Study On The Microwave Absorbing Performance Of Biomass-based Coiled Carbon Fibers

Nowadays,electromagnetic wave technology has provided great convenience for human life,but at the same time,it also has produced many negative effects,such as endangering human health,aviation safety,and national defense security.Microwave absorption materials,as an effective way to alleviate the pollution of microwaves,have been widely studied and concerned,and the research of new high-efficiency microwave absorption materials is in full swing.Carbon-based microwave absorbing materials are favored by scientists because of their low density,lightweight,and high dielectric properties.Among them,the coiled carbon fibers(CCFs)are gradually emerging in the field of microwave absorption because of their unique chiral helical structure,high specific surface area,superelasticity,good stability,high conductivity,electromagnetic cross-polarization ability,and excellent field emission performance.However,traditional CVD and other methods in the preparation of CCFs need to use a variety of catalysts,and high-cost raw materials.The preparation process is complex,low yield,and environmental unfriendly,which limits the further application and development of CCFs.Therefore,it is very important to develop a new method for preparing CCFs microwave absorbing material with low-cost,catalysts-free and high efficiency.Inspired by the natural helical structure in nature,this paper implements the research on the synthesis of CCFs with catalysts-free and low-cost stralegy based on the natural spiral vessel(SVs).Further more,porous structure and magnetic manoparticles are introduced to optimize the absorbing performance of CCFs through structure design and interface regulation.The results provide a good theoretical and practical basis for the development and application of biomass drived CCFs.The main research results are as follows:(1)A novel calalyst-free method for preparing CCFs was proposed,in which the CCFs can be easily obtained by high temperature carbonization using natural SVs from discarded tea leaves as templates.Microstructural characterization showed that SVs and CCFs are both have obvious helical structure.The diameter of a single fiber is about 1?m and the helical diameter is about 10?14 ?m.The microwave absorption results showed that the minimum reflection loss(RL)of CCFs can be obtained at 7.28 GHz and 5.50 mm matching thickness when the load is 10 wt.%.(2)Nano-scale porous structures were constructed on the surface of CCFs by KOH etching.The pore structures were controlled by changing the amount of KOH activator,and the porous spiral carbon fibers(PCCFs)with high specific surface area and pore volume are readily available through this process.When the ratio of CCFs to KOH is 1:5,the maximum specific surface area of PCCFs can reach 3124.66 m2 g-1,the pore volume is up to 1.74 cm3 g-1,and the average pore size is about 2.1 nm.PCCFs show excellent microwave absorption performance:under the ultra-low load 5 wt.%and 3.33 mm thickness,the minimum RL of PCCFs is as high as-51.99 dB at 9.36 GHz,and the maximum effective absorption bandwidth is also up to 5.84 GHz.The unique three-dimensional helical and porous structure makes PCCFs have excellent wave absorption performance,which is expected to become a kind of light and efficient microwave absorption materials with practical application value in the future.(3)Fe3O4/CCFs and Ni/CCFs composites were successfully constructed by hydrothermal method and thermal decomposition method.The Fe3O4/CCFs sample,the surface of CCFs modified with magnetic Fe3O4 particles with a diameter of 50?100 nm,present the RLmin is about-13.60 dB and the maximum effective absorption bandwidth can reach 5.70 GHz under the 10 wt.%loading,which can effectively attenuate the incident microwaves by 90%.While the Ni/CCFs sample,grown a small amount of Ni nanoparticles on the surface of CCFs,display the RLmin is-30.12 dB and the maximum effective absorption bandwidth is 5.88 GHz at the 30 wt.%loading,which can effectively lose 99.9%incident microwave.The results show that introducing magnetic metals to biomass-based CCFs can effectively improve its microwave absorption performance,which provides the possibility for the research and development of coiled carbon fiber matrix composites in the field of microwave absorption.