Preparation And Electromagnetic Wave Absorption Performance Of Composite Absorbers Based On One-Dimensional Dielectric Materials

With the rapid development of modern technology and the electronic industry,many electronic products have entered people’s daily life,which not only brings convenience but also causes a large amount of electromagnetic radiation.The electromagnetic pollution has become a new social hazard to threaten human health.Therefore,developing and researching new-generation electromagnetic wave absorption materials have become the key issue to achieving electromagnetic protection.Substantial progress has proved that one-dimensional dielectric materials possess more stronger dissipation ability on electromagnetic energy due to their superiority in specific surface area and shape anisotropy.Besides,the structural characteristic also determines their potential to develop multifunctional electromagnetic wave absorption materials.Integrating one-dimensional dielectric materials with carbon-based or magnetic materials,the loss mechanism can be enriched and the impedance matching can be optimized,resulting in more efficient electromagnetic wave absorption.Through the design of microstructure and material components,the composite of one-dimension dielectric materials and carbon/magnetic particles can not only take advantage of each component,but also can achieve synergistic effects between them,thus obtaining enhanced electromagnetic wave absorbing performance.Therefore,a variety of onedimension dielectric materials and carbon/magnetic particle composite absorbers are studied in this thesis as follows:(1)Boron carbonitride(BCN)/C/Co composite with a tubular microstructure is prepared by high-temperature pyrolysis method.The size of the Co particles can be characterized as approximately 20 nm and are uniformly dispersed on the walls of the BCN nanotubes.The presence of the BCN nanotubes not only optimizes the impedance matching but also promotes the dispersity of the Co nanoparticles,contributing to the efficient utilization of the excellent dielectric loss and magnetic loss capabilities of the metal-organic framework(MOF)derivatives.In addition,the one-dimensional BCN/C/Co nanocomposites have abundant heterogeneous interfaces that induce interfacial polarization,which is confirmed by further electromagnetic simulations.As a result,the one-dimensional BCN/C/Co composite exhibits excellent electromagnetic wave absorption performance.The minimum reflection loss of the BCN/C/Co nanocomposites is-56.7 dB at 12.4 GHz and the maximum effective absorption bandwidth is 5.5 GHz at the thickness of 2.6 mm.(2)In order to reduce the filling ratio and further reduce the density of the material,SiO2/reduced Graphene Oxide(rGO)composite aerogel is synthesized by a freezedrying and high-temperature pyrolysis processes.The three-dimensional porous structure of the aerogel not only reduces the density,but also provides a large number of electromagnetic wave transmission channels and reflection interfaces,which can enhance the loss capacity of electromagnetic wave.The introduction of onedimensional SiO2 nanofibers solves the problem of agglomeration of graphene nanosheets and modulates the electromagnetic parameters,which is conducive to obtain excellent electromagnetic wave absorption performance of the SiO2/rGO composite aerogel.The minimum reflection loss of the SiO2/rGO composite aerogel is-74.5 dB at 1.8 mm,and the effective absorption bandwidth is 5.7 GHz at the thickness of 2.1 mm.In addition,because of the assembly of flexible SiO2 nanofibers with graphene,coupled with the porous structure,excellent performance in mechanical properties,photothermal properties,and thermal insulation properties could also achieve.The SiO2/rGO composite aerogel shows further promising application in multifunctional electromagnetic wave absorption material.(3)In order to further enhance the loss mechanism and expand the maximum effective absorption bandwidth,by introducing metallic magnetic components into the SiO2/rGO system,SiO2/rGO/Co ternary composite aerogel is prepared via directed freeze-drying and high-temperature pyrolysis.The Co metal particles uniformly disperse on the graphene surface,inevitably forming many defects on the graphene surface during the reduction process.The defect sites trap carriers and disrupt the charge distribution balance,thus inducing the occurrence of polarization processes.The addition of Co not only introduces magnetic losses,but also optimizes the impedance matching characteristics.As a result,SiO2/rGO/Co exhibits excellent absorption performance,with a minimum reflection loss of-69.2 dB at a thickness of 2.6 mm and a maximum effective absorption bandwidth of 7.12 GHz(10.96-18.00 GHz)at a thickness of 3.0 mm,completely covering the Ku band and achieving effective absorption over a wide frequency range at almost all matched thicknesses.The electromagnetic wave absorption performance of SiO2/rGO/Co is much higher than that of other reported graphene-based composite materials,further demonstrating its potential as a highly efficient electromagnetic wave absorber.