Enhanced Microwave Absorption Properties Research Articles

Enhanced microwave absorption properties of spherical Fe4N derived from spherical Fe

Enhanced microwave absorption properties of spherical Fe4N derived from spherical Fe

Enhanced microwave absorption properties of Ni decorated flaky graphite powders with frequency selective surfaces incorporation

Reasonable design of composition and structure is an effective way to improve microwave absorption performance of absorber. In this study, flaky Ni@Graphite composite powders containing various Ni contents were successfully fabricated through a facile electroless plating process. The phase compositions and microstructure of the composite powders were characterized. XRD and SEM results showed that the Ni particles are successfully reduced from the solution and anchored on the flaky Graphite. The electromagnetic and microwave absorption properties of the Ni@Graphite composite powders were also studied. The results illustrated that although the composite powders with 45 % Ni owned the minimum reflection loss (RLmin) of −18 dB, the maximum effective absorption bandwidth (EABmax) was only 1.1 GHz for the sample with 2.0 mm thickness. So periodic frequency selective surfaces (FSS) were designed to further improve the microwave absorption performance. As the structural parameters of the FSS were C= 14 mm, T1 = 1.78 mm, e= 1.18 mm, R= 1.86 mm and a= 1.6 mm, the optimized RLmin and EABmax of the Ni@Graphite powders were −19.27 dB and 3.2 GHz, respectively. It was worth noting that the strategy of balancing the electromagnetic properties of dual-loss composites by controlling the composition and structure can effectively improve microwave absorption performance. This work contributes to the development of high-performance Ni@Graphite microwave absorption materials.

Manganese phosphate coated flaky FeSiAl powders with enhanced microwave absorbing properties and improved corrosion resistance

The electromagnetic wave absorption in X frequency band is every important for various applications. Except desired electromagnetic properties, excellent corrosion resistance is also required for the microwave absorbing materials used in harsh environments. Herein, the flaky FeSiAl (FSA) powders with large aspect ratios were coated with an insulation layer by manganese phosphating treatment. The electric insulating Mn3(PO4)2 coating reduces the eddy current between the particles. The heterointerface also improves the impedance matching of the absorbing materials and introduces additional loss mechanisms. By optimizing the thickness of the absorber, the composite consisting of 40 wt% FSA@Mn3(PO4)2 and 60 wt% paraffin wax with a thickness of 2.38 mm shows excellent microwave absorption properties with a minimum reflection loss of −62.86 dB at the frequency of 9.42 GHz and an optimized effective absorption bandwidth of 2.72 GHz. The anti-corrosion properties of the FSA@Mn3(PO4)2 and Teflon composites were also investigated. The corrosion rate of the optimally Mn3(PO4)2 coated FSA is 3 times slower than the naked FSA particles. The high stability of FSA@Mn3(PO4)2 composite in the corrosion environment results from the superior impermeability Mn3(PO4)2 coating. The present work provides a relatively low cost phosphating process for manufacturing anti-corrosion microwave absorbers working in the widely-used X frequency band.

Three-dimensional polyaniline/cerium oxide composite aerogel with enhanced microwave absorption properties

In order to develop microwave absorbing materials with strong absorption capacity, wide bandwidth and light weight, three-dimensional (3D) PANI/CeO2 composite aerogel was prepared by in-situ synthesis method in this work. The CeO2 nanorods are observed to be interlinked with PANI aerogel to form a porous nanofiber structure. The PANI/CeO2 composite aerogel exhibits excellent absorption performance with an absorption peak of − 53.68 dB under a moderate thickness of 2.5 mm, and the effective absorption bandwidth (EAB) achieves 4.44 GHz. The excellent microwave absorption performance of PANI/CeO2 composite aerogel was ascribed to the interfacial polarization relaxation and space charge polarization by virtue of the 3D conductive network. Furthermore, the oxygen vacancy defects arising from the CeO2 nanostructure also contribute greatly to the microwave absorption.

Facilitating enhanced microwave absorption properties of barium hexaferrite/polyaniline composites based on tunable interfacial polarization by rare earth doping

Barium hexaferrite (BaM)/polyaniline (PANI) is a typical microwave absorbing composite that effectively integrates magnetic and electric losses. To enhance its microwave absorption properties, a facile method based on rare earth element doping was explored; the effects of rare earth elements on the microstructures and properties of both BaM nanopowders and the subsequent BaM/PANI composites were investigated. The use of rare earth elements, including La, Nd, and Ce, in the BaM particles alleviated the constraints of the electric polarization in PANI near the surfaces of the BaM particles; this resulted in more electric polarization at the interfaces of the Re-BaM and PANI phases. This provided a versatile way to enhance the absorption efficiency, expand the absorption frequency range, and reduce the thickness. The La-BaM/PANI composite demonstrated a maximum reflection loss of approximately − 63.6 dB at 7.76 GHz with an optimum thickness of 3.28 mm. The effective absorption range of the Nd-BaM/PANI composite was 4.72 GHz. Ce-BaM/PANI composites released a relatively broad effective frequency range of approximately 3.88 GHz and a small thickness of 1.58 mm.

Facile synthesis of yolk-shell pompon-like Fe@void@CeO2@Ni nanospheres with enhanced microwave absorption properties

Due to the multiple scattering of microwaves and the existence of electron aggregation polarization at heterogeneous interfaces, the design of hollow or anisotropic microstructures has always been one of the research focuses of microwave absorption materials (MAMs). In this work, an effective strategy has been proposed reasonably to manufacture yolk-shell pompon-like Fe@void@CeO2@Ni nanospheres via hydrogen reduction and multiple solvothermal procedures. The results show that the metallic iron core with a diameter of 300 nm and the outer CeO2 layer with a thickness of 70 nm compound to form a yolk-shell structure, and the metallic nickel nanosheets with a length of about 100 nm are evenly embedded in the CeO2 layer to form a pompon-like structure. These unique microstructures provide heterogeneous interfacial polarization, three-dimensional conductive networks, and multiple electromagnetic scattering which bring excellent dielectric loss to the composites. Combined with the inherent strong magnetic loss of magnetic metals, as-prepared composites exhibit excellent microwave absorption properties. The minimal RL value reaches −48.9 dB and the efficient absorption bandwidth reaches 14 GHz with the thickness ranges from 2.5 to 7 mm. Hence, this unique microstructural design scheme has great prospects in the field of MAMs.

Lightweight Chain-Typed Magnetic Fe3O4@rGO Composites with Enhanced Microwave-Absorption Properties.

A lightweight microwave-absorbing material with a strong electromagnetic-absorption capability of practical significance in the field of electromagnetic compatibility was obtained by adjusting the ratio of Fe3O4 and rGO. A nanoparticle material with a chain-typed structure consisting of a combination of Fe3O4 and rGO was produced by a hydrothermal method under an applied magnetic field. The electromagnetic loss property of the Fe3O4@rGO composites is studied in the frequency range from 2 to 18 GHz. In addition, the reflection loss and the mechanism of microwave absorption are explored. By changing the amounts of rGO, the electromagnetic loss of the Fe3O4@rGO composites can be effectively regulated, which obtain better reflection loss. The minimum reflection loss of the Fe3O4@rGO composites is −49.4 dB at 16.2 GHz only with a thickness of 1.75 mm. Thus, the Fe3O4@rGO composites have an extremely thin thickness and a strong electromagnetic wave absorption capacity, which is a candidate for the development of lightweight magnetic absorbing materials.

SiO2-modified Y2Co8Fe9 multifunctional alloys with efficient microwave absorption, oxidation resistance and corrosion resistance

The application of a single metallic magnetic absorbing materials in harsh environments such as high temperature and corrosion reduces its absorption capacity significantly. Therefore, it is urgent to develop multifunctional composite materials with good absorption properties, oxidation resistance and corrosion resistance. In this work, SiO2-modified Y2Co8Fe9 (YCF) alloys with tunable tetraethyl orthosilicate content are prepared by the Stӧber method. The SiO2 coating efficiently enhances the microwave absorption properties due to the improved impedance matching characteristics. The SiO2 coating also provides effective physicochemical protection to prevent the alloys from oxidation and corrosion. Importantly, the YCF@SiO2-6 composite possesses enhanced microwave absorption properties with a minimum reflection loss (RLmin) of − 58.5 dB at 12.46 GHz with a thickness of 1.5 mm. The starting oxidation temperature of the YCF@SiO2-6 composite was 280 ℃ and 50 ℃ higher than that of the YCF and YCF@SiO2-2 samples, respectively. In addition, the corrosion resistance of the YCF@SiO2-6 composite in 3.5 wt% NaCl solution and hot and humid environment was tested by two different methods. The results indicate that the SiO2-modified sample shows good corrosion resistance. Therefore, this research provides a simple and practical method for the preparation of multifunctional composites in the field of electromagnetic wave absorption.

Enhanced microwave absorbing properties of Y2O3 modified PDC SiCN ceramics with heterogeneous amorphous interface

Polymer derived SiCN ceramics (PDC SiCN) are the key high-temperature matrix materials for structural and stealth integrated ceramic matrix composites (CMC). However, low crystallization degree and homogeneous microstructure of PDC SiCN ceramics results in the lack of effective microwave attenuation mechanism. Hence, a new kind of nonmagnetic metal oxide (Y2O3) was in-situ formed in SiCN ceramics to enhance the conductivity loss as well as the polarization loss. Y2O3 modified PDC SiCN ceramics (SiCN-Y2O3 ceramics) were fabricated by pyrolysis polysilazane with different Y(NO3)3 content at 900 ºC. For the SiCN-Y2O3 ceramic, Y2O3 nanoparticles were dispersed in SiCN ceramic uniformly forming a large number of Y2O3-SiCN heterogeneous amorphous interface, defects and dipole polarization to enhance its microwave absorbing properties. Due to the multiple polarization loss mechanism, SiCN-Y2O3 ceramic with 10 wt% Y(NO3)3 content achieved excellent microwave absorption performance at a wide thickness range with the microwave absorbing efficiency more than 90% in the whole X band, and the RCmin could reach − 50.2 dB at the thickness of 3.5 mm.

Hard Carbon Embedded with FeSiAl Flakes for Improved Microwave Absorption Properties.

Carbon-based composites have been proven to be strong candidates for microwave absorbers in recent years. However, as an important member, magnetic hard carbon (HC)-based composites have rarely been studied in the field of microwave absorption. In this study, HC embedded with FeSiAl (FeSiAl@HC) was synthesized by pyrolyzing a mixture of FeSiAl flakes and phenolic resin (PR). The as-synthesized HC-FeSiAl exhibited a layered structure, and the detailed microstructures were modified by changing the mass ratio of FeSiAl flakes and PR. Thus, the as-synthesized HC-FeSiAl exhibited tunable magnetic properties, wealthy functional groups, excellent thermal stability, and enhanced microwave absorption properties. The optimal minimum reflection loss is lower up to −36.1 dB, and the effective absorption bandwidth is wider up to 11.7 GHz. These results indicated that HC-FeSiAl should be a strong candidate for practical applications of microwave absorption, which may provide new insight into the synthesis of magnetic HC-based composites.

Grow defect-rich bamboo-like carbon nanotubes on carbon black for enhanced microwave absorption properties in X band

• By in-situ growing bamboo-like CNTs on CB, a developed conductive network was constructed and plentiful CB/CNT interfaces were introduced to improve the electromagnetic wave loss ability. • Defect-rich CNTs with open atomic edges can endow nanocarbons with a better balance between good impedance matching and strong loss capacity, causing an effective microwave absorption. • The minimum reflection loss and effective absorption bandwidth of CB-CNT with the CNTs growth time of 40 min reach to −53.6 dB and 4.1 GHz with the matching thickness of 2.7 mm, respectively. Due to the limited electromagnetic wave (EMW) loss capacity and agglomeration, carbon black (CB) gradually fails to meet the increasingly harsh demanding conditions. Herein, defect-rich bamboo-like carbon nanotubes (CNTs) were grown on CB by the process of chemical vapor deposition. CNTs prepared in situ on CB can assist it to build a developed multilevel conductive network and introduce plentiful CB/CNTs nano-interfaces. What's more, the defects that accompany the growth of CNTs endow CNTs with a moderate conductivity and good impedance matching, thereby causing an effective microwave absorption (MA). Meanwhile, the high-density defects on CNTs can induce dipole polarization to further strengthen the EMW loss ability. The influence of CNTs with different growth time on MA performance has been explored. Profiting from the structural merits, the synthesized CB-CNT with CNTs growth time of 40 min exhibits the optimal absorbing property, which has the minimum reflection loss of -53.6 dB and maximum effective absorption bandwidth of 4.1 GHz with the thickness of 2.7 mm, covering almost the entire X band. The introduction of defect-rich CNTs significantly enhances the EMW loss ability of CB, which provides a rational strategy for the design of high-efficient microwave absorption materials.

Tunable and enhanced microwave absorption properties by adjusting the distribution of Co/CoFe embedded into the carbon nanohorns and graphene microspheres

Designing unique structures of magnetic particle/carbon composites with multiple heterogeneous interfaces is an effective strategy for improving the properties of microwave absorption. Herein, hierarchical spacing arrangements for Co@carbon nanohorns and Co@graphene microspheres (Co@CNHs/G) with N enrichment were synthesized by a simple self-assembly method. As a result, Co@CNHs/G exhibited excellent electromagnetic wave absorption performance, and its reflection loss (RL) values of − 44.72 dB and − 41.39 dB at the C band had thicknesses of 2.9 mm and 2.5 mm, respectively. Additionally, the maximum effective absorption bandwidth (RL ≤ −10 dB) was 5.7 GHz at 1.4 mm. More importantly, the distribution of metal nanoparticles into CNHs and graphene microspheres were adjusted by forming the CoFe alloy embedded into CNHs and graphene microspheres during arc discharge process. Consequently, the frequency of RL ≤ −40.00 dB was from the C band to the X band by changing the multiple scattering paths, and the corresponding thickness for the minimum RL (−40.00 dB) was 1.8 mm. The outstanding electromagnetic absorbing performance was mainly attributed to the enhanced dielectric loss involving interfacial polarization derived from multiple heterogeneous interfaces, dipolar polarization induced by N-doping, and defects in the CNHs and graphene. In addition, multiple complex scattering paths can further improve the attenuation of electromagnetic waves.

Segregated structure of poly (vinylidene fluoride-co-hexafluoropropylene) composites loaded with polyaniline@carbon nanotube hybrids with enhanced microwave absorbing properties

Polyaniline@carbon nanotube (PAni@CNT) hybrid with electrical conductivity of 5.2 S/cm was successfully prepared by inverted emulsion polymerization of aniline in the presence of CNT dispersed in toluene assisted by cetyl-trimethyl ammonium bromide (CTAB). Conductive composites based on poly (vinylidene fluoride-co-hexafluoropropylene) (PVDFH) loaded with different amounts of PAni and PAni@CNT were prepared by dry-blending the powders in a ball-mill followed by hot compression molding. This procedure resulted in a segregated structure of the fillers, as indicated by scanning electron microscopy (SEM). The composite with 10 wt% of PAni@CNT (9.5: 0.5 wt%) hybrid exhibited electrical conductivity near 10−3 S/m and outstanding electromagnetic wave (EMW) attenuation. Indeed, reflection loss (RL) of − 34 dB (more than 99.9% EMW attenuation) at 11.7 GHz and effective absorption bandwidth (EAB) frequency with RL < −10 dB (more than 90% EMW attenuation) corresponding to 7.3 GHz were observed for this composition with thickness of 3 mm. A comparative analysis of measured and calculated RL was conducted. Considering the simple and cost effective preparation procedure, these composites loaded with 5 wt% and 10 wt% of the hybrid material are promising alternatives for developing efficient microwave absorbing material for both military and civil applications.

The double-coating structure of C/Cu/NiP microfiber composites for enhanced microwave absorption properties

The double-coating structure of C/Cu/NiP microfiber composites for enhanced microwave absorption properties

Experimental study on microwave absorption properties of HMA containing copper slag

In order to enhance the microwave absorption efficiency of asphalt mixture, copper slag (CS) was used to partially replace natural aggregates in the hot mix asphalt (HMA). The effect was analyzed on heating rate, crack healing properties and mechanical performance of asphalt concrete. A fiber optic thermometer was employed to test the internal temperature of the specimen and heating rate at different heights in the mixture cylinder. Also, the surface temperature was recorded by the infrared thermometer. The effects of copper slag content, heating power and aging of the mix were investigated on the healing performance of the mixture through semicircle three-point bending tests. It was concluded that adding CS aggregates can significantly enhance microwave absorption properties and improve the heating rate of asphalt concrete. And, the heating power played an essential role in the heating rate and induced healing efficiency. The aggravation of aging degree had a negative impact on the healing efficiency. The incorporation of copper slag was also helpful for improving the mechanical properties of the mixture. Overall, the use of copper slag as aggregate in asphalt mixture is a good option when adopting microwave-induced heating technology to repair and maintain pavements.

Enhanced microwave absorption property of ferroferric Oxide: The role of magnetoelectric resonance

• Direct fluorination was applied to decorate Fe 3 O 4 . • Core–shell fluorinated Fe 3 O 4 was fabricated by controlling the fluorination conditions. • The microwave absorption property of Fe 3 O 4 was enhanced after fluorination. • Electromagnetic wave dissipation model of magnetoelectric resonance was proposed. • The in-depth mechanism of magnetoelectric resonance was elucidated. The modification of ferrites can effectively improve their microwave absorption (MA) properties. However, attempts to improve their high-frequency performance were still limited and considerably cumbersome for practical application. Herein, we present a facile method that effectively improves the MA behavior of Fe 3 O 4 through direct fluorination using F 2 /N 2 gas. Specifically, we fabricated core–shell structured fluorinated Fe 3 O 4 (F-Fe 3 O 4 ) with a fluorine-doped shell and an unmodified Fe 3 O 4 core by carefully controlling the F 2 concentration and fluorination temperature. We found a unique ‘magnetoelectric collaborative resonance’ (MDR) effect in F-Fe 3 O 4 , manifested by the co-occurrence of double dielectric and magnetic resonance peaks at 14.8 and 16.6 GHz. Band gap measurements and molecular simulations results indicated that the smaller energy gap derived from fluorine doping facilitates both electron hopping between the mixed-valence Fe 2+ /Fe 3+ states and electron accumulation at the core–shell interface, which induce simultaneous magnetic exchange interactions and the Maxwell–Wagner effect (interface polarization). As a result, the incident electromagnetic wave can be dissipated via magnetic exchange resonance coupled with dielectric resonance, thereby improving the MA properties at the same frequency of MDR. Compared with those of pristine Fe 3 O 4 , the minimum reflection loss of F-Fe 3 O 4 was four times higher, reaching −64.9 dB, and the effective absorption bandwidth was 5.03 GHz, which is almost 1.6 times higher. We believe this facile and effective modification method and the unique loss mechanism of MDR will advance the structural design of high-performance MA materials.

Rational design of hierarchical structure of carbon@polyaniline composite with enhanced microwave absorption properties

Reasonable combination of components and ingenious structure design are effective strategies to achieve superior microwave absorption (MA). In this work, polyaniline was grown in situ on hollow porous carbon microspheres prepared by polymerization and pyrolysis-etching processes. The synthesized hollow porous carbon@polyaniline (HPC@PANI) shows a specific hierarchical structure and possesses extraordinary MA properties. The optimal minimum reflection loss (RL) of HPC@PANI is as high as −64.31 dB at 13.80 GHz with a thin thickness of 1.86 mm, and the corresponding effective absorption bandwidth (EAB, RL ≤ −10 dB) is as wide as 4.85 GHz (11.90 GHz–16.75 GHz). The mechanism of such superior MA properties is associated with well impedance matching, strong loss capabilities and well-defined structural characteristics. It is expected that the design of HPC@PANI with hierarchical structures in this work could provide ideas for the structural design of efficient MA materials.

Divalent-Doped Li1.3Al0.3Ti1.7(PO4)3 Ceramics with Enhanced Microwave Absorption Properties in the X-band

Divalent-Doped Li1.3Al0.3Ti1.7(PO4)3 Ceramics with Enhanced Microwave Absorption Properties in the X-band

Exchange coupled CoFe2O4/CoFe composites for enhanced microwave absorption properties by in-situ hydrothermal reduction

Exchange coupling magnetic composites have been proven to help improve the microwave absorption performance of absorbents. However, composite systems reported showed unsatisfactory exchange coupling effect due to poor particle dispersion and interface contact. Herein, exchange-coupled CoFe2O4/CoFe composites were prepared by in-situ hydrothermal reduction. The influence of surfactant on the microstructure and properties were studied in detail. The results showed that the CoFe2O4/CoFe samples with hexadecyltrimethylammonium bromide (CTAB) as the surfactant had more two-phase interfaces and excellent dispersion, the grain size of CoFe2O4 and CoFe were 45 nm and 38.4 nm. Close contact interface and small grain size caused suitable exchange coupling effect, which enhanced the microwave absorption performance of CoFe2O4/CoFe composites. The CoFe2O4/CoFe sample displayed maximum reflection loss (RLmax) of −54.8 dB at 3.5 mm thickness and effective absorption bandwidth (EAB) of 3.16 GHz, revealing promising prospect in the electromagnetic wave absorption field.

Hydrothermal synthesis of NixCo10-x nanoalloys with an enhanced microwave absorption performance

By using a facile hydrothermal synthesis, NiCo alloys with a particle size of 50–300 nm were prepared. The effects of the Ni:Co molar ratios on the microwave absorption properties in NiCo alloys were studied. The results showed that for Ni:Co molar ratios from 4:6 to 6:4, the morphology of the alloys changed from flower-like to nanoball-shaped. Specifically, the average size of Ni6Co4 was 84 nm, which showed a large specific surface area and produced increased interfacial polarization and multiple scattering. Ni6Co4 alloys exhibited excellent dielectric and magnetic properties, which enhanced microwave absorption properties. The optimum reflection loss in Ni6Co4 alloys was −53.29 dB at 9.44 GHz, and its thickness was 3.29 mm. The effective absorption bandwidth reached 6.64 GHz when the Ni6Co4 alloy thickness was 2.84 mm, which covered the C, Ku, and whole X bands. Additionally, the potential microwave dissipation mechanisms of as-fabricated NiCo alloys were illuminated, which were primarily derived from the optimized impedance matching, strengthened interfacial polarization, dipole polarization relaxation, and magnetic loss. These designs supply an effective way of obtaining promising candidate materials as high-efficient microwave absorbers.