Study On Design, Preparation And Electromagnetic Properties Of The Carbon Nanotube (CNT)/Magnetic Metal Heterostructure Absorbents

An excellent electromagnetic (EM) wave absorbent must have light-weight, thin-thickness, strong-absorption, broad-band width, tunable absorption frequency, and multi-functionality. However, traditional absorbents are difficult to meet the high requirements of both civil and military applications. Currently, studies on excellent absorbents are being faced with two major problems:One is certain contradictions between effective absorption and impedance matching. The other is the interface control among different materials, which is the key to improve the properties of composite absorbents. On the basis of previous studies and EM-wave absorption mechanism, carbon nanotube (CNT)/magnetic metal hetero structure absorbents can overcome the defects of single materials, and promote the properties.For this reason, three heterostructure composite absorbents have been designed and prepared in this paper, including rambutan-like Ni/MWCNT heterostructures, centipede-shaped iron/cementite/multiwalled carbon nanotube (Fe/Fe3C/MWCNT) heterostructures, and novel EG/Ni/CNT hybrid materials. The composition, construction, and performance of these heterostructure absorbents can easily be controlled through changing the synthetic conditions. Moreover, their formation mechanism and the influencing factors, as well as static magnetic and microwave electromagnetic characteristics were systematically investigated. The main results of this paper follow:(1) Rambutan-like Ni/MWCNT heterostructures with tunable morphology and composition were synthetized; meanwhile, their microwave electromagnetic and absorbing characteristics were systematically investigated. As the PEG 20000/NiO feeding ratio (5) increased from 3.0 to 15, the C mass fraction increased and the sample morphology varied from Ni/C film core-shell structures to rambutan-like Ni/MWCNT heterostructures. An optimal microwave absorption property with a minimum RL value of -37.9 dB occurring at 12.8 GHz can be observed for Ni/MWCNT heterostructures coated by short MWCNTs formed at δ=7.5.(2) For the first time, we have developed a novel and simple gas-flow-induced in situ two-step CVD method for synthesizing centipede-shaped Fe/Fe3C/MWCNT heterostructures. The formation of centipede-shaped heterostructures is ascribed to the cooperation of the carrier gas flow and the spontaneous magnetization. Compared with Fe nanofibers, centipede-shaped Fe/Fe3C/MWCNT heterostructures exhibited multiresonance behaviors, higher dielectric loss, and enhanced microwave absorption performances because of their special heterostructure.(3) A lightweight EG/Ni/MWCNT hybrid absorbents with controllable morphology and composition were synthesized via a dipping-CVD method. The effects of carbon source and Ni2+concentration on the composition, phase structure, and morphology of the products were systematically investigated.The property studies indicate that the soft magnetic and microwave absorbing properties of products can be tuned by changing Ni particle content and crystal size.