Preparation And Performances Regulation Of Multicomponent Composite Microwave Absorption Materials Based On Carbon Nanofibers And CeO₂

In recent decades,the widespread application of high-frequency electromagnetic waves is making changing rapidly in human life.However,the increasingly serious electromagnetic pollution not only threatens human physical and mental health but also causes certain interference with precision equipment.Meanwhile,modern military equipment requires reducing the radar reflection cross-section to achieve radar stealth and enhance survival and strike capabilities.Therefore,the research of novel electromagnetic wave absorbing materials with thin thickness,light weight,wide bandwidth,and strong absorption has attracted much attention both domestically and internationally.Carbon nanomaterials are a microwave absorbing materials with great application prospects due to their low density,low cost,strong dielectric loss,and corrosion resistance.However,their high permittivity makes them mismatched with free space impedance,thus it is often difficult to achieve excellent microwave absorbing performance with single carbon materials.The research shows that introducing ferrites,magnetic metals,transition metal oxides or sulfides into carbon nanomaterials can optimize impedance matching and enhance microwave absorbing performance.CeO₂is a common rare-earth oxide,and is widely used in energy storage,catalysis,and other fields.The semiconductor properties of CeO₂can effectively improve the impedance matching of carbon-based materials,while a large number of oxygen vacancies inside it can further enhance polarization loss,making it a potential microwave absorbing material.In this thesis,CeO₂modified carbon nanofibers were used as research objects and further optimize their electromagnetic characteristics and microwave absorption performance in terms of both material composition and microstructure.Clarified the regulatory and microwave absorbing mechanisms.The main research content and results of this thesis are as follows:（1）Carbon nanofibers composites embedded with ultrafine CeO₂nanoparticles（CeO₂/CNFs）were prepared by electrospinning combined with high-temperature carbonization treatment.With the increase of CeO₂content,the impedance matching is improved,but the dielectric loss ability is weakened.Thus,the introduction of the appropriate amount of CeO₂can achieve a better balance between impedance matching and electromagnetic attenuation,and significantly enhance the microwave absorbing performance.For a sample with a CeO₂content of 24.6 wt%,a minimum reflection loss of-45.4 d B was obtained at a matching thickness of 3.0 mm,and an effective absorption bandwidth of less than-10 d B（EAB）can reach 5.6 GHz.（2）The CeO₂/CNFs porous composites（CeO₂/P-CNFs）were prepared using PMMA as the pore-forming agent,and the effects of the additional amount of pore-forming agent and absorbent filling quantities on electromagnetic parameters and microwave absorption performance were systematically studied.The impedance matching characteristics are further improved due to the presence of a cavity in the nanofibers.This absorber obtained a larger EAB at a thinner matching thickness.For the sample obtained at a PMMA/PAN mass ratio of 3:10,the reflection loss and EAB at a matching thickness of 2.0 mm were-38.1 d B and 6.8 GHz,respectively,when the absorbent filling quantities was 10 wt%.In addition,although the increase in filling quantities leads to a decrease in absorption intensity and EAB,the matching thickness corresponding to the strongest absorption also decreases.The optimal microwave absorbing performance of its 15 wt%and 20 wt%absorbers was obtained at matching thicknesses of 1.8 mm and 1.5 mm,respectively.（3）On the basis of the above CeO₂/P-CNFs,Ni/CeO₂/P-CNFs and Co/CeO₂/P-CNFs ternary composites were further prepared by introducing metal Ni and Co,and their microwave absorption properties were modulated by introducing magnetic substances.The introduction of magnetic metal makes the dielectric loss capability decrease,so the microwave absorption performance at 10 wt%filling quantities is not significantly improved.However,the absorption strength or EAB was improved to varying degrees at 15wt%filling quantities.For the sample obtained at a Ni salt/Ce salt mass ratio of 1:5,the optimal microwave absorption performance was achieved at a matching thickness of 2.2mm,with corresponding reflection loss and EAB of-24.4 d B and 6.6 GHz,respectively.For the sample obtained at a Co salt/Ce salt mass ratio of 2:5,the optimal microwave absorption performance was achieved at a matching thickness of 1.8 mm,with corresponding reflection loss and EAB of-24.4 d B and 5.5 GHz,respectively.