Preparation Of Ferric Oxide Based Composite Materials And Its Study In Microwave Absorbing Properties

With the widespread use of electronic products,electromagnetic wave pollution has become more and more serious.Scientists have conducted in-depth research on microwave-absorbing materials to meet the requirements of"strong,wide,light and thin".Fe₃O₄ is a magnetic ferrite with anti-spinel structure,it has dual absorbing ability of magnetic loss and dielectric loss widely applied in the field of microwave absorbing.Iron-cobalt alloy?FeCo?has extremely high saturation flux,density suitable for making light-weight and small-sized absorbing materials;carbon-based materials are often used to adjust the impedance matching of ferrite materials in absorbing materials due to their low density,high electrical conductivity and high stability.However,there are few papers on the combination of Fe₃O₄,FeCo and carbon materials to improve the absorbing properties of materials.In this paper,hollow Fe₃O₄ microspheres,double-shell hollow Fe₃O₄/C microspheres,double-shell hollow Fe₃O₄/FeCo microspheres and three-shell hollow Fe₃O₄/FeCo/C microspheres were prepared,and the effects reacting conditions of hollow structure and different material compositions on absorbing properties were investigated.Based on the magnetic properties,electromagnetic parameters and absorbing properties of microspheres.Through the above research,the following results were obtained:The hollow Fe₃O₄ microspheres were successfully prepared by solvothermal method.The particle size was about 300 nm,the morphology was regular and the particle size was uniform.The hollow Fe₃O₄ microspheres had a saturation magnetization of 85.1 emu/g.When the thickness was 2.2 mm,the reflection loss reached-45.9 dB at-13.9 GHz,and the bandwidth of the reflection loss less than-10 dB?90%absorption?was 2.6 GHz?11.5-11.8 GHz,13.2-15.1 GHz,17.6-18 GHz?.In order to improve the impedance matching of the material,the double-shell hollow Fe₃O₄/C microspheres were successfully prepared by hydrothermal method,and the particle size was about 400 nm,and the thickness of the carbon layer was about 50 nm.The double-shell hollow Fe₃O₄/C microspheres had a saturation magnetization of 73.8 emu/g.When the thickness was 2.0 mm,the reflection loss reached-32.1 dB at-16.4 GHz,and the bandwidth of the reflection loss less than-10 dB?90%absorption?was 3.5 GHz?14.5-18 GHz?.In order to enhance the absorbing properties of materials in different frequency bands and broaden the effective absorbing bandwidth of materials,the double-shell hollow Fe₃O₄/FeCo microspheres were successfully prepared by liquid phase reduction method.The particle size was about 460 nm and the thickness of FeCo layer was about 80 nm.The double-shell hollow Fe₃O₄/FeCo microspheres had a saturation magnetization of 72.1 emu/g.When the thickness is 2.2 mm,the reflection loss reached-36.9 dB at 13.3 GHz,and the the bandwidth of the reflection loss less than-10 dB?90%absorption?was 5.5 GHz?12.1-17.6 GHz?.In order to improve the impedance matching of materials,enhance the absorbing properties of materials in different frequency bands and broaden the effective absorbing bandwidth of materials,three-shell hollow Fe₃O_4/FeCo/C microspheres were successfully prepared by hydrothermal method.The three-shell hollow Fe₃O₄/FeCo/C microspheres had a particle size of about 500nm,the carbon layer thickness was about 50 nm.The three-shell hollow Fe₃O₄/FeCo/C microspheres had a saturation magnetization of 40.9 emu/g.When the thickness was 2.6 mm,the reflection loss reached-37.4 dB at 13.4 GHz,and bandwidth of the reflection loss less than-10 dB?90%absorption?was 5.9 GHz?11.7-17.7 GHz?.In this study,iron-cobalt and carbon materials were introduced on the basis of hollow Fe₃O₄ microspheres,and three-shell hollow Fe₃O₄/FeCo/C microspheres were prepared by structural design,which effectively improved the narrow absorption band of single Fe₃O₄ absorber.The composite microspheres cooperate with each other in composition and structure,which not only enriches the absorbing mechanism,improves the impedance matching,and broadens the effective absorbing bandwidth of the material,thereby achieving the effective absorption of electromagnetic waves by the material.