Electromagnetic Wave Absorption Properties Research Articles

Carbon nanotubes decorated FeNi/nitrogen-doped carbon composites for lightweight and broadband electromagnetic wave absorption

Magnetic-dielectric component modulation and heterogeneous interface engineering were considered as an effective strategy for designing lightweight and broadband electromagnetic wave (EMW) absorbors. Herein, a series of carbon nanotubes (CNTs) decorated core-shell nitrogen-doped carbon (CNTs/FeNi/NC) composites were successfully fabricated via the carbonization of CNTs/NiFe2O4/PDA precursors obtained by hydrothermal and polymerization method. The EMW absorption (EMWA) properties of CNTs/FeNi/NC composites were explored by varying the CNTs content. When the CNTs content was 15%, the minimum reflection loss (RLmin) value was -51.13 dB at 9.52 GHz and the corresponding effective absorption bandwidth (EAB) value was 2.96 GHz (8.96–11.12 GHz) at 2.5 mm. Particularly, the maximum EAB value can reach up to 4.64 GHz (12.80–17.44 GHz) at 1.7 mm. The excellent EMW attenuation capability resulted from the enhanced conductive loss, polarization loss, magnetic loss, and improved impedance matching. This work offers a novel reference for designing lightweight and broadband EMWA materials.

Synthesis and Electromagnetic Wave Absorption Properties of Micro Composites Reduced Graphene Oxide/Ferrite Based Dendrocalamus Asper Charcoal and Natural Ferrite

Keywords: bamboo, micro composite, natural ferrite, reduced graphene oxideAbstract. Reduced graphene oxide/ferrite (rGO/Fe3O4) micro composites as radar absorber materials have been successfully synthesized from Petung bamboo (Dendrocalamus Asper) and iron sand using a mechanical mixing method. Reduced graphene oxide (rGO) as dielectric material was synthesized from Petung bamboo charcoal using the carbonization method, and Fe3O4 as magnetic material was synthesized from iron sand using the extraction-milling method. The as-prepared samples rGO/Fe3O4 (1:1, 1:2, 1:3, 2:1, 3:1 wt%) was made by dry mixing and mechanically pressed. Magnetics and morphology of samples were characterized by vibrating sample magnetometry (VSM) and scanning electron microscopy (SEM). Microwave absorption was measured using a vector network analyzer (VNA) at 8 – 12 GHz. The results of measurement by using VNA showed that at the micro-scale, rGO had a higher absorption power with maximum reflection loss (RLm) value of -12.98 dB at matching frequency (fm) 10.15 GHz compared with Fe3O4 (RLm value of -4.25 dB at fm 10.42 GHz) at a thickness of 2 mm. The rGO/Fe3O4 (3:1 wt.%) microcomposites radar wave absorber shows the best absorption with maximum reflection loss (RLm) value of −14.30 dB at matching frequency (fm) 10.15 GHz at a thickness of 2 mm. Natural materials and the controlled rGO/Fe3O4 microcomposites structure with simple synthesis methods shows the great potential application in high performance microwave absorbing materials.

Co3O4 Nanoparticle-Modified Porous Carbons with High Microwave Absorption Performances

Carbon materials derived from natural biomaterials have received increasing attention because of their low cost, accessibility, and renewability. In this work, porous carbon (DPC) material prepared from D-fructose was used to make a DPC/Co3O4 composite microwave absorbing material. Their electromagnetic wave absorption properties were thoroughly investigated. The results show that the composition of Co3O4 nanoparticles with DPC had enhanced microwave absorption (-60 dB to -63.7 dB), reduced the frequency of the maximum reflection loss (RL) (16.9 GHz to 9.2 GHz), and had high reflection loss over a wide range of coating thicknesses (2.78-4.84 mm, highest reflection loss <-30 dB). This work provided a way for further research on the development of biomass-derived carbon as a sustainable, lightweight, high-performance microwave absorber for practical applications.

Excellent electromagnetic wave absorption properties of SiCN ceramic aerogels via a controlled hydrosilylation reaction

AbstractPolymer‐derived ceramic materials exhibit adjustable composition, microstructure, and dielectric properties and are widely used as high temperature microwave absorption materials in the aerospace field. In this study, polymer‐derived SiCN ceramic aerogels with excellent electromagnetic wave absorption (EMA) properties were successfully fabricated through a combination of the sol‐gel, freeze‐ drying, and polymer precursor conversion methods. The hydrosilylation reaction between the Si‐H bond in polysilazane (a polymer ceramic precursor) and the C = C bond in divinylbenzene (a cross‐linking agent) occurs to form a wet gel. The effects of the molar ratios of the two bonds (C = C/Si‐H) on the microstructure and EMA properties of the SiCN ceramic aerogels were systematically studied. At a C = C/Si–H molar ratio of 1.25:1, the minimum reflection loss of the SiCN ceramic aerogels is −37.57 dB at 10.88 GHz. Moreover, the corresponding effective absorption bandwidth covers almost the entire X‐band, showing excellent EMA properties.

Hierarchical architecture bioinspired CNTs/CNF electromagnetic wave absorbing materials

One dimensional carbon nano material has attracted extensive attention in the field of electromagnetic wave (EMW) absorption due to its large aspect ratio, ultrafine nano networks, good thermal stability and designable surfaces. However, one-dimensional nanomaterials are easy to agglomerate, loss and impedance are mismatched, which seriously restricts their application. How to overcome the agglomeration of one-dimensional nanomaterials, as well as design nano-interface and precisely control the dielectric loss are the key to the research of EMW absorbing materials. Inspired by the dense and regular hierarchical structure of pine branches, we use carbon nano fiber (CNF) converted from bacterial cellulose (BC) as the matrix, and in situ growth amorphous carbon nanotubes (CNTs) on its surface, so as to construct a hierarchical architecture similar to pine leaves in nanoscale, which not only solves the common aggregation problem of one dimensional nanomaterial, but also obtains stronger interface polarization capability through hierarchical nano structure. Furthermore, the amorphous CNTs network have moderate conductivity, which does not lead to impedance mismatch. The reflection loss of CNTs/CNF with a CNTs content of 63.2 wt% can reach −68.2 dB at a thickness of 2.7 mm, and the maximum effective absorption bandwidth reaches 5.5 GHz. The design strategy of hierarchical amorphous carbon nanocomposite integrates strong EMW absorption and good impedance characteristics, the synthesized CNTs/CNF composites exhibit excellent EMW absorption properties.

Electromagnetic wave absorption property of SiC whiskers regulated by stacking faults and SiC@SiO2 core-sheath microstructure

In this study, SiC whiskers were prepared by chemical vapor deposition using graphite powder mixed with resin powder and silicon powder as raw materials. The crystal structure, morphology, surface chemical state and electromagnetic wave absorption properties were studied. The density and number of stacking faults inside the SiC whiskers can be controlled by changing the proportion of nitrogen atmosphere during the preparation of SiC whiskers which in turn affects the wave absorption properties. We found that the whiskers prepared in a nitrogen-free atmosphere with a large number of stacking faults ‘have better electromagnetic wave absorption performance. This is mainly due to the large number of stacking faults inside the SiC whiskers that can act as polarization and scattering centers to enhance dielectric losses under alternating electromagnetic fields. The minimum reflection loss (RL) can reach −20 dB near 17 GHz, and an effective absorption (RL ≤ −10 dB) bandwidth of 1.1 GHz (16.9–18) at the absorber layer thickness of 5 mm.In addition, after proving that a large number of stacking faults are beneficial, a SiO2 shell was designed outside the SiC whiskers through a simple oxidation process. The minimum RL can reach −35 dB near 17 GHz, and an effective absorption (RL ≤ −10 dB) bandwidth of 2.5 GHz (15.5–18) at the absorber layer thickness of 5 mm.

Significantly enhancing electromagnetic wave absorption properties of BaFe12O19 hexaferrites via KOH mineralizer

To further study the microwave absorbing properties of hexagonal barium ferrites (abbreviated as BaM) fabricated by using an innovative hydrothermal method with different mineralizers, the crystal structure, morphology, magnetoelectric and the microwave absorption properties of BaM were systematically studied. X-ray diffraction patterns (XRD) show that all samples exhibit a pure phase for BaM. At the same time, the grain size and morphology can be controlled and the thicker and regular hexagonal flakes were obtained using KOH mineralizer. The maximal magnetization in the field 15 kOe of BaM can be improved by using KOH mineralizer compared to NaOH mineralizer, while the coercivity (Hc) is slightly reduced. The maximal magnetization in the field 15 kOe is 31.83 emu/g and 43.36 emu/g for BaM synthesized with NaOH and KOH mineralizers, and the Hc is 860.23 Oe and 842.00 Oe, respectively. Meanwhile, the RL values of BaM synthesized with NaOH mineralizer are greater than − 3.00 dB indicating poor absorbing property. While, as for the BaM synthesized with KOH mineralizer, the electromagnetic wave absorption performance is enhanced greatly. The minimum value of the reflection loss (RLmin) is − 17.59 dB obtained at 13.2 GHz with a thickness of 1.5 mm, and the effective absorption bandwidth is up to 3.2 GHz (11.6∼14.8 GHz) for BaM with KOH mineralizer. This work provides a kind of effective method to enhance the microwave absorption properties of BaM material by changing the mineralizer, and suggests that BaM is a microwave absorbing material with great potential engineering applications for 5 G communication.

Synthesis, Characterization, and Electromagnetic Wave Absorbing Properties of La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt;

Perovskite manganese La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; (LSMO) powders were prepared by sol-gel synthesis and calcination in the temperature (&lt;i&gt;T&lt;/i&gt;) range of 500~1200 o C and their structures and electromagnetic (EM) wave absorption properties were investigated. X-ray diffraction (XRD) analysis revealed that the crystalline perovskite phase can be formed at &lt;i&gt;T&lt;/i&gt; ≥ 600 &lt;sup&gt;o&lt;/sup&gt;C. The average grain size was ~15 nm at the calcination temperature (T&lt;sub&gt;cal&lt;/sub&gt;) = 600 &lt;sup&gt;o&lt;/sup&gt;C and it increased to ~1 μm when T cal increased up to 1200 &lt;sup&gt;o&lt;/sup&gt;C. &lt;i&gt;M&lt;/i&gt;-&lt;i&gt;H&lt;/i&gt; curves of the samples showed soft magnetic behaviors for all the crystallized samples, and the value of saturation magnetization increased with increasing &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;cal&lt;/sub&gt;. The real and imaginary parts of permittivities and permeabilities were measured on LSMO powder-epoxy (10 wt%) composites using a network vector analyzer in the frequency range of 100 MHz ≤ &lt;i&gt;f&lt;/i&gt; ≤ 18GHz. The complex permittivities (ε', ε") increased significantly in samples calcined above 800 &lt;sup&gt;o&lt;/sup&gt;C because the concentration of free electrons increased, due to the LSMO's unique magnetotransport effect, as the crystallinity and the &lt;i&gt;M&lt;/i&gt;&lt;sub&gt;S&lt;/sub&gt; value increased significantly. As the &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;cal&lt;/sub&gt; increased, the height of the μ' and μ" spectra also gradually increased. The large values of ε', ε" of the LSMO-epoxy are dominant factors in the EM wave absorption characteristics, and it showed good absorption characteristics when it had a thickness of 1.5 mm or less at a frequency of 12 GHz or higher. At the same time, it also exhibited EM wave shielding ability by reflection in the several GHz band.

Constructing FeCo@C core-shell structure with strong polarization behavior towards excellent microwave absorption performance

In this study, the electromagnetic wave absorption properties of derivatives of metal-organic frameworks (Prussian blue analogues) were investigated. Here, we use the co-precipitation method to combine metal ions (Mn2+, Ni2+, Co2+) with potassium ferricyanide to obtain cubic precursors. Subsequently, a series of carbon-coated bimetallic alloy absorbers with a core-shell structure were obtained by pyrolysis in a vacuum thermal environment. Moreover, the effect of temperature on the structure and electromagnetic absorption properties of FeCo@C was further explored. FeCo@C-600 achieves an effective bandwidth of 5.63 GHz at a thickness of 1.8 mm, and the minimum reflection loss is as high as −66.69 dB. Its best microwave absorption performance comes from the polarization sites provided by the abundant heterogeneous planes and defects, enabling it to obtain enhanced polarization loss. The final results show that the method of optimizing performance by enriching polarization methods can provide a new idea for obtaining high-efficiency absorbing materials with thin thickness and wide frequency coverage.

SiCN ceramics with controllable carbon nanomaterials for electromagnetic absorption performance

AbstractDifferent kinds of carbon nanomaterials, free carbon (Cfree), graphene, and N‐containing graphene (NG), in single‐source‐precursors‐derived SiCN ceramics, were in situ generated by modifying polysilazane with divinylbenzene, dopamine hydrochloride and melamine, respectively. Adjusting the carbon source brings phase structure and electromagnetic wave absorption (EMA) properties differences of SiCN/C ceramics. In situ Cfree enhances the EMA capacity of SiCN ceramics by improving their electrical conductivity of 9.2 × 10−4 S/cm. The electrical conductivity of SiCN ceramics with 2D graphene sheets balloons to 2.5 × 10−3 S/cm, causing poor impedance match thus leading to a worse EMA performance. In situ NG in SiCN ceramics has a low electrical conductivity of 5.6 × 10−8 S/cm, making for excellent impedance match. The corrugated NG boosts dielectric loss, interfacial, and dipole polarization. NG‐SiCN nanocomposites possess an outstanding EMA performance with RLmin of −61.08 dB and effective absorption bandwidth of 4.05 GHz, which are ∼2.4 times lower and ∼4 times higher than those of SiCN, respectively.

Nanoarchitectonics of SiC/multilayer graphene composite powders with wave absorbing properties

SiC/multilayer graphene composite powders and SiC nanopowders (SiCNPs) were successfully synthesized via a simple catalyst-assisted carbothermal reduction method using silicon dioxide and expanded graphite. The influences of the catalyst content, heat treatment temperature, and graphite/SiO2 molar ratio on the synthesis of powders were studied. The phase composition and their relative content, morphologies, chemical structures, and microstructures were detected using XRD, SEM, AFM, RAMAN, XPS, FTIR, BET, and TEM, respectively. Electromagnetic wave absorption properties of the products were studied at frequencies from 2 to 18 GHz. The results show that the introduction of Fe catalyst has a pronounced catalytic effect on the synthesis of 3 C-SiC powders. The formation temperature of 3 C-SiC is reduced to 1673 K with 0.5 wt% Fe addition as the catalyst. When the expanded graphite is appropriately excessive (the molar ratio of graphite/SiO2 is 3.5), multilayer graphene with a thickness of about 3.5 nm is formed in-situ in the composite powders. The 3 C-SiC/multilayer graphene composite powders exhibit the optimal electromagnetic wave absorption property. When the filling ratio of 3 C-SiC/multilayer graphene composite powders is 30 wt%, the minimum reflection loss reaches − 53.62 dB at a thickness of 2.04 mm and a frequency of 13.95 GHz. Graphene has a unique internal microstructure, high dielectric loss and good conductivity, which improve the impedance matching of the material and then increase the magnetic loss. It is predicted that the SiC/multilayer graphene composite powder has the potential to become an excellent electromagnetic wave absorber.

In situ construction of ZIF-67 derived Mo2C@cobalt/carbon composites toward excellent electromagnetic wave absorption properties

Electromagnetic wave (EM) absorption materials with multi-loss mechanisms and optimized impedance matching have attracted considerable attention as a means to combat the ever-increasing electromagnetic pollution. Molybdenum carbide (Mo2C) with outstanding environmental stability and high conductivity is becoming popular as EM absorption materials. Herein, the CoMoO4@ZIF-67 precursor was synthesized by an in situ sacrificial template method, followed by calcining to synthesize porous Mo2C@cobalt/carbon (Mo2C@Co/C) composites. The homogeneously dispersed Mo2C and Co nanoparticles as well as the porous structures resulted from the novel in situ fabrication strategy could generate abundant interfaces and induce effective multi-loss mechanisms including polarization loss, conductivity loss, magnetic loss, and so on. The as-prepared optimal composite (Mo2C@Co/C-10) demonstrates superior electromagnetic (EM) wave absorption performance with a maximum reflection loss value of −37.9 dB at the matching thickness of 2.3 mm, and the effective absorption bandwidth (EAB) of 5.52 GHz was realized at 1.9 mm. The excellent EM wave absorption properties can be attributed to the good impedance matching, synergistic effects among different loss mechanisms, multiple reflection and scattering. This work not only developed an effective ternary EM absorption materials of Mo2C@Co/C, but also propose a facile in situ strategy to fabricate more highly- dispersed mecarbide-basedased materials.

Synergistic utilization of porous coral sand and fly ash for multifunctional engineered cementitious composites with polyethylene fibers: Intensified electromagnetic wave absorption and mechanism

The large-scale consumption of industrial solid waste for fly ash is imperative for clean material production. Among these, abundant coral sand is a potential alternative to river silica sand in construction materials. This study proposes an environmentally friendly synergistic utilization of coral sand as a natural porous aggregate that can be incorporated with fly ash and polyethylene (PE) fibers to prepare multifunctional engineered cementitious composites (ECCs) with good electromagnetic (EM) wave absorption and mechanical properties. The effects of porous coral sand, PE fibers, and fly ash on the EM parameters, hydration products, pore distribution, microstructure, and reflection loss of the ECCs were systematically investigated. The mechanical properties and environmental impact were also examined. The results showed that the synergistic integration of porous coral sand, PE fibers, and fly ash optimized the pore distribution, attenuation paths, impedance matching, multiscattering effect, nanoscale effect, and interfacial polarization of the ECCs, which were conducive to the intensification of EM wave absorption. In particular, the appropriate use of natural coral sand as porous aggregates increased the EM wave absorption, while retaining the mechanical strength and excellent tensile properties of the ECCs. Environmental impact assessment showed that the alkalis of the prepared multifunctional ECCs were solidified in the C–S–H gels, which cannot be easily ionized, thereby inhibiting environmental pollution.

Enhanced electromagnetic wave absorption properties of ZIF-67 modified polymer-derived SiCN ceramics by in situ construction of multiple heterointerfaces

Enhanced electromagnetic wave absorption properties of ZIF-67 modified polymer-derived SiCN ceramics by in situ construction of multiple heterointerfaces

Fabrication of a flexible and efficient electromagnetic wave absorber based on reduced graphene oxide/Fe7Co3 filled into polydimethylsiloxane

A flexible and efficient reduced graphene oxide/Fe7Co3/polydimethylsiloxane (rGO/Fe7Co3/PDMS) composite electromagnetic wave (EMW) absorber was prepared by a fast and simple liquid reduction and subsequent liquid phase blend method. The introduction of rGO tunes the dielectric constant and dielectric loss of the composite absorber, and Fe7Co3 imparts magnetic loss characteristics to the material. The rheological properties of PDMS enable rGO/Fe7Co3 to be well dispersed within it, forming a homogeneous structure, which contributes to the synergistic effect of the components and improves the impedance matching conditions and attenuation capability of the composite absorber. It is worth noting that the EMW absorption properties of the composites can be effectively adjusted by changing the amount of rGO/Fe7Co3 added to the PDMS. When the amount of rGO/Fe7Co3 is 8.00 wt%, rGO/Fe7Co3/PDMS-8 shows superior EMW absorption property. The minimum reflection loss (RLmin) of − 52.58 dB at 1.80 mm, and the widest effective absorption bandwidth (EAB, RL≤−10 dB) can reach 6.40 GHz (11.40–18.00 GHz) at only 1.60 mm. Furthermore, the twist test shows that the RLmin and widest EAB of rGO/Fe7Co3/PDMS-8 remained at 92.64 % and 97.50 % of its initial values after 1500 twists, respectively, demonstrating its excellent flexibility. These results indicate that such rGO/Fe7Co3/PDMS-8 composite is very promising as a next generation flexible and efficient EMW absorbing material.

Preparation and electromagnetic wave absorption properties of PDC–SiC/Si3N4 composites using selective laser sintering and infiltration technology

Polymer-derived silicon carbide/silicon nitride (PDC–SiC/Si3N4) composites were prepared by additive manufacturing and infiltration technology. The composite green bodies were prepared using selective laser sintering (SLS) three-dimensional (3D) printing technology. Carbon-rich PDC–SiC was generated via precursor infiltration and pyrolysis (PIP) to increase the dielectric constant and enhance the electromagnetic wave (EMW) attenuation ability of the composites. Low-dielectric materials, including Al2O3, TiO2, and AlPO4, were introduced by sol infiltration to improve the impedance-matching characteristics of the composites. The results showed that the EMW absorption ability of the PDC–SiC/Si3N4 composites enhanced after two and four PIP cycles, whereas it degraded with further increasing the PIP cycle number. Among all the samples, the PDC–SiC/Si3N4 composite after four PIP cycles displayed an excellent EMW absorption ability with the minimal reflection loss of −46.79 dB, whereas its effective absorption bandwidth was narrow. Comparing to the sample without infiltration, the effective absorption bandwidth of the samples after the infiltration treatment with TiO2 or Al(H2PO4)3 sol increased from 1.44 GHz to 4.08 GHz and 3.52 GHz, respectively. These results demonstrate that the PIP process and infiltration with TiO2 or Al(H2PO4)3 sol resulted in a 3D-printed PDC–SiC/Si3N4 ceramic that is a promising EMW absorption material suitable for high-temperature environments.

Multiprincipal Element M2 FeC (M = Ti,V,Nb,Ta,Zr) MAX Phases with Synergistic Effect of Dielectric and Magnetic Loss.

Electromagnetic (EM) wave pollution is harmful to human health and environment, thus it is absolutely important to develop new electromagnetic wave absorbing materials. MAX phases have been attracted more attention as a potential candidate for electromagnetic wave absorbing materials due to their high conductivity and nanolaminated structure. Herein, two new magnetic MAX phases with multiprincipal elements ((Ti1/3 Nb1/3 Ta1/3 )2 FeC and (Ti0.2 V0.2 Nb0.2 Ta0.2 Zr0.2 )2 FeC) in which Fe atoms replace Al atoms in the A sites are successfully synthesized by an isomorphous replacement reaction of multiprincipal (Ti1/3 Nb1/3 Ta1/3 )2 AlC and (Ti0.2 V0.2 Nb0.2 Ta0.2 Zr0.2 )2 AlC MAX phases with Lewis acid salt (FeCl2 ). (Ti1/3 Nb1/3 Ta1/3 )2 FeC and (Ti0.2 V0.2 Nb0.2 Ta0.2 Zr0.2 )2 FeC exhibit ferromagnetic behavior, and the Curie temperature (Tc ) are 302 and 235 K, respectively. The dual electromagnetic absorption mechanisms that include dielectric and magnetic loss, which is realized in these multiprincipal MAX phases. The minimum reflection loss (RL) of (Ti1/3 Nb1/3 Ta1/3 )2 FeC is -44.4dB at 6.56GHz with 3mm thickness, and the effective bandwidth is 2.48GHz. Additionally, the electromagnetic wave absorption properties of the magnetic MAX phases indicate that magnetic loss also plays an important role besides dielectric loss. This work shows a promising composition-design strategy to develop MAX phases with good EM wave absorption performance via simultaneously regulating dielectric and magnetic loss together.

Study on electromagnetic wave absorption properties of graphene/FeSiAl/polylactic acid composites prepared by fused deposition modeling

Study on electromagnetic wave absorption properties of graphene/FeSiAl/polylactic acid composites prepared by fused deposition modeling

Synthesis and electromagnetic wave absorption performances of a novel (Mo0.25Cr0.25Ti0.25V0.25)3AlC2 high-entropy MAX phase

• A new two-step solid state reaction process was proposed to synthesize single-phase high-entropy MAX phases. • A novel (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 high-entropy MAX phase was successfully prepared. Investigations on electromagnetic (EM) wave absorption properties and effects of oxidation on EM wave absorption performances of (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 were conducted for the first time. • (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders exhibit excellent EM wave absorption properties, whose minimum reflection loss value can reach -45.80 dB (at 1.7 mm thickness) and maximum effective absorption bandwidth is 3.60 GHz (at 1.5 mm thickness). • After oxidation at 400-800°C, (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 can retain good EM wave absorption properties in a certain frequency range. Herein, a novel kind of high-entropy MAX phases, (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders were successfully synthesized by a newly proposed two-step solid state reaction process. The oxidation experiments demonstrate that the oxidation products of Al 2 Mo 3 O 12 and rutile TiO 2 are formed at about 600 and 800 ℃, respectively. Besides, the dielectric and electromagnetic (EM) wave absorption properties of (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders and those after oxidation at different temperatures were also examined. The results show that the as-synthesized (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders possess excellent EM wave absorption performances with the minimum reflection loss ( RL ) of -45.80 dB (at 1.7 mm thickness) and the maximum effective absorption bandwidth ( E AB ) of 3.6 GHz (at 1.5 mm thickness). After oxidation at 400-800 ℃, due to the coupling of conductivity loss and polarization loss, (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25 ) 3 AlC 2 powders can retain good EM wave absorption properties in a certain frequency range. In this paper, the effects of oxidation on EM wave absorption properties of high-entropy MAX phases were systematically investigated for the first time. This work manifests that high-entropy MAX phases are promising EM wave absorbing candidates and can maintain good EM wave absorption performances after oxidation.

Constructing a two-layer oblique honeycomb sandwich structure by LCD 3D printing for efficient electromagnetic wave absorbing

• A kind of two-layer oblique honeycomb sandwich structure of flaky carbonyl iron powder (FCIP)/photosensitive resin (PR) composites with high precision was prepared by liquid crystal display (LCD) 3D printing method. • The two-layer oblique honeycomb sandwich structure is beneficial to improve the microwave absorption strength, and has the characteristics of light weight and low material consumption. • LCD 3D printing technology has the advantages of high precision, free forming and less time consumption. Carbonyl iron powder (CIP) is one of the most widely used magnetic loss absorbents due to its high saturation magnetization, strong wave absorption performance and low cost. However, CIP has a very high density (7.86g/cm 2 ) and requires a high addition amount (more than 50wt%) when used as a microwave absorbing filler, which leads to high weight and low mechanical properties of the composite. Taking the diverse attenuation mechanisms during the electromagnetic energy conversion process into considerations, this paper designs a two-layer oblique honeycomb sandwich structure, which was prepared by liquid crystal display (LCD) 3D printing. This structure combines porous structure with strong absorbing materials to achieve strong electromagnetic wave (EMW) absorption performance at low concentrations and improve mechanical properties. When the inclined honeycomb core angle is 15° with only 15wt% FCIP addition, the EMW absorption and mechanical properties of the composite are significantly improved compared with the full-filled structure.