Preparation And Properties Of Carbon Based Electromagnetic Wave Absorbing Materials

Using absorbing materials is an effective means to prevent electromagnetic pollution and improve military stealth technology.Traditional absorbing materials have various defects,such as high density and no high temperature resistantance of ferrite,narrow absorbing band width and poor impedance matching of carbon materials,etc.Single-component electromagnetic wave absorbing materials can not meet the requirements of light weight,wide frequency bandwidth and strong absorption.Electromagnetic wave absorbing composite materials with multiple loss mechanisms are the research hotspots in this field.In this paper,the following two carbon-based electromagnetic wave absorbing composites were prepared by in-situ synthesis of ferroferric oxide particles?Fe₃O₄?on a carbonaceous material substrate by in-situ reduction method:?1?Activated carbon fiber loaded ferroferric oxide composite?ACF/Fe₃O₄?Activated carbon fiber felt?ACF?was prepared by chemical activation method using viscose fiber felt as raw materials.The effects of phosphoric acid concentration and carbonization activation temperature on the electromagnetic absorption properties of ACF were investigated.The results show:The change of phosphoric acid concentration has no significant effect on the electromagnetic wave absorption performance of ACF,and the change of carbonization activation temperature has a great influence on the electromagnetic wave absorption performance.With the increase of carbonization activation temperature,the maximum reflectivity of ACF increases first and then decreases.When the activation temperature of carbonization is 600-650?,ACF has better electromagnetic wave absorption performance.When the phosphoric acid concentration is1mol/L and the carbonization activation temperature is 650?,the prepared ACF has a maximum reflectance of-25.8d B at 12.4GHz and an effective bandwidth of 9.8GHz.The electromagnetic wave absorption performance of ACF comes from dielectric loss.ACF was used as the matrix,FeCl₃ was used as the iron source,and glucose was used as the reducing agent.ACF/Fe₃O₄ was prepared by the in-situ reduction method.Fe₃O₄ and ACF are physically connected,the particle size is about 15-60nm,and the composite material is ferromagnetic.The effects of Fe³⁺concentration and reduction temperature on the electromagnetic wave absorption properties of the composites were studied.When the Fe³⁺concentration was 2mol/L and the reduction temperature was 500?,the composite had the largest reflection loss,and the maximum reflectance reached-36.5d B at 13.5GHz.The bandwidth reaches 9.8GHz.Composite materials have both dielectric and magnetic loss properties,with dielectric losses predominating.?2?Ferroferric oxide intercalated graphene oxide composite?GO@Fe₃O₄?Graphene oxide?GO?was successfully prepared by the modified Hummers method.After hydrothermal treatment of GO,FeCl₃ was used as intercalation agent,Na Cl was used as intercalation dispersant,glucose was used as reducing agent,and GO@Fe₃O₄ was prepared by in-situ reduction method.Fe₃O₄ is bonded to GO by a C-O-Fe bond and exhibits good paramagnetism.The effects of GO to Fe³⁺molar ratio and reduction temperature on the morphology and structure of the composites were dispersibility;when the reduction temperature is higher than 400?,Fe₃O₄with higher crystal phase purity can be obtained.The electromagnetic wave absorption performance analysis of GO shows that there is only a dielectric loss mechanism in GO.The maximum absorption peak appears at 9.52GHz.When the thickness is 2mm,the reflectivity is-9.28d B.GO@Fe₃O₄ has multiple dielectric loss and magnetic loss.The effect of GO to Fe³⁺molar ratio and reduction temperature on the electromagnetic wave absorption performance of composites is studied.The maximum reflectivity increases first and then decreases with the increase of Fe³⁺ratio and the increase of reduction temperature.When the molar ratio of GO to Fe³⁺is 1:1,the reduction temperature is 600?,and the thickness is 3mm,the maximum reflectance at 8.6GHz reaches-49.6d B.