| The radar stealth technology of high-temperature components is facing severe challenges,and there is an urgent need to develop radar absorbing materials that can be applied under high-temperature working conditions.The research on high-temperature absorbing materials is currently mostly focused on absorbers.Cr2AlC is the only ternary compound in the Cr-Al-C system.Its unique layered structure makes it have excellent performance in anti-oxidation and corrosion resistance,and is expected to be used in the field of high-temperature wave absorption.In this paper,Cr powder,Al powder,and Cr3C2 powder are used as raw materials,BaCl2,KCl,NaCl,and activated carbon(C)are used as co-solvents.The salt bath method at 970?for 2 hours is used to prepare Cr2AlC powder,which has high purity and layered structure,and its electromagnetic absorption performance has been studied.In addition,for the application of Cr2AlC at high temperature,the Cr2AlC powder was oxidized at different temperatures,and the oxidation behavior and the electromagnetic wave absorption performance after oxidation of Cr2AlC powder are studied.In order to further improve the oxidation resistance of Cr2AlC powder,a layer of SiO2 was coated on the surface of Cr2AlC powder by the hydrolysis-condensation method of TEOS.The effects of different coating durations on the oxidation resistance and electromagnetic wave absorbing properties of Cr2AlC@SiO2 powder were studied.The main research contents and results of this article are as follows:1.The powder prepared by the salt bath method has typical layered structure,and only contains a small amount of Cr7C3.Mixing Cr2AlC powder and paraffin to make a Cr2AlC/paraffin composite.The real part of the dielectric constant of the composite decreases with the increase of frequency,and the imaginary part increases with the increase of frequency.The content of Cr2AlC powder in the Cr2AlC/paraffin composite has a certain effect on its electromagnetic absorption performance.At the same time,considering impedance matching and attenuation characteristics,when the content of Cr2AlC powder is 70 wt%,it has the best electromagnetic absorption performance.2.According to the application environment of high-temperature stealth design,the oxidation behavior of Cr2AlC powder was analyzed,and the oxidation kinetic parameters of the solid-state oxidation stage were calculated by the FWO method.Oxidation experiments on Cr2AlC powder at different temperatures have been carried out,and the morphology and substance of the oxidized powder have no significant difference below 650?.When the temperature exceeds 800?,some oxidation phases gradually appear.The oxide content of the oxidized samples at different temperatures is different,which has a certain impact on the electromagnetic absorption performance of the oxidized Cr2AlC powder,and the absorption performance gradually decreases with the increase of the oxidation temperature.3.The surface of Cr2AlC powder is coated with a layer of SiO2 by the hydrolysis-condensation method of TEOS.As the coating time increases,the coated powder gradually agglomerates and presents an irregular shape,and the thickness of the coating layer increases.The sample with a coating time of 4h showed a spherical shape with the thinnest coating thickness.The anti-oxidation performance of the coated powder has been improved to a certain extent,but the surface of the coated powder is covered with a thick insulating layer,and its electromagnetic wave absorption performance becomes worse. |
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