Study On Synthesis And Function Of Electromagnetic Wave Absorption And Shielding Materials

With the advancement of science,technology and the high development of the information society,the threat of electromagnetic waves can be seen everywhere,from human health to defense security,which has become a matter of close concern to society.Therefore,the demand for electromagnetic protective materials is increasing.Microwave absorption materials and electromagnetic shielding materials are two major weapons to deal with electromagnetic pollution.Nowadays,microwave absorption materials are faced with many problems,for example,the loss peaks are too concentrated,and the applicable frequency is narrow.In this essay,the carbon-coated iron-coated hollow magnetic microspheres with adjustable cavities were prepared by the template method,and used as light-weight hollow magnetic microsphere absorbing agents with adjustable absorption frequency and bandwidth.In order to change these shortcomings,we used a template method to prepare hollow magnetic microspheres composed of iron coated by carbon with adjustable cavities,and used it as a light-weight hollow magnetic microsphere absorber with adjustable absorption frequency and bandwidth.The three-dimensional conductive network has attracted widespread attention in the field of electromagnetic interference shielding due to its light weight,porosity,and excellent conductivity.At the same time,MXene shows great potential in the field of electromagnetic shielding due to its outstanding electrical properties.However,due to the limitation of functional groups on the surface of MXene and the weak force between nanosheets,it is difficult to assemble pure MXene into a lightweight and stable three-dimensional structure.Therefore,we built an ultra-lightweight MXene-based multifunctional electromagnetic shielding aerogel based on the synergy of MXene nano sheets and acidified carbon nanotubes.This MXene-based aerogel has excellent electromagnetic shielding properties,super elasticity and thermal insulation.The main research contents are as follows:(1)Preparation and microwave absorbing properties of hollow magnetic microspheres composed of iron coated by carbon with adjustable cavities(Fe@C HS)by template method:three kinds of polystyrene(PS)microspheres with different sizes were synthesized as hard templates.Then,their surface was sequentially coated with ferric hydroxide and polydopamine through a buffer solution,and finally three kinds of Fe@C HS with different cavities sizes were obtained through a carbothermal reaction.Microwave absorption performance and absorption frequency obviously depend on the size of the cavity.More importantly,Fe@C HS-780 with the largest cavity has an effective absorption bandwidth of up to 7.5 GHz and a maximum reflection loss of 37.7 dB.These outstanding properties are attributed to not only the good synergy of dielectric and magnetic losses,but also the increased attenuation capability and improved impedance matching of hollow structures.This work can provide an effective method for designing and manufacturing high-performance and broadband microwave absorbers with adjustable peak frequency.(2)Ultra-light,Recoverable and electromagnetic shielding MXene/CNTs aerogel(MCA):based on the synergy between MXene nanosheets and acidified carbon nanotubes(CNTs),the ultra-light MXene-based multifunctional aerogel is constructed with the help of directional freezing and freeze-drying methods.MXene nanosheets are used to construct a porous frame structure,and acidified CNTs tangle,connect in series and hydrogen bond with MXene,thereby enhancing the network strength,and endowing MCA light weight and super elasticity,high conductivity as well as small resistance changes during compression.It is possible to prepare conductive nanocomposites by compounding this aerogel with paraffin wax,and the excellent electromagnetic shielding performance of about 45 dB can be obtained in the X-band with extremely low filler content(0.295 vol%).In addition,due to its highly porous structure and extremely low density,the aerogel has an excellent thermal insulation ability.The thermal insulation effect of MCA-1 is significantly better than that of commercial melamine foam and expanded polystyrene foam.Thanks to the inorganic system,MCA can still be compressed and rebound in the tube furnace of 300? or liquid nitrogen,showing great potential in dealing with extreme environments.