Superior Microwave Absorption Research Articles

One-step green synthesis of multi-morphological carbon nanotube forests for superior microwave absorption and electrocatalysis

Porous carbon materials with multiscale distinctive morphologies hold significant promise in electromagnetic wave stealth/protection and catalysis; however, formidable challenges are highly verbose and resource/time-consuming fabrication processes. Here, we report a one-step solvent/template-free self-expanding carbonization strategy for rapidly fabricating porous carbon foams (Ni/CNT) with zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanotube forests, and three-dimensional (3D) hollow microvesicles. Owing to the multi-morphological structure and low-density feature, the resulting porous carbon foam Ni/CNT-800 achieves a minimum reflection loss of −56.48 dB and an effective bandwidth of 5.44 GHz at a low filler loading of only 9 wt%. Moreover, altering the electronic structure and surface chemistry of carbon foam by phosphorus doping enables a highly reduced durable overpotential (η) of 275 mV for oxygen evolution reaction. This work emphasizes a straightforward strategy for the facile design and efficient fabrication of carbon-based materials with unique multiscale porous morphologies, customizable functions, and various applications.

Fabrication of hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns for high-performance microwave absorption

Due to the increasingly serious electromagnetic radiation and pollution problems, it is urgent to develop high-performance electromagnetic wave absorbing materials. Herein, the hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns (H-Fe3O4@SWCNHs) have been synthesized via facile solvothermal approach. The obtained H-Fe3O4@SWCNHs composite exhibits a unique hollow core-shell structure and superior microwave absorption performance. When the matching thickness is 2.0 mm, the composite shows a minimum reflection loss value of −42.2 dB at 13.6 GHz and a maximum effective absorption broadband value of 6.2 GHz covering from 11.8 to 18 GHz. The excellent microwave absorption performance of the H-Fe3O4@SWCNHs composite is mainly attributed to the unique hollow core-shell structure, optimal impedance matching, and synergistic effects of dielectric loss and magnetic loss. Therefore, the present work provides a new kind of ideal microwave absorbing material with light weight, thin thickness, wide bandwidth and strong absorption capability for high-performance microwave absorption.

Ultralight Cellulose-Derived Carbon Nanofibers from Freeze-Drying Emulsion Towards Superior Microwave Absorption

Carbon nanofibers (CNFs) are usually prepared by the carbonization of cellulose aerogels obtained from freeze-drying. However, cellulose with low concentration (below 1 wt%) is required to maintain the good porosity of the aerogels due to the strong hydrogen bonding between the cellulose molecules. In order to address this problem, here, ultralight cellulose-derived CNFs have been fabricated by freeze-drying cyclohexane (CHE)/cellulose nanofiber emulsions and carbonization. Field emission scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are used to characterize the resulting CNFs. It is found that the CNFs consist of three-dimensional carbon networks, whose microstructure is easily adjusted by changing the CHE ratio (from 0 to 25 vol%) in the emulsions. The CNFs with high porosity are attributed to the fact that CHE as the oil phase can effectively weaken the hydrogen bonding and reduce the aggregation of the cellulose nanofibers. Carbon lattice defects and residual oxygen-containing functional groups are regarded as polarization centers, leading to the enhancement of dielectric loss. The conductive carbon networks also improve the conductive loss. All these factors improve the microwave absorption performance of the CNFs. So, the produced CNFs exhibit a superior electromagnetic wave performance with a minimum reflection loss of −42.18 dB and effective absorption bandwidth up to 4.9 GHz at 2 mm with a filling ratio of 2 wt%. This work provides a simple, low-cost, and sustainable synthesis route for CNFs used for ultralight high-performance microwave absorption materials.

Graphene-Wrapped Magnetic Multichamber Ti3C2Tx Spheres for Stable Broadband Microwave Absorption.

Two-dimensional transition metal carbides/nitrides (MXenes) have aroused widespread interest in the field of microwave absorption because of their unique layered structures. However, the inherent aggregation, poor impedance matching, and low chemical stability of MXenes inevitably obstruct their practical applications. Herein, a multichamber Fe3O4/Ti3C2Tx@reduced graphene oxide (FT@RGO) hierarchical structure was constructed through self-assembly and sacrificial template strategies where the Ti3C2Tx nanosheets were assembled into hollow microspheres that were decorated with Fe3O4 nanospheres and wrapped by RGO nanosheets. The massive heterointerfaces and interior cavities favor enhanced microwave absorption performance via interfacial polarization, multiple scattering/reflections, and dielectric-magnetic synergistic effects. Consequently, the synthesized ultralight FT@RGO foam (0.009 g/cm3) presents superior microwave absorption ability with the minimum reflection loss of -50.5 dB at the matching thickness of 2.5 mm and effective absorption bandwidth of 8.0 GHz covering the frequency range of 10.0-18.0 GHz at the thickness of 2 mm. Furthermore, the encapsulation of hollow Ti3C2Tx spheres by RGO nanosheets avoids direct contact with external air, which considerably improves the stability of Ti3C2Tx and ensures the long-term application of FT@RGO foam in a conventional environment. This work provides a reference for the structural design of MXene-based materials as broadband and durable microwave absorbers.

A novel approach to obtain superior microwave absorption using Non-Conducting polymer jacket coated Multi-Layer Hexaferrite-TMDC nanocomposite film

This article represents the imposing electromagnetic interference (EMI) shielding behaviour of non-conducting polymer jacket-coated Co2Y-hexaferrite-MoS2 binary nanofillers incorporated PVDF multi-layer nanocomposite films. The presence of Co2Y-hexaferrite inside PVDF enhanced the magnetic permeability, whereas the incorporation of semiconducting transition metal dichalcogenide (TMDC), MoS2, inside the PVDF matrix improves the polarization effects of the nanocomposite films. The crystalline phases corresponding to Co2Y-hexaferrite, MoS2 nanoparticles and the multi-phase nanocomposite films have been justified using XRD analysis and Rietveld refinement study. FESEM micrographs confirm the hexagonal and cotton-ball structures of Co2Y-hexaferrite and MoS2 nanoparticles, respectively; in addition, the presence of Co2Y-MoS2 binary nanofillers inside the PVDF matrix has been confirmed. The stability of the nanocomposite films against electrical breakdown is clearly demonstrated by the minimum leakage current observed at 90 kV/m under J-E characteristics. The room temperature maximum magnetization of 33.32 emu/g of Co2Y-hexaferrite at an external magnetic field of 50,000 Oe helps in incurring magnetic losses and the corresponding improvement of shielding effectiveness due to absorption (SEA) of the nanocomposite films. This article demonstrates the modulation of SEA of the nanocomposite films depending on both the binary nanofillers loading percentage inside PVDF and the thickness of the nanocomposite films. Also, a unique mechanism corresponding to the coating of a non-conducting polymer jacket over a multi-layer structure has been opted herein to improve SEA in the frequency range of 12–18 GHz. This unique mechanism demonstrates that the maximum SEA for the non-conducting polymer jacket-coated multi-layer nanocomposite film is −51.23 dB at 14.03 GHz, and the corresponding total shielding effectiveness (SET) is −74.51 dB at 13.23 GHz, along with > 99.9999 % attenuation.

Fe3C/Fe implanted hierarchical porous carbon as efficient electromagnetic wave absorber

The rapid development of communication technology has led to severe microwave pollution, which presents a challenge for microwave-absorbing composites. Current research suggests achieving superior microwave absorption requires the use of multi-component operation and ingenious structural design. Consequently, the present study has prepared continuous porous carbon (CPC) materials doped with large amounts of Fe3C/Fe nanoparticles (Fe@CPC) using carbonization and acid etching. By balancing the advantages of the above strategies, it is possible to address issues such as poor impedance match, single loss capacity, easy oxidation of magnetic metals/alloys, and the limited absorption bandwidth of conventional absorbing materials at the same time. The material exhibits a minimum reflection loss of −23.2 dB with an efficient absorption range of 5.3 GHz at 1.9 mm at a filler content of just 10 wt% in the paraffin matrix. In this paper, the samples with a continuous porous structure were prepared by a simple method, and the properties were excellent due to the appropriate preparation method and the synergistic effect of the multi-component composite. The porous structure facilitates the presence of a considerable number of active sites, which enables the loading of a substantial quantity of metal ions. Furthermore, nanoparticles are capable of aggregating and dispersing on the surface. This paper presents a theoretical framework for understanding the synergistic effect of microwave radiation through interfacial polarization and micro-scale magnetic interaction. Nevertheless, there are still obstacles to overcome in terms of achieving precise control over the structural design and ensuring the compatible integration of metal components.

Ni doped carbon-based composites derived from waste cigarette polypropylene filter rod with electromagnetic wave absorption performance

Abstract Polypropylene is widely used in the plastics industry, especially in the tobacco industry, served as cigarette filters to reduce tar and harm. However, it’s difficult to degrade these polypropylene plastics and suitable methods for recycling and reuse is urgent. This research proposes an efficient method for the reuse of polypropylene cigarette filters by mixing waste polypropylene filters with nickel source in different proportions, followed by a facile calcination treatment to prepare nickel-modified carbon-based composite materials with excellent microwave absorption properties. Morphology and magnetic properties of as-prepared samples were analyzed via XRD, SEM, and VSM, exhibiting an increase in carbon content with raising nickel content. Nickel ion anchored on polypropylene fiber may facilitate better fixation of carbon chains during the polypropylene decomposition process. Among the as-prepared samples, CN2 exhibited superior microwave absorption performance, with an optimal absorption peak of -26.76 dB at 7.97 GHz when matched with a given thickness of 4.3 mm, and an effective absorption bandwidth of 3.64 GHz (8.04 GHz to 11.68 GHz) with a matching thickness of 3.5 mm, covering the X band. Therefore, the as-prepared microwave absorbers provides a feasible solution for the recycling and reuse of polypropylene filters, aligning with the tobacco industry requirements for green and sustainable development.

Template-free synthesize of PANI nanostructures: Modulating structure for enhanced dielectric characteristics and superior electromagnetic wave absorption

To provide electromagnetic protection for intelligent equipment, advanced electromagnetic wave absorption (EWA) materials are highly desired. To reveal the interaction mechanism of structure and electromagnetic waves, polyaniline (PANI) with various structures, including nanosheets, clusters, and nanofibers, is synthesized via a template-free approach. The self-assembly process of PANI can be regulated by camphor sulfonic acid due to the formation and guidance of charge transfer complexes. A comprehensive analysis of structure, chemical constitution, and electromagnetic characteristics is conducted. Clusters with three-dimensional micro-nano structure exhibit superior microwave absorption, achieving a minimum reflection loss of −52.22 dB at 9.84 GHz with a 3.2 mm thickness and an absorption bandwidth of 6.12 GHz at 2.3 mm thickness. The outstanding EWA performance is attributed to the unique architecture, strong dielectric loss capabilities, and effective impedance matching. Moreover, the fabrication process is cost-effective and scalable, making it conducive to practical applicability.

Facile synthesis of hierarchical Fe–S co-doped carbon-based composites with superior microwave absorption

Difficulty of multi-component coupling and hierarchical pore structure preparation make it challenging to manufacture highly efficient microwave absorption materials (MAMs). Herein, hierarchical porous carbon composites anchored with various types of iron sulfides are successfully fabricated using a simply feasible heating-induced self-assembly approach. Controllable electromagnetic parameters and impedance matching features of FexSy/AC (amorphous carbon) composites are obtained by varying carbonization temperature. Besides, AC and FexSy provide dielectric and magnetic losses, while defect-rich AC can effectively disperse FexSy nanoparticles, exhibiting high sintering resistance and high-density interfaces, which contributes to polarization losses. Moreover, the unique hierarchical porous structure not only offers better impedance matching, but also enhances microwave loss. The thorough investigation indicates that FexSy/AC nanocomposites exhibit outstanding microwave absorption performance by the joint effect of unique hierarchical porous structure and coupling loss of multi-components. The optimal sample (FSC-700) shows a strongest reflection loss value of up to −78.96 dB with a matching thickness of 2.85 mm, an effective absorption bandwidth (EAB, RL<−10 dB) of 6.98 GHz (11.02–18.0 GHz, spanning Ku-band), and a radar cross section (RCS) reduction value of 21.75 dBm2. In addition, the EAB can reach 13.8 GHz with the simulated thickness varies from 1.0 to 5.5 mm, covering 86 % of the measured frequency range. The in-depth research of the multi-component system with hierarchical porous structure offers an innovative and practical method for high-performance MAMs.

Coupled multiple heterogeneous interfaces lychee-like FeSiAl@C@SiO2@BTA for self-healing corrosion protection and enhanced microwave absorption

Corrosion-resistant ferromagnetic absorbers (FMAs) with self-healing properties are crucial for enhancing their durability under harsh conditions. Herein, we fabricated lychee-like FeSiAl (FSA)@C@SiO2@1H-Benzotriazol (BTA) coupled with multiple heterogeneous interfaces by coating FSA with a C@SiO2@BTA layer using sol-gel, thermal reduction, and molecular encapsulation techniques. The FSA@C@SiO2@BTA showed superior microwave absorption (MA) performance than FSA, with a widest absorption bandwidth of 10.44 GHz at 1.98 mm and a maximum reflection loss of −57.81 dB at 2.98 mm. The enhanced MA performance was due to the better impedance matching and the synergistic effects of interfacial and dipole polarization induced by the C@SiO2@BTA layer. Moreover, the FSA@C@SiO2@BTA exhibited a remarkable corrosion resistance, with a corrosion rate of 3.28 × 10−10 m/s, which was two orders of magnitude lower than that of FSA, and a corrosion protection efficiency of 99.0 %. The epoxy resin coating containing FSA@C@SiO2@BTA also demonstrated a self-healing ability within 5 min after being damaged mechanically. This study presents a novel model that integrates MA, corrosion resistance, and self-healing, heralding new avenues for developing corrosion-resistant FMAs in marine applications.

Exquisite regulation of LZ-BaM/PPy composites for compatible absorption across centimeter-wave and millimeter-wave bands

The increasing complexity of the electromagnetic environment necessitates materials to exhibit superior microwave absorption performance for multitudinous bands. However, reaching satisfactory compatibility for absorption across centimeter-wave and millimeter-wave bands still remains a formidable challenge. In this work, a composite composed of Polypyrrole (PPy) and La3+-Zr4+ co-doped barium ferrite (LZ-BaM) is elaborately designed to address the issue facing us today. By exquisitely regulating the chemical composition, absorption peaks ascribed to different integral orders of interference can appear simultaneously in millimeter-wave and centimeter-wave bands. Ultimately, the as-prepared LZ-BaM/PPy composite reveals an efficient absorption (RL < −5 dB, absorptivity of 68.37 %), covering the centimeter-wave band of 8∼17 GHz and millimeter-wave band of 27∼40+ GHz concurrently under a matching thickness of 2.4 mm. This study thus offers valuable insights for the development of high-efficient absorbers across multiple frequency bands.

Construction of chiral magnetic structure with enhancement in magnetic coupling for efficient Low-Frequency microwave absorption

Construction of chiral magnetic structure is considered as a promising strategy to achieve efficient low frequency microwave absorption. However, it is not clear that how the magnetic loss is enhanced by the chiral morphology. Herein, a novel chiral magnetic structure containing FeCo2O4-FeCo nanosheets has been constructed by using helical carbon nanocoils (CNCs) as the chiral template. For comparison, the FeCo2O4-FeCo nanosheets are also combined with the linear carbon nanofibers (CNFs). The enhanced magnetic coupling between FeCo2O4-FeCo nanosheets and the magnetic anisotropy induced by the chiral structure are confirmed by the off-axis electron holography and the micro-magnetic simulation. Due to the synergistic effect between chirality, magnetism, and dielectricity, the chiral magnetic structure exhibits superior microwave absorption performance than the linear one with a wide effective bandwidth of 7.1 GHz at an ultra-low filling ratio of 8 %. Meanwhile, the minimum RL value of −60.7 dB is achieved at low frequency (6 GHz). This study provides further evidence of the special mechanisms of the chiral structure for microwave absorption.

Rationally controlling interfaces and oxygen vacancies of CeO2@C core–shell nanorods/nanofibers for superior microwave absorption and thermal conduction

High-performance thermally conductive-microwave absorbing integrated materials are highly required to mitigate the severe electromagnetic pollution and overheating generated in electronic devices. However, the incompatibility between thermal conduction and microwave absorption impedes their collaborative development. Herein, an adjustment strategy for interface- and oxygen-vacancy-linkage was adopted to rationally construct CeO2@C core–shell nanorods/nanofibers (CSNRs/NFs) and cooperatively boost their electrical, thermal, and microwave absorption properties. A hydrothermal-annealing technique was employed to synthesize CeO2@C CSNRs/NFs. Their core–shell structure, oxygen vacancies/lattice defects, and length-to-diameter ratio were accurately adjusted by changing the annealed temperature (Ta) and toluene volume (V). The CeO2@C CSNRs/NFs produced under Ta = 600 °C and V = 1.5 mL exhibit high thermal conductivity (TC = 2.94 W/(m·K)) at a small load of 40 wt%. The large TC is mainly due to the weak phonon defect/interface scattering and electron/phonon co-transfer in a 3D continuous path consisting of a 1D structure. Furthermore, the CeO2@C CSNRs/NFs display strong microwave absorption (EABmax/d = 3.27 GHz/mm; RLmin=− 50.98 dB) due to their various polarizations, tunable conduction loss, and multiple internal reflections. These results demonstrate that the CeO2@C CSNR/NFs are an ideal multifunctional material that protects against concurrent EM interference and excess heat in electronic packaging materials.

Well-Dispersed CoNiO2 Nanosheet/CoNi Nanocrystal Arrays Anchored onto Monolayer MXene for Superior Electromagnetic Absorption at Low Frequencies

Developing microwave absorbers with superior low-frequency electromagnetic wave absorption properties is one of the foremost important factors driving the boom in 5G technology development. In this study, via a simple hydrothermal and pyrolysis strategy, randomly interleaved CoNiO2 nanosheets and uniformly ultrafine CoNi nanocrystals are anchored onto both sides of a single-layered MXene. The absorption mechanism demonstrated that the hierarchical heterostructure prevents the aggregation of MXene nanoflakes and magnetic crystallites. In addition, the introduction of the double-magnetic phase of CoNiO2/CoNi arrays can not only enhance the magnetic loss capacity but also generate larger void spaces and abundant heterogeneous interfaces, collectively promoting impedance-matching and furthering microwave attenuation capabilities at a low frequency. Hence, the reflection loss of the optimal absorber (M–MCNO) is −45.33 dB at 3.24 GHz, which corresponds to a matching thickness of 5.0 mm. Moreover, its EAB can entirely cover the S-band and C-band by tailoring the matching thickness from 2 to 7 mm. Satellite radar cross-section (RCS) simulations demonstrated that the M–MCNO can reduce the RCS value to below −10 dB m2 over a multi-angle range. Thus, the proposed hybrid absorber is of great significance for the development of magnetized MXene composites with superior low-frequency microwave absorption properties.

Construction of ZIF/CS and ZIF/CS-derivatives with high-efficiency adsorption for dyes/antibiotics and strong microwave absorption performance

Bimetallic Zn/Co-ZIF was in situ loaded onto the surface of chitosan (CS) to form ZIF/CS composites with high-efficiency adsorption of antibiotics (tetracycline (TC)) and dyes (Congo Red (CR), Malachite Green (MG)). The particle size and surface roughness of Zn/Co-ZIF can be effectively adjusted by changing the mass ratio of Zn and Co in ZIF, which helps to regulate the adsorption active sites on the surface of the composites. Meanwhile, the introduction of CS changes the pore structure of the composites, making the molecules of TC, CR and MG easily enter into the pores of ZIF/CS. When the mass ratio of Zn to Co is 1:1, the ZIF/CS composite has the optimal adsorption performance with the ultra-high adsorption capacity qm of 781.3, 1644.2 and 3243.6 mg g−1 for TC, CR and MG, respectively. Impressively, the ZIF/CS-derivative (ZC3–700) from sample ZC3 after calcination at 700 °C under N2 atmosphere owns a good conductive network, which results in its superior microwave absorption performance. Herein, at 30 wt% filler loading, the effective absorption bandwidth and RLmin of ZC3–700 reach 5.28 GHz at 1.90 mm and −68.92 dB at 1.83 mm, respectively. Analyses on microwave absorption mechanism point out the synergistic effect of conduction loss, dipolar polarization and interfacial polarization and magnetic loss on the attenuation of electromagnetic wave. Therefore, ZIF/CS composites and ZIF/CS-derivatives exhibit superior performance on the removal of water pollutants and the absorption of electromagnetic wave, which essentially reveals a multifunctional application of the ZIF/CS composites in the field of environmental protect.

Ultralight Three-Layer Gradient-Structured MXene/ Reduced Graphene Oxide Composite Aerogels with Broadband Microwave Absorption and Dynamic Infrared Camouflage.

Infrared and radar detectors posed substantial challenges to weapon equipment and personnel due to their continuous surveillance and reconnaissance capabilities. Traditional single-band stealth devices are insufficient for dual-band detection in both infrared and microwave bands. To overcome this limitation, a gradient-structured MXene/reduced graphene oxide (rGO) composite aerogel (GMXrGA) is fabricated through a two-step bidirectional freeze casting process, followed by freeze-drying and thermal annealing. GMXrGAexhibits a distinct three-layered structure, with each layer playing a crucial role in microwave absorption. This deliberate design amplifies both the efficiency of microwave absorption and the material's effectiveness in dynamic infrared camouflage. GMXrGA displays an ultralow density of 5.2 mg∙cm-3 and demonstrates exceptional resistance to compression, enduring 200 cycles at a maximum strain of 80%. Moreover, it shows superior microwave absorption performance, with a minimum reflection loss (RLmin) of -60.1dB at a broad effective absorption bandwidth (EAB) of 14.1GHz (3.9-18.0GHz). Additionally, the aerogel exhibits low thermal conductivity (≈26 mW∙m-1∙K-1) and displays dynamic infrared camouflage capabilities within the temperature range of 50-120°C, achieving rapid concealment within 30 s. Consequently, they hold great potential for diverse applications, including intelligent buildings, wearable electronics, and weapon equipment.

A three-dimensional BaFe11.6(ZrSm)0.2O19/rGO composite aerogel with superior microwave absorption properties

The combination of dielectric and magnetic materials can significantly improve microwave absorption properties. In this work, we introduce a novel Zr–Sm doped barium ferrite BaFe11.6(ZrSm)0.2O19, which is compounded with rGO aerogel and presents superior microwave absorption properties. The results show that the BaFe11.6(ZrSm)0.2O19/rGO composite aerogel exhibits a unique three-dimensional porous network structure which enhances the reflection and scattering of electromagnetic waves. Meanwhile, the addition of BaFe11.6(ZrSm)0.2O19 abounds the folds and defects on the surface of rGO sheet layer, generating a large amount of polarisation and relaxation. In addition, with the increase of BaFe11.6(ZrSm)0.2O19 content, the permeability gradually increases, while the dielectric constant gradually decreases. At a certain content, both of them can be well balanced to obtain high attenuation constants and great impedance matching, which regulates the wave-absorbing properties of the material. The minimum reflection loss (RLmin) of BaFe11.6(ZrSm)0.2O19/rGO composite aerogel can reach −53.17 dB at a matching thickness of 2.9 mm, and the absorption bandwidth reaches 7.04 GHz, which has been improved by 40% than pure BaFe11.6(ZrSm)0.2O19. Therefore, it is expected to be a candidate for lightweight, thin, high loss, large bandwidth microwave absorbing materials.

NiCo2O4 NANOCHAINS SYNTHESIS WITH EFFECTIVE MICROWAVE ABSORPTION CHARACTERISTICS

Nanochains-like NiCo2O4 material was synthesized via the hydrothermal method utilizing D-glucose template to facilitate microwave absorption across the frequency range of 2 - 18 GHz. Comprehensive characterization employing various analytical techniques was employed to investigate the structural, microstructural, magnetic, and electromagnetic properties. Leveraging the presence of Oxalic acid and D-Glucose, a nanochain morphology comprising spherical nanoparticles (400 - 600 nm) was achieved. The resultant NiCo2O4 demonstrated a single-phase structure and exhibited the reflection loss (RL) value lower than -20 dB was up to 5.9 GHz within the Ku (12 - 18 GHz) frequency band, at a matching thickness of 2.0 mm. Remarkably, the optimal reflection loss reached -52.5 dB at 15 GHz for samples with a thickness of 2.0 mm, while the widest effective bandwidth extended up to 14.1 GHz for samples with a thickness of 5.0 mm. The superior microwave absorption performance of the chains-like NiCo2O4 powders was attributed to the synergistic interplay between their dielectric and magnetic properties, facilitating excellent impedance matching. These results indicate that NiCo2O4 chains-like powders have great promise as a material for microwave absorption.

Superior microwave absorption properties of anisotropic Y2Fe16‒xCoxSi/paraffin composites by orientation tuning

Y2Fe16-xCoxSi/paraffin composites were prepared by three different orientation methods. The effect of these orientation methods and the magnetocrystalline anisotropy of Y2Fe16‒xCoxSi alloys on the electromagnetic parameters and the microwave absorption properties were investigated. The results demonstrated that orientation tuning improved the electromagnetic parameters and microwave absorption properties. Anisotropy in dielectric properties and magnetic properties of Y2Fe16-xCoxSi/paraffin composites were achieved by tuning the orientation of Y2Fe16-xCoxSi powders. The planar and conical anisotropic materials had superior microwave absorption properties than uniaxial anisotropic materials for the same orientation method. The Y2Fe16‒xCoxSi/paraffin composite had an effective absorption bandwidth of 8.4 GHz (9.6–18 GHz) and a reflection loss of ‒59.6 dB which can almost cover the X–Ku bands and exceed the performance of many reported absorbing materials, showing its great prospects for microwave absorption in the X–Ku bands.

In Situ Loading of Ni3ZnC0.7 Nanoparticles with Carbon Nanotubes to 3D Melamine Sponge Derived Hollow Carbon Skeleton toward Superior Microwave Absorption and Thermal Resistance.

The simple and low-cost construction of a 3D network structure is an ideal way to prepare high-performance electromagnetic wave (EMW) absorption materials. Herein, a series of carbon skeleton/carbon nanotubes/Ni3ZnC0.7 composites (CS/CNTs/Ni3ZnC0.7) are successfully prepared by in situ growth of Ni3ZnC0.7 and CNTs on 3D melamine sponge carbon. With the increase ofprecursor, Ni3ZnC0.7 nanoparticles nucleate and catalyze the generation of CNTs on the surface of the carbon skeleton. The minimum reflection loss (RL) value of the S60min composite (loading time of 60 min) reaches -86.6dB at 1.6mm and effective absorption bandwidth (EAB, RL≤-10dB) is up to 9.3GHz (8.7-18GHz). The 3D network sponge carbon with layered micro/nanostructure and hollow skeleton promotes multiple reflection and absorption mechanisms of incident EMW. The N-doping and defects can be equivalent to an electric dipole, providing dipole polarization to increase dielectric relaxation. The uniform Ni3ZnC0.7 nanoparticles and CNTs play a key role in dissipating electromagnetic energy, blocking heat transfer, and enhancing the mechanical properties of the skeleton. Fortunately, the composite displays a quite low thermal conductivity of 0.09075Wm·K-1 and good flexibility, which can provide insulation and quickly recover to its original state after being stressed.