Study On Thermal Conductive And Absorbing Electromagnetic Wave Composite Material Of FeSiAl

With the rapid development of modern communication technology and computer industry,FeSiAl soft magnetic composite?SMCs?is widely used because of its high permeability,high saturation susceptibility and low cost.In this paper,a uniform and dense oxide insulation layer with high resistivity was grown on the surface of FeSiAl by high-temperature surface oxidation method.Meanwhile,Al₂O₃ coated FeSiAl magnetic powder composite material was prepared by the method of lysogen with aluminum nitrate as the aluminum source.The phase composition,surface morphology and element composition of the coated powder were analyzed by XRD,SEM and EDS.The complex dielectric constant and complex permeability of coated powders were measured by waveguide method.The results showed that after high-temperature oxidation,the surface of FeSiAl powder was smooth with no crack,and all diffraction peaks were Fe₃Si_0.7Al_0.3 phase.The powder did not undergo high-temperature decomposition chemical reaction,and the oxygen content on the surface of the powder increased with the increase of oxidation temperature.At the beginning of the reaction,oxygen molecules and metal atoms are ionized.The reaction of aluminum and oxygen gives priority to the formation of a continuous external oxide film,and the dense alumina film prevents the further oxidation of the internal FeSiAl powder.The oxidation temperature has a significant influence on the complex dielectric constant and complex magnetic permeability of FeSiAl powder.With the increase of the oxidation temperature,the complex dielectric constant and complex magnetic permeability of FeSiAl powder decrease significantly.The lowest peak reflectance of all samples moved to low frequency with the increase of sample thickness.When the oxidation temperature was 700?,the minimum reflectivity of FeSiAl powder was significantly lower than that of the original powder,and the frequency band was less than-5db,reaching 4.8 GHz.With the increase of the oxidation temperature,the thermal conductivity of FeSiAl powder also decreased.After oxidation at 700?,the thermal conductivity was 2.2 W/m·K.FeSiAl powder was coated with pH=3 and pH=8,and an oxide shell was formed on the surface of the powder.The coated FeSiAl powder phase are composed of the original FeSiAl phase.No oxide coating is found.Under pH=3,the coated powder surface are relatively compact,while under pH=8,a large number of cracks and holes were found on the coated powder surface.After coating,the content of oxygen element increased significantly,and Si and Al elements are evenly distributed without obvious agglomeration.When pH=3,the coating mechanism of FeSiAl powder is mainly through the hydrolysis coating process;when pH=8,the coating mechanism of FeSiAl powder is mainly the precipitation coating of Al?OH?₃.Under the condition of pH=3coating,due to the large coating thickness,the powder polarization ability is limited,which is manifested as the decrease of the sample complex dielectric constant and complex permeability.The lowest peak reflectance of all samples moved to low frequency with the increase of sample thickness.When covering pH=3,and the thickness of absorbing material is 2.4 mm,the minimum reflectance at 7.9 GHz is-46.7dB,which is less than 5.8 GHz⁹.9 GHz in the frequency band of-5db.The thermal conductivity test shows that the thermal conductivity of FeSiAl powder after coating is1.9 W/m·K under pH=8,and that of FeSiAl powder after coating is 1.5 W/m·K under pH=3.The relatively thick coating layer leads to the relatively low thermal conductivity of the powder.