Design And Performance Study Of Spiral Carbon Coil-Based Composite Absorbing Materials

The interference and radiation caused by electromagnetic waves has greatly increased with the rapid development of communication technology.In order to reduce electromagnetic pollution,high-performance wave absorber materials have received extensive attention and research.Carbon-based wave absorber materials have been a favourite of researchers due to their unique advantages in terms of physical and chemical properties.In particular,spiral carbon coils（SCCs）have special structural advantages in the field of microwave absorption due to their special spiral structure,excellent electromagnetic cross-polarisation ability and field emission performance.However,catalyst-free preparation,interfacial structure design and modulation of the absorption properties of spiral carbon coils are the urgent difficulties and challenges to be solved.In this paper,we adopt the catalyst-free and low-cost preparation technology of biomass-based spiral carbon coils（BSCCs）to regulate their microwave absorption performance by constructing graded porous spiral structures and composite interfacial structures such as Mo-C and Fe Ni₃-C,and investigate the influence of the surface/interfacial structures of porous interfaces and composites on microwave absorption performance and their mechanisms,so as to achieve microstructure control and synergistic design of wave absorption performance.The main research results are as follows:（1）Biomass-based porous spiral carbon coils（BPSCCs）were prepared by chemical activation method,and the effects of different activators（K₂CO₃,Zn Cl₂ and KOH）on the pore structure of porous spiral carbon coils were investigated,with emphasis on the wave absorption performance and the wave absorption mechanism of porous spiral carbon coils under KOH activation.The results show that different activators have a great influence on the specific surface area and pore structure of porous spiral carbon coils.Under the same conditions KOH activation is the best,followed by Zn Cl₂,while K₂CO₃ activation is the worst.The BPSCCs-1sample has a higher specific surface area of 1010.67 m²·g^-1 and pore volume of 0.58 cm³·g^-1.The absorption performance test shows that the strongest reflection loss(RL_min)of BPSCCs-1 is-45.09 d B at low filling rate;the maximum effective absorption bandwidth（1）₀),RL<-10 d B)is up to 5.5 GHz.The results indicate that biomass-based graded porous spiral carbon coils are a new absorbing material with good prospects for wave absorption applications.（2）BSCCs/Mo O₂ and BSCCs/Mo₂C composites were prepared by high-temperature pyrolysis,and their growth processes and mechanisms were discussed in detail,and the electromagnetic response parameters and wave absorption properties of the samples before and after the composite were studied comparatively.The results show that after the introduction of Mo O₂ and Mo₂C particles,the dielectric parameters of BSCCs are significantly improved,while the magnetic permeability is correspondingly reduced,so that the impedance matching is optimized,which effectively improves the microwave loss capability of BSCCs and achieves the modulation of microwave absorption performance.At a filling rate of 25 wt.%,the RLmin of BSCCs/Mo₂C is as high as-58.86 d B,and the reflection loss intensity is significantly increased by nearly 13 times compared with that of BSCCs.This BSCCs/Mo₂C composite absorbing material provides a useful theoretical and practical basis for the absorption of electromagnetic waves in the middle and high frequency region.（3）BSCCs/Fe Ni₃ composites were successfully prepared by high-temperature pyrolysis.The formation mechanism of Fe Ni₃ alloy was analyzed,and the influence of the change of electromagnetic parameters on the wave absorption performance of BSCCs/Fe Ni₃ samples under annealing at 800 and 1000°C was discussed.The results show that the introduction of Fe Ni₃ alloy successfully improves the impedance matching and microwave absorption performance of BSCCs.With the increase of temperature,the specific surface area of the composite increases,the average pore size decreases,the pore structure becomes more abundant,and the maximum reflection loss is greatly increased.15 wt.%filling rate of Fe Ni-800 at a thin thickness（1.46 mm）,RLmin is-23.12 d B,and the effective absorption bandwidth is 4.74 GHz（13.24 GHz-17.9 GHz）;10 wt.%fill rate of Fe Ni-1000 at 2.90 mm thickness RLmin up to-53.85 d B,effective absorption bandwidth of 3.16 GHz（8.02 GHz-11.26 GHz）,in addition,the maximum effective absorption bandwidth of Fe Ni-1000 at1.94 mm thickness is 5.16 GHz（12.84 GHz-18 GHz）,which can effectively absorb 99.9%of the incident microwaves in this frequency band.