Microwave Absorption Capacity Research Articles

Desirable microwave absorption performance of ZnFe2O4@ZnO@rGO nanocomposites based on controllable permittivity and permeability

ZnO decorated ZnFe2O4 nanoparticles were synthesized and combined with reduced graphene oxide (rGO) to form ZnFe2O4@ZnO@rGO ternary hierarchical nanocomposites by a controllable method. The microstructure, morphology, and microwave absorption performance of the ZnFe2O4@ZnO@rGO nanocomposites were investigated in detail. The permittivity and permeability of the composites can be effectively regulated by controlling the content of ZnO and rGO to achieve a good impedance matching. Due to the synergistic effect of dielectric loss and magnetic loss, the ZnFe2O4@ZnO@rGO nanocomposites exhibited strong wave absorption and wide absorption bandwidth. The optimal reflection loss (RL) of the ZnFe2O4@ZnO@rGO nanocomposites reached −35.2 dB at 12.0 GHz with a thickness of 2.0 mm and the effective absorption bandwidth was 3.7 dB. The ZnFe2O4@ZnO@rGO hierarchical architecture produced lots of heterogeneous interfaces which made a significant contribution to the wave absorption performance. The combination of interfacial polarization, dipole polarization, and eddy current loss enhanced the microwave absorption capacity of the ZnFe2O4@ZnO@rGO system. This work provides a feasible approach for the design and preparation of wave absorption materials with tunable permittivity and permeability.

Facile preparation and properties of cubic TiN@CN nanocapsules as electrode materials for supercapacitors and as microwave absorbers

We adopted a facile method consisting of the arc discharge method combined with the in situ self-polymerization process to synthesize the cubic TiN@CN nanocapsules in this work, and we also investigated the electrochemical performance and microwave absorption properties of the TiN@CN nanocapsules in detail. The results show that the TiN@CN nanocapsules exhibit excellent electrochemical performance. The specific capacitance of the TiN@CN nanocapsules is 119 F g−1 at 1 A g−1, and their capacitance retention rate is 92% after 5000 cycles at the current density of 2 A g −1. Besides, the cubic TiN@CN nanocapsules also exhibit powerful microwave absorption capacity. The reflection loss (RL) below − 20 dB is achieved in a wide frequency range of 7.2–15.5 GHz with a thickness range of 1.1–2.3 mm, and the optimal RL value is − 40.6 dB at 10.6 GHz with a relatively thin thickness of 1.6 mm. Therefore, TiN@CN nanocapsules are promising and applicable as electrode materials for supercapacitors and as microwave absorbers.

Zeolitic imidazolate framework derived Fe-N/C for efficient microwave absorbers

Abstract Three main strategies for designing efficient microwave absorber includes the intrinsic dielectric/magnetic properties, the novel structure and the single atom doping. The Fe-N/C nanocomposites integrate the advantages of above three strategies into one system. In this work, the method for preparing Fe-N/C nanocomposite by calcining the FePc@ZIF-8 precursor under a flowing N2 gas is described. Fe-N/C nanocomposites, displaying respectable dodecahedron-like morphology, have the merits of strong absorption ability, wide effective absorption bandwidth, thin thickness, and excellent microwave absorption efficiency, which are attributed to the synergistic effect of good electromagnetic loss capacity and proper impedance matching originating from intrinsic dielectric/magnetic properties, the novel structure and the single atoms (Fe and N) doping. Fe-N/C-24 composite delivers an optimal reflection loss of −30.98 dB, an effective absorption bandwidth of 5.04 GHz, the microwave absorption capacity of 87.61 dB GHz the absorption efficiency of 51.53 dB GHz/mm at 1.7 mm.

Effect of Porous Structure on the Microwave Absorption Capacity of Soft Magnetic Connecting Network Ni/Al2O3/Ni Film.

Microwave radar absorbing materials have been the focus of the radar stealth research field. In this study, ceramic structured porous honeycomb-like Al2O3 film was prepared by anodic oxidation, and an Ni layer was deposited on the Al2O3 film via electrodeposition in a neutral environment to form a flower- and grain-like structure in a three-dimensional (3D) network Ni/Al2O3/Ni film. The films both have a through-hole internal structure, soft magnetic properties, and absorb microwaves. The dielectric loss values of two films were little changed, and the maximum microwave absorption values of flower- and grain-like Ni/Al2O3/Ni film were −45.3 and −31.05 dB with relatively wide effective bandwidths, respectively. The porous ceramic structure Al2O3 interlayer prevented the reunion of Ni and isolated the eddy current to improve the microwave absorption properties. The material presented in our paper has good microwave absorption performance with a thin thickness, which indicates the potential for lightweight and efficient microwave absorption applications.

Tuning the microwave absorption capacity of TiP2O7 by composited with biomass carbon

Impedance matching is a vital consideration for a microwave absorbing material (MAM) design. Incorporating carbon materials with dielectric absorbents can not only tune the impedance matching characteristics, but also ameliorate the absorption performance through dual-loss mechanism. Here, TiP2O7 is applied to composite with coconut shell derived carbon to tune the impedance, thus an excellent absorbing performance is achieved. The TiP2O7/C composites were obtained through a facile sol-gel process with subsequent thermal treatment. The TiP2O7 particles with sizes of 500 nm are found to be decorated on the surface of the carbon matrix. Electromagnetic characterization shows that the TiP2O7/C composites possess a reflection loss peak value of –32.4 dB at 15.8 GHz with a thickness of 2 mm. In addition, the effective absorption bandwidth reaches 6 GHz. Our findings confirm that TiP2O7 is a promising candidate for microwave absorption, which could be further enhanced by incorporating carbon nanomaterials.

Controlled synthesis and photocatalytic performance of biocompatible uniform carbon quantum dots with microwave absorption capacity

Carbon quantum dots (CQDs) were successfully prepared via a facile microwave-assisted method combined with a controlled drainage time using glucose as the carbon source. XRD analysis, FT-IR spectroscopy, UV spectroscopy, XPS, and PL spectroscopy were performed to characterize the structures and properties of the samples. The results showed that the average particle size of the prepared CQDs was about 2 nm, and there were two UV absorption at the wavelengths of 228 nm and 280 nm, respectively, corresponding to the π-π* transition of CC (atomic group) and the n-π* transition of the oxygen containing group (CO) on the surface of the carbon core. According to the unique optical and microwave absorption properties of the CQDs, a suitable photocatalytic system, namely, a microwave electrodeless discharge lamp (MEDL) system was used. In the MEDL system, the degradation rate of rhodamine B (RhB, 50 mL, 30 mg L−1) by 0.02 g CQDs-2 in 10 min could reach 85.79%. The photocatalytic activity of CQDs-2 was about twice that of P25. In addition, the biocompatibility of the CQDs was investigated, which revealed that the CQDs could be absorbed by microorganisms as a carbon source. The prepared CQDs are a promising environmentally friendly photocatalyst.

Microwave-assisted calcined olivine catalyst steam reforming of tar for hydrogen production

ABSTRACT It is very important to study catalysts with a good microwave absorption capacity and catalytic capacity for tar catalytic reforming by microwave-assisted heating. In this paper, olivine was used as catalysts in a small fixed-bed reactor for experimental study. The experimental results show that the calcination temperature of olivine has an effect on hydrogen production from microwave-assisted catalytic reforming tar. In the range of 650–1,000°C, tar conversion and hydrogen product concentration first increase and then decrease with the increase of calcination temperature of olivine. The optimum calcination temperature was 900°C. The study also found that olivine catalyst has better tar catalytic reforming effects than charcoal catalyst.

Preparation of copper-cobalt-nickel ferrite/graphene oxide/polyaniline composite and its applications in microwave absorption coating

A copper-cobalt-nickel ferrite/graphene oxide/polyaniline tri-composite was prepared by a two-step method. The prepared tri-composite was used as the absorbing agent and waterborne-polyurethane as matrix which coated on cotton fabric to prepare a flexible absorbing material. The absorbing property and electromagnetic shielding performance of the coated fabrics were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), anti-electromagnetic radiation and vector network analyzer. Compared with polyaniline and graphene oxide, the microwave absorption capacity of the copper-cobalt-nickel ferrite/graphene oxide/polyaniline tri-composite was significantly enhanced, which can achieve to -33 dB at 10.8 GHz. When the content of coating agent was 40 % and thickness of the coated fabric was 2.0 mm, the shielding performance could reach -47 dB in the frequency of 300 kHz to 3.0 GHz. Meanwhile, the mechanical property was better than that of uncoated cotton fabric.

A novel plate-like BaFe12O19@MoS2 core-shell structure composite with excellent microwave absorbing properties

In this study, a novel core-shell BaFe12O19@MoS2 composite was successfully prepared by the hydrothermal process. The dielectric loss of the as-prepared BaFe12O19@MoS2 composite can be well regulated by altering the additive amount of thiourea. Particularly, when the amount of thiourea added is 28 mmol, the RLmax (maximum reflection loss) of BaFe12O19@MoS2 is −61.0 dB with a thickness of 1.7 mm as well as an effective absorption bandwidth (reflection loss below −10 dB) of 4.4 GHz. The results indicate that the BaFe12O19@MoS2 core-shell composites are characterized by low cost, facile synthesis and strong microwave absorption capacity. Therefore, the as-prepared core shell structure BaFe12O19@MoS2 composite can be a promising candidate for the efficient microwave absorbing applications.

Three-dimensional graphene supported Fe3O4 coated by polypyrrole toward enhanced stability and microwave absorbing properties

The composites GFPs were prepared through anchoring the microspheres of Fe3O4 cores coated with polypyrrole shells (Fe3O4@Ppy) on the three-dimensional (3D) graphene areogel (GA) with the one-step chemical reduction method. Good microwave absorption properties of the composites in 2−18 GHz can be obtained through tuning the content of Fe3O4@Ppy. For GFP1:3 the minimum reflection loss (RL) can reach −40.53 dB at 6.32 GHz and the effective bandwidth of the reflection loss peak with the thickness of 2.5 mm reaches 5.12 GHz. Especially, the stability of Fe3O4 can be improved due to the coating of Ppy shells. As expected, the enlarged dielectric properties derived from Ppy itself, the enhanced conductivity and abundant interfaces due to the introduction of Ppy as shells largely contribute to the improved microwave absorption capacity. The component synergy of 3D graphene, Ppy and Fe3O4 leading to the good impedance matching condition also plays a key role in achieving the enhanced microwave absorption performance. Most importantly, GFPs still maintain ultra-light nature. The contribution provides an effect avenue to prepare stable and light-weighted materials in a simple method for practical microwave absorption.

Facile preparation of flower-like MnO2/reduced graphene oxide (RGO) nanocomposite and investigation of its microwave absorption performance

Flower-like MnO2/reduced graphene oxide (RGO) nanocomposite with excellent microwave absorption properties was successfully fabricated via a facile hydrothermal method. SEM images showed that the flower-like MnO2 particles were grown on the surface of RGO nanosheets. The thickness of lower-like MnO2/RGO nanocomposite was 2.0 mm. The microwave absorption capacity of it was significantly enhanced compared with pure MnO2, the maximum reflection loss achieved −37.1 dB at 10.8 GHz, and the corresponding effective absorption bandwidth at −10 dB and 20 dB is 4.1 GHz (8.6–12.7 GHz) and 1.0 GHz (10.2–11.2 GHz), respectively. The unique flower-like framework structure of MnO2 plays a crucial role in the microwave absorption.

Rational construction of Co NPs embedded N-doped carbon layer/ZrSBA-15 composites with hierarchical succulent-like nanostructures for enhanced microwave absorption

Abstract The configurations and compositions of an absorber play crucial role on the microwave absorption performance. Accordingly, the attenuation mechanism on the nanostructure with skillfully integrated components (e.g. dielectric loss and magnetic loss substances) is a highlight for constructing excellent absorbers. Herein, utilizing hierarchical succulent-like ZrSBA-15 as a template, the N-doped carbon layer containing Co nanoparticles embedded within ZrSBA-15 (Co-NCL@ZrSBA-15) composites were rationally constructed to acquire enhanced microwave absorption performance for the first time. The resultant Co-NCL@ZrSBA-15 composites exhibited high-performance microwave absorption capacity with low loading content of 25 wt % in a wax matrix. The minimum reflection loss (RL) value of −61 dB was achieved with the thickness of 2.0 mm at 16.8 GHz, and an effective frequency bandwidth (RL

Trimetallic FeCoNi@C Nanocomposite Hollow Spheres Derived from Metal-Organic Frameworks with Superior Electromagnetic Wave Absorption Ability.

Organic ligands and metal ions in the metal-organic frameworks (MOFs, a type of porous magnetic metal/carbon nanocomposites obtained through high-temperature carbonization) have caused widespread concerns in the field of microwave absorption because of the existence of various microwave loss mechanisms in these materials. However, MOF-driven microwave absorbing materials with high absorption intensity and wide absorption band still require further research and development. In this work, hollow sphere trimetallic FeCoNi@C microwave absorbing materials via high-temperature carbonization were obtained using FeCoNi-based MOF-74 (FeCoNi-MOF) as the precursor. The effects of different carbonization conditions on the microwave absorption properties of the materials were studied. FeCoNi-MOF-74 annealed at 700 °C showed superior microwave absorption capacity, where the RL value reached -64.75 dB at 15.44 GHz corresponding to the actual application thickness of the absorber (only 2.1 mm), and the minimum RL values reached -69.03 dB at 5.52 GHz. Furthermore, the as-prepared sample can fully cover the Ku band and X band at only 2.1 and 3.1 mm, respectively. The maximum EAB reached 8.08 GHz (9.92-18 GHz) when the thickness of the absorber was 2.47 mm. Such remarkable absorption performance is attributed to the synergetic effects between the multiple loss mechanisms of the FeCoNi@C, and the improved impedance matching characteristic came from the hollow sphere morphology.

The influence of Nd substitution in Ni–Zn ferrites for the improved microwave absorption properties

Nanocrystalline Ni–Zn ferrites with different neodymium contents (Ni0.5Zn0.5NdxFe2-xO4) were synthesized by sol-gel route combined with self-propagating combustion (SPC) method. The presence of surface functional groups, crystal structure and morphology of the samples were studied by FT-IR, XRD and SEM. The results show that the prepared samples are composed of spinel phase under the condition of low neodymium content, like the pure Ni–Zn ferrite. While neodymium oxide appears after the content of Nd3+ exceeds a certain limit (x > 0.04) and there exist two phases in the ferrite. The results of vibrating sample magnetometer (VSM) and vector network analyzer (VNA) show that adjusting the content of Nd is significant in improving the dielectric properties and microwave absorption capacity of the materials, specifically at low frequencies. When x < 0.04, the enhancement of dielectric loss ability of spinel ferrites by doping Nd3+ is the dominant factor affecting microwave absorption ability of samples. The secondary phase Nd2O3 hardly appears under this condition, thus the weakening effect of Nd3+ addition on magnetic loss ability is not obvious. When x = 0.04, the optimal absorption peak of the material reaches −20.8 dB at 4.4 GHz with a thickness of 8.5 mm and the effective absorption bandwidth (RL < −10 dB) was 3.2 GHz. On the contrary, when x > 0.04, the magnetic loss ability decreases rapidly (e.g., Ms decreases from 82.47 emu/g to 59.77 emu/g). Meanwhile, the dielectric loss increases slowly and the microwave absorption capacity decreases.

Broadband and strong electromagnetic wave absorption of epoxy composites filled with ultralow content of non-covalently modified reduced graphene oxides

High-efficiency microwave absorption epoxy nanocomposites filled with ultralow content of non-covalently modified reduced graphene oxides (rGO) are prepared via an in-situ polymerization method. Here, the porous and folded rGO nanosheets are successfully functionalized by strong π-π interaction between conjugated imidazole and graphene sheets. The combination of electron microscope and synchronous radiation X-ray small angle scattering (SAXS) techniques unambiguously illustrates that the non-covalently modified graphene nanosheets in the epoxy composites are well-dispersed and extensively winkle. Hence, compared with pristine rGO/epoxy composites, the composites containing the highly dispersed rGO demonstrate more ideal impedance matching and stronger microwave dissipation based on the experimental and simulated results. The composites remarkably achieve excellent microwave absorptions (minimum reflection loss of −65 dB, with a matching thickness of 1.8 mm), an extremely broad absorbing bandwidth of 7.48 GHz (RL < −10 dB) and ultralow filler loading (1–2 wt%). Moreover, the composites possess high hydrophobicity, endowing them attractive functions of self-cleaning. This work provides a promising, facile and scalable approach for designing and fabricating graphene-based nanocomposites with hydrophobicity and excellent microwave absorption capacities.

Fe@CNx Nanocapsules for Microwave Absorption at Gigahertz Frequency

In order to solve growing electromagnetic wave pollution issues, development of high-performance microwave absorption materials composed of dielectric loss and magnetic loss characteristics has been attracting considerable attention. Herein, we demonstrate an effective approach for the transformation of Fe@C into Fe@CNx nanocapsules by in situ microwave-assisted heating effect. Ascribed to the high effective microwave absorption capacity, the microwave energy could be localized around the nanoscale environment of Fe@C nanocapsules, resulting in the in situ chemical decomposition of urea precursor and the transformation of the initial graphitic shells to CNx shells. Microstructure characterizations coupled with complex permittivity spectra further reveal that the intrinsic dielectric enhancement for the Fe@CNx nanocapsules originates from the atomic-scale C–N complexes that induce the space charge separation and form the electric dipoles. The present study indicates a novel approach for in situ synthesizin...

Magnetic aligned Fe3O4-reduced graphene oxide/waterborne polyurethane composites with controllable structure for high microwave absorption capacity

Fe3O4-reduced graphene oxide (FRGO)/waterborne polyurethane (WPU) composites with controllable structure and high microwave absorption capacity were developed. The aligned structure of FRGO in the FRGO/WPU composites was realized by a magnetic-field-induced method. WPU dispersion with nano-scaled particles could suppress the aggregation of FRGO during the drying process. The FRGO/WPU composites have much high complex permittivity, dielectric loss tangent, and microwave absorption capacity owing to the magnetic alignment. WPU with 2% FRGO achieved the minimum reflection loss value of −67.8 dB, which can be attributed to the orientation and three-dimensional structure of FRGO. The effective bandwidth wider than 14 GHz can be reached by a combination of two layers of composites with different permittivity through theoretical calculation. The aligned FRGO/WPU composites have a great future in the application of microwave absorption materials.

Effect of Cr2O3 content on high-temperature dielectric properties and crystallisation of CMAS glass-ceramics

CaO–MgO–Al2O3–SiO2 (CMAS) glass-ceramics were prepared using fly ash and Bayan Obo West Mine tailings as the main raw materials by microwave heating. The effects of Cr2O3 content on the structure and properties of the glass-ceramics were investigated by differential thermal analysis, x-ray diffraction, scanning electron microscopy, and physical and dielectric property analysis. Diopside was the main crystalline phase of the glass-ceramics, and Cr2O3 evidently refined the grain size. The sample with 0.7 wt% Cr2O3 showed the best dielectric properties. Moreover, the microwave absorption capacity of glass and degree of coupling between the sample and microwave was enhanced at 600 °C and various frequencies (2.6–4.0 GHz). With increase in the Cr2O3 content, the density, bending strength, and Vickers hardness increased. The sample with 0.7 wt% Cr2O3 exhibited the maximum bending strength (149.30 MPa) and Vickers hardness (796.32 kg · mm−2). All samples showed better alkali resistance (>98 %) than acid resistance.

PVA-doped NiNd Fe2-O4 nanoferrites: Tuning of dielectric and magnetic properties

Abstract Polyvinyl alcohol (PVA)-blended spinel phase NiNdxFe2-xO4 nanoferrites were successfully prepared with a different composition (x = 0.01, 0.03, 0.05, 0.07, and 0.09). The spinel cubic structure was revealed from X-ray diffraction pattern. These nanoferrites showed insulating behavior with an enhanced energy bandgap when compared with PVA-unblended nanoferrites. The obtained dielectric loss and real and complex dielectric constants were in the microwave region (frequency ∼2.9–5.95 GHz). Pseudocapacitance and resistive behavior were explored from impedance analysis. The magnetization hysteresis plot of nanoferrites showed a soft ferromagnetic nature. It was found that reduction in saturation magnetization of NiNdxFe2-xO4 nanoferrites obtained by PVA doping has the strong microwave absorption capacity.

Double-shell PANS@PANI@Ag hollow microspheres and graphene dispersed in epoxy with enhanced microwave absorption

Double-shell hollow conductive poly(acrylonitrile) microspheres@polyaniline@Ag (PANS@PANI@Ag) was synthesized by a facile two-step method. Polyaniline-coated poly(acrylonitrile) microspheres (PANS@PANI) prepared by in situ polymerization exhibited a porous, corrugated and compact conductive network, making for the formation and attachment of Ag nanoparticles. Incorporating these hollow conductive spheres and reduced graphene oxide (RGO) into epoxy resin, a lightweight microwave absorber was brought out. The chemical composition, micro-structure surface morphology and electromagnetic properties were thoroughly characterized and analyzed. The calculated results showed that the optimal reflection loss (RL) was − 44.9 dB at 9.16 GHz with a constitution of 1 wt% dielectric RGO and 1 wt% conductive PANS@PANI@Ag, and the corresponding effective bandwidth was about 2 GHz. However, the microwave absorption capacity gradually reduced with the raise of PANS@PANI@Ag content, derived from the high conductivity leading to more microwave reflection. As the PANS@PANI@Ag content increased to 5 wt%, the minimum RL was − 14.7 dB and still remained an effective absorption performance with a lower density of 0.47–0.53 g/cm3. Therefore, the as-obtained composites paved a new route for lightweight and strong absorption microwave absorbers in commercial and military application.