The Microwave Absorption Properties Of Carbon-based Nanomaterial

With the wide application of electronic and electrical equipment, electromagnetic wave pollution has become a "invisible killer" in twenty-first century. At present, electromagnetic wave absorption is an effective way to solve the electromagnetic wave pollution. Absorbing material is not only widely used in military field, but also used in civil area. Carbon nanotubes (CNTs) and carbon coated iron magnetic metal nanoparticles (M@C) are new-type carbon-based materials, and they have excellent microwave absorption performance. Moreover, multilayer microwave absorbing coating with various electromagnetic loss mechanisms is a hotspot in recent years.The diameter of CNTs can influence the electromagnetic wave absorption of CNTs. The microwave absorption property of CNTs with different diameters (20-40 nm,40-60 nm and 60-100 nm) were studied in this paper. And meanwhile, the measured reflection loss (measured RL) of CNT/silicone coatings were studied. The results show that the microwave absorption property of CNTs with a diameter of 20-40 nm is excellent. The widest bandwidth of measured RL<-10 dB is 3.46 GHz with 5 wt.% CNT loading and 2 mm in thickness. The minimum measured RL reaches -45.21 dB with 11 wt.% CNT loading and 2 mm in thickness.In this paper, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to identify the phase composition, microstructure and morphology of carbon coated nickel nanoparticles (Ni@C) and carbon coated iron-nickel alloy nanoparticles ((Fe,Ni)@C). The experimental results show that Ni@C nanoparticles and (Fe,Ni)@C nanoparticles possess typical core-shell structures, they are of sphere-like shape and their diameter were 45-60 nm and 80 nm. Compared with (Fe,Ni)@C nanoparticles, Ni@C nanoparticles have excellent microwave absorption property. The widest bandwidth of measured RL<-10 dB is 3.14 GHz with 60 wt.% Ni@C loading and 2 mm in thickness.Building double-layer coating is an important method to improve the microwave absorption performance. The results show that double-layer carbon-based coatings can broaden the absorption bandwidth more effectively, compared with the single-layer coatings. When the surface layer of the double-layer coating is S1 (CNTs/silicone coating, the diameter of CNT is 20-40 nm, the CNT loading is 5 wt.%, the coating thickness is 1 mm), and the bottom layer of the double-layer coating is S2 (CNTs/silicone coating, the diameter of CNT is 20-40 nm, the CNT loading is 11 wt.%, the coating thickness is 1 mm), the bandwidth of measured RL<-10 dB is 3.70 GHz. When the surface layer is S1, and the bottom layer is S3 (Ni@C/silicone coating, the Ni@C loading is 60 wt.%, the coating thickness is 1 mm), the microwave absorption property of double-layer coating is good. When the surface layer is S2 and the bottom layer is S3, the bandwidth of measured RL is expanded effectively.