Synthesis And High-frequency Electromagnetic Properties Of Fe-Si-C System Nanocapsules

In this paper,Fe3Si@C nanocapsules,nano-SiC and hollow carbon nanwires were prepared by the arc-discharge method with Fe-Si-C system as the research object,and Co9S8-DETA composite was prepared by a hydrothermal method.Their electromagnetic wave absorption performance was systematically studied in the frequency range of 2-18 GHz.It was found that by adjusting the thickness of the nanocapsule shell,introducing doping elements,and changing the morphology to adjust the microstructure of the above nanomaterials,the EM parameters of the above nanomaterials can be adjusted to conrol their EM-wave absorption properties.In this paper,a new type of nanocapsule of Heusler soft magnetic Fe3Si alloy wrapped by amorphous C shell was designed and synthesized.During the preparation process,doped Si atoms were introduced into the C shell to generate a large number of Si-C bonds,so that the crystalline C shell is transformed into an amorphous C shell.By modulating the crystalline state of the shell,the dielectric polarization is enhanced,the dielectric properties of the C shell are significantly improved,and the impedance matching between the amorphous C shell and the soft magnetic Fe3Si is more appropriate.It shows enhanced electromagnetic wave absorption characteristics.When the absorber thickness is 2.1 mm,Fe3Si@C nanocapsules have the highest absorption intensity of-68.3 dB at 13 GHz,and when the absorber thickness is 1.4 mm,the absorption bandwidth is 4.6 GHz(RL<-10 dB).As a new type of electromagnetic wave absorbing material,this nanocapsule has very important potential application value.In this paper,a one-step synthesis strategy was adopted to prepare nano-SiC with in-situ morphology control.By introducing a new N source and gas catalyst,N-doped nano-SiC was synthesized in-situ using acetonitrile(C2H3N).It was found that the micro-morphology of nano-SiC changed from a spherical shape without N-doping to a nano-sheet shape with N-doping.The surface area of the N-doped SiC nanoflake is significantly expanded to support more quantity and types of electric dipoles Combined with the optimized N-doping concentration,the imaginary part of the dielectric constant(?")and the value of the dielectric loss tan ?e are significantly increased,resulting in enhanced polarization relaxation.The N-doped nano-SiC prepared in this work has significantly improved its dielectric properties and electromagnetic wave absorption characteristics in the 2-18 GHz range compared with similar materials reported previously.When the thickness of the absorber is only 1.58 mm,the absorption bandwidth with a reflection loss of less than-10 dB can reach 4.1 GHzBy dealloying Al4C3@C nanowires with shell-core structure,hollow carbon nanowires with a large number of surface defects and a large specific surface area were prepared.Due to these characteristic defects and their unique hollow structure,the surface of the hollow carbon nanowires has a large number of non-interacting electric dipoles,resulting in the enhanced broadband absorption characteristics of the hollow carbon nanowires.Compared with conventional carbon nanomaterials,the electromagnetic absorption characteristics of the hollow carbon nanowires have been significantly improved in the 2-18 GHz range.When the absorber thickness is 1.9 mm,the minimum reflection loss of-47.1 dB can be obtained at 15.7 GHz.When the absorber thickness is 2.0 mm,the absorption bandwidth with reflection loss higher than 90%(RL<-10 dB)can reach 5.5 GHz.Co9S8-DETA organic-inorganic hybrid materials were synthesized using hydrothermal method.By adjusting the reaction time,the morphological evolution of the product with the reaction time was studied.The product Co9S8-DETA hybrid material with the reaction time of 72 h has the best crystallinity.With Co9S8-DETA as the precursor,the organic intercalation DETA was removed by heat treatment to obtain Co9S8 with an inorganic layered structure.Compared to Co9S8 inorganics,Co9S8-DETA hybrid materials show excellent electromagnetic wave absorption properties.When the thickness of the absorber is only 1.6 mm,the effective absorption bandwidth with a reflection loss of less than-10 dB reaches 4.1 GHz.The excellent electromagnetic wave attenuation characteristics are attributed to the optimized electromagnetic matching of Co9S8-DETA organic-inorganic hybrid materials and the unique structure of the two-dimensional sheet morphology.In addition,Co9S8 inorganic substance and glucose are uniformly mixed and then calcined at high temperature to obtain Co9S8@C nanocomposite material.The measurement results of electrochemical properties show that Co9S8@C nanocomposites have excellent lithium storage performance.At a current density of 0.2 A g-1,after 110 cycles,the capacity of Co9S8@C nanocomposite is higher than that of Co9S8 nanocomposite.The excellent lithium-ion battery performance of Co9S8@C comes from its unique two-dimensional structure and improved conductivity after carbon coating.