科研之友
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摘要
Carbon nanofibers embedded with (Fe1-xCox)(0.8)Ni-0.2 (x=0.25, 0.50 and 0.75) alloy nanoparticles were synthesized by carbonizing electrospun polyacrylonitrile nanofibers containing metallic acetylacetonate salts in argon atmosphere. The phase composition, morphology, microstructure, static magnetic properties and electromagnetic characteristics of them were characterized and analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA), and their microwave absorption performances in the frequency range of 2-18 GHz were calculated according to transmission line theory. The results indicate that the as-prepared composite nanofibers have a typical ferromagnetic characteristics and are composed of amorphous carbon, graphite and face centered cubic structured Fe-Co-Ni alloy. The in situ formed alloy nanoparticles are uniformly dispersed along carbon-based nanofibers and encapsulated by ordered graphite layers. The silicone-based absorbing coatings with only 5%(w/w) of (Fe1-xCox)(0.8)Ni-0.2/C composite nanofibers as absorbers exhibit excellent microwave absorption properties, which are attributed to the synergistic effect between the magnetic loss and dielectric loss and the special particle/graphite core/shell microstructures in the nanofibers. The minimum reflection loss reaches -78.5, -80.2 and -63.4 dB for the x=0.25, 0.50 and 0.75 samples, respectively, and the absorption bandwidth of reflection loss under 20 dB is respectively up to 14.9, 14.8 and 14.5 GHz for an absorber thickness of 1.1 similar to 5.0 mm, almost covering the entire C-band to Ku-band. Furthermore, the electromagnetic characteristics and microwave absorption performances can be tuned to some extent by adjusting the composition of Fe-Co-Ni alloy.
