Design Of Cobalt-based Materials And Study On Electromagnetic Wave Absorption Properties

With the increasing maturity of the fifth-generation mobile communication technology,wireless technology has brought huge convenience to human society.However,the accompanying electromagnetic interference and pollution can cause irreversible damage to human health,equipment operation and the natural environment.Therefore,the development of electromagnetic wave absorption materials is a necessary prerequisite to improve the quality of human life.Electromagnetic wave absorption materials can absorb external electromagnetic radiation then attenuate electromagnetic energy through multiple attenuation mechanism inside the materials,which can avoid the secondary pollution caused by reflection and refraction on the surface.At present,“thin,light,wide,strong”is an important standard to meet military and civilian electromagnetic wave absorption materials.In this thesis,we start from the structural design and component optimization.the magnetic cobalt（Co）-base materials are combined with different dielectric materials to introduce the multiple attenuation mechanisms.Then the electromagnetic parameters are regulated by changing the relevant technological parameters,so as to optimize the impedance matching and realize the construction of high-performance electromagnetic wave absorbers.Specific research contents are as follows:（1）Firstly,the CoCu alloy with magnetic loss was prepared from the point of view of composition optimization.In this work,the ternary MOF was synthesized by one-step method,Then the CoCu/C was obtained by high temperature annealing.Finally,the ultra-thin WSe₂ nanosheet was coated on the surface of CoCu/C(Co²⁺:Cu²⁺=1:1)during hydrothermal process.resulting in the WSe₂/CoCu/C composites with polyhedral structure and multiple heterogeneous.When content of WSe₂ was 30 mg The minimum reflection loss(RL_min)at 2.1 mm reached-53.43 d B.The effective absorption band（EAB）is 6.0 GHz at 1.8 mm.The excellent electromagnetic wave absorption performance of WSe₂/CoCu/C composites comes from the synergistic effect of dielectric and magnetic components to optimize the impedance matching,resulting in more electromagnetic waves incident inside the absorber.Subsequently,the electromagnetic wave attenuation ability is maximized through the conduction loss of high conductivity C,dipole polarization,the interface polarization between CoCu,C and WSe₂ components,as well as magnetic loss of CoCu alloy.（2）In order to avoid the adverse eddy current effect of highly conductive magnetic material,magnetic component CoO for suitable resistance was prepared further.Starting from the structure design,the hollow multi-layer hexagonal MWCNTs/Mn F₂/CoO composites were prepared by adjusting the content of MWCNTs in the hydrothermal process.The unique hollow structure facilitates multiple reflection and scattering of incident waves,enhancing the synergistic effect of polarization relaxation and conduction loss.In addition,the dielectric/magnetic loss provided by the dielectric component MWCNTs and the magnetic component CoO reached the maximum synergistic effect through reasonable regulating the load of MWCNTs,which further optimized the impedance matching.Therefore,when the content of MWCNTs is 30 mg,the RL_min value of MWCNTs/Mn F₂/CoO composites is-64.73 d B at 2.1 mm,and the EAB value is 6.64GHz at 2.0 mm.（3）Finally,CoFe₂O₄ component with high saturation magnetization,high permeability and resistivity was prepared from the point of view of composition optimization and structure regulation.Snowflake-like and nanoflower-like Cu_xS/CoFe₂O₄ composites were prepared successfully by adjusting different metal salts and solvents.High concentration of sulfur vacancy and snowflake-like Cu₂S/CoFe₂O₄ with large heterogeneous interfaces are contribute to trigger defect-induced polarization and interfacial polarization.In addition,the dielectric and magnetic components are properly matched to avoid impedance mismatch and enhance dielectric/magnetic loss.The content of CoFe₂O₄ was adjusted to50 mg,the RL_min of snowflake Cu₂S/CoFe₂O₄ increases to-66.58 d B and the maximum EAB is 6.64 GHz at 2.1mm.（mixture ratio of sample to paraffin is 1:4）In this thesis,CoCu alloy,CoO,CoFe₂O₄ materials were synthesized starting from Co-based materials.Then combined with carbon materials and sulfide dielectric materials,so as to obtain the outstanding electromagnetic wave absorption materials.The structure and components of the composites are reasonably designed and optimized by adjusting various parameters.Subsequently,the electromagnetic parameters are changed in order to achieve the improvement of impedance characteristics and attenuation ability,obtaining electromagnetic wave absorption materials with high performance.