Preparation And Microwave Absorption Properties Of Boron-Nitrogen Co-Doped Carbon Nanotube Composites With Embedded Metal Particles

In recent years,microwave electronics and communication technology have developed rapidly,and people have used electronic equipment more and more frequently,while these electronic instruments bring many conveniences to people,electromagnetic interference and electromagnetic radiation also affect people's health and living environment at all times.In order to prevent electromagnetic pollution from becoming more and more serious,countries currently have higher requirements for the design of electromagnetic wave absorbing materials.The development and preparation of absorbing materials that meet human needs has become a serious challenge for materials science research.Carbon nanotubes have attracted people's attention because of their high electrical conductivity,light weight,strong oxidation resistance and large specific surface area,and have become an electromagnetic wave absorbing material with unlimited potential.Due to many limitations,carbon nanotubes are usually not used alone.Many researchers prefer to study carbon nanotubes coated with nano-metal particles.The metal particles are embedded in the carbon nanotubes,which can prevent the particles from agglomerating and help prevent the metal particles from being oxidized.The carbon nanotubes are doped with boron and nitrogen elements,and magnetic metal particles are embedded in the carbon nanotubes,the boron-nitrogen co-doped carbon nanotube composite nanomaterial with embedded metal particles can be used as a new high-performance absorbing material.It has the characteristics of strong controllability,good compatibility,thin thickness,light weight and bandwidth,so it has attracted much attention.This thesis studied and prepared boron and nitrogen-codoped CNTs with embedded metal nanoparticles,and change the type of metal particles embedded in carbon nanotubes and the alloy ratio,and carefully discuss and analyze the absorbing performance and main mechanism of this type of material as electromagnetic wave absorbers.The research contents are as follows:(1)Based on the influence of heteroatom-doped carbon nanotubes on the electromagnetic wave absorption properties of the material,a composite material of boron and nitrogen co-doped carbon nanotube with embedded nickel nanoparticles was prepared(Ni@BNCNTs).In order to confirm the influence of the doping of boron atoms on the electromagnetic wave absorption performance of the material,we used a composite material of nitrogen-doped carbon nanotube with embedded nickel nanoparticles(Ni@NCNTs)as a control group.Ni hydroxide was prepared by simple acid-base neutralization reaction,and then annealed and heat treated under the same conditions to obtain Ni@NCNTs composite material.Experiment result shows that the Ni@BNCNTs composite material has a minimum reflection loss of-37.5 d B at an annealing temperature of 800~oC,an absorption thickness of 2.5 mm,and a frequency of 8.6 GHz;when the absorption thickness is1.5 mm,there is an effective bandwidth(the reflection loss is less than or equal to the frequency range covered by-10 d B)is 3.92 GHz.It is concluded that the doping of B atoms significantly improves the electromagnetic wave absorption performance of the material.The Ni@BNCNTs prepared in this thesis have potential applications prospects in the field of electromagnetic wave absorption.(2)Based on the urgent need for high-performance electromagnetic wave absorbing materials,the boron-nitrogen co-doped carbon nanotube composite material with embedded nickel-iron alloy nanoparticles(NiFe@BNCNTs)was prepared by a simple and easy-to-operate method,and the influence of the introduction of Ni on the microwave absorbing properties of the nanocomposite was discussed.First,a composite material of boron-nitrogen co-doped carbon nanotubes embedded with iron nanoparticles(Fe@BNCNTs)was prepared,and its electromagnetic wave absorption properties at different calcination temperatures were studied.By testing its microscopic morphology,it is found that the sample carbon nanotubes calcined at 900~oC have the optimal growth of carbon tubes.By testing its electromagnetic parameters and the reflection loss intensity under different absorbing layer thicknesses in the range of 2-18 GHz,compared with the Ni@BNCNTs prepared in this thesis,it is found that nickel particles embedded in carbon nanotubes have more advantages than iron particles in electromagnetic wave absorption performance.Then changed the type of metal,change the iron to a nickel-iron alloy,and prepare a composite material of boron and nitrogen co-doped carbon nanotube with embedded nickel-iron alloy nanoparticles(NiFe@BNCNTs).The electromagnetic wave absorption performance of different alloy ratios(Ni:Fe=1:2,Ni:Fe=1:1,Ni:Fe=2:1)was studied under the same calcination temperature.Through the research and analysis of the attenuation ability and impedance matching performance of the NiFe@BNCNTs composite material,it is concluded that the combined action of the appropriate Ni/Fe ratio and the special microstructure in the material give the material excellent wave absorbing performance.And it is concluded that the more Ni content,the better the electromagnetic wave absorption performance of the composite material.When the NiFe ratio is 2:1 and the thickness is 4.5 mm,the absorber has the best reflection loss intensity of-40 dB at a frequency of 5.2 GHz.