Preparation And Properties Of Magnetite Hollow Fe₃O₄ Matrix Nanocomposites Absorbing Materials

In this paper, the hollow Fe₃O₄ and the mesoporous Fe₃O₄ was prepared by solvothermal method. The hollow sphere Fe₃O₄ powders were mixed with Co particles（prepared by arc-discharge）. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy tests were carried to confirm the microstructure and size of samples prepared. Vibrating sample magnetometer and vector network analyzer microstructure tests were carried to confirm the magnetic and absorbing properties of them.The results show that the size of hollow Fe₃O₄ particles are about 150-200 nm, saturation magnetization is 37.1Am2/Kg and the coercive force is 5.53KA/m. The size of mesoporous Fe₃O₄ particles are about 20-50 nm, saturation magnetization is 26.5Am2/Kg and the coercive force is 2.79KA/m. The microwave absorption properties study reveals that the optimal reflection of hollow Fe₃O₄ absorbent was-31.33 dB at 7.63 GHz with the thickness of 3.5mm. The reflection absorption coefficient below-10 dB is in the range of 1.85-9.84 GHz with the thickness of 3-6mm. The optimal reflection of hollow Fe₃O₄ has increased and the peak position of hollow Fe₃O₄ have moved to low frequency while increasing the coating thickness. It is worth mentioning that the optimal reflection of mesoporous Fe₃O₄ increased while increasing the coating thickness at 14 GHz but peak position almost without changing. It attributes to the small size effect, molecular level quantization and the existence of the defect level of mesoporous Fe₃O₄.In addition, the hollow Fe₃O₄ powders were mixed with Co particles（the size about 30-100nm）, the results show that the optimal reflection was-40.1dB at 6.61 GHz with the thickness of 3.5mm and the-10 dB below is the frequency band range of 1.85-18 GHz with the thickness of 2-6mm when quality ratio of Fe₃O₄ and Co is 4:1.Studies show that the hollow Fe₃O₄ particles with light weight characteristic can cause multiple scattering, which is due to large surface area and porous structure. The scattering and the polarization increased the absorption and attenuation of electromagnetic wave. The composite of hollow Fe₃O₄ and Co improves electromagnetic parameters to broaden the absorption bands.