Preparation Of Transition Metal(Co)matrix Composites And Their Application In The Field Of Electromagnetic Wave Absorption

In recent years,the demand for new electromagnetic wave absorbers in the military and aerospace fields has accelerated many disruptive technological changes.Exploring efficient electromagnetic wave absorbing materials is one of the effective means to deal with electromagnetic wave problems such as microwave radiation,electronic security and military defense.An ideal electromagnetic wave absorber can allow electromagnetic waves to pass through its interior and enhance the dissipation of electromagnetic microwave energy.Therefore,people have carried out research on electromagnetic wave absorbing materials in the gigahertz frequency range,and perfected their absorption theory.At present,electromagnetic wave absorbing materials should have the advantages of thin thickness,wide absorption frequency range,strong absorption capacity and light weight.Many researchers have made a lot of reports on carbon-based,ceramic-based,and metal-based composite materials with different structures.In this paper,we use CoSnO3 as a template to design its composition and structure,preparation of multivariate metal oxides,metalorganic framework-derived alloys on N-doped carbon composites,and metal elementdoped carbon nanofibers,expected to utilize enhanced heterointerfacial polarization,vacancy,and heteroatom replacement induced dipoles.The synergistic effect of chemical and dielectric loss can improve the absorption performance of the wave absorber.The research content and results of this paper are as follows:(1)In this research,through a two-step synthesis,hollow CoSnO3 is grown in situ between self-assembled flower-like Zn Co2O4 layers in a solvothermal process.The multilayer sheet-like structure of Zn Co2O4 nanoflowers provides growth space for CoSnO3,which can increase the interface polarization and natural resonance.The hybrid structure expands the propagation path of the electromagnetic wave and the number of reflections and scattering.By adjusting the content of CoSnO3 between the Zn Co2O4 sheets,the changes of the dielectric and magnetic properties of the composites were explored.The results show that the lowest reflection loss(RL)of the sample is-56.0 d B at 12.4 GHz,and an effective absorption bandwidth(EAB)of 6.24 GHz is obtained at a thinner thickness with a matching thickness of 2.6 mm.The Zn Co2O4@CoSnO3 composite exhibits satisfactory impedance matching in the frequency range of 2-18 GHz.Therefore,the Zn Co2O4@CoSnO3 composite provides a new research idea for the design of electromagnetic wave absorption morphology.(2)Metal-organic framework-derived composites have been widely used for electromagnetic wave(EMW)absorption,but traditional synthetic strategies greatly limit the structure and variety of MOFs.This study provides a solvent-free method for the synthesis of Co-MOF and its derivatives.Using CoSnO3 as the precursor,the Co-MOF was prepared by bridging the cobalt(II)ion of CoSnO3 and the 2-methylimidazole skeleton.Co Sn/N-doped carbon(Co Sn/NC)composites derived from CoSnO3-MOF(Co-MOF with CoSnO3 as Co source)at high temperature retain the original morphology of CoSnO3.In addition,the polarization effect generated by the N-doped carbon layer is also beneficial to improve the EMW absorption performance of the Co Sn/NC composite,which is mainly reflected in the minimum reflection loss(RL)of-48.2 d B at 2.2 mm and the effective efficiency at 5.84 GHz.Bandwidth(EBA).This work provides a new avenue for the construction of Co-MOFs that can be extended to other Co-based oxides and greatly expands the variety of metallic Co-based MOFs.(3)The design of one-dimensional chain-like porous structures has gradually been proved to be an effective strategy for obtaining high-performance microwave absorbers.Here,we report a one-dimensional N-doped carbon nanofiber material that encapsulates hollow Co3 Sn C0.7 nanocubes in the fiber lumen by electrospinning.The dielectric constant of the fiber is closely related to the carbonization temperature,and suitable impedance matching can be achieved through the synergistic effect of Co3 Sn C0.7 and the carbon network.At 800 °C,the 5% low-loaded pod-like Co3 Sn C0.7/CNF composite achieves the lowest reflection loss(RL)of-51.2 d B at a thin thickness of 2.3 mm and an effective absorption of 7.44 GHz at a thickness of 2.5 mm bandwidth.Multiple electromagnetic wave(EMW)reflections and interfacial polarization between fibers and their interiors play an important role in attenuating EMW.These strategies for tuning electromagnetic properties can be extended to other electromagnetic functional materials to facilitate the research and development of emerging absorbers.