Study On Preparation And Electromagnetic Properties Of CNTs/Co/rGO Composite Materials

In recent years,with the large-scale entry of electronic products into daily life,the widening of working frequency of electronic devices and the need of national defense development,more and more attention has been paid to microwave absorbing materials.Ferromagnetic metals have high saturation magnetization and high Snoke limit,which theoretically makes ferromagnetic metal particles have high permeability in high frequency range.It is one of the potential hot-spot absorbing materials.However,there are still some shortcominOe,such as its single absorbing mechanism,poor impedance matching,agglomeration and oxidation of metal nanoparticles,and strong eddy current effect,which limits its application as absorbing materials.In this paper,cobalt-glycolates with different morphologies,such as sphere,disc,flower,cluster and snowflake,were prepared by metal alkoxide method.On the basis of cobalt-glycolates percursor,Co/CNTs composites with different morphologies and sizes were prepared simply using dicyandiamine as carbon source and Co as active site in situ catalytic growth of carbon nanotube.Because the magnetic loss of Co is prominent in the low frequency band,while the dielectric loss of carbon nanotubes is strong in the high frequency band,the composite of Co and carbon nanotubes can effectively broaden the absorbing frequency range of materials.Moreover,the combination of Co and CNT introduces a large number of interfaces and defects,which greatly increases the number of electric dipole moments and dielectric loss.Among these materials,the snowflake-like Co/CNTs composites obtained by 600~oC calcination not only have good geometric effect,but also have abundant dielectric loss mechanism.When mixed with paraffin wax at20wt.%filling rate,the strongest absorption value reaches-72.65dB(matching thickness4.09mm),with an effective absorption bandwidth of 3.2GHz.In order to obtain composites with higher saturation magnetization,CoFe/C nanoribbon composites were prepared by using(Co,Fe)-glycolate nanoribbons as templates.CoFe/C nanoribbons exhibit a strongest reflection loss of-63.02dB with an effective absorption bandwidth of7.3GHz.In order to further enrich the loss mechanisms of materials,CNTs/Co/rGO ternary composites were prepared using Co-glycolate/GO as precursor.Reduced graphene oxide has a high specific surface area and a large number of interfacial polarization processes,so it has a strong dielectric loss,which makes it be considered as a potential microwave absorbing material.However,simple combination of rGO and Co will cause the agglomeration of Co particles and decrease the dielectric relaxation interface with the increase of preparation temperature.Co-glycolate was coated on GO by metal alkoxide method.To effectively inhibit the polymerization of Co,Co/CNTs was grown in situ on reduced graphene oxide using Co as active site catalyst,so that the CNTs/Co/rGO composite was prepared.CNTs/Co/rGO composite synthesized by reflux reaction at160~oC for 1 h and calcination at 600 ~oC for 2 h in hydrogen atmosphere has uniform Co/CNTs structure,rich dielectric loss mechanism,and weak eddy current effect,thus it can get better impedance matching.When the material is mixed with paraffin at 20wt.%filling rate,the max reflection loss is-63.7dB(matching thickness is 2.28mm),and the effective absorption bandwidth reaches 5.12GHz.