CNTs/rGO composite material.When the thickness of the absorption layer1.5 mm,at 25.7 GHz,the minimum RL of the 33.3% CoNi/CNTs/ rGO composite material is-54.7 dB,and the effective bandwidth(RL <-10 dB,90% microwave dissipation)is covered at full frequency in the K-band.Because CoNi/CNTs/rGO has strong matching and strong dissipation ability,the special porous structure also helps microwave absorption,which causes multiple reflections and scattering of microwaves.Therefore,the prepared porous structure CoNi/CNTs/ rGO aerogel can bring new ideas for the design of broadband,strong absorption and thin microwave absorbers. |
