Controllable Preparation And Performance Regulation Of New Microwave Absorbing Materials

With the rapid advancement in information technology,electronic devices are getting smarter and smaller,and growing in number every day.People are enjoying benefits from advanced technologies,at the same time,disturbed by them.The electromagnetic interference（EMI）resulting from explosive usage of electronic devices will have a detrimental influence on military application and civil fields.More importantly,the increasing of electromagnetic pollution has a harmful impact on human health.Therefore,the requirement for high-performance electromagnetic wave absorption materials to solve the EMI problems has been placed a highly value in the midst of recent years.As an ideal electromagnetic wave absorber,it is proposed to have wide absorption bandwidth,strong absorption performance,light weight and stable chemical composition and physical performance.In this study,two kinds of bio-based/metal-carbon composites EMW absorbers were designed and synthesized to meet the ideal electromagnetic wave absorber requirements.In section one,biomass sodium alginate（SA）was used as porous biomass carbon,N-doped three-dimensional（3D）carbonaceous composites with highly dispersed nickel nanoparticles（N-SA/Ni-X,X=3%,6%,9%）were successfully fabricated via a facile one-step encapsulation process and carbonization treatment.The performance of absorber has a significant enhancement due to the introduction of nitrogen elements into carbon network for controlling the dispersion and size distribution of Ni nanoparticles.When a 6%Ni²⁺mass percentage was used,it could lead to a maximum reflection loss（RL）that reaching-42.2 dB at 9.8 GHz.Moreover,the effective absorption（below-10 dB）bandwidth can reach 2.3 GHz from 8.5 to 10.8 GHz with the absorber thickness of only 2 mm and it can be tuned between2.8 to 14.4 GHz by adjusting the thickness from 1.5 mm to 5 mm.The excellent electromagnetic wave absorbing performance could be assigned to the combinatorial advantages of the light-weight conductive porous network with favorable dielectric loss and magnetic loss features induced by highly dispersed Ni nanoparticles.However,the EM wave bandwidth with RL below-10 dB for for N-SA/Ni-X at each thickness is relatively narrow which might not be good enough for further application in the filed of EM wave absorption.Therefore,in later work,the structure and the composition of the absorber are further optimized to broaden the absorption bandwidth.A new type of honeycomb-like carbonaceous composites with tailored porous architectures and magnetic Fe₃O₄ components derived from walnuts shells were fabricated by solvothermal method and used as effective microwave absorbers.The porous composites were achieved by twice carbonizations process at varied temperatures and an etching process with potassium hydroxide.The introduction of developed porous architecture inside resultant materials distinctly improved the microwave absorption performance.Taking the combinatorial advantages of the light-weight conductive biochar-like porous framework with favorable dielectric loss and Fe₃O₄ nano-particles with magnetic loss features,this newly fabricated porous carbonaceous composites presented excellent microwave absorption performance.A reflection loss（RL）of-51.6 dB can be achieved at a frequency of 13.6 GHz.Besides,the effective absorption（below-10 dB）bandwidth can reach 5.8 GHz from 11.9 to 17.7 GHz with the absorber thickness of only 2 mm.These newly fabricated Fe₃O₄/Porous corbon composites could be regarded as promising candidates for lightweight and high-performance microwave absorption materials.