Design Of Micro And Nano Structures Of Carbon-Based Magnetic Composites And Their Wave Absorption Properties

With the rapid development of mobile base stations,high-speed processors,broadband radar,satellite communications and other electronic information technology equipment,electromagnetic interference and pollution are serious.In order to solve this problem,many efforts have been made to attenuate electromagnetic waves by using high performance electromagnetic wave absorbing materials that convert electromagnetic waves into thermal energy.In this study,three-dimensional/two-dimensional/one-dimensional carbon materials were used as the research objects respectively,and the modulation of the microstructure of carbon-based magnetic composites was realized based on different preparation processes,and the effects of microstructure,size,selected composite components on electromagnetic parameters and the relationship between them and wave absorption performance were investigated,and the broadband absorption of electromagnetic waves was achieved at a lower filling ratio.The main research contents and results of this thesis are as follows:Based on three-dimensional porous carbon,Fe/Fe₃C@C/C composites with pomegranate-like structure were constructed by sol-gel and chemical vapor deposition methods.The Fe³⁺ions were immobilized on the glucose polymer template by the sol-gel method,and Fe³⁺was converted to monomeric Fe after the carbothermal reduction reaction.during the chemical vapor deposition process,the supplementation of gaseous carbon source promoted the formation of Fe-C solid solution.When the solubility of the carbon source in the Fe particles reached the peak,with the decrease of temperature,it precipitated again on the surface of Fe particles to form graphitized carbon shells,and the remaining carbon inside the particles reacted with Fe to form Fe₃C.It can be found by transmission electron microscopy that this pomegranate-like structure with Fe/Fe₃C as the seed and graphitic carbon layer as the shell successfully achieved the separation of magnetic metals at the micro-and nano-scale.The synergistic effect of dielectric loss and magnetic loss balances the excessive dielectric constant of pure carbon material and improves the impedance matching.The minimum reflection loss at 8.88 GHz is-33.2 d B when the sample to paraffin ratio is 1:6,and the effective absorption bandwidth is up to 6.08 GHz when the matched thickness is 2.5 mm.Ni@C/RGO hybrid aerogels with Checkerboard-like structures were prepared by electrostatic self-assembly and chemical vapor deposition based on two-dimensional graphene.The prepared Ni（OH）₂nanosheets and graphene oxide（GO）were electrostatically self-assembled to form a tessellated stacked structure,and the product Ni（OH）₂/RGO aerogel was obtained by hydrothermal reduction and then lyophilized in a vacuum environment.During the subsequent thermal treatment,the Ni（OH）₂nanosheets were converted into metallic Ni monomers and catalyzed the decomposition of RGO.The decomposed RGO re-enters the Ni nanoparticles as a gaseous carbon source and precipitates on the surface of the Ni nanoparticles with decreasing temperature to form a conformal carbon shell.The unique tessellation-like structure reduces the density of the composite,and the lowest RL can reach-48.68 d B at a filling of 6.2 wt%,which occurs at12.3 GHz.The effective absorption band reaches 4.56 GHz（8.32～12.88 GHz）when the thickness is 2.5 mm.One-dimensional biomass-based carbon micron tubes with scale-like surfaces were prepared by growing ZIF-67 coatings on their surfaces by vacuum impregnation.The ZIF-67 coating was homogeneously grown on the surface by vacuum impregnation method using the fruit hairs of Pendula sylvestris as raw material.It can be understood from previous studies that the metal ions in MOF have good dispersion and the Co²⁺in the ZIF-67 particles are converted to Co monomers after the carbonization process.It can be observed from the SEM images that the morphology of ZIF-67 is largely preserved,thus ensuring the separation of magnetic metals.The one-dimensional biomass carbon tubes with high aspect ratio are interlaced and intricately lapped together to form a conductive network,extending the electromagnetic wave transmission path.The sample can reach a minimum RL of-29.94 d B at 5.92 GHz,and the effective absorption band is as wide as6.08 GHz（11.92～18.00 GHz）when the matched thickness is 2.6 mm,covering the entire Ku band（12～18 GHz）.