The Preparation And Microwave Absorbing Properties Of Intermetallic Compounds Of Ce₂Fe₁₇N_3-? Powders

With the extensive use of electronic devices as well as the rapid development of radar communication and detection technology,lots of research attention has been paid to electromagnetic wave absorbing materials owing to their military applications in the field of stealth technology and civil applications for reducing electromagnetic interference emissions as well as for protecting humans from electromagnetic wave pollution.High permeability and high resonance frequency as well as moderate permittivity are demanded in order to satisfy the ever-growing requirements for microwave absorbers with strong absorption ability in the wide band combined with light weight and thin thickness.However,conventional magnetic materials are limited by Snoek limit,which has been unable to fully meet the requirements of Research & development and application for absorbing materials owing to their quite low magnetocrystalline anisotropy and saturation magnetization.In this paper,Rare-earth intermetallic compound of Ce₂Fe₁₇N_3-? was choosen as research object owing to its planar-anisotropy and large saturation magnetization,and the Ce₂Fe₁₇N_3-? powders was prepared by the optimized experimental conditions of nitriding and following by ball milling.The effects of magnetic powder volume concentration and magnetic orientation on the high frequency magnetic properties and microwave absorption performances of Ce₂Fe₁₇N_3-? powders/Silicone were studied,the evolution and formation mechanism for the high frequency magnetic properties and microwave absorption properties of the composites were also elucidated by the ?/4 interface-reflection model,the main conclusions are as follows:Firstly,Ce₂Fe₁₇N_3-? powders with size distribution of 3⁵ ?m was prepared by strip casting combined with ball milling and nitridation process.The effect of the process parameters on the homogeneity of the quenching zone was studied.The as-casted ribbons were broken into micrometer-sized particles in an agate mortar and then sieved to produce fine powders,and the nitrogenation reaction of the fine powders was performed in a stainless steel tube?pressure: 0.8 MPa,volume: 3000 cm3?with high-purity nitrogen gas for 1 h at 743 K.As a result,Ce₂Fe₁₇N_3-? powders shows high saturation magnetization of 149 emu/g and high nitrogen content of 3+0.14 as well as relative low coercivity of 60 Oe.Secondly,the effects of magnetic powder concentration?Vc?on the high frequency magnetic properties and microwave absorption performances of Ce₂Fe₁₇N_3-? powders/Silicone composites were systematically studied.It is found that the electromagnetic parameters of the composites increase linearly with Vc as Vc<30%.While Vc>30%,both the real part and imaginary part of complex permittivity of the composites increase rapidly.When Vc=25%,Ce₂Fe₁₇N_3-? powders/Silicone composite presented excellent microwave absorbing performance in X-band: the RL exceeding –10 dB is achieved in the whole X-band as well as the optimal RL reaches –60.5 dB at 9.97 GHz for the absorber with the thickness of 1.72 mm,indicating that the rare-earth Ce₂Fe₁₇N_3-? composite is suitable for high frequency microwave absorption.The peak frequency of the reflection loss and the corresponding thickness of the composite satisfy the ?/4 interface reflection model.Finally,the influence of magnetic orientation on the high frequency magnetic properties and microwave absorption properties of Ce₂Fe₁₇N_3-? powders/Silicone composites were also studied.The complex permeability of the composite increased by 1.2 to 1.4 times after the rotational orientation with magnetic field strength of 1.7 T and the orientation degree of 81%.Magnetic orientation is helpful to improve the impedance matching conditions for low volume concentration composites.Therefore,Vc=15% and 20% Ce₂Fe₁₇N_3-? powders /Silicone composites can meet RL <–10 dB in X-band after orientation,which indicates that the magnetic orientation is an effective method to optimize the microwave absorption of rare-earth composites with planar-anisotropy.In conclusion,through the preparation of Ce₂Fe₁₇N_3-? powders and the control of magnetoelectric parameter as well as the study of X-band absorbing performance of the composites,a thin layer of absorbing material with effective electromagnetic wave absorption in the whole X-band was obtained.The study on the regulation law and the action mechanism of absorbing properties of composite by magnetic orientation also provides technical reservation and theoretical basis for the development of thin layer absorbing materials.