Rational design of core-shell Co@C microspheres for high-performance microwave absorption

With the booming development of electronic information technology, the problems caused by electromagnetic (EMs) waves have gradually become serious, and EM wave absorption materials are playing an essential role in daily life. Carbon nanostructures stand out for their unique structures and properties compared with the other absorption materials. Graphene, carbon nanotubes, and other special carbon nanostructures have become especially significant as EM wave absorption materials in the high-frequency range. Moreover, various nanocomposites based on carbon nanostructures and other lossy materials can be modified as high-performance absorption materials. Here, the EM wave absorption theories of carbon nanostructures are introduced and recent advances of carbon nanostructures for high-frequency EM wave absorption are summarized. Meanwhile, the shortcomings, challenges, and prospects of carbon nanostructures for high-frequency EM wave absorption are presented. Carbon nanostructures are typical EM wave absorption materials being lightweight and having broadband properties. Carbon nanostructures and related nanocomposites represent the developing orientation of high-performance EM wave absorption materials.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201801057

Toward the Application of High Frequency Electromagnetic Wave Absorption by Carbon Nanostructures

Co/C nanoparticles (NPs) with a size of 45 nm have been prepared by an arc plasma method under a mixed methane and argon atmosphere. They display a uniform carbon shell of 3 nm in thickness and have a low graphitization degree. The saturation magnetization (MS) and coercivity (HC) of the NPs are 159.9 emu g−1 and 275.7 Oe, respectively. The microwave absorption properties of the Co/C NPs mixed with paraffin wax (PW) at 25, 50 and 75 wt% NPs have been investigated in the range of 2–18 GHz. The Co/C-PW composite with 50 wt% NPs exhibits the best microwave absorption performance. It has a minimum reflection loss (RL) value of −43.4 dB at a thickness of 2.3 mm, and the absorption bandwidth for RL ≤ −20 dB is as large as 7.2 GHz, which is the highest value among the reported Co-based absorbers. The high microwave absorption performance is interpreted in terms of impedance matching, core/shell structure and nanosize effects. The carbon-coated magnetic metal NPs prepared by methane plasma arc are potential microwave absorbers with strong absorption intensity and wide absorption bandwidth.

Co/C nanoparticles with low graphitization degree: a high performance microwave-absorbing material

A method combining liquid–liquid phase separation and the pyrolysis process has been developed to fabricate the wormhole-like porous carbon/magnetic nanoparticles composite with a pore size of about 80 nm (WPC/MNPs-80). In this work, the porous structure was designed to enhance interaction between the electromagnetic (EM) wave and the absorber, while the magnetic nanoparticles were used to bring about magnetic loss ability. The structure, morphology, porosity and magnetic properties of WPC/MNPs-80 were investigated in detail. To evaluate its EM wave attenuation performance, the EM parameters of the absorber and wax composite were measured at 2–18 GHz. WPC/MNPs-80 has an excellent EM wave absorbency with a wide absorption band at a relatively low loading and thin absorber thickness. At the absorber thickness of 1.5 and 2.0 mm, minimum RL values of −29.2 and −47.9 dB were achieved with the RL below −10 dB in 12.8–18 and 9.2–13.3 GHz, respectively. The Co and Fe nanoparticles derived from the chemical reduction of Co0.2Fe2.8O4 can enhance the graphitization process of carbon and thus improve dielectric loss ability. Polarizations in the nanocomposite absorber also play an important role in EM wave absorption. Thus, EM waves can be effectively attenuated by dielectric loss and magnetic loss through multiple reflections and absorption in the porous structure. WPC/MNPs-80 could be an excellent absorber for EM wave attenuation; and the design strategy could be extended as a general method to synthesize other high-performance absorbers.

A wormhole-like porous carbon/magnetic particles composite as an efficient broadband electromagnetic wave absorber

Large-scale core–sheath heterostructural SiC nanowires were facilely grown on the surface of carbon fibers using a one-step chemical vapor infiltration process. The as-synthesized SiC nanowires consist of single crystalline SiC cores with a diameter of ∼30 nm and polycrystalline SiC sheaths with an average thickness of ∼60 nm. The formation mechanisms of core–sheath heterostructural SiC nanowires (SiCnws) were discussed in detail. The SiCnws-CF shows strong electromagnetic (EM) wave absorption performance with a maximum reflection loss value of −45.98 dB at 4.4 GHz. Moreover, being coated with conductive polymer polypyrrole (PPy) by a simple chemical polymerization method, the SiCnws-CF/PPy nanocomposites exhibited superior EM absorption abilities with maximum RL value of −50.19 dB at 14.2 GHz and the effective bandwidth of 6.2 GHz. The SiCnws-CF/PPy nanocomposites in this study are very promising as absorber materials with strong electromagnetic wave absorption performance.

In Situ Growth of Core–Sheath Heterostructural SiC Nanowire Arrays on Carbon Fibers and Enhanced Electromagnetic Wave Absorption Performance

Electromagnetic characteristics and microwave absorption properties of carbon-encapsulated cobalt nanoparticles in 2–18-GHz frequency range

The coating optimization has been carried out for the design of microwave absorbing materials of advanced carbon and metal powder based on genetic algorithm. An optimum designing program for multilayer absorbing material has been compiled by matlab language. The program can transfer the electromagnetic parameters of advanced carbon and metal powder which measured by vector network analyzer, and can process thickness optimum design of different absorbing materials in the range of 0.5~6GHz. The result shows that, the best absorbing layers can easily gained from the electromagnetic parameter database by computing with this program according to our requirement. The objective function in genetic algorithm has great effect on the optimization results. The multi-constant weight method is very helpful to design the microwave absorbing layers of broad-frequency and high absorption.

http://www.aicit.org/JCIT/ppl/JCIT3616PPL.pdf

Danfeng Zhang

Papers

Electromagnetic characteristics and microwave absorption properties of carbon-encapsulated cobalt nanoparticles in 2–18-GHz frequency range

Designing of Multilayer Microwave Absorbing Coating of Advanced Carbon and Metal Powder Based on Genetic Algorithm