Construction Of Tin-iron Carbon(Oxygen)/Carbon Composite Micro-nanostructure And Its Application As A Light And Efficient Microwave Absorbent

In recent ten years,in order to solve the increasingly serious electromagnetic radiation pollution and electromagnetic interference,as well as to meet the needs of modern military equipment for radar stealth,the research and development of lightweight,efficient,broadband absorbing materials has been a research hotspot in the field of functional materials.Micronano carbon material is a kind of light absorbing material with great application potential due to its advantages such as low density,good stability and strong dielectric loss,etc.However,the high dielectric properties of single carbon materials lead to poor impedance matching level,which greatly reduces the absorption capacity of electromagnetic waves and limits their further application.In view of the problem of carbon materials,it is widely adopted to introduce magnetic materials to improve the permeability or low dielectric materials to reduce the dielectric constant and improve the impedance matching characteristics,so as to effectively enhance the wave absorption performance.In this thesis,carbon nanofibers and silk cocoon carbon were studied.By introducing low dielectric Fe₃SnC or magnetic SnFe₂O₄micro-nano particles,they were modified in order to develop new high performance absorbing materials.The main research work and results are as follows:(1)The Fe₃SnC/C composite nanofibes were prepared by electrospinning combined with carbonization treatment in situ.The effects of carbonization temperature,carbonization time,metal salt /PVP ratio and fiber filling amount on its structure,composition,electromagnetic and wave absorption properties were systematically studied.The results show that with the increase of carbonization temperature,carbonization time,metal salt /PVP ratio or fiber filling amount,the absorption intensity and reflection loss(RL)below 20 d B effective absorption bandwidth(EAB20)all show a trend of first increasing and then decreasing.The Fe₃SnC /C nanofibers formed after carbonization at 700 ? for 3 h with a metal salt /PVP ratio of 1.5showed relatively better microwave absorption performance when the filling amount was 20wt%.The matching thickness was 2.3 mm,the minimum RL value reached(-119.2 d B)at17.1 GHz,and the effective absorption bandwidth was 5.2 GHz(12.8¹8.0 GHz).In addition,the maximum EAB20 was 8.4 GHz(9.4¹7.8 GHz)when the coating thickness was 3.0 mm.The introduction of Fe₃SnC particles significantly reduces the dielectric constant of carbon fiber,effectively improves the impedance matching between the composites and the free space,and significantly improves the wave absorption performance of the composites.(2)Carbon nanofibers loaded with SnFe₂O₄(SFO)nanoparticles were synthesized by electrospinning combined with solvo-thermal method.The effects of mass ratio of metal salt to carbon fiber on the composition of the products,electromagnetic and wave absorption properties were investigated.The results show that with the increase of metal salt/carbon fiber mass ratio,the amount of SFO nanoparticles loaded on the surface of carbon nanofibers increases,while the absorption intensity and effective absorption bandwidth first increase and then decrease.When the metal salt/carbon fiber mass ratio is 2:1,the composite has the best absorbing performance,and the mass percentage of SFO is about 23.6 wt%.When the filling amount is only 5 wt%,the matching thickness is 2.6 mm,and the minimum RL value is reached at 8.6 GHz(-120.0 d B,EAB20 is 3.0 GHz(7.4-10.4 GHz).In addition,at a coating thickness of 1.6 mm,the EAB20 can reach 5.0 GHz(13.0 to 18GHz),covering more than 80%of the Ku band.More importantly,the intensity of the absorption peaks exceeded-40 d B(99.99% microwave absorption)over the thickness range(1.3-5.0 mm)examined,and the frequency range of RL <-40 d B covered 4-18 GHz.The improved absorbing performance of the composites is mainly attributed to the synergistic effect of magnetic loss and dielectric loss,improved impedance matching and enhanced interfacial polarization relaxation.(3)Silk cocoon(SC)loaded with SFO nanoparticles was synthesized by solvothermal method.It was found that with the increase of metal salt/cocoon carbon mass ratio,the content of SFO nanoparticles in the product also increased,and the absorption intensity and effective absorption bandwidth showed a trend of increasing first and then decreasing.When the metal salt/cocoon carbon mass ratio is 2:1,the composite material has the best absorbing performance.When the filling amount is 10 wt%,the matching thickness of absorbing coating is 1.9 mm,and the minimum RL value reaches-111.9 d B at 12.5 GHz.EAB20 was 4.1 GHz(10.9¹5.0 GHz).When the coating thickness varies between 1.0 and 5.0 mm,the frequency ranges of RL <-20 d B is 3.6 to 18.0 GHz,and the absorption bandwidth of RL <-40 d B reaches 14 GHz(4.0 to 18 GHz),covering the whole C to Ku band.Compared with pure cocoon carbon,the enhanced absorbing performance of SFO/ cocoon carbon composites can be attributed to a better balance between electromagnetic loss capacity and impedance matching.