Microwave Absorption Capacity Research Articles

Improving the Electromagnetic Properties of Bitumen Using SiC-Fe3O4 Composites

AbstractIt is important to further improve the microwave absorption capacity of bitumen to promote the application of microwave heating in pavement maintenance. SiC-Fe3O4 composites were prepared a...

Rational design of FeCo/C/FA by recycling of fly ash for electromagnetic pollution

In order to realize the sustainable development of turning waste into treasure and treating pollution with waste, the feasibility of resource utilization of fly ash (FA) to solve electromagnetic pollution was investigated. In this study, FeCo/carbon-loaded FA composites (FeCo/C/FA) were successfully synthesized via a facile one-pot method using solid waste FA as the raw material. Such ingenious design endowed FA enhanced microwave absorption (MA) capacity, and the MA mechanism derived from conductivity loss, multiple interface polarization and impedance matching. As expected, the FeCo/C/FA composites exhibited the excellent MA performance, its minimum reflection loss (RL min ) reached − 32.5 dB with the coating thickness of 1.5 mm. When the coating thickness was adjusted to 2.0 mm, the maximum value of effective absorption band was measured to be 4.7 GHz. This work confirms that FA can be directly recycled to construct a low-cost microwave absorber in the treatment of electromagnetic pollution. A facile one-pot method is put forward to construct FeCo/C/FA composites with outstanding microwave absorption performances. • The low-cost absorber is synthesized by the facile one-pot method. • The novel method realizes the recycling of FA and solves electromagnetic pollution. • The FeCo/C/FA composites are lightweight and possess excellent performance. • Impedance matching and interfacial polarization play a key role to performance.

Granitic quarry waste as a dual functional filler for high density polyethylene‐based composites: Mechanical and microwave absorbing properties

AbstractCost‐effective polymeric composites were successfully prepared by melt blending granitic quarry waste (GQW) with high‐density polyethylene (HDPE). The GQW is a waste generated during the production of manufacture fine aggregates (MFA) from crushed gneiss rock and contains significant amount of mica with iron in its structure. Different sieving and milling procedures were employed. The materials were characterized by mechanical and dynamic‐mechanical properties and scanning electron microscopy. Moreover, the influence of the GQW on the microwave absorbing properties in the X‐band frequency range was investigated. The presence of mica and iron compound in the GQW provides a dual function to the filler: toughening agent with microwave absorbing capacity. Indeed, the addition of 5 wt% of GQW previously sieved and milled by dry or wet‐grinding approach resulted in composites with outstanding toughness, modulus and elongation at break. Simulated RL studies revealed electro‐magnetic attenuation of −25 dB at 8.7 GHz. Such successful use of a waste generated in the production of a concentrate (MFA) not only contributes to the economics of the quarrying operation, but also to its environmental sustainability, since it replaces disposal of this product, which could lead to dust emissions, given its fine size and low moisture content.

Anchoring of SiC and Fe3Si nanocrystallines in carbon nanofibers inducing interfacial polarization to promote microwave attenuation ability

Carbon-based nanomaterials are widely employed for microwave absorption. However, reasonable methods to enhance microwave absorption capacity remain worth exploring. Herein, carbon nanofibers (CNFs) modified by silicon carbide and metal silicide (SiC/Fe3Si/C) were fabricated through electrospinning and high-temperature pyrolysis processes, and their phase composition, micro-morphology, micro-structure, and magnetic characteristics evaluated. The composite nanofibers (SiC/Fe3Si/CNFs) exhibited excellent microwave absorption, with minimum reflection loss (RLmin) values of −41.6 dB at 12.8 GHz and a matching thickness of 4.5 mm. Further, the maximum effective absorption bandwidth (EAB, RL<−10 dB) of the as-synthesized sample is 11.5 GHz with a matching thickness of 5 mm. These novel carbide and intermetallic compounds loaded CNFs are remarkable candidates for lightweight, tunable, and efficient microwave absorbers.

Microwave directional pyrolysis and heat transfer mechanisms based on multiphysics field stimulation: Design porous biochar structure via controlling hotspots formation

The microwave pyrolysis of biomass and the directional design of biochar structure are examined in this study by exploring the internal connection between energy conversion and biochar structure evolution. Through the optimization of process parameters (microwave power and sample volume), the average utilization efficiency of microwave energy increased from 11.96% to 32.84%, and the specific surface area of the biochar increased from 453.89 m2/g to 638.82 m2/g. According to the simulation results of the COMSOL Multiphysics software, the distribution of the temperature field was closely related to the evolution of the microwave electric field intensity. The local high temperature areas (hotspots) were primarily located in the center of the biochar, and the temperature distribution gradually decreased from the inside to the outside. The hotspots contributed to the promotion of the conversion of amorphous carbon to graphite carbon. Meanwhile, the graphite carbon with a stronger microwave absorption capacity formed a local hotspot and promoted the growth of the pore structure. The rich pore structure of the biochar facilitated the multiple reflection of microwave energy and prolonged the microwave residence time. Graphite carbon can absorb microwave energy and convert it into heat energy to improve the utilization efficiency of microwave energy. This paper combined the experimental and simulation results to reveal the heat transfer mechanism in the microwave pyrolysis process, which provided a new perspective for the directional reduction of microwave pyrolysis energy consumption and the optimization of the microstructure of biochar.

Performance evolution of Fe3O4 used in the production of sustainable self-healing asphalt materials

Studies have shown that the sustainable self-healing ability of asphalt materials under microwave radiation is related to the microwave absorption of the constituent materials. As a typical absorbing material, Fe3O4 and its derivatives have the potential to heal the micro cracks of asphalt materials multiple times by themselves, and enhance the sustainable self-healing properties. However, former researchers have neglected the fact that Fe3O4 will be gradually oxidized at high temperatures, such as 100 °C, resulting in the changes in material properties, microwave absorption and heat-generating capability. Therefore, the effects of different temperatures on the properties of controllable synthesized Fe3O4 were studied at 125 °C (mixing temperature of WMA), 150 °C (mixing temperature of HMA), 175 °C (mixing temperature of HMA with modified binder) and 200 °C (extreme mixing temperature). The phase compositions, chemical structure of synthesized Fe3O4 were characterized firstly. Then, their electromagnetic parameters, reflection loss were studied at a microwave frequency ranging from 1 to 18 GHz. Additionally, heat-generating abilities of them were characterized at usual microwave frequency of 2.45 GHz. Finally, the effects of different content of Fe3O4 on the rheological properties of pure asphalt were studied. The results show that the proportion of γ-Fe2O3 in the samples gradually increase with exposure temperature, and the static magnetic properties gradually deteriorate. The reflection loss of the modified asphalt decreases firstly and then increases. The F-150 modified asphalt has the strongest microwave absorption capacity. Under the 2.45 GHz microwave radiation, the F-150 modified asphalt presents the strongest heat-generating capability and is consistent with the results of reflection loss. It can be seen that the ratio of γ-Fe2O3 and Fe3O4 in F-150 has the best attenuation effect on microwave radiation, and Fe3O4 is more suitable as microwave absorber for self-healing enhancement of HMA.

Effects of temperature and frequency on the dielectric properties of thiophene compounds and its application in coal microwave-assisted desulfurization

This study aimed to clarify the influence of medium composition, microwave frequency, and temperature on the dielectric properties and desulfurization rates of thiophene components in coal. Thiophene compounds with different structures were selected, and the dielectric parameters at different frequencies and temperatures were investigated. The coal-like substance samples loaded with benzothiophene were prepared and subjected to 915 and 2450 MHz microwave-assisted citric-acid desulfurization at different temperatures. Using X-ray absorption near-edge structure (XANES), changes of organic sulfur components structures and contents in coal-like substances after microwave desulfurization were observed. Results showed that thiophene compounds containing a conjugated structure had poor dielectric properties. The dielectric loss of benzothiophene at 915 MHz was better than that at 2450 MHz. In the temperature range of 20–100 °C, the dielectric loss of benzothiophene increased with the increasing temperature, and both peaked at 90 °C. With the further increase of temperature, the microwave absorbing capacity of benzothiophene decreases. Microwave-assisted citric acid can oxidize part of the benzothiophene in coal-like substances into phenethyl alcohol, sulfoxide, sulfone, sulfonate, sulfite and sulfate. Phenyl alcohol, sulfonate, sulfite and sulfate can be removed by washing with water to remove benzothiophene from coal-like substances. The desulfurization rate was directly related to the dielectric loss of benzothiophene, and the desulfurization rate was highest when the dielectric loss was the largest. When the reaction temperature was 90 °C, 915 MHz frequency microwave radiation citric acid can obtain the best desulfurization effect of benzothiophene in coal-like substances, and the desulfurization rate reached 42.87%.

Fabrication of one-dimensional ZnFe2O4@carbon@MoS2/FeS2 composites as electromagnetic wave absorber

In this work, one-dimensional (1D) ZnFe2O4@carbon@MoS2/FeS2 composites were synthesized by hydrothermal method, magnetic-field-induced distillation-precipitation polymerization and high-temperature carbonization. The structure, morphology, composition, magnetic performance and electromagnetic (EM) wave absorbing properties of the composites were systematically studied. The composites show strong microwave absorption (MA) capacity with a minimum reflection loss (RLmin) value of −52.5 dB at 13.2 GHz, and have an effective absorption frequency range of 10.10–15.08 GHz with a bandwidth of 4.98 GHz when the thickness is 2.23 mm. It is expected that as-synthesized 1D ZnFe2O4@carbon@MoS2/FeS2 composites can be a promising EM wave absorption material.

Thermal transfer characteristics of asphalt mixtures containing hot poured steel slag through microwave heating

Hot poured steel slag (HPSS) was adopted as microwave absorber to replace partial limestone aggregate to prepare asphalt mixtures in this work. Thermal transfer characteristics of asphalt mixtures through microwave heating (MH) were discussed. Firstly, the MH capacity of HPSS with different particle sizes were studied. Then, the morphology and element percentage of HPSS were characterized with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Subsequently, surface temperature, heating uniformity and thermal transfer characteristics were analyzed. The results show that HPSS has good microwave absorption capacity and the increment of HPSS in asphalt mixtures can increase the surface temperature. The surface temperature of asphalt mixtures with HPSS can be evidently influenced by microwave power due to the correlation between microwave energy and microwave power. Besides, the heating uniformity of asphalt mixtures decreases with the increase of HPSS content, which is mainly related to the spatial distribution and heat generating rate of HPSS. Finally, the thermal transfer characteristics of asphalt mixtures with HPSS are divided into three types according to thermal source intensity and thermal transfer efficiency. Overall, it can be used as functional asphalt mixtures to improve the sustainability of pavement because of the good microwave absorption performance of asphalt mixtures containing HPSS.

Ultralight and High-Strength SiCnw@SiC Foam with Highly Efficient Microwave Absorption and Heat Insulation Properties.

An ultralight and high-strength SiCnw@SiC foam with highly efficient microwave absorption and heat insulation properties was successfully synthesized using the template sacrifice method and chemical vapor deposition process. The microstructure is a novel double network structure, which is formed by the coupling of the morphology-controlled SiCnw and the SiC skeleton. The introduction of SiCnw can not only provide more interface polarization and dielectric loss to the SiC foam, which greatly enhances the microwave absorption capacity of the composite foam, but also can enable it to act as an excellent radiation absorbent, which can effectively reduce the thermal conductivity of the foam, especially at high temperatures. In this study, a minimum reflection loss (RLmin) of -52.49 dB was achieved at 2.82 mm thickness with an effective absorption bandwidth of 5.6 GHz. As the length/diameter ratio of SiCnw decreases, the composite foam exhibits excellent high-temperature thermal insulation and mechanical properties. For the SiCnw@SiC foam, the thermal conductivity is only 0.304 W/mK at 1200 °C and the compressive strength reaches 1.53 MPa. This multifunctional SiCnw@SiC foam is an outstanding material, which has potential applications in microwave absorption and high-temperature heat insulation in harsh environments.

Facile fabrication of hierarchical flowerlike γ-AlOOH hollow spheres decorated with MWCNTs for electromagnetic wave absorption

To explore a type of high-performance microwave absorber with lightweight and thin thickness, the flowerlike γ-AlOOH hollow spheres decorated with multi-walled carbon nanotubes (MWCNTs) were fabricated by a facile hydrothermal method. The microscopic morphology characterization showed the γ-AlOOH microspheres consisted of a hollow inner core and a shell made of numerous flakes. The γ-AlOOH/MWCNTs composites exhibited excellent microwave absorption performance with the reflection loss of − 49.8 dB at 11.1 GHz and effective absorption bandwidth of 4.56 GHz (from 13.44 to 18 GHz) at a thickness of 1.5 mm, which covered almost the entire X band. Furthermore, the unique microstructure of γ-AlOOH exerted a considerable effect on the obtained microwave absorption capacity of the composites, leading to interfacial polarization, multiple reflections, and scattering of electromagnetic wave. Meanwhile, the suitable MWCNTs additive amount played a crucial role in the improvement of impedance matching, conduction loss, and dipole polarization, which benefit the performance of microwave absorption. It is expected that the flowerlike hollow spheres structure in our work can provide a method of designing the novel microwave absorbers.

One-step arc synthesis and enhanced microwave absorption performances of Al-doped SiC nanoparticles

Here, a facile one-step arc-discharge method was applied to synthesize the Al-doped SiC nanoparticles. Compared to undoped SiC, the shifts of bound-hole around AlSi defects in the Al-doped SiC crystal at the alternating electromagnetic field from one equilibrium position to another must overcome a potential barrier, producing forceful relaxation polarization. Meanwhile, the abundant defects caused by Al doping in Al-doped SiC nanoparticles not only act as polarization centers contributing to the enhanced polarization loss but also create more current carriers increasing the leakage loss. Furthermore, the weak magnetism caused by the AlSi defects can further optimize the balance of dielectric loss and magnetic loss and achieve a better impedance matching for Al-doped SiC nanoparticles. Therefore, Al-doped SiC nanoparticles have the enhanced microwave absorption capacity, which exhibits the minimum reflection loss (RL) value of − 43.7 dB at a thickness of 3 mm and RL below − 10 dB covered 3.2–18 GHz with the changeable thickness of 1.22–5.5 mm. This work provided a defect-engineering strategy in modifying SiC-based high-temperature dielectric ceramics of microwave absorption performances.

Fabrication of hexagonal cerium oxide nanoparticles decorated nitrogen-doped reduced graphene oxide hybrid nanocomposite as high-performance microwave absorbers in the Ku band

With the aim to obtain microwave absorbers simultaneously possessing broad absorption bandwidth, strong absorption intensity and thin matching thickness, nitrogen-doped reduced graphene oxide decorated by cerium oxide particles (NRGO/CeO2) hybrid nanocomposite was prepared through a hydrothermal and calcination two-step route. Results of micromorphology analysis showed that numerous hexagonal CeO2 nanoparticles were evenly anchored on the crumpled surfaces of NRGO. Moreover, both nitrogen doping and hybridization with RGO could notably strengthen the microwave absorption capacity of CeO2. Remarkably, the NRGO/CeO2 hybrid nanocomposite exhibited the minimum reflection loss of −57.2 dB at 13.4 GHz (Ku band) under a matching thickness of 1.66 mm and maximum absorption bandwidth of 4.6 GHz (from 13.2 to 17.8 GHz) at an ultrathin thickness of only 1.5 mm. Meanwhile, the hybrid nanocomposites displayed strong absorption intensity (≤-20 dB, 99% absorption) in almost the whole measured thicknesses range. Furthermore, the relationship between absorption intensity and filler loadings was uncovered. The potential microwave absorption mechanisms were further revealed. Therefore, this work opened a novel idea for designing RGO-based hybrid nanocomposites as high-performance microwave absorbers.

Preparation and Properties of Microwave-Absorbing Asphalt Mixtures Containing Graphite and Magnetite Powder

Abstract The concept of microwave-absorbing asphalt concrete has been proposed to create an asphalt mixture with high microwave heating efficiency. A mixture of 20 % graphite powder and 80 % magnetite powder was used as the microwave-absorbing composite to replace the common mineral filler in asphalt mixtures to improve its microwave absorption capacity. This study aimed to evaluate the effect of proposed absorbent composite on the properties and microwave heating efficiency of asphalt mixtures. The results indicate that the addition of graphite and magnetite powder exhibited an improvement in the microwave heating efficiency of asphalt mixtures. The heating rate of asphalt mastic was improved by more than 10 times, whereas the heating rate of asphalt mixtures containing the absorbent composite was improved by 47.8 %. The pavement performance test results show that the mechanical performances including the dynamic stability, bending strain, residual Marshall stability, and ratio of splitting tensile strength after and before the freeze-thaw cycle satisfy the relevant specification requirements.

MOF-derived Co@C nanoparticle anchored aramid nanofiber (ANF) aerogel for superior microwave absorption capacity.

High-efficiency, porous and renewable magnetic microwave absorbing (MA) materials have been enthusiastically pursued due to their suitable impedance matching, light weight, strong multiple scattering and the synergy effect of dielectric and magnetic loss. Herein, a three-dimensional (3D) Co@C/ANF aerogel, composed of magnetic MOF derivatives embedded in biomass aramid nanofiber (ANF), was prepared for the first time through a directional-freezing method followed by an annealing process. To evaluate their MA attenuation performance, the electromagnetic parameters of Co@C/ANF composites with different component ratios were measured at 2–18 GHz. Profiting from the preserved porous structure of MOF derivatives, the construction of multiple heterogeneous interfaces and suitable electromagnetic parameters, Co@C/ANF 2 : 1 exhibited a good MA performance of RLmin = −64.3 dB (indicating more than 99.99996% microwaves were absorbed) and EABmax = 6.8 GHz. Considering the admirable overall performance, the Co@C/ANF aerogel is deemed to be a promising candidate for the next-generation of lightweight, reproducible, and high-performance MA materials.

Enhanced heat-resistance property of aluminum-coated carbonyl iron particles as microwave absorption materials

Nano aluminum (Al)-coated carbonyl iron particles (CIPs) with high microwave absorption capacity and heat-resistance property were prepared by ball-milling. To test the performance of Al@CIPs, raw CIPs were also processed under the same ball-milling process for comparison. Afterwards, both materials were subjected to the same heat treatment process in order to examine their heat resistance. The morphology, structure, electromagnetic and microwave absorption properties were evaluated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and vector network analysis, respectively. The bond properties of CIPs- or Al@CIPs-based coatings were determined through pull-out test. Morphological and structural analysis results indicated that Al nanoparticles were homogeneously distributed on the surface of CIPs. Compared with raw CIPs, Al@CIPs composites had the better oxidation resistance. The significant improvement in the antioxidation capacity was mainly attributed to the compact and dense alumina layer formed at the higher temperature, which further prevented oxygen in the air from entering the CIPs core. The ball-milling method proposed in the study can uniformly coat Al on the surface of CIPs in a simple and effective way and provide an efficient way to prepare antioxidized CIPs as microwave absorption materials.

Microwave vacuum evaporation as a potential technology to concentrate sugar solutions: A study based on dielectric spectroscopy

Traditional vacuum evaporation in the sugar industry generally relies on steam and is characterized by low energy efficiency. Microwaves may be an alternative heat source to steam. In this study, three sugar solutions (glucose, maltose, and trehalose) were concentrated by lab-scale microwave vacuum evaporation (MVE). The dielectric spectroscopy in the frequency range of 0.1-6.5 GHz and the temperature range of 5-90 °C was determined and analyzed. Results showed that the dielectric loss factor increased with concentration and decreased with temperature at 2.45 GHz. The maltose solution had a lower microwave absorption and conversion capacity than glucose or trehalose solution. Meanwhile, the hydrogen bond interactions of trehalose solution were stronger, contributing to higher intermolecular interactions. These results may account for the distinct evaporation efficiencies of MVE on the three sugar solutions. Due to the rapid heating rate (up to 2.86 ± 0.08 °C/s) and massive water loss (closer to 2/3 total mass of the feed solution) over a short period of time (10 min at a microwave power density of 40 W/g and a vacuum pressure of 50 kPa), MVE may be a substitute for conventional methods. Furthermore, the dielectric spectroscopy can be an effective tool to help guide MVE to obtain sugars with high quality. • Dielectric spectroscopy of three sugar solutions was determined and analyzed. • Maltose solution had weaker microwave absorption and conversion ability. • Strong intermolecular interactions in trehalose solution impeded evaporation. • Rapid heating and massive water loss occurred during microwave vacuum evaporation. • Microwave vacuum evaporation may be a substitute for conventional evaporation.

Heterostructure design of Fe3N alloy/porous carbon nanosheet composites for efficient microwave attenuation

The self-dissipation and attenuation capacity of materials play an important role in realizing efficient electromagnetic absorption, in this case, the roles of macroscopic composition and micro-structure should be emphasized simultaneously in the reasonable design of microwave absorbent. Given that, Fe3N alloy embedded in two-dimensional porous carbon composites were fabricated via facile sol-gel and sacrificial template methods. Satisfactorily, the magnetic/dielectric materials combination and porous structure introduction are conductive to the optimization of impedance matching property, as result of the enhancement of microwave absorption capacity. In addition, sufficient magnetic loss capacity, strong conductivity as well as polarization attenuation bring about the outstanding microwave absorbing performance with an effective absorption bandwidth of 6.76 GHz and a minimum reflection loss value of -65.6 dB. It is believed that this work not only lay a foundation to achieve microwave response materials in a wide frequency range, but also emphasize the significant role of the component selection and structural design.

FeCoNiCuAl high entropy alloys microwave absorbing materials: Exploring the effects of different Cu contents and annealing temperatures on electromagnetic properties

The FeCoNiCuxAl (x = 0.2–0.7) high-entropy alloy powders were synthesized by ball milling and then the prepared FeCoNiCu0.5Al powders were annealed at different temperatures (673K, 773K and 873K). The characteristics of powders were discussed, including microstructure, morphology, particle sizes, magnetic and electromagnetic properties. The crystal structures of powders are simple FCC and BCC phases with flaky microscopic morphologies. The FeCoNiCuxAl alloys with various Cu contents are soft magnetic materials, which possess high saturation magnetization and low coercivity. High conductivity and improved surface polarization with large aspect ratio of flaky powders can enhance permittivity. High saturation magnetization of soft magnetic materials can reinforce permeability. These can promote the microwave absorbing capacity of FeCoNiCuxAl alloy powders, the reflection loss (RL) of FeCoNiCuxAl alloy powders all can reach −10dB or less and the minimum RL value is −28.04 dB at Cux=0.5. Meanwhile, phases, morphology, conductivity and saturation magnetization are changed during different temperatures annealing treatment, which makes the RL values improved differently, and the minimum RL value is −40.05 dB at 673K annealing. These studies have shown that high-entropy alloys have great potential to become promising absorbers.

Broadband metamaterial microwave absorber based on asymmetric sectional resonator structures

In this paper, we present a novel design of broadband metamaterial microwave absorber (MWA) based on asymmetric sectional resonator structures (SRSs), which has been verified by simulation, calculation based on circuit theory, and experiment. The broadband perfect absorption of the MWA can be obtained by assembling four asymmetric SRSs with different sizes. The numerical results indicate that the bandwidth of the broadband MWA based on asymmetric SRSs is about 16.2 times of the ones based on single SRS or four complete symmetric SRSs. The broadband perfect absorption of the proposed MWA mainly originates from the excitation of the fundamental resonance mode of the SRS. The numerical results also demonstrate that the broadband MWA exhibits an angle-insensitivity microwave absorption capacity, which is manifested as a high absorption level at large incident angles for both transverse electric and transverse magnetic modes. Thus, the proposed broadband MWA turns out to be suitable for a wide variety of potential applications in stealth technology and energy harvesting.