Preparation And Microwave Absorption Properties Of Halloysite/Carbon Nanotubes/Magnetic Particle Composites

EM wave absorption materials have drawn extensive attention due to their ability to convert incident EM wave energy into thermal energy.It has become one of the effective ways to solve electromagnetic pollution and guarantee national property security and residents health.In this paper,the composite absorbing material is prepared from the perspective of impedance matching characteristics and attenuation characteristics.Hollow tubular halloysite with lightweight and wave-transmitting was introduced as the material’s impedance matching modifier,combined with the electromagnetic attenuation of microwaves by carbon nanotubes and ferromagnetic materials,two multi-component composite microwave absorbing materials with excellent performance were prepared.Their basic characteristics such as phase,morphology,and electromagnetic properties were also studied.In general,the material has the advantages of simple process and low cost,and has a certain application prospect in the field of wave absorption.The mineral-based composite microspheres HNTs/CNTs were prepared by the entanglement of halloysite and carbon nanotubes by spray drying process.Then,the outer coating of Co Fe₂O₄ is completed by hydrothermal loading,and finally,Co Fe₂O₄ is converted into Fe Co alloy under H₂atmosphere to form a composite HNTs/CNTs/Fe Co.The experimental results show that the absorption performance of the reduced sample is the best when the loading of Co Fe₂O₄ is 50%of the total mass of the HNTs/CNTs/Co Fe₂O₄ composite.In the frequency range of 2-18GHz,the frequency width of the reflection loss value less than-10d B reached 6.24GHz（11.76-18.00 GHz）,and the thickness is only 1.63 mm,which can completely cover the Ku band.When the thickness is 1.81 mm,the minimum reflection loss（RL）reached-57.77 d B at 12.10 GHz.In this experimental system,the introduction of halloysite not only effectively regulates the complex permittivity of the material and improves the impedance matching,but also provides a unique hollow tubular shape to extend the reflection path of electromagnetic waves inside the material and improve the loss efficiency.Three kinds of composite materials,HNTs/CNTs/Co Fe₂O₄,HNTs/CNTs/Fe₃O₄,and HNTs/CNTs/Fe,were prepared by a one-step spray drying process by compounding halloysite,carbon nanotubes,and magnetic metal particles.The microwave absorption performance was regulated by changing the doping amount of halloysite and carbon nanotubes.The results show that when the thickness of the sample 0.4HNTs/CNTs/Co Fe₂O₄ is only 1.7 mm,the effective absorption bandwidth can reach 5.6 GHz（12.24 GHz-17.84 GHz）,and the maximum reflection loss can reach-23.06 d B at 15.44 GHz;the sample 0.4 HNTs/CNTs/Fe₃O₄,exhibits an effective absorption bandwidth of 5.76 GHz（12.16 GHz-17.92GHz）at a thickness of 1.6 mm,and reaches a maximum reflection loss value of-22.07 d B at 15.52 GHz.As for sample 0.3 HNTs/CNTs/Fe,it shows the best absorption performance,in which when the thickness is1.35 mm,the maximum reflection loss can reach-24.60 d B at 18 GHz,and the effective absorption bandwidth is 6.32 GHz（11.68 GHz-18.00 GHz）,which can completely cover the Ku band.It can well meet the requirements of new high-performance microwave absorbing materials,and the spray drying process is simple,and it is expected to be put into large-scale production.