Maximum Reflection Loss Value Research Articles

Enhanced Magnetic and Microwave Absorbing Properties of Nd3+ Ion Doped CoFe2O4 by Solid‐State Reaction Method

CoNdxFe(2−x)O4 (x = 0.0–0.05) spinel ferrites are successfully synthesized by mechanical milling using solid‐state reaction. The effects of Nd3+ ions on structural, microstructure, and magnetic and microwave‐absorbing properties of samples are analyzed. The X‐ray diffraction pattern shows a single‐phase cobalt ferrite for all compositions. Refinement of the structure shows that an increase in the concentration of Nd3+ ions leads to the structure parameter and volume of unit cell to decrease. Lattice strain arises in the crystal, and limiting the crystallite growth is confirmed from the Williamson–Hall analysis. The particle size of the doping samples decreases compared to that without doping. The magnetic parameters, namely coercivity field and saturation magnetization, are strongly affected by the insertion of Nd3+ ions. Another important role of Nd3+ ions is in tuning the performance of microwave absorption. The maximum reflection loss values are gradually increased from −12.65 dB (≈94.35% microwave attenuation) up to −28.57 dB (≈99.86% microwave attenuation) in the concentration of x = 0.0–0.05. Their effective bandwidth also shows an increase from 0.05 up to 1 GHz. The results exhibit that Nd3+ ion‐doped cobalt ferrite has potential properties in designing novel microwave‐absorbing materials.

Reduced graphene oxide-ferrite microcomposites based on petung bamboo (dendrocalamus asper) charcoal and iron sand as lightweight microwave absorbing materials

Reduced graphene oxide-ferrite (rGO/Fe3O4) microcomposites as lightweight microwave absorbing materials has been successfully synthesized from petung bamboo and iron sand by mechanical mixing method at different rGO content (0:1, 1:0, 1:1, 1:2, 1:3, 2:1 and 3:1 wt%). Reduced graphene oxide as dielectric material was synthesized from petung bamboo charcoal using carbonization method and ferrite as magnetic material was synthesized from iron sand using extraction-milling method. Structural characterization by x-ray Fluorosence, Fourier Transform Infrared, Vibrating Sample Magnetometry, x-ray Diffraction, Scanning Electron Microscopy proved that micrometer sized reduced graphene oxide ferrite in the microcomposites was responsible for the ferromagnetic behavior of the composites. The reflection loss of microcomposites measured in the microwave frequency range of 8–12 GHz using a Vector Network Analyzer. The results showed that at the micro scale, rGO had a higher absorption power with maximum reflection loss (RL m ) value of −21.81 dB at matching frequency (f m ) 10.85 GHz compared with Fe3O4 (RL m value of −9.25 dB at f m = 10.60 GHz) at thickness of 1 mm. The rGO/Fe3O4 (2:1 wt%) microcomposites microwave absorber shows the optimum absorption with maximum reflection loss value of −16.51 dB at matching frequency (f m ) 10.74 GHz at thickness of 1 mm. The use of natural materials and the controlled rGO/Fe3O4 microcomposites structure with simple synthesis methods, which the urgent need for developing high performance lightweight microwave abrsorbing materials and are environmentally friendly.

Microwave absorbing characteristics of porphyrin derivates: a loop of conjugated structure.

Microwave absorbing architectures have gained a great deal of attention due to their widespread application in diverse fields, especially in refining electromagnetic pollution. The aim of this study is to investigate the metamaterial characteristics of porphyrin derivatives as conjugated rings in the microwave region and evaluate the influence of electron-withdrawing and donating groups on microwave attenuating performance. Initially, an innovative microwave curing procedure was applied to synthesize the derivates; following that, the phenyl, aniline, and nitrophenyl-coupled structures were identified by XRD, FTIR, FESEM, and DRS analyses. The optical features illustrated that the characteristic band gap of the conjugated loops is obtained and that the optical performance can be manipulated by coupling the functional groups. Eventually, the achieved results demonstrated that the best microwave absorbing performance is related to aniline-coupled porphyrin with a maximum reflection loss (RL) value of -104.93 dB at 10.09 GHz with 2.80 mm in thickness attaining an efficient bandwidth (EB) (RL ≤ 10 dB) higher than the X-band. Noticeably, polyethylene (PE) was applied as an absorbing matrix presenting a meaningful idea for the development of practical microwave absorbers as a new generation of electromagnetic refining and stealth materials. The presented research provides precious inspiration to tailor novel microwave absorbing materials with metamaterial capability to promote their microwave absorbing performance.

UTILIZATION OF Zn-DISPERSED WASTE MATERIALS FOR REALIZING THIN META-STRUCTURE WITH IMPROVED MICROWAVE ABSORPTION

In the present work, emphasis has been given on the utilization of waste materials to make cost-effective microwave absorbing composites. Rice husk and exhausted activated charcoal (EAC) were used as waste material, where rice husk is a form of agricultural waste and exhausted activated charcoal was extracted from an exhausted water filter cartridge. Thereafter, zinc metal powder was dispersed in different weight ratios in the mixture of rice husk and exhausted activated charcoal using a planetary ball mill. The X-ray fluorescence (XRF), X-ray diffraction (XRD), and the particle size analyses were done to analyze element composition and particle size. For dielectric properties analysis, vector network analyzer (VNA) was used. Results reveal that composites have the potential for microwave absorption in 2-18 GHz frequency range, sample RHZ 3 having 6 wt.% Zn content gives the maximum reflection loss value of -21.27 dB at 9.2 GHz for a material thickness of 13.9 mm. The experimental results were then used to design a metamaterial microwave absorber. The simulated results show the good microwave absorption characteristics. The metamaterial absorber showed an absorption bandwidth of around 4.1 GHz which ranges from frequency of 14.1 GHz to 18.2 GHz at total thickness of 1.7 mm.

Oleaster seed-derived activated carbon/ferrite nanocomposite for microwave absorption in the X-band range

Conjugated carbonaceous structures achieved from biological materials were significantly considered electromagnetic wave absorbing materials due to their eye-catching dielectric, lightweight, low-cost, and chemical stability features. To strengthen the microwave absorbing performance of the porous carbon (Oleaster seeds), Fe3O4 magnetic nanoparticles have been successfully anchored onto the surface of biomass-derived material through a co-precipitation method. Noticeably, the dielectric constant, impedance matching, permeability, and microwave absorbing capability were improved by changing the carbon content. The optimized Fe3O4/activated carbon (AC) illustrated the excellent electromagnetic wave absorption performances with a maximum reflection loss (RL) value of −51.12 dB and an effective absorption bandwidth of ∼4 GHz (RL < 10 dB) with a thickness of 1 mm. The promoted microwave absorbing characteristics of Fe3O4/AC composites are rooted in improved impedance matching, eddy current loss, natural and exchange resonance, and specific surface area, bringing more polarization loss and multiple reflection and scattering. The presented research shed new light on the fabrication of practical microwave-absorbing materials based on biomass-derived materials with a facile experimental procedure.

Ultralight Hierarchically Structured RGO Composite Aerogels Embedded with MnO2/Ti3C2Tx for Efficient Microwave Absorption.

Although intensive efforts have been devoted to fabricating Ti3C2Tx MXene composites for microwave absorption, it remains a great challenge to achieve excellent MA performance at low loading and thin thickness. Herein, a three-dimensional (3D) lightweight hierarchically structured MnO2/Ti3C2Tx/RGO composite aerogel with abundant heterointerfaces was fabricated via a hydrothermal and chemical reduction self-assembly method. The RGO aerogel embedded with laminated MnO2/Ti3C2Tx provides a lot of heterogeneous interfaces, 3D porous interconnected conductive networks, and reasonable combination of various loss materials for rich interfacial polarization, conductivity loss, multiple reflections and scattering, and good impedance matching. Benefiting from the synergy of different loss mechanisms, the maximum reflection loss (RL) is up to -66.5 dB (>99.9999% energy absorption) at only 10 wt % loading and 2.0 mm thickness, and even at only 1.5 mm thickness, the maximum RL value remains at -36 dB (>99.9% energy absorption). The work provides a promising route to construct 3D hierarchically heterogeneous composite aerogels for efficient MA at thin thickness and low loading.

A Novel Hierarchically Lightweight Porous Carbon Derived from Egg White for Strong Microwave Absorption

Egg custard is a common dish on the dining table and exhibits a uniform porous structure after freeze-drying. The protein within egg custard is a rich source of carbon and nitrogen, and the custard’s unique microstructure and adjustable electrical properties make it a potential porous carbon precursor. Herein, nitrogen in situ doped porous carbons (NPCs) and potassium-carbonate-modified NPCs (PNPCs) are obtained through a simple gelation and carbonization process using egg white as the raw material. The unique morphologies of the porous carbon are inherited from the protein and include fibrous clusters, honeycomb holes, and a grooved skeleton. Their excellent impedance matching and effective internal loss make the obtained porous carbons good candidates for lightweight electromagnetic (EM) wave absorbers without the need to dope with metal elements. As a representative porous carbon, PNPC10-700 has multiple structures, including fibrous clusters, honeycomb holes, and a porous skeleton. Moreover, it achieves a maximum reflection loss value of −66.15 dB (with a thickness of 3.77 mm) and a broad effective absorption bandwidth of 5.82 GHz (from 12.18 to 18.00 GHz, with a thickness of 2.5 mm), which surpasses the reported values in most of the literature. Thus, gelation combined with the further carbonization of egg white (protein) is a new method for designing the morphology and EM properties of porous carbon absorbers.

Achieving electromagnetic wave absorption capabilities by fabrication of flower-like structure NiCo2O4 derived from low-temperature co-precipitation

In this work, The NiCo2O4 with 3D hierarchical multilayer flower-like structure was prepared by the low-temperature (55 °C) co-precipitation method combined with the calcination process, avoiding the traditional high-temperature hydrothermal synthesis method. The prepared flower-like NiCo2O4 with a large specific surface area was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and automatic surface area and porosity analyzer (BET) and vector network analyzer (VNA). A novel evaluation approach was proposed to evaluate the electromagnetic wave (EMW) absorbing properties of various samples (different calcination temperatures), which was to defined the ΔS as the area enclosed by the curve when the reflection loss (RL) value was less than −10. In order to take the material thickness into account, and then the effective reflection loss (RLE) value was defined ΔS/d to measure the electromagnetic wave (EMW) loss capability of the different samples. The results showed that NiCo2O4 exhibited excellent EMW absorption effect when the calcination temperature was 400 °C, and the maximum RL value reached −43.17 dB at 14.32 GHz with the thickness of 1.5 mm and the effective absorption bandwidth (fe) was 4.48 GHz (12.08 GHz–16.56 GHz). The excellent EMW absorption property was mainly due to NiCo2O4 with particular porous flower-like structure, which could achieve impedance matching to loss EMW by dielectric loss and magnetic loss.

In Situ Formation of CoS2 Hollow Nanoboxes via Ion-Exchange for High-Performance Microwave Absorption.

Hollow nanoboxes structure have raised great attention as microwave absorption materials on account of their ultralow density and large specific area. By introducing an adjustable interior cavity structure, the dielectric loss and microwave absorption performance were affected by the tunable complex permittivity and impedance matching was improved. In our study, hollow CoS2 nanoboxes with designable interspaces were successfully fabricated based on the surfactant-assisted solution method and followed by an in situ ion-exchange process. The structure, elemental compositions and morphology of the products were characterized by XRD, XPS, EDX, SEM and TEM, respectively. In addition, microwave absorption performance and the intrinsic mechanism are investigated in-depth. The paraffin-based composites with 20 wt.% filling contents exhibited superior microwave absorption capacities in view of both maximum reflection loss value (RLmax, −54.48 dB) and effective absorption bandwidth (EAB, below −10 dB, 6.0 GHz), which can be ascribed to unique hollow structure and good impedance matching. With these considerations in mind, this study provides a reference for the construction of high-performance microwave absorbers with unique hollow structure.

Electromagnetic properties in the structure of Cerium-Copper substituted barium hexaferrite

In this study Ce3+-Cu2+ doped barium hexaferrite Ba0.5Ce0.5CuFe11O19 composite sample was synthesized by a conventional method and barium hexaferrites/CeO2 phase composition, X-Ray Diffractometer were examined. Sample morphology was observed by SEM. A VSM was used to analyze the magnetic properties of the ferrites. Complex permittivity, permeability, reflection loss, absorption loss and shielding effectiveness were analyzed by using a VNA measuring the transmission/reflection coaxial airline method. The phase changes of the crystal structure because of the effect of Ce3+ ions into Ba2+ site and Cu2+ ions into Fe3+ areas were investigated. The resulting composition in these two resonance phases has a maximum absorption loss value at ∼6.48 GHz and ∼11.25 GHz and a maximum reflection loss value at the same frequencies. In this synthesized composition structure, it has been observed that it has a maximum reflection loss value of approximately –22.2dB and the highest shielding effectiveness value of 33.3 dB at microwave frequency 11.25 GHz.

Vertically implanting MoSe2 nanosheets on the RGO sheets towards excellent multi-band microwave absorption

It is still a challenging project for developing electromagnetic (EM) wave absorption materials with the properties of multi-band absorption in the field of microwave absorption. Herein, honeycomb-like MoSe2@reduced graphene oxide (RGO) composites are successfully constructed by a facile one-step solvothermal method. The polarization and conductive loss can be precisely tailored by vertically implanting MoSe2 nanosheets on the RGO sheet. It is notable that three-band absorption, including S, X, and Ku bands, was achieved in the composites. The optimized MoSe2@RGO composite exhibits excellent microwave absorption performance, the maximum reflection loss (RL) value can reach −56.9 dB and an effective absorption bandwidth (EAB) value can reach 4.12 GHz. The excellent microwave attenuation capability is attributed to the synergy effect of conductive loss, multiple relaxations, and excellent impedance matching in the composites. Therefore, this work provides a new paradigm for developing efficient multifunctional EM wave absorbers.

Growth of magnetic metals on carbon microspheres with synergetic dissipation abilities to broaden microwave absorption

• Facile electrostatic assembly approach for preparation of core-shell C/magnetic metal composite microspheres. • Excellent microwave absorption performance including a maximum reflection loss value of −54.1 dB and a broad effective absorption bandwidth of 6.7 GHz. • Profound magnetic coupling effect and magnetic-dielectric synergy mechanism for enhancing microwave absorption performance. Microwave absorption (MA) materials have been captured extensive attentions due to the serious electromagnetic (EM) pollution. Numerous interests focus on the MA performances of core-shell structural composites with magnetic constituents as cores and dielectric constituents as shells, which inevitably suppressed the magnetic coupling causing the decrease of magnetic loss to some extent. Herein, the core-shell structural carbon (C) microsphere/magnetic metal composites were fabricated through the combination of an electrostatic assembly approach and subsequent in-situ reduction reaction. The complex permittivity and permeability of core-shell C@magnetic metal composite system can be effective adjusted by the constituent and microstructure of shells. Thanks to the distinct magnetic coupling from the subtle designed structures and the promotion of the magnetic-dielectric synergy, the C@magnetic metal composite exhibited enhanced MA properties. The optimal reflection loss (RL) of C@Ni composite was -54.1 dB with a thickness of 3.4 mm, meanwhile the effective absorbing band could reach over 5.5 GHz at only a 1.8 mm thickness. Broad absorption bandwidth with RL below -10 dB could achieve 6.0 GHz and 6.7 GHz for C@Co and C@NiCo composites with a thin 2.1 mm thickness, respectively. Our exciting findings might lead a guide on the novel structure design for the functional core-shell structural composites used for microwave absorption. Graphical Abstract .

Design and synthesis of core-shell structure 3D-graphene/Fe3O4@N-C composite derived from Fe-MOF as lightweight microwave absorber

To improve the microwave absorption performances of Fe3O4@N-C composite derived from Fe-MOF, 3D-graphene particles have been successfully dotted on the surface of Fe3O4@N-C composite through pyrolyzing 3D-graphene/Fe-MOF composites. Moreover, it is obvious that the electromagnetic parameters of the composites can be effectively adjusted by controlling the addition of 3D-graphene. Consequently, the optimal composite displays outstanding microwave absorption performances. The value of maximum reflection loss achieves −57.53 dB at 10.72 GHz with the effective absorption bandwidth of 3.92 GHz (9.18–13.10 GHz) at 2.30 mm matching thickness. In addition, the maximum effective absorption bandwidth with the value of 5.62 GHz (12.38–18.00 GHz) can be achieved at 1.81 mm matching thickness, which almost covers the whole Ku band. This work is expected to provide a reference for the mass preparation of new lightweight microwave absorption composites.

The effect of Zn-dopant on the anisotropy constant and reflection loss of the Ba0.6Sr0.4Fe10-xZnxMnTiO19 (x = 0.1, 0.3, and 0.5)

In the case of absorption of microwave energy, the overall interaction is represented by impedance matching between the material and the microwave (Zin = Zo) through the resonant frequency mechanism. While the resonant frequency is influenced by the anisotropy field of the material. This research investigated the effect of Zn-dopant on the anisotropy constant and reflection loss of the Ba0.6Sr0.4Fe10-xZnxMnTiO19 (x = 0.1, 0.3, and 0.5). Hexaferrite samples Ba0.6Sr0.4Fe10-xZnxMnTiO19 with × = 0.1, 0.3, and 0.5 have been successfully prepared using high energy milling and by sintering at 1000 °C. Characterization using XRD resulted that all samples being in phase with the hexagonal crystalline structure (P63/mmc). The average crystal size of the three samples is about 44 nm. The shape and size of the surface particles obtained from characterization using scanning electron microscopy are still heterogeneous with particle sizes ranging from 150 to 300 nm. The vibrating sample magnetometer used for magnetization characterization shows that increasing the value of × increases the magnetic saturation value, hence decreasing the anisotropic magnetic field. A vector network analyzer is used to characterize the ability to absorb microwaves, which reveals that the greater the × value, the better the absorbing microwaves. With a bandwidth of 3.6 GHz, the maximum value of reflection loss (RL) recorded for × = 0.5 is – 34.7 dB. It was concluded that the addition of Zn2+ dopant ions into the hexaferrite structure of Ba0.6Sr0.4Fe10-xZnxMnTiO19 can reduce the anisotropy field and increase the reflection loss value, so it is hoped that this composition can be a potential candidate as a microwave absorbent material.

Flexible N-doped carbon fibers decorated with Cu/Cu2O particles for excellent electromagnetic wave absorption

Flexible N-doped carbon fibers decorated with Cu/Cu2O particles (NCF-Cu/Cu2O) are synthesized through electrospinning, preoxidation and carbonization processes in this work. The characterization results indicate that HKUST-1 is embedded in polyacrylonitrile (PAN) fibers, and a special structure in which Cu/Cu2O particles are strung together by carbon fibers is formed after preoxidation and carbonization. NCF-Cu/Cu2O is mixed with paraffin in different mass ratios (5%, 10%, 15%, 20% and 25%) to study electromagnetic (EM) wave absorption performance at frequencies from 2.0 GHz to 18.0 GHz. When the filling ratio is 10%, the maximum reflection loss (RL) value is −50.54 dB at 14.16 GHz with a thickness of 2.4 mm, and the maximum effective absorption bandwidth (EAB) value reaches 7.2 GHz (10.8 ∼ 18.0 GHz) with a thickness of 2.6 mm. The NCF-Cu/Cu2O composite fibers exhibit strong absorption, broad bandwidth, low filling ratio and thin thickness, and the corresponding absorption mechanism is analyzed in detail. The excellent EM wave absorption performance is attributed to a suitable attenuation ability, good impedance matching, conductive loss, interfacial polarization, dipole polarization, multiple reflections and scattering. This work provides a research reference for the application of flexible carbon-based composite fibers in the field of EM wave absorption.

Supramolecular self-assembly derived Mo2C/FeCo/NC hierarchical nanostructures with excellent wideband microwave absorption properties

Developing highly efficient electromagnetic wave absorption materials with tunable properties has been attracting extensive concern for tackling severe electromagnetic pollution. Composition and microstructure of absorber are two determinative factors for properties. Herein, we proposed supramolecular self-assembly combined with carbonization strategy to construct hierarchical carbon molybdenum/iron-cobalt alloy/nitrogen doped carbon (Mo2C/FeCo/NC) nanocomposites. By adjusting pH values and the kinds of surfactants, the nanostructures with flower shaped balls, lily clusters and bowknots morphologies were obtained. The highly dispersed Mo2C nanoparticles could induce multilevel heterostructural interfaces and enhance absorption peculiarity for carbon-based materials. The FeCo nanoparticles could produce strong magnetic coupling networks to improve synergy effect. Impressively, the as-synthesized optimal sample (8.5-Mo2C/FeCo/NC) exhibited superior electromagnetic wave absorption performances with the maximum reflection loss (RL) value of −56.03 dB and wide effective absorbing bandwidth of 10.27 GHz at 3.4 mm matching thickness, meanwhile, the effective absorption area was up to 135.57 (dB GHz). In addition, the RL of anion-Mo2C/FeCo/NC was up to −60.18 dB with the matching thickness of 2.8 mm, and the maximum RL of the cation-Mo2C/FeCo/NC composites reached up to −77.37 dB at 2.2 mm. Remarkably, even if at the thickness of 2.2 mm, the effective bandwidth of 7.25 GHz could be obtained. The excellent absorbing performance was attributed to 3D carbon conductive network, favorable dipolar/interfacial polarization, natural resonance/eddy current effect, multiple reflection and scattering, and satisfied impedance matching. Thus, this work may pave new avenues for designing high-performance and lightweight absorbing materials.

Mixed-dimensional hierarchical configuration of 2D Ni2P nanosheets anchored on 1D silk-derived carbon fiber for extraordinary electromagnetic wave absorption

• Mixed-dimensional hierarchical of 2D Ni 2 P nanosheets anchored on 1D silk-derived carbon fiber composites were prepared. • A minimum reflection loss of −56.9 dB and a broad effective bandwidth of 7.2 GHz with 20 wt% filling ratios were achieved. • Ni 2 P not only shows remarkable dielectric characteristic and EMW absorption ability, but also denote to dual-conductive loss and polarization relaxation loss. Considering a series of electromagnetic pollution problems brought by the development of electronic communication technology, more attention has been paid to the research of electromagnetic wave (EMW) absorbing materials with unique composition and structure. Herein, under the inspiration of mixed-dimensional hierarchical structure, 2D Ni 2 P nanosheets anchored on 1D silk-derived carbon fiber is successfully fabricated as a gratifying resistor-dielectric type absorber. By a controllable pyrolyzation strategy and disproportionated reaction, high-density 2D Ni 2 P nanosheets were grown vertically and cross-linked on the surface of 1D silk-derived carbon fiber. The sample exhibited superior EMW absorption performance with maximum reflection loss value of – 56.9 dB at the thickness of 2.32 mm and the effective absorption bandwidth can reach to 7.2 GHz at the thickness of 1.93 mm. In addition, the pure Ni 2 P shows remarkable dielectric characteristic and EMW absorption ability as well. The integration of dual-conductive loss, enhanced polarization relaxation loss and the multiple scattering in the composites was proved to contribute to the good EMW absorption performance. Therefore, this work confirms the great potentials of Ni 2 P as a high-efficient EMW absorbing materials and light a new way in construction of multidimensional absorber.

Lightweight TiO2@C/Carbon Fiber Aerogels Prepared from Ti3C2Tx/Cotton for High-Efficiency Microwave Absorption.

Carbon fiber aerogel (CFA) derived from cotton wool as a potential microwave absorbing material has received intensive attention owing to the low density, high conductivity, large surface area, and low cost, but its applications are limited by the relatively high complex permittivity. To solve this problem, TiO2@C (derived from Ti3C2Tx) is introduced into CFA to prepare lightweight TiO2@C/CFA composites based on electromagnetic (EM) parameter optimization and enhanced EM wave attenuation performance. The microwave absorption capacity of TiO2@C/CFA-2 composite is obviously better than that of CFA. It is confirmed that good impedance matching derived from the combination of TiO2@C and CFA is the main factor to achieve excellent microwave absorption. Moreover, the improved microwave absorption capabilities are closely related to multiple EM wave absorbing mechanisms including multiple reflections and scattering, dipolar and interfacial polarization, and conductivity loss. TiO2@C/CFA-2 possesses a maximum reflection loss (RL) of -43.18 dB at a low response frequency of 6.0 GHz. As the matching thickness is less than 2.0 mm, the maximum RL values can still exceed -20 dB, and at the same time, the wide effective absorption bandwidth (EAB) below -10 dB achieves 4.36 GHz at only 1.9 mm thickness. Our work confirms that the lightweight and high-performance TiO2@C/CFA composites are promising choices and offer a new approach to design and construct carbon-based microwave absorbents derived from biomass.

Integrating hierarchical interfacial polarization in yeast-derived Mo2C/C nanoflower/microsphere nanoarchitecture for boosting microwave absorption performance

Integration of hierarchical polarizations within one nanoarchitecture combines superiorities of strong dielectric polarization loss and matched characteristic impedance for enhancing microwave absorption (MA) performance. However, accurate regulation of polarization relaxations in hierarchical composites remains a considerable challenge. Herein, novel Mo2C@N, P dual-doped carbon microspheres with excellent MA performance have been prepared via a facile yeast-template method. The collaborative composite consists of a hierarchically porous carbon substrate, the embedded ultrafine Mo2C nanoparticles, and the decorated Mo2C/C nanoflowers. Their maximum reflection loss value reaches as much as −50.6 dB and the effective absorption bandwidth is up to 5.4 GHz with a thickness of 2.5 mm, which are superior to those of most carbonaceous absorbents reported previously. These excellent data mainly result from the following three mechanisms. First, multiple heterointerfaces among the air, carbon matrix, and Mo2C nanoparticles contribute to the strong dielectric polarization loss capacity. Second, the doping of heteroatoms doped can trigger intensive dipole polarization. Third, porous structure induces strong space charge polarization and multiple scattering of electromagnetic waves. These achievements provide a biotemplate method for the general preparation of porous metals or metal compounds/carbon composites with broad application prospects in the MA field.

Fe3O4/PANI nanocomposite core-shell structure in epoxy resin matrix for the application as electromagnetic waves absorber

Fe3O4/polyaniline (Fe3O4/PANI) nanocomposite was prepared and used as filler in the preparation of Epoxy (EP) based coatings on Aluminum (Al) substrates for electromagnetic wave absorption application. The Fe3O4 nanoparticles were synthesized by chemical precipitation (1-Fe3O4) and hydrothermal (2-Fe3O4) methods and were used as core followed by the polymerization of aniline as shell layer. The XRD, FT-IR and FE-SEM analysis were confirmed the successful synthesis of Fe3O4 nanoparticles, and preparation of Fe3O4/PANI core-shell nanocomposite. Fe3O4/PANI nanocomposite as well as graphite (G) powder were used as filler in EP matrix for the preparation of Epoxy/Fe3O4/polyaniline/graphite (EP/Fe3O4/PANI/G) composite coating on Al substrates. The electromagnetic wave absorption properties of EP based composite coatings was evaluated by the analysis of reflection loss (RL) and loss factors against the Fe3O4 synthesis method, Fe3O4/PANI percentage and coating thickness on Al substrates. The refractive index of Epoxy/chemical precipitation Fe3O4/polyaniline/graphite (EP/1-Fe3O4/PANI/G) and Epoxy/hydrothermal Fe3O4/polyaniline/graphite (EP/2-Fe3O4/PANI/G) nanocomposites coatings on Al substrates was measured. The maximum RL values of respectively −34.28 dB and −31.1 dB at 11.2 GHz and 11 GHz frequencies were obtained for EP/1-Fe3O4/PANI/G and EP/2-Fe3O4/PANI/G coatings respectively with the coating thickness of 2 mm. Results showed that the simultaneous presence of superparamagnetic Fe3O4 nanoparticles as well as PANI chains and graphite powder with dielectric properties achieved synergetic and complementary effects on the electromagnetic interference (EMI) absorption properties of EP based composite coatings.