Microwave Absorption And High-frequency Magnetic Properties Of Ce₂Fe₁₇N_3-? Micropowder Composite

With the development of electronic information technology and communication technology,microwave absorbing materials have been widely developing and applying in the field of communication and military radar stealth to strengthen electromagnetic interference resistance,and avoid human radiation damage and achieve military equipment stealth.An excellent microwave absorbing materials need to have the strong absorption,wide effective absorption bandwidth and thin thickness to meet the standard.According to the quarter wavelength theory(d=c/4f|?_r?_r|^0.5),increasing the permittivity(?_r)and permeability(?_r)can reduce the thickness at a specific frequency,while the?_ris too large to achieve impedance matching.Therefore,increasing the?_r is the most effective way to reduce the thickness of absorbers.The Ce₂Fe₁₇N_3-?composite has attracted wide attention as excellent wave absorbing materials in the X and Ku-band because of their high permeability at high frequency and high magnetic loss.However,in the past decades,the Ce₂Fe₁₇N_3-?composites were usually prepared by smelting process using high-purity cerium metal as raw material,which leads to high costs and limits the practical application of Ce₂Fe₁₇N_3-?composite.Moreover,the higher permittivity of the Ce₂Fe₁₇N_3-?composite is usually not conducive to impedance matching.In this paper,a low-cost reduction-diffusion process and a phosphating process are proposed for the preparation and modification of Ce₂Fe₁₇N_3-?powder to solve these above problems.The Ce₂Fe₁₇N_3-?/polyurethane absorbing material with essentially full coverage absorption in X and Ku bands at lower thickness were prepared.In the specific experiments,the process conditions of the reduction-diffusion method,including the ratio of raw materials,reduction-diffusion temperature,and reaction time,were explored.Then,the influence of ball milling process,ball milling time and volume fraction on microwave absorption properties were explored,and finally a stable and reproducible production process was formed.The reflection loss(RL)of the Ce₂Fe₁₇N_3-?composite with the volume fraction of 30%can reaches-63 d B at 11.4 GHz,and the corresponding effective bandwidth(EBW)reaches 3.83 GHz.For the Ce₂Fe₁₇N_3-?composite with the volume fraction of 35%,the effective band in the Ku-band reaches5.5 GHz with the thickness of 0.95 mm.In the above study of microwave absorption properties of Ce₂Fe₁₇N_3-?composite material,it was found that such materials not only have the imaginary part of permeability in the MHz band,but also have the higher magnetic flux density compare to ferrite,which indicates that the Ce₂Fe₁₇N_3-?composite also has the potential to be used as the high frequency magnetic powder cores with small volume and low loss.For further validation,we prepared several Ce₂Fe₁₇N_3-?/Fe/polyurethane composites based on reduction-diffusion and mechanical ball milling process.Then,the core loss was tested and separated,and the loss mechanism and the performance factors are analyzed.With the improvement of the preparation process,the real part of permeability of Ce₂Fe₁₇N_3-?/Fe is effectively increased and the core loss is reduced.The real part of permeability of the Ce₂Fe₁₇N_3-?/Fe composite with 65%volume fraction is 36.8 and the core loss is 397.35 k W/m~3 at 3 MHz(stimulated at 10 m T).