Microwave Absorbing Properties Of Core-shell Magnetic/Carbon Composites Prepared By The Pyrolysis Of Precursors

In recent years,to meet the requirements of electromagnetic wave absorbers with the features of broad frequency,strong absorption intensity,especially thin thickness and light weight,carbon-based materials with low density and strong microwave attenuation abilities have attracted an increasing attention.In this thesis,a series of core-shell structured magnetic/carbon composites were synthesized by the pyrolysis of precursors under inert atmosphere.?1?Firstly,Ni@C nanorods were synthesized via the pyrolysis of precursor,which was obtained by the solvothermal method.The morphology and electromagnetic parameters of the absorbers could be adjusted by the annealing temperature.The composites annealed at 500 ^oC possess the most regular nanorods and the best attenuation ability.The minimum reflection loss?RL?value of-26.3 dB can be gained at 10.8 GHz with a thickness of 2.3 mm.Moreover,the effective bandwidth?RL?-10 dB?of5.2 GHz?12.24¹7.4 GHz?under an absorber thickness of 1.8 mm can be achieved.?2?Then,Fe₃O₄@C and Fe₃C composites were synthesized by the annealing of oleic acid coated Fe₃O₄ precursor at different temperatures.Compared with Fe₃O₄@C,Fe₃C composites exhibited higher reflection loss and broader effective bandwidth at lower thickness.For an absorber thickness of1.9 mm,its reflection loss value and effective bandwidth are-34.6 dB and 5.5 GHz,respectively.After analyzing,its preferable microwave absorbing performance is tightly related with more than one polarization processes and better matched impedance.?3?Finally,to further decrease the density of the composites,we prepared the honeycomb-like structured Fe₃C@C composites using the pyrolysis of precursor obtained by chemical bowling method.By changing the content of ferric salt,the honeycomb-like structure with scads of pores and electromagnetic parameters could be successfully tailored.When the content of ferric salt is 2 g,the composite had the distinctive three-dimensional structure and the best electromagnetic attenuation ability,even mixed with 90wt%paraffin.Its minimal reflection loss is-37.4 dB at 13.6 GHz and effective bandwidth can reach to 5.6 GHz when the thickness is 2.0 mm,indicating its great potential in light-weight and high efficient microwave absorbers field.