Controlled synthesis of Fe3O4@SnO2/RGO nanocomposite for microwave absorption enhancement

A ternary nanocomposite of Fe₃O₄@SnO₂/reduced graphene oxide (RGO) with different contents of SnO₂ nanoparticles was synthesized by a simple and efficient three-step method. The transmission electron microscopy and field emission scanning electron microscopy characterization display that plenty of Fe₃O₄@SnO₂ core–shell structure nanoparticles are well distributed on the surface of RGO sheets. The X-ray diffractograms show that the products consist of highly crystallized cubic Fe₃O₄, tetragonal SnO₂ and disorderedly stacked RGO sheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the products at room temperature. The microwave absorption properties of paraffin containing 50 wt% products were investigated at room temperature in the frequency range of 2–18 GHz by a vector network analyzer. The electromagnetic data show that the maximum reflection loss is −45.5 dB and −29.5 dB for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. Meanwhile, the reflection loss less than −10 dB is up to 14.4 GHz and 13.8 GHz for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. It is believed that such nanocomposite could be used as promising microwave absorbers.     

Effect of various dielectric and magnetic nanofillers on microwave absorption properties of carbon fiber reinforced composites structures

Carbon fiber reinforced unidirectional composite (CFRC) structures were developed by impregnating various dielectric and magnetic nanofillers at a 2% loading concentration of the weight of the matrix. Microwave absorption properties were studied in a broad frequency range of 0.1–13.6 GHz covering the L, S, C, and X frequency ranges. The variation of radar absorption properties with frequency were studied in detail. The effect of dielectric and magnetic materials on microwave absorption properties was also investigated. The results shows that the microwave absorption properties increases with increasing the measuring frequency and maximum absorption was at X frequency range (8.2–12.4 GHz). The Dielectric nanoparticles showed better absorption properties compared with magnetic nanoparticles. Among dielectric nanoparticles, silicon carbide showed maximum reflection loss properties of ?15.32 dB with an absorptance value of 97.06%. Among magnetic nanoparticles, ferric oxide showed a maximum reflection loss of ?9.14 dB with an absorptance value of 87.81%. The addition of nanoparticles significantly improved the complex permittivity, permeability, and loss tangent properties.     

One-step synthesis of Fe nanoparticles wrapped in N-doped carbon nanohorn microspheres as high-performance electromagnetic wave absorber

Designing cost-effective and eco-friendly electromagnetic absorbing materials is important for their widespread practical applications. Herein, Fe nanoparticles wrapped in carbon nanohorn microspheres enriched with N (Fe@NCNHs) were produced by a simple one-step method, which is a nonequilibrium strategy that involves evaporating a graphite anode and Fe wire in an arc plasma. The total pore volume for CNHs was calculated to be 0.38 cm³ g^?1, corresponding to its naturally inherited micropore and mesopore-dominate porosity. In addition, the N-doping content reached up to 9.3 at%. The electromagnetic wave-absorption performance of Fe@NCNHs can be controlled using the size and loading amount of Fe nanoparticles wrapped in CNHs, depending on the number of Fe wires inserted into the anode. When two Fe wires are inserted into the anode, Fe nanoparticles with uniform size are well wrapped in CNHs, exhibiting excellent electromagnetic wave absorption property with a minimum reflection loss (RL) of ?44.52 dB at 10.86 GHz matching an extremely low thickness of 1.6 mm at X band. The effective absorption bandwidth (RL < ?10 dB) was up to 13.86 GHz, and the matching thickness ranged between 1.2 and 5.0 mm. The results obtained in this study indicate that Fe@NCNHs are promising microwave-absorbing materials with enhanced dielectric loss and good impedance matching, which is attributed to the multiple reflections induced by the hollow structure of CNHs, interfacial polarization between the CNHs and Fe nanoparticles, dipole polarization induced by N-doping, and pentagonal and hexagonal defects on CNHs.     

Effects of Sr doping on the structure,magnetic properties and microwave absorption properties of LaFeO3 nanoparticles

Lightweight, broadband microwave absorbing materials, with strong absorption capacities, are an urgent demand for practical applications. The microstructural and microwave absorption properties of LaFeO₃ samples prepared by a sol-gel method using different amounts of Sr are investigated systematically. X-ray diffraction and Rietveld refinement studies showed that Sr²⁺ doping can distort the crystal structure of LaFeO₃, leading to lattice expansion and spin tilt of the Fe-O-Fe bond angle. The improvement of magnetic properties mainly originates from the synergistic effect of the bond angle spin tilt and crystal structure defects. Oxygen vacancies will be generated due to the fluctuations in the valence state of Fe³⁺ resulting from the substitution of La³⁺ by Sr²⁺ as deduced from the X-ray photoelectron spectroscopy analysis. The generation of oxygen vacancies, electronic hopping and polarization loss may be one of the main reasons for changes in the electromagnetic parameters. The minimum reflection loss (RL) of La_1–xSr_xFeO₃ nanoparticles with the Sr doping of 0.2 can reach approximately -39.3 dB at 10 GHz for the thickness of 2.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) can reach approximately 2.56 GHz. In addition, the La_1–xSr_xFeO₃ nanoparticles also can obtain better microwave absorbing performance in the C-band (4–8 GHz) with the minimum RL of -36.8 dB for the matching thickness of 3.0 mm and Sr content of 0.3. Consequently, La_1–xSr_xFeO₃ nanoparticles are promising materials for use in a high-performance and adjustable electromagnetic wave absorber, particularly in C-band and X-band.     

Magnetic and microwave properties of BaFe12O19 substituted with magnetic,non-magnetic and dielectric ions

Barium hexaferrite particles were synthesized with conventional solid state reaction route. 1% boron (B₂O₃) was added to the initial mixture of oxides to inhibit crystal growth at lower temperatures. Magnetic (Mn²⁺, Co²⁺, Ni²⁺and Cu²⁺), non-magnetic (Zn²⁺) and dielectric (Ti⁴⁺) ions were replaced by one Fe³⁺ ion of barium hexaferrite to shift the ferromagnetic resonance frequency to low frequencies and to increase the magnetic and dielectric losses. The structural and morphological characterization of samples was done by X-ray powder diffractometer and scanning electron microscopy. Magnetic and microwave properties were determined by vibrating sample magnetometer and vector network analyzer, respectively. The maximum saturation magnetization and the highest reflection losses of −34 dB at 10 GHz, with absoption bandwidth of 1.6 GHz at −20 dB, were observed in Cu²⁺–Ti⁴⁺ and Zn²⁺–Ti⁴⁺ substituted samples. The mechanism of microwave energy dissipation is due to the impedance matching at matching thickness. It was also observed that as the sample thickness increases, the resonance frequency decreases exponentially.     

Targeted design of polyaniline-graphene oxide,barium-strontium titanate,hard-soft ferrite,and polyester multi-phase nanocomposite for highly efficient microwave absorption

The current paper focuses on synthesizing a high-efficiency microwave absorber via incorporating the nanofillers of graphene oxide-polyaniline (GO-PANI), barium-strontium titanate (BST), and soft-hard ferrite within the polyester matrix. The nanocomposite magnets of (Ba_0.5Sr_0.5Fe₁₂O₁₉)_1-x hard/(CoFe₂O₄)_x soft (x = 0.2, 0.5, and 0.8) were prepared using sol-gel auto-combustion method. The GO-PANI and BST were successfully synthesized by in situ polymerization and improved polymerization, respectively. The phase structure, chemical structure, morphology, and microwave absorption properties of the synthesized nanocomposites were characterized by X-ray diffractometer (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM), vector network analyzer (VNA) techniques, respectively. The results showed that the synergistic effects of the combination of dielectric (BST), conductive (GO-PANI), and magnetic materials (hard-soft ferrites) provided the reflection loss values of less than ?20 dB (>99% absorption) in the X-band region. The minimum reflection loss of ?35 dB (>99.99% absorption) was obtained by the optimal formulation including (Ba_0.5Sr_0.5Fe₁₂O₁₉)_0.2 (CoFe₂O₄)_0.8, and the weight ratio of 1: 2 for both BST/soft-hard ferrite and hard-soft ferrite + BST/GO-PANI with the thickness of 1 mm. According to the results, the thickness factor plays a key role in improving the impedance matching. Consequently, the proposed nanocomposite can be employed as a novel kind of microwave absorbers with good impendence matching and high absorption.     

Confined tailoring of CoFe2O4/MWCNTs hybrid-architectures to tune electromagnetic parameters and microwave absorption with broadened bandwidth

Multi-walled carbon nanotubes (MWCNTs) are highly alluring as an electromagnetic (EM) wave absorber owing to their multi-dimensional structure, high chemical stability, low density, and significant conduction loss, which provide great promises as an excellent EM wave absorber in practical applications. Herein, a simple and controllable solvothermal technique is applied to synthesize cobalt ferrite/MWCNTs (CoFe₂O₄/MWCNTs) hybrid composite. Various analytical techniques were used to investigate the composition, morphological structure, and electromagnetic parameters of the as-prepared hybrid composite. The obtained results revealed that, a strong network of CoFe₂O₄ microspheres interweaved with MWCNTs in the prepared hybrid composite. The resultant CoFe₂O₄/MWCNTs composites achieve a minimum reflection loss (RL_min) of ?50.80 dB at a thickness of 4.2 mm and effective absorption bandwidth (EAB) of 3.36 GHz at a thickness of 1.6 mm exhibiting the superior RL_min compared to the typical magnetic composite derived absorbers. This research advocates the precise development and designing of unique MWCNTs-based composites as a high-efficient and lightweight electromagnetic wave absorber.     

Structural,dielectric and magnetic manifestation in BaM/PEEK nanocomposite for X band shielding blocks

The microwave absorber nanocomposites consisting of substituted M-type hexaferrite Ba_0.8Gd_0.2Fe_11.5Co_0.5O₁₉ and polyetheretherketone (PEEK) have been investigated for X-band applications. Composites with hexaferrite to PEEK ratios 5:0, 4:1, 3:2, 2:3, 1:4, 0:5 have been synthesized by a micro-emulsion method. XRD results confirm the hexagonal structure of the hexaferrite with average crystallite size up to 37.2 nm. Magnetic properties reveal that saturation magnetization M_s increases whereas coercivity H_c decreases by increasing the ferrite content in the composites. Complex permittivity and permeability have been tailored with ferrite content in the X-band. The dielectric constant reduces from 5.3 to 3.25 while permeability increases up to 1.37 with increasing ferrite concentrations. The microwave results show the minimum reflection loss of ?10.79 dB for composite with 80% ferrite.     

Investigation of structural,magnetic and dielectric properties of SrM/PEEK: A potential microwave absorber

The current study aims to investigate the effect of Polyether Ether Ketone (PEEK) on the structural, magnetic, and microwave properties of substituted M-type SrFe_11.5Co_0.5O₁₂ (SrM) hexaferrite. Nanocomposites based on SrM/PEEK in ratios 4:0, 3:1, 2:2, and 0:4 were prepared by employing the micro-emulsion method. The composites were further characterized using XRD, SEM, FTIR, and VNA. XRD results exhibited a single-phase hexaferrite structure with an average crystallite size of 40 nm for pure SrM, which decreased due to increasing PEEK concentration. FESEM micrographs revealed the surface morphology and nature of the grains in the prepared nanocomposites. EDAX plots showed the presence of the constituent elements e.g., Fe, Sr, C, and O, at the respective standard energies. VSM results revealed the diamagnetic and ferromagnetic nature of PEEK and pure SrM/nanocomposite samples, respectively. FTIR spectra of SrM depicted the formation of hexaferrite due to the presence of Fe–O stretching peak at 525 cm^?1. Reflection loss was found to decrease due to increasing ferrite concentration in PEEK. This indicates that SrM/PEEK composites are potential microwave absorbers for microwave applications in the X band.     

铜铁尾矿制酸烧渣制备纳米Fe/SiO2核壳复合粒子的微波吸收性能

以铜铁尾矿制酸烧渣为原料,经熟化、酸浸、还原和净化等步骤制备亚铁离子;在乙醇-水液相体系中,以NaBH₄作为还原剂,反应生成纳米Fe粒子;最后通过正硅酸四已酯（TEOS）水解包覆制得纳米Fe/SiO₂核壳复合粒子。产物分别采用XRD、TEM、IR等手段进行表征。进一步地,使用矢量网络分析仪在2.0 ~ 18.0 GHz波段内来研究样品的吸波性能。结果表明,IR光谱上在1389 cm^-1和878 cm^-1分别出现对应于四配位Si—O键和Si—O—Fe键的特征吸收峰,说明在Fe粒子表面包覆有SiO₂。通过测试计算得知,当吸波样品厚度为4.5 mm时,其微波吸收性能在17.2 GHz处达到最小值-39.0 dB。由此可见,以铜铁尾矿制酸烧渣为原料,可制得吸波性能优良的纳米Fe/SiO₂核壳复合粒子微波吸收材料。     

Enhanced electromagnetic microwave absorption of Fe/C/SiCN composite ceramics targeting in integrated structure and function

The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics.     

Synthesis of multi-walled carbon nanotube/doped barium hexaferrite nanocomposites: An investigation of structural,magnetic and microwave absorption properties

Nanocomposite BaCu_xMg_xZr_2xFe_12−4xO₁₉/MWCNTs with different substitutions (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) was synthesized using a two stage chemical route. The reported structural, magnetic and microwave absorption properties of samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM) and vector network analysis (VNA). Results showed that the doped hexaferrite nanoparticles and BaCu_xMg_xZr_2xFe_12−4xO₁₉/MWCNTs nanocomposites were synthesized successfully in all samples. The SEM and TEM micrographs proved that the MWCNTs structure was not destroyed after the acid treatment process while the nanoparticles could be absorbed on the surface of MWCNTs as a layer. The evaluation of VSM analysis also proved the maximum magnetization increase at first, and then decreased on the further increase of the dopant content. The values of coercivity varied in the range of 4689–251 (G). The values of real and imaginary parts of the permittivity of the BaM samples (x=0.0–0.5) with MWCNT was much higher than those of the BaM samples without MWCNT. It was also found that the highly doped sample (x=0.5)/MWCNT had a minimum reflection loss value of –23.1 dB with a suitable bandwidth about 6 GHz at a matching thickness of 2.1 mm. In addition, the reflection loss proved to be dependent on the absorber thickness; while with increasing the thickness of absorbers, the resonance frequencies shifted to a lower regime.     

铜铁尾矿制酸烧渣制备纳米Fe/SiO2核壳复合粒子的微波吸收性能

以铜铁尾矿制酸烧渣为原料,经熟化、酸浸、还原和净化等步骤制备亚铁离子;在乙醇-水液相体系中,以NaBH₄作为还原剂,反应生成纳米Fe粒子;最后通过正硅酸四已酯（TEOS）水解包覆制得纳米Fe/SiO₂核壳复合粒子。产物分别采用XRD、TEM、IR等手段进行表征。进一步地,使用矢量网络分析仪在2.0 ~ 18.0 GHz波段内来研究样品的吸波性能。结果表明,IR光谱上在1389 cm^-1和878 cm^-1分别出现对应于四配位Si—O键和Si—O—Fe键的特征吸收峰,说明在Fe粒子表面包覆有SiO₂。通过测试计算得知,当吸波样品厚度为4.5 mm时,其微波吸收性能在17.2 GHz处达到最小值-39.0 dB。由此可见,以铜铁尾矿制酸烧渣为原料,可制得吸波性能优良的纳米Fe/SiO₂核壳复合粒子微波吸收材料。     

A sonochemical method for synthesis of Fe3O4 nanoparticles and thermal stable PVA-based magnetic nanocomposite

Fe₃O₄ nanoparticles were synthesized via a simple surfactant-free sonochemical reaction. Room temperature synthesis without using inert atmosphere is the novelty of this work. The effect of different parameters on the morphology of the products was investigated. The magnetic properties of the samples were also investigated using an alternating gradient force magnetometer. Fe₃O₄ nanoparticles exhibit a ferromagnetic behavior with a saturation magnetization of 66 emu/g and a coercivity of 39 Oe at room temperature. For preparation magnetic nanocomposite, Fe₃O₄ nanoparticles were added to the polyvinyl alcohol (PVA). Nanoparticles can enhance the thermal stability and flame retardant property of the PVA matrix.     

XRD,HRTEM, magnetic,dielectric and enhanced microwave reflection loss of GaFeO3 nanoparticles encapsulated in multi-walled carbon nanotubes

Nanoparticles of GaFeO₃ are prepared by a sol–gel method where ultrasonication is used to reduce the distribution of sizes and agglomeration among nanoparticles. To obtain the well crystallographic phase, the as prepared sample is annealed at 800 °C for 6 h. To explore the applications in the field of microwave devices, multiferroic nanoparticles of GaFeO₃ are incorporated in multi-walled carbon nanotubes (MW-CNTs). The formations of the desired crystallographic phases of both the bare and encapsulated samples are confirmed by X-ray diffractograms. Results of high resolution transmission electron microscopy of the coated sample confirm the encapsulation of nanoparticles of GaFeO₃ in the matrix of MW-CNTs. Raman spectra are recorded at room temperature and the observed spectra are analyzed to extract different informations like the presence of any impurity, position of different Raman active modes, shift of Raman peak etc. of the sample. The reflection loss of the bare and coated samples in the X and K_u bands of microwave regions (8–12 GHz and 12–18 GHz) are measured and interestingly, the microwave reflection loss is significantly enhanced due to encapsulation of GaFeO₃ by MW-CNTs. This enhancement will improve the quality of applications of GaFeO₃ in microwave devices.     

Role of exchange coupling between the hard and soft magnetic phases on the absorption of microwaves by SrFe10Al2O19/Co0.6Zn0.4Fe2O4 nanocomposite

(1-x)SrFe₁₀Al₂O₁₉/(x)Co_0.6Zn_0.4Fe₂O₄-(SFAO/CZFO) hard/soft nanocomposite ferrite materials were synthesized by ‘one-pot’ self-propagating combustion route. The co-existence of the two magnetic phases were confirmed by XRD, FESEM, EDS and VSM. The prepared nanocomposite samples were also characterized by TGA/DSC, Raman spectroscopy and VNA. Exchange coupling between the hard and the soft magnetic grains was observed by determining the switching field distribution (SFD) curve. As a result of the competing effects of exchange interaction and dipolar interaction, magnetic parameters were observed to be sensitive to the incorporation of soft magnetic phase into the nanocomposite. Results showed that with the inclusion of soft magnetic phase, exchange coupling behaviour between the hard and the soft ferrite phases had significant influence on the microwave absorption capacity of the samples. Related electromagnetic parameters and impedance matching ratio of the nanocomposite system were discussed. A minimum reflection loss of ?42.9 dB with an absorber thickness of 2.5 mm was attained by the nanocomposite (90 wt%)SrFe₁₀Al₂O₁₉/(10 wt %)Co_0.6Zn_0.4Fe₂O₄ at a matching frequency of 11.45 GHz. This assured the candidacy of SrFe₁₀Al₂O₁₉/Co_0.6Zn_0.4Fe₂O₄ nanocomposite as a promising microwave absorption material in the X-band (8–12 GHz).     

Preparation of carbon fibers@NiS/Ni3S4@MoS2 with core-sheath structure for high efficiency and wide-bandwidth microwave absorption

Numerous studies have focused on the preparation of carbon fibers (CFs)-based high-efficiency microwave absorbers with reasonable structural design and surface morphology control, which simultaneously meet the required impedance matching and loss ability. Here, CFs@NiS/Ni₃S₄@MoS₂ (CNNM) with core-sheath structure was prepared through several simple hydrothermal reactions. The morphology of the as-prepared CNNM nanocomposite is controlled by the amount of added sodium molybdate dihydrate, which causes the difference in minimum reflection loss (RL) and effective attenuation bandwidth among the samples. For the microwave absorbing performance, the minimum RL is ?18 dB and the effective attenuation bandwidth is 8.7 GHz, which appear at the thickness of 2.8 mm and cover most of the X- and Ku-bands. The excellent absorbing performance is attributed to optimized impedance matching and enhanced polarization loss. These results originate from the transition metal sulfides, which not only effectively prevent the skin effect by decreasing the conductivity of CFs but also increase interfaces and flaws, leading to interface polarization and dipole polarization losses.     

A novel method for the synthesis of Fe3O4 nanoparticles/CdS nanowires heterostructure nanocomposite and uses in photodegradation of methylene blue

We report here a simple, efficient, practical, and novel method for the preparation of Fe₃O₄ nanoparticles (NPs)/CdS nanowires. The CdS nanowire/Fe₃O₄ NP reported here was characterized by transmission electron microscopy (TEM), X-ray Diffraction (XRD), vibrating sample magnetometer (VSM), and energy-dispersive X-ray. Cadmium diethyl dithiophosphate has been used as a 3 in 1 precursor (cadmium, sulfur, and ligand source) for the synthesis of high-quality one-dimensional Fe₃O₄ NPs/CdS nanowires using a simple hydrothermal method in the presence of Fe₃O₄ NPs in water. Photocatalytic activity studies show that the nanocomposite has good photocatalytic activity toward the photodegradation of methylene blue in an aqueous solution.