Investigation On Synthesis And Electromagnetic Wave Absorption Characteristics Of Carbon-based Composite Materials

With the rapid development of electronic equipment,wireless communication tools and local area networks,electromagnetic interference has greatly threatened human health and disrupted various commercial or industrial equipment.The demand for electromagnetic absorbers is imminent.Nowadays,the requirements for absorbing materials are becoming higher and higher.Not only the materials are required to have strong absorption and frequency bandwidth,but also require thin thickness and light weight,and have good chemical stability to adapt to a variety of complex environments.Carbon materials are promising candidates for absorbing materials due to their high electrical conductivity,abundant resources,low density,and excellent thermal stability.However,carbon materials can only attenuate electromagnetic waves through a single dielectric loss,and their high conductivity usually leads to poor impedance matching performance,which hinders their further development in microwave absorption.Combining lightweight carbon materials with magnetic materials to make full use of the synergistic effect between magnetic and dielectric components in composite materials to improve poor impedance matching performance is an effective solution.In addition,the morphology,geometry,microstructure and composition of the composite material are critical to its electromagnetic absorption performance.By optimizing the composition and structure of the nanocomposite absorber,the dielectric constant and permeability of the composite can be adjusted while significantly reducing the weight to achieve strong absorption of electromagnetic wave energy in a wide frequency range.Some carbon materials,such as graphene,carbon nanotubes,and carbon fiber,have complicated preparation methods,relatively high production costs,and even pollute the environment.Therefore,it is very important to explore economic,sustainable and easy mass production synthesis strategies.In this paper,a new carbon-based nanocomposite was successfully prepared by adjusting the loss components,constructing core-shell structure,three-dimensional structure,porous structure,flower structure,honeycomb structure,surface modification and graphitization.Graphite,graphene,metal-organic framework and biomass-derived carbon materials are mainly studied as the research objects,and the effects of the loss component,morphological structure and geometry of the composite materials on the electromagnetic properties of the carbon materials are studied.The study is mainly as follows:The iron carbonyl@graphite microsphere composite material was successfully prepared by mechanical ball milling.This synthesis strategy is simple,controllable,and low-cost,and can be mass-produced.Using various characterization methods to analyze the microstructure and composition and electromagnetic properties of the composite material,it was found that the composite material fully utilized the three loss mechanisms of conduction loss material,dielectric loss material and magnetic loss to improve the matching performance and enhance the electromagnetic wave attenuation ability.In addition,by changing the grinding time and adjusting the proportion of carbonyl iron particles in the composite,the microstructure and electromagnetic properties of the composite can be well adjusted.A simple hydrothermal process was used to prepare the three-dimensional nano MnO2/graphene foam composite material.MnO2 nanoparticles are evenly deposited on the surface of the aerogel skeleton,the composite material still maintains a cross-linked 3D porous network structure,and also shows good compressibility.The influence of the content of MnO2 nanoparticles in the nanocomposite on its morphology,electromagnetic parameters and electromagnetic properties was explored.It was found that this interconnected three-dimensional porous network structure has very high impedance matching properties,which is conducive to the incidence of electromagnetic waves and generates multiple Scattering and reflecting,and there is strong interface polarization between the MnO2 nanoparticles and the graphene skeleton.The core-shell Ni@C nanocomposites were prepared by pyrolysis with nickelbased metal organic framework as the precursor.The thermal decomposition preparation.By controlling the pyrolysis temperature,the microstructure and graphitization degree of the composite material can be well adjusted.By optimizing the composition and structure of the nanocomposite absorber,the dielectric constant and permeability of the composite material can be adjusted while significantly reducing the weight,and strong electromagnetic wave energy absorption in a wide frequency range is achieved.Porous floral Ni/C composites were prepared by pyrolysis of Zn-doped NiMOF.Various characterization methods were used to analyze the microstructure and composition and electromagnetic properties of the composite material.It was found that its morphology,geometry and microstructure and other factors were crucial to determine the electromagnetic absorption performance.This special three-dimensional flower-like structure can disperse electromagnetic waves between the various layers,increasing the conduction path and scattering of electromagnetic waves is beneficial to the loss of electromagnetic waves.By changing the pyrolysis temperature,the surface microstructure and electromagnetic properties of the composite material can be adjusted simply.Using honeycomb corn kernels as raw materials,honeycomb graded porous carbon materials were prepared by microwave heating expansion and high temperature graphitization.Compared with previous reports on biomass layered porous structure,the additive-free microwave heating expansion step is a novel and environmentally friendly method that can form a regular honeycomb layered porous structure finely.Various characterization methods were used to characterize the microstructure,chemical composition and electromagnetic properties of the composite materials.The effects of graphitization degree on the electromagnetic parameters,impedance matching performance and microwave absorption performance of carbon materials were studied.Introduce magnetic substances to enhance the electromagnetic wave absorption of biomass porous carbon materials.A simple and scalable dry production process is proposed to produce carbon-coated 3D mesh Fe@C nanocomposites.Using various characterization methods to analyze the microstructure and composition and electromagnetic properties of the composite material,it was found that the composite material fully utilized the three loss mechanisms of conduction loss material,dielectric loss material and magnetic loss to improve the matching performance and enhance the electromagnetic wave attenuation ability.The effects of different annealing temperatures on the composition,microstructure,electromagnetic parameters,impedance matching,and electromagnetic attenuation capabilities of Fe@C nanocomposites were studied.