Study On Microwave Absorption Properties Of Carbon-Coated Iron-group Magnetic Nanomaterials

The demand for microwave absorbing materials with strong absorption capability and wide absorption band is increasing due to serious electromagnetic interference issues and defense stealth technology needs.Numerous studies have demonstrated that the electromagnetic wave absorbers with single structure and composition are difficult to fulfill the increasingly high requirements of microwave devices in practical applications.Developing the core-shell composite materials with structural designability and adjustability of electromagnetic parameters is considered as an effective strategy to improve their wave absorption performance.Especially,nanostructured core-shell or yolk-shell absorbers with magnetic nanoparticles as core and dielectric layer as shell can give full play to the cross-coupling effect of magnetic and dielectric components and introduce additional wave loss mechanism,which becomes a good structural model to construct high-efficiency MAMs.Details are as follows:?1?We developed a novel strategy based on volume shrinkage from the release of oxygen anions to successfully fabricate the carbon-coated Fe₃O₄?Fe₃O₄@C?yolk-shell structure.The TEM,XRD,XPS and Raman results show that the Fe₃O₄ nanoparticles are uniformly coated with a thin carbon layer about 10 nm in thickness and a clear void about 1 nm in width between Fe₃O₄ core and carbon shell.The obtained yolk-shell composites exhibit excellent microwave absorption properties.The absorption bandwidth with RL values exceeding-10 dB is up to 5.4 GHz for the absorber with a thickness of 2.2 mm.The optimal RL can reach up to-45.8 dB at 10.6 GHz for the composite with a thickness of 3.0 mm.?2?The MIL-101?Fe?materials were prepared by a hydrothermal method using FeCl₃·6H₂O and terephthalic acid as raw materials.Then the Fe₂O₃/C composites were synthesized by high temperature pyrolysis of MIL-101?Fe?.The results show that the Fe₂O₃ were well encapsulated by carbon shells.The obtained Fe₂O₃/C composites exhibit excellent microwave absorption properties.The absorption bandwidth with RL values exceeding-10 dB is up to 4.6 GHz for the absorber with a thickness of 1.7 mm.The optimal RL can reach up to-55.2 dB at 10.6 GHz for the composite.?3?The Co₃O₄/Co?OH?₂ precursors were prepared by a hydrothermal method using aqueous ammonia and Co?NO₃?₂ as raw materials.The Co@C composites were synthesized by catalyzing the pyrolysis of acetylene with Co₃O₄/Co?OH?₂.The TEM,XRD,XPS and Raman results show that the cores were well coated by the carbon layer and the carbon layer was highly graphitized.The obtained core-shell Co@C composites exhibit excellent microwave absorption properties.The absorption bandwidth with RL values exceeding-10 dB is up to 4.6 GHz for the absorber with a thickness of 1.8 mm.The optimal RL can reach up to-54.2 dB at 10.6 GHz for the composite with a thickness of 2.6 mm.