Good Electromagnetic Wave Absorption Properties Research Articles

The Effect of Synthetic and Commercial Nano-Magnetite on the Electromagnetic Absorbance Behavior of Magnetic Wood

Magnetic wood with good electromagnetic wave absorption properties was prepared by comparing synthetic and commercial nano-magnetite (Fe3O4-NP) as sengon (Falcataria moluccana) wood impregnation solution. The co-precipitation method produced a synthetic nano-magnetite with NH4OH as a weak base precursor. Meanwhile, the commercial one was purchased from a supplier. Three levels of nano-magnetite concentration (1%, 2.5%, and 5%) were dispersed in deionized water. The impregnation process was done by applying a vacuum of 0.5 bar for 120 minutes, followed by a pressure of 1 bar for 120 minutes. The results showed that the commercial nano-magnetite caused more improvements in weight percent gain, density, and hardness than the synthetic nano-magnetic, although they were insignificantly different. There was also a reduction in brightness with the overall color change being categorized into other colors because the color became darker with increasing nano-magnetite concentration in both woods. The absorbance capacity of the synthetic nano-magnetite-treated wood was larger than the commercial nano-magnetite-treated wood. This synthetic nano-magnetite-treated wood had been optimally treated at a 5% concentration, making it suitable for use as electromagnetic wave shielding material because it can absorb almost 100% electromagnetic waves. Keywords: Fe3O4, impregnation, nano-magnetite, sengon wood, shielding materials

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.

One-step synthesis and electromagnetic absorption properties of high entropy rare earth hexaborides (HE REB6) and high entropy rare earth hexaborides/borates (HE REB6/HE REBO3) composite powders

Considering the emergence of severe electromagnetic interference problems, it is vital to develop electromagnetic (EM) wave absorbing materials with high dielectric, magnetic loss and optimized impedance matching. However, realizing the synergistic dielectric and magnetic losses in a single phase material is still a challenge. Herein, high entropy (HE) rare earth hexaborides (REB6) powders with coupling of dielectric and magnetic losses were designed and successfully synthesized through a facial one-step boron carbide reduction method, and the effects of high entropy borates intermedia phases on the EM wave absorption properties were investigated. Five HE REB6 ceramics including (Ce0.2Y0.2Sm0.2Er0.2Yb0.2)B6, (Ce0.2Eu0.2Sm0.2Er0.2Yb0.2)B6, (Ce0.2Y0.2Eu0.2Er0.2Yb0.2)B6, (Ce0.2Y0.2Sm0.2 Eu0.2Yb0.2)B6, and (Nd0.2Y0.2Sm0.2Eu0.2 Yb0.2)B6 possess CsCl-type cubic crystal structure, and their theoretical densities range from 4.84 to 5.25 g/cm3. (Ce0.2Y0.2Sm0.2Er0.2 Yb0.2)B6 powders with the average particle size of 1.86 µm were found to possess the best EM wave absorption properties among these hexaborides. The RLmin value of (Ce0.2Y0.2Sm0.2Er0.2Yb0.2)B6 reaches −33.4 dB at 11.5 GHz at thickness of 2 mm; meanwhile, the optimized effective absorption bandwidth (EAB) is 3.9 GHz from 13.6 to 17.5 GHz with a thickness of 1.5 mm. The introduction of HE REBO3 (RE = Ce, Y, Sm, Eu, Er, Yb) as intermediate phase will give rise to the mismatching impedance, which will further lead to the reduction of reflection loss. Intriguingly, the HEREB6/HEREBO3 still possess wide effective absorption bandwidth of 4.1 GHz with the relative low thickness of 1.7 mm. Considering the better stability, low density, and good EM wave absorption properties, HE REB6 ceramics are promising as a new type of EM wave absorbing materials.

Imprinted adsorption of 4,4′-diaminodiphenyl ether under charge

In order to improve the electrochemical synthesis efficiency and enhance the electromagnetic wave absorption properties of 4,4′-diaminodiphenyl ether molecularly imprinted polymer (4,4′-ODL-MIP) composite poly 4,4′-diaminodiphenyl ether (P-4,4′-ODL) (4,4′-ODL-MIP-P-4,4′-ODL), it is very important to investigate the mechanism of 4,4′-ODL imprinted adsorption by its MIP, which is involved to the process of the second electropolymerization of composite 4,4′-ODL-MIP-P-4,4′-ODL. The amount of charge carried by 4,4′-ODL-MIP-P-4,4′-ODL,closely relating to its electromagnetic wave absorption, can be conducted to be the amount of adsorption in this paper. At the temperature of 298 K, Langmuir, Brunauer-Emmett-Teller (BET), Freundlich, D-R,Temkin and Henry adsorption models were fitted by the charge of composite.The fitting data showed that the three isothermal adsorption models of Langmuir, Dubinin-Radushkevich and Henry were more suitable for simulating the imprinted adsorption of 4,4′-ODL-MIP on 4,4′-ODL in solution during the second electropolymerization. Meanwhile, the results of the four adsorption kinetic rate equations fitted by charge (quasi-first-order, quasi-second-order, Elovich and intragranular diffusion) exhibited that 4,4′-ODL-MIP adsorption 4,4′-ODL was followed the quasi-first-order, while its rate was controlled by the liquid film and intra-particle diffusion. Also, in the temperature range from 273.15 to 313.15 K, the thermaldynamic parameters estimated by charge of this imprinted adsorption showed that Δ<italic>H</italic> and Δ<italic>S</italic> were both larger than zero, while Δ<italic>G</italic> was less than zero. This indicated that the above spontaneously imprinted adsorption was an endothermic process, while its disorder increased at the same time. Therefore, this imprinted adsorption was advantage to perform the second electropolymerization fastly, to safeguard the good electromagnetic wave absorption properties of the composite.

Electromagnetic wave absorption and mechanical properties of silicon carbide fibers reinforced silicon nitride matrix composites

It is difficult for ceramic matrix composites to combine good electromagnetic wave (EMW) absorption properties (reflection coefficient, RC less than -7 dB in X band) and good mechanical properties (flexural strength more than 300 MPa and fracture toughness more than 10 M P·m1/2). To solve this problem, two kinds of wave-absorbing SiC fibers reinforced Si3N4 matrix composites (SiCf/Si3N4) were designed and fabricated via chemical vapor infiltration technique. Effects of conductivity on EM wave absorbing properties and fiber/matrix bonding strength on mechanical properties were studied. The SiCf/Si3N4 composite, having a relatively low conductivity (its conduction loss is about 33% of the total dielectric loss) has good EMW absorption properties, i.e. a relative complex permittivity of about 9.2-j6.4 at 10 GHz and an RC lower than −7.2 dB in the whole X band. Its low relative complex permittivity matches impedances between composites and air better, and its strong polarization relaxation loss ability help it to absorb more EM wave energy. Moreover, with a suitably strong fiber/matrix bonding strength, the composite can transfer load more effectively from matrix to fibers, resulting in a higher flexural strength (380 MPa) and fracture toughness (12.9 MPa▪m1/2).

Fabrication and microwave absorption properties of carbon-coated cementite nanocapsules

By utilizing a simple and low-cost arc-discharge method in either liquid nitrogen or ethanol at ambient temperature and pressure, carbon-coated cementite (Fe3C) nanocapsules, with size ranges of 10–60 nm and 10–20 nm, respectively, have been synthesized on a large scale. The Fe3C/C nanocapsules synthesized in different media possess similar permeability but different permittivity, which results from the different defect amounts within the carbon shell. It has been found that the as-prepared products exhibit different electromagnetic wave absorption abilities: for the ones prepared in liquid nitrogen, the optimal reflection loss is above −10 dB in the range of 1–18 GHz with the thickness ranging from 1 to 10 mm; meanwhile, for those fabricated in ethanol, the reflection loss could be below −20 dB within the thickness range of 1.5–2.4 mm in the frequency range of 10–15 GHz, and reach −38 dB at a thickness of 1.9 mm with a matching frequency of 12.9 GHz. This indicates that the nanocapsules prepared in ethanol exhibit good electromagnetic wave absorption properties. These results provide a new way to fabricate carbon-coated Fe3C nanocapsules with the ability of electromagnetic wave absorption.

Novel rare earth recovery process on Nd–Fe–B magnet scrap by selective chlorination using NH 4Cl

Extraction of rare earth elements from the Nd–Fe–B magnet scraps through the chlorination with NH 4Cl was performed to study the effective process for reusing metal iron as well as rare earths. The Nd 2Fe 14B primary phase was selectively converted to NdCl 3 in ca. 90% yield, together with α-Fe and Fe–B solid residues by chlorinating at 573 K for 3 h. The resin compacts prepared from the resultant solid residues mainly composed of the α-Fe phase provided the good electromagnetic wave absorption properties.

Electromagnetic wave absorption properties of nanocomposite powders derived from intermetallic compounds and amorphous carbon

Nanocomposite materials consisting of Y 2Fe 17 and amorphous carbon (a-C) were prepared by a mechanical grinding method. Mean crystalline size of the Y 2Fe 17 particles in the nanocomposite materials was evaluated to be 20 nm from the line broadening of diffraction peaks. Complex permittivity, permeability and electromagnetic wave absorption properties of resin compact containing 75 wt.% Y 2Fe 17/a-C powders showed the good electromagnetic wave absorption properties of the minimum reflection loss (RL) value of – 48 dB at 17 GHz with a matching thickness of a 1.3 mm because the eddy current loss was effectively suppressed by increasing the electric resistance for Y 2Fe 17 particle with hybridization with a-C as an insulator.

Electromagnetic wave absorption properties of Fe 1− xCo x/Y 2O 3 ( x = 0.33, 0.5, 0.67) nanocomposites in gigahertz range

The electromagnetic wave absorption properties of Fe 1− x Co x /Y 2O 3 ( x = 0.33, 0.5, 0.67) nanocomposites were characterized in a frequency range of 0.05–20.05 GHz. The real part ( ε ′ r ) and imaginary part ( ε ″ r ) of relative permittivity almost kept at low constant in 0.05–12 GHz. The imaginary part of relative permeability ( μ ″ r ) exhibited a wide peak over 0.5–12 GHz range, in which the μ ″ r value pertained still high. Compared with α-Fe/Y 2O 3 composites, the natural resonance frequency ( f r) of Fe 1− x Co x /Y 2O 3 shifted to the higher frequency range due to the larger magnetic anisotropy of Fe 1− x Co x nanoparticles. As a result, the resin composites with 80 wt.% Fe 1− x Co x /Y 2O 3 powders exhibited good electromagnetic wave absorption properties (RL < −20 dB) in the frequency range of 1.9–9.7 GHz, with thickness of 2.0–7.4 mm, respectively.

Complex permittivity, permeability and electromagnetic wave absorption of α-Fe/C(amorphous) and Fe2B/C(amorphous) nanocomposites

The complex permittivity, permeability and electromagnetic (EM) wave absorption properties have been investigated for resin compacts containing 75 wt% composite powders of α-Fe/C(a) and Fe2B/C(a). The real and imaginary parts ( and εr′) of relative permittivity for the resin composites remained almost constant in the 0.05–20.05 GHz range. The imaginary part of the relative permeability (μr′) exhibited a wide peak in the 1–9 GHz range for α-Fe/C(a) and in the 2–18 GHz range for Fe2B/C(a). Both resin composites exhibited good EM wave absorption properties (RL < −20 dB) in the 4.4–8.3 GHz range with an absorber thickness of 1.9–3.4 mm, and in the 7.5–16 GHz range for an absorber thickness of 1.2–2.2 mm, respectively.

GHz Range Absorption Properties of α-Fe/Y2O3 Nanocomposites Prepared by Melt-spun Technique

Abstract Nanocomposite materials of α-Fe/Y2O3 prepared by melt-spun technique exhibited good electromagnetic wave absorption properties (RL&amp;lt;−20 dB) in a 2.0-3.5 GHz range as absorbers with thickness ranging from 3 to 5 mm, and a minimum reflection loss of −36 dB was obtained at 2.6 GHz with an absorber thickness of 4 mm.

GHz microwave absorption of a fine α-Fe structure produced by the disproportionation of Sm 2Fe 17 in hydrogen

In this study, the possibility of using the disproportionation reaction of the Sm 2Fe 17 compound for the production of powders with a fine α-Fe structure was investigated, for use as electromagnetic wave absorbers that can operate in the GHz frequency range. A fine α-Fe/SmH 2 or α-Fe/SmO structure with a sub-micrometer size is formed from the Sm 2Fe 17 compound after disproportionation in hydrogen or air, respectively. In this way, magnetic powders with a fine structure of α-Fe were obtained. The powders disproportionated in hydrogen, were heated in air in order to oxidize the Sm hydride, to give a α-Fe/SmO two-phase microstructure, and thereby increase the resistivity of the powders. Toroidally shaped epoxy-resin composites were made from this powder, and the microwave absorption properties of these samples were measured. An undisproportionated sample did not show any electromagnetic wave absorption in this frequency range. However, the disproportionated samples (heated in hydrogen at 873 K for 1 h, milled for 30 min and oxidized at 473 K for 2 h in air) exhibited electromagnetic wave absorption (RL<−20 dB) in the frequency ( f m) range 0.73–1.30 GHz, for absorber thicknesses ( d m) ranging from 13.1 to 7.9 mm, respectively. The disproportionated samples in air (heated at 473 K for 2 h and milled for 30 min) also showed good electromagnetic wave absorption properties ( f m=1.21–2.50 GHz and d m=8.0–4.2 mm). It is concluded that the disproportionation reaction, in either hydrogen or in air, is a useful method for the production of powders with a fine α-Fe structure, which can be used for microwave absorbers that operate in the several GHz range.

Effect of Crystal Orientation on the Magnetic Resonance Properties of M-Type Hexagonal Ferrites

This paper describes the effect of crystal orientation on the electromagnetic wave absorption properties of barium M-type (Ba-M) ferrite, in which Fe3+ was substituted by (Ti0.5Mn0.5)3+. The BaFe9(Ti0.5Mn0.5)3O19 sintered samples were prepared by a conventional powder metallurgy technique, in which and the c-axes of the powder particles were aligned in a magnetic field during compaction. After sintering, toroidally shaped samples were formed whose c-axes were aligned at certain angles (θ) to the sample thickness (d), and their microwave absorption properties were investigated in the GHz frequency range. It was found that the maximum values of the complex permeability (μr=μr′−jμr″) increased with decreasing θ. The θ=0° sample exhibited the highest μr″ value, which resulted in the smallest matching thickness (dm) of 0.57 mm with a reflection loss (R.L.) less than −20 dB at 12.05 GHz. In addition, increasing the sintering time had the effect of increasing μr″; reaching a μr″ value of 6.0 after sintering for 100 h. As a result, the matching thickness decreased from 0.72 to 0.51 mm, which is 30% smaller than for an isotropic sample sintered for 10 h. Therefore, it is concluded that the degree of crystallographic alignment of the sample and the sintering time used are both important factors in obtaining good electromagnetic wave absorption properties with a smaller matching thickness, in Ba M-type microwave absorbers.