Preparation And Properties Of Carbon Nanotube Composite Absorbing Materials

With the rapid development of science and technology,human dependence on electronic equipment is increasing.These new products bring us convenience,but also with a series of electromagnetic pollution,which has a threat to human health and nature,and also to the electronic equipment itself,military secrets and other aspects.Therefore,scientists are committed to developing a kind of material with high microwave absorption efficiency,which is an effective measure to solve the problem of electromagnetic pollution.As a typical representative of carbon materials,carbon nanotubes（CNTs）are also widely used in the field of electromagnetic absorption.They produce conductivity loss and dipole polarization to consume electromagnetic waves through their excellent conductivity.However,CNTs also have some disadvantages,such as high permittivity and low permeability,resulting in poor impedance matching,poor electromagnetic absorption performance,narrow effective absorption bandwidth and so on.In this paper,CNTs and other magnetic materials were prepared by two methods:（1）CNTs/NiFe₂O₄ composite prepared by CNTs and NiFe₂O₄;（2）Co-CNTs were synthesized by the combination of CNTs and zeolitic imidazolate frameworks ZIF-67,and then calcined at high temperature.The main results are as follows:（1）CNTs/NiFe₂O₄ composites were prepared by spraying different amount of NiFe₂O₄and anhydrous ethanol on the surface of CNTs.From the micro morphology,the distribution of NiFe₂O₄ on the CNTs beam is more uniform at a lower amount of NiFe₂O₄.With the increase of NiFe₂O₄ content,the magnetic properties of CNTs/NiFe₂O₄ composites are enhanced.The results show that the CNTs/NiFe₂O₄ composite with mass ratio of 1:1 has better electromagnetic absorption performance.When the thickness is 4.5 mm and the filling content is 20%,the minimum reflection loss RL=-44.12 d B and the absorption rate is99.996127%at the frequency of 17.11 GHz are achieved,and the effective absorption bandwidth of RL<-10 d B is 4 GHz.（2）By changing the mixing ratio of CNTs/NiFe₂O₄ and paraffin,the influence of CNTs/NiFe₂O₄ on the microwave absorption performance was tested and analyzed.It was found that when the filling amount of CNTs/NiFe₂O₄（1:1）was increased to 30%,the electromagnetic absorption performance was significantly improved at the thickness of 2 mm.The RL_min=-28.2 d B at the frequency of 13.9 GHz,the absorption rate reached 99.8486%,and the effective absorption bandwidth of RL<-10 d B was 3.86 GHz.When the filling amount of CNTs/NiFe₂O₄（1:1）is increased to 40%,the RL_min=-41.8 d B at the frequency of16.9 GHz with the thickness of 1.5 mm,the absorption rate reaches 99.99339%,and the effective absorption bandwidth of RL<-10 d B is 7.6 GHz.（3）The precursor of CNTs/ZIF-67 was successfully prepared by spraying Co（NO₃）₂·6H₂O solution on the surface of CNTs and soaking it in the mixed solution of2-methylimidazole and methanol.The results show that the purity of ZIF-67 crystal is high,and the size of ZIF-67 crystal is 200 nm.（4）Co-CNTs composites were prepared by calcining CNTs/ZIF-67 precursors at different temperatures in N₂ atmosphere.After calcination,the morphology collapses and is no longer dodecahedral structure.It is found that Co phase and Co O phase exist in the calcined samples.With the increase of calcination temperature,the magnetic properties of Co-CNTs increase gradually.It is found that the Co-CNTs calcined at 500℃have the best electromagnetic absorption performance,which is mainly reflected in the effective absorption bandwidth.When the filling amount is 20%,the minimum reflection loss is about-30 d B and the absorption rate is 99.9%at the frequency of 14.23 GHz when the thickness is 1.5 mm,and the maximum effective absorption bandwidth is 7.8 GHz when RL<-10 d B.In addition,the Co-CNTs（500℃）with the best performance were used to simulate the microwave absorption performance at low temperature,and it was found that even at low temperature,the influence on the electromagnetic absorption performance was very small,which indicated that the synthesized Co-CNTs had strong low temperature adaptability.