Preparation Of Fe Based Core-shell Nanocomposites And Their Microwave Absorbing Properties

In information technology combat conditions,the research of wave-absorbing materials is the most important to achieve military stealth.Wave-absorbing materials can shield electromagnetic interference,have the advantages of light mass,high-temperature resistance,and corrosion resistance,and have a large absorption rate in a wider frequency band.At present,the main focus is on the composite structure of materials and material morphology optimization to enhance wave absorption performance,the composite of magnetic materials,and dielectric materials with multiple loss mechanisms and synergies.The core-shell structure can regulate both the microstructure and the interface effect between the core and the shell to enhance the performance of the material.Therefore,we consider selecting the core-shell absorbing material with ferrite as the core and outer layer wrapped with carbon material and adopting suitable methods to realize the complementary advantages of the two.TEM,XRD,XPS,VSM,and vector network analyzer are used to analyze and test the morphology,physical phase,elemental composition,magnetic properties,and absorbing properties of the composite materials,and the main chapters and research contents included in this paper are as follows:In the first chapter experiments,we prepared Fe₃O₄@SiO₂@C nanocomposites by hydrothermal method,St（?）ber method and template method step by step,where changing the carbonization temperature can control the state of the core and the morphology of the composites,and the carbonization was carried out at 500℃,600℃ and 700℃ in this chapter,and the results showed that the core-shell structure has excellent morphology and good dispersion at 600℃.At the dosage of tetraethyl orthosilicate（TEOS）of 1 m L,the minimum reflection loss of the material reaches-31.2 d B at the matched thickness of 5.5 mm,and the maximum effective absorption bandwidth is 5.1 GHz;at the dosage of TEOS of 0.5 m L,the maximum effective absorption bandwidth of this chapter is 6.7GHz achieved at the matched thickness of 5.5 mm.Considering the unique structure and excellent absorption performance,the prepared Fe₃O₄@SiO₂@C nanocomposites can be one of the candidates for high-performance wave-absorbing materials.Although the absorbing performance of the material prepared in Chapter 1 is excellent,the overall matching thickness is large and the material loses some of its magnetism under high-temperature conditions,so in order to improve the impedance matching of the material,we introduced magnetic nanoparticles Ni to compensate the magnetic properties lost under high-temperature conditions based on Chapter 1 to achieve the purpose of improving the impedance matching.The Fe₃O₄@SiO₂@C/Ni nanocomposites were prepared by the hydrothermal method and modified St（?）ber method,and the minimum reflection loss of the prepared absorbing materials reached-38.5 d B at the matched thickness of 4.5 mm when the TEOS dosage was 0.6 m L,dopamine dosage was 30 mg,and nickel chloride dosage was 75 mg,and the maximum effective absorption bandwidth was 7 GHz.The maximum effective absorption bandwidth is 8 GHz at a matched thickness of 3.5 mm,with a TEOS dosage of 0.6 m L,a dopamine dosage of 45 mg,and a nickel chloride dosage of 112.5 mg.The performance of the prepared material is enhanced due to the synergistic effect of the unique core-shell structure and the absorbing properties and electromagnetic parameters of the material can be improved by controlling the thickness of the silica layer and the thickness of the carbon layer with the Ni The thickness of the silica layer and the thickness of the carbon layer with the introduction of Ni can be adjusted,resulting in a relatively excellent absorbing performance in different frequency ranges.The results of this chapter provide an effective way to prepare high-performance wave-absorbing materials.The second chapter has improved the wave absorption performance compared with the first chapter,but the matching thickness has not been greatly improved.ZSM-5zeolite has a special porous structure and skeleton structure,light mass,excellent thermal stability,and wave transmission rate,and the ion exchange of zeolite does not affect the skeleton structure,so this chapter prepares ZSM-5/Fe_xO_y@C/Ni composites and studies the effect of carbon layer thickness and Ni loading on the wave absorption performance at different ratios of Fe loading,and the effect of carbon layer thickness and Ni loading on the wave absorption performance was investigated.The prepared zeolite ZSM-5/Fe_xO_y@C/Ni absorbers showed relatively good wave absorption performance in the range of 2～18 GHz.The minimum reflection loss of the material reaches-25 d B at a matched thickness of 5.5 mm at 8%Fe loading dosage,and the maximum effective absorption bandwidth is 5.3 GHz;the maximum effective absorption bandwidth in this chapter is 6 GHz at 10%Fe loading and a matched thickness of 5.5mm.It can be found through the experiments that the matched thickness of the maximum effective bandwidth is around 3 mm for different samples in general.This indicates that the maximum effective absorption bandwidth and the minimum reflection loss of the material can be adjusted towards the thin side by adjusting the loading of ferrite in relation to the thickness of the carbon layer and the loading of Ni.