Preparation And Microwave Absorption Properties Of Quasi-one-dimensional Fe-Co Alloy/Dielectric Oxides Fibrous Composite Materials

In recent years, with the expanding business of various communication and electronic devices using the GHz range electromagnetic wave, electromagnetic interference pollution and electromagnetic radiation have become a concerning issue. In order to solve this problem and meet the electromagnetic stealth demand in the modern military field, the research of the new type high-performance microwave absorbing materials has become a hot spot both in civil and military regions internationally. In this thesis, a series of?1-x?Co Fe₂/?x?Ba Ti O₃?x = 0¹? and?1-x?CoyFe1-y/?x?Zn O?x = 0¹, y = 0¹? composite nanofibers with average diameters of 90³40 nm have been prepared by the electrospinning method combined with stablization and hydrogenthermal reduction processes. These nanofibers are characterizaed by means of thermogravimetric and differential thermal analysis?TG-DTA?, X-ray diffraction?XRD?, scanning electron microscope?SEM?, transmission electron microscope?TEM?, transmission electron microscope?VSM? and vector network analyzer?VNA?. The effects of the heat treatment temperature before reduction, the hydrogenthermal reduction temperature, ferroelectric phase?Ba Ti O₃ or Zn O? content, and Co concentration in Fe Co alloy on the phase structure, static magnetic, and microwave absorption performances of these composite nanofibers have been investigated in detailed. The results indicate that all the in-situ synthesized composites nanofibers are composed of both bcc-structured Co-Fe alloy and tetragonal perovskite-structured Ba Ti O₃?or wurtzite-structured Zn O? phases. The excellent microwave absorption performances for these composite nanofibers exhibit should be mainly attributed to the improved impedance matching and the enhanced electromagnetic attenuation capacity due to the synergistic effect between dielectric and magnetic medium. Furthermore, their electromagnetic characteristics and microwave absorption properties can be tuned effectively through adjusting the heat treatment temperature before reduction, the hydrogenthermal reduction temperature and chemical compositions.For the?1-x?Co Fe₂/?x?Ba Ti O₃ composite nanofibers, when the heat treatment temperature before reduction is 750 °C, the hydrogenthermal reduction temperature 450 °C, and the Ba Ti O₃ conent 30wt%?i.e. x = 0.3?, the corresponding silicone-based coatings display a relatively better microwave absorption performances over the whole investigated frequency range. As the coating thicknesses are between 1.0 and 3.0 mm, the reflection loss?RL value? below –20 d B can be achieved in the frequency ranges of 3.2¹8.0 GHz, covering 40% of S-band and the entire C-band to Ku-band, and the minimum RL value is –68.2 d B.For the?1-x?CoyFe1-y/?x?Zn O composite nanofibers, when the heat treatment temperature before reduction is 750 °C, the hydrogenthermal reduction temperature 450 °C, x = 0.8, and y = 0.33, the corresponding nanofiber/silicone composites show a relatively stronger microwave absorption ability. When the thicknesses of coatings are in the range of 1.0–3.0 mm, the minimum RL value reaches –93.4 d B and the absorbing bandwidth with RL value less than –20 d B is up to 14.8 GHz ranging from 3.2 to 18.0 GHz, covering 40% of S-band and the whole C-band to Ku-band.Compared with those Fe-Co alloy/oxide nanocomposite materials recently reported, the present Co Fe₂/Ba Ti O₃ and Co Fe₂/Zn O composite nanofibers possess better microwave absorption performances with a relatively thinner coating thickness, highlighting potential application prospect in the electromagnetic wave absorbing and shielding fields.