Study On The Structure And Performance Control Of Bio-based Metal/Carbon Composite High Performance Wave Absorbing Materials

Due to the rapidly increasing application of electromagnetic technology in military and civilian products,electromagnetic pollution has become the fourth largest pollution after air pollution,water pollution and noise pollution.Electromagnetic radiation not only poses a threat to human health,but also causes great damage to electronic devices.Given all that,the development of materials with the function of absorbing electromagnetic waves to remove electromagnetic pollution has become a hot topic in recent years.However,there is a continuing need for the study of thin,lightweight,broadband,and strongly absorbing electromagnetic wave absorbing materials.Meaning fully bio-based/metal-carbon composites also have extensive research in the field of electromagnetic absorption.The advantages of simple development,wide source,economical synthesis processes and methods,and excellent properties make it attractive.In this dissertation,biomass sodium alginate was used as an example.Two kinds of macro-structured bio-based metal carbon composites were prepared via sol-gel and high-temperature carbon reduction methods using sodium alginate and metal salts as precursors.And its absorption properties were studied.By comparing these two methods,we found that the modified sodium alginate-based magnetic carbon spherical composite has a broader application prospect in wave absorbing.It is known that biomass such as sodium alginate would transform into biochar in an inert gas protection atmosphere?such as nitrogen?under high-temperature treatment,and metal salts can form magnetic nanoparticles through carbothermal reduction.By combining above two characteristics,metal ions are used to cross-link sodium alginate through high-temperature carbonization to form porous carbon bioabsorbing materials with magnetic properties and special physicochemical properties.And using its special morphological structure and large anisotropy to enhance the absorption of electromagnetic waves.In section one,a magnetic porous carbon bio-based composite material Fe-SA-X?X represents the carbonization temperature?was prepared,and the effects of different carbonization temperatures?600,700,800,and 900 ^oC?on the microstructure and wave-absorbing properties of the material were investigated.With the increase of temperature,absorbing performance gradually weakens,indicating that high temperature seriously affects materia microstructure.Magnetic porous carbon composite Fe-SA-600 was obtained under600 ^oC carbonization,which has and excellent electromagnetic wave absorption performance,with the maximum reflection loss value?RL?reaches-24 dB,and the absorption exceeds-10dB at 4.8 GHz.More importantly,the corresponding matching thickness is only 1.5 mm.Undoubtedly,the good electromagnetic wave absorption performance is inseparable from special hole structure and high anisotropy performance.Based on the first study,we have introduced the ion-exchange mechanism in second work.By introducing magnetic carbon nanotube and cross-linking in nickel solution,alginate-based magnetic carbon sphere SA-Ni-?Fe₃O₄/CNTs?-X?X represents the mass fraction of Fe₃O₄/CNTs?was finally obtained by high-temperature carbonization.According to the results of the first experiment,samples were carbonized at 600 ^oC and electromagnetic wave absorption performance was optimized by adjusting the amount of magnetic carbon nanotubes.The results showed that SA-Ni-?Fe₃O₄/CNTs?-25%had a best performance with the maximum absorption intensity?RL?reaches-32dB and the effective frequency bandwidth3.2GHz.This is due to the synergistic interactionof porous carbon and metal particles and Fe₃O₄/CNTs.At 600 ^oC,the impedance matching could be better,and more electromagnetic waves entered the interior of the composite material through multiple reflections and scattering.The ternary composite materials prepared from magnetic loss material Ni and Fe₃O₄,dielectric lossy material bio-carbon and CNTs showed excellent microwave absorbing properties,and it is expected to become a novel micro-wave absorbing material.