Synthesis Of Iron-based Core-shell Composites And Studies On The Microwave-absorbing Properties

The continuous development of electronic communication and electronic equipment brings convenience to people's life,but also produces a lot of electromagnetic pollution.Electromagnetic wave pollution will not only interfere with normal communication,but also harm health and worsen the natural environment.Therefore,in order to shield electromagnetic radiation as much as possible,it has become a research hotspot to prepare environmental functional absorbing materials with the characteristics of"thin,light,wide and strong".In this paper,?-Fe₂O₃ and Fe₄N nanocomposites were synthesized by hydrothermal synthesis and solid gas reaction respectively.The core-shell nanocomposites of?-Fe₂O₃@Si O₂ and Fe₄N@Si O₂ were synthesized by a sol-gel method.A systematic investigation of the formation and microwave absorption properties of?-Fe₂O₃,Fe₄N,?-Fe₂O₃@Si O₂ and Fe₄N@Si O₂ nanocomposites was conducted using X-ray diffractometer(XRD),field emission scanning electron microscope(FESEM),vibrating sample magnetometer(VSM)and vector network analyzer(VNA)and so on.The main work and conclusions are as follows:(1)The results of XRD,FESEM and FETEM show that the factors such as reaction temperature,reaction time and additives have important effects on the formation of?-Fe₂O₃ nanoparticles.Taking Fe Cl₃·6H₂O as raw material,the cubic?-Fe₂O₃ nanoparticles with the best crystallinity and the size of 50-60 nm were obtained under the condition of adding 15 m L glycol and being hydrothermal synthesized at 200?for 12 hours.The factors such as nitriding temperature and time play an important role on the formation of Fe₄N,and the pure phase Fe₄N with irregular interlaced strips and net shape was obtained under the condition of nitriding at 520?for 3 to 5 hours.(2)The results of XRD,FESEM and FETEM show that the core-shell?-Fe₂O₃@Si O₂ nanoparticles with different coating thickness were prepared by a sol-gel method using?-Fe₂O₃ as precursor.The coating thickness of Si O₂ increases from 5 nm to 150 nm.The results of VSM show that the coercive force of?-Fe₂O₃@Si O₂(500 mg)with an average coating thickness of 35 nm is the largest,and its value is 1100 Oe.The results of VNA show that both the coating treatment and the thickness of the coating can affect the microwave absorption properties of the samples.When the thickness of the absorbing agent is 5.0 mm,the maximum reflection loss of the uncoated?-Fe₂O₃ is-1.2 d B,and the maximum reflection loss of the?-Fe₂O₃@Si O₂composite with the average Si O₂ coating thickness of 35nm is-3.0d B.(3)The results of XRD,FESEM and FETEM show that the core-shell Fe₄N@Si O₂ with different coating thickness can be prepared by a sol-gel method with Fe₄N as precursor.The coating thickness can be increased from 15 nm to 80 nm.The results of VSM show that nitriding treatment will reduce the saturation magnetization and increase the coercive force.The saturation magnetization M_s of Fe₄N,Fe₄N@Si O₂(500 mg)and Fe₄N@Si O₂(1000 mg)are 176.5 emu/g,132.1 emu/g and 156.9 emu/g,respectively.The coercive force H_c are 81.5 Oe,83.0 Oe and 86.5 Oe,respectively.The results of VNA show that both the coating treatment and the coating thickness can affect the microwave absorption properties of the samples.The absorption of Fe₄N@Si O₂ after coating is better than that of uncoated Fe₄N.When the thickness of the absorbing agent is 5.0mm,the absorption performance of Fe₄N@Si O₂(500mg)with an average coating thickness of 35 nm is the best.There are two absorption peaks,among which the maximum reflection loss is-16.76 d B at 17.41 GHz and the effective absorption bandwidth is 1.87 GHz.