An Equivalent Substitute Strategy for Constructing 3D Ordered Porous Carbon Foams and Their Electromagnetic Attenuation Mechanism

Three-dimensional(3D)ordered porous carbon is generally believed to be a promising electromagnetic wave(EMW)absorbing material.However,most research works targeted performance improvement of 3D ordered porous carbon,and the specific attenuation mechanism is still ambiguous.Therefore,in this work,a novel ultra-light egg-derived porous carbon foam(EDCF)structure has been successfully constructed by a simple carbonization combined with the silica microsphere template-etching process.Based on an equivalent substitute strategy,the influence of pore volume and specific surface area on the electromagnetic parameters and EMW absorption properties of the EDCF products was confirmed respectively by adjusting the addition content and diameter of silica microspheres.As a primary attenuation mode,the dielectric loss originates from the comprehensive effect of conduction loss and polarization loss in S-band and C band,and the value is dominated by polarization loss in X band and Ku band,which is obviously greater than that of conduction loss.Furthermore,in all samples,the largest effective absorption bandwidth of EDCF-3 is 7.12 GHz under the thickness of 2.13 mm with the filling content of approximately 5 wt%,covering the whole Ku band.Meanwhile,the EDCF-7 sample with optimized pore volume and specific surface area achieves minimum reflection loss(RL_(min))of−58.08 dB at 16.86 GHz while the thickness is 1.27 mm.The outstanding research results not only provide a novel insight into enhancement of EMW absorption properties but also clarify the dominant dissipation mechanism for the porous carbon-based absorber from the perspective of objective experiments.

Wave attenuation mechanism of cross-plates applied in landslide-induced tsunami in river course

Since the impounding of the Three Gorges Reservoir, the channel of the Yangtze River has become a busy watercourse and the probability of landslide-induced tsunamis has increased. In the case of landslide-induced tsunamis in the Three Gorges Reservoir, even after shipping closures in advance, there are still facilities and objects in urgent need of protection within the risk zone of the watercourse, such as wharfs, marine fueling stations, berthed ships. The emergency protection against and decay of landslide-induced tsunamis in inland watercourses is a new challenge. In this study, 37 sets of wave decay experiments were conducted with the hydromechanics numerical method. The wave decay efficiencies of common simple structures including submerged horizontal plate, horizontal plate on the water surface, inclined thin plate and cross-plates in coastal areas were compared and analyzed. Cross-plates structure showed better wave decay capacity than other simple plates. The wave decay performance of cross-plates was related to five modes of energy dissipation and transformation, namely run-up/run-down, overtopping, reflecting, return flow and disturbed wave orbital path. The type of wave had little relation with the decay performance of cross-plates, but a strong correlation with cross-plates structure, especially the height of the vertical emerged plate. The best decay performance was observed when the ratio of wave amplitude to emerged vertical plate height was between 1 and 1.5, which can reduce up to about 8o% of the incoming wave amplitude. Finally, the emergency way of cross-plates applied to the decay of landslide-induced tsunami in river course is discussed. This study provides a conceptual reference for related studies to practice the attenuation of landslide-induced tsunami in reservoirs.

Surface Deposition of Ni(OH)_(2) and Lattice Distortion Induce the Electrochromic Performance Decay of NiO Films in Alkaline Electrolyte

NiO,an anodic electrochromic material,has applications in energy-saving windows,intelligent displays,and military camouflage.However,its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood,making it challenging to improve NiO thin films.We studied the phases and electrochemical characteristics of NiO films in different states(initial,colored,bleached and after 8000 cycles)and identified three main reasons for performance degradation.First,Ni(OH)_(2)is generated during electrochromic cycling and deposited on the NiO film surface,gradually yielding a NiO@Ni(OH)_(2)core-shell structure,isolating the internal NiO film from the electrolyte,and preventing ion transfer.Second,the core-shell structure causes the mode of electrical conduction to change from first-to second-order conduction,reducing the efficiency of ion transfer to the surface Ni(OH)_(2)layer.Third,Ni(OH)_(2)and NiOOH,which have similar crystal structures but different b-axis lattice parameters,are formed during electrochromic cycling,and large volume changes in the unit cell reduce the structural stability of the thin film.Finally,we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films,which will promote the development of electrochromic technology.

Carbon-Based MOF Derivatives:Emerging Efficient Electromagnetic Wave Absorption Agents

To tackle the aggravating electromagnetic wave(EMW)pollution issues,high-efficiency EMW absorption materials are urgently explored.Metal-organic framework(MOF)derivatives have been intensively investigated for EMW absorption due to the distinctive components and structures,which is expected to satisfy diverse application requirements.The extensive developments on MOF derivatives demonstrate its significantly important role in this research area.Particularly,MOF derivatives deliver huge performance superiorities in light weight,broad bandwidth,and robust loss capacity,which are attributed to the outstanding impedance matching,multiple attenuation mechanisms,and destructive interference effect.Herein,we summarized the relevant theories and evaluation methods,and categorized the state-of-the-art research progresses on MOF derivatives in EMW absorption field.In spite of lots of challenges to face,MOF derivatives have illuminated infinite potentials for further development as EMW absorption materials.

Enhancing electromagnetic wave absorption in carbon fiber using FeS_(2)nanoparticles

Carbon-based electromagnetic wave absorbing materials(absorbers)adhered with metallic sulfide nanoparticles of good electrical conductivity attract increasing researchers’attention.In this study,on the basis of carbon fiber(C_(f))@Fe_(3)O_(4) nanocomposites obtained by the electrostatic spinning and reflow method,C_(f)@FeS_(2)nanocomposite was successfully prepared during a further hydrothermal process.The products exhibit excellent electromagnetic wave absorption performances with a minimum reflection loss(RLmin)of-54.11 dB at 2.13 mm matching thickness.At the same time,the optimal effective absorption bandwidth(EAB)value of 6.04 GHz at a thickness of 1.98 mm covers the whole Ku band,suggesting its excellent electromagnetic wave absorption performances.In addition,the interlaced network structure constructed by carbon fiber,outstanding conductivity of FeS_(2)nanoparticles,and interfacial polarization from hetero-structure play significant parts in enhancing the electromagnetic parameters and absorption performances.All these results suggest that the C_(f)@FeS_(2)nanocomposites can be taken as a new electromagnetic wave-absorbing material under their low density,simple craft,and strong absorption characteristics.

Boosted electromagnetic wave absorption performance from synergistic induced polarization of SiC_(NWs)@MnO_(2)@PPy heterostructures

In the last decade,electromagnetic pollution has caused people’s considerable attention.Developing absorbing material with low cost,lightweight,simple preparation,and high electromagnetic attenuation efficiency has become a feasible means to deal with this problem.In this work,core–shell SiC_(NWs)@MnO_(2)@PPy(NWs:nanowires,PPy:polypyrrole)heterostructures composed of SiC nanowires core,MnO_(2)nanosheets inter-layer,and PPy coating were successfully prepared through chemical vapor deposition and two-step electrodeposition process.Taking advantage of the interfacial polarization and dipole polarization,the obtained product displays excellent electromagnetic wave absorption performances with the minimum reflection loss(RLmin)of−50.59 dB when the matching thickness is 2.41 mm,and the optimal effective absorption bandwidth(EAB)value reaches to 6.64 GHz at a matching thickness of 2.46 mm,revealing that the SiC_(NWs)@MnO_(2)@PPy nanocomposite could be served as a promising electromagnetic wave absorbing material.On the basis of systematic analysis concerning the electromagnetic parameters,the dissipation process of the incident electromagnetic wave was demonstrated reasonably,which may provide a referable preparation strategy for novel heterostructures,especially nonmagnetic lightweight absorbing material.

Construction of multiple interfaces and dielectric/magnetic heterostructures in electromagnetic wave absorbers with enhanced absorption performance:A review

The construction of structures with multiple interfaces and dielectric/magnetic heterostructures enables the design of materials with unique physical and chemical properties,which has aroused intensive interest in scientific and technological fields.Especially,for electromagnetic(EM)wave absorption,enhanced interface polarization and improved impedence match with high Snoek's limitation could be achieved by multiple interfaces and dielectric/magnetic heterostructures,respectively,which are benificial to high-efficiency electromagnetic wave absorption(EWA).However,by far,the principles in the design or construction of structures with multiple interfaces and dielectric/magnetic heterostructures,and the relationships between those structures or heterostructures and their EWA performance have not been fully summarized and reviewed.This article aims to provide a timely review on the research progresses of high-efficency EM wave absorbers with multiple interfaces and dielectric/magnetic heterostructures,focusing on various promising EWA materials.Particularly,EM attenuation mechanisms in those structures with multiple interfaces and dielectric/magnetic heterostructures are discussed and generalized.Furthermore,the changllenges and future developments of EM wave absorbers based on those structures are proposed.

Monodispersed Co@C nanoparticles anchored on reclaimed carbon black toward high-performance electromagnetic wave absorption

Recently,developing carbon-based hybrid materials loaded with magnetic components has been generally regarded as a promising and practically feasible strategy when it comes to constructing lightweight electromagnetic wave absorbers.In the current work,reclaimed carbon black(CB)nanopowder was firstly produced by simple burning of wheat straw,which was then employed as sustainable carbon-based host materials(carrier)and successfully decorated Co@C nanoparticles via a simple thermal reduction process.Remarkably,both the as-fabricated nanocomposites and corresponding electromagnetic wave absorption performances could be effectively tuned by tailoring the dosage of the Co@C nanoparticles.The minimum reflection loss(RLmin)of–53.989 d B was achieved for CB/Co@C-2#at 2.28 mm thickness,meanwhile,CB/Co@C-3#was featured by a wide effective absorption band(EAB)of 6 GHz(6.72–12.72 GHz)at a 2.73 mm matching thickness,which covered the entire X band,suggesting that the CB/Co@C nanocomposites were an attractive candidate for electromagnetic wave absorber.According to the synergistic influence of dielectric loss and magnetic loss from CB and Co@C,respectively,as well as the properly matched impedance,a reasonable electromagnetic wave attenuation mechanism was illustrated.It is noteworthy that the preparation process of CB is a facile,recycled,and low-cost strategy for achieving nanoscale carbon-based absorbing materials,moreover,the CB/Co@C nanocomposites provide a reference for constructing lightweight dielectric-magnetic products with superb electromagnetic wave absorption performances.

Ferrite-based composites and morphology-controlled absorbers

The exploration of lightweight and efficient electromagnetic wave(EMW)absorption materials is a crucial focus topic because the human body and precision instruments are exposed to the increasingly serious electromagnetic pollution.Ferrite,as the first type of EMW absorption material,is still the indelible superstar in the EMW absorption field due to its unique double loss mechanism,controllable morphology and high permeability.This review briefly introduces the EMW absorption and attenuation mechanism of ferrite-based composite absorbers,including dielectric loss dominated by charge transfer and polarization relaxation,and magnetic loss consisted of eddy current and resonance.Moreover,we comb the advances in synthesis of ferrite materials.In particular,this paper summarizes the advantages and defects of pure ferrite as EMW absorption material.And the approach to tackling the imbalance of impedance matching and highdensity in ferrite is also reviewed,including ion substitution,design of micro-morphology and doping with dielectric loss materials.