Microwave absorbers with layered structures that can provide abundant interfaces are highly desirable for enhancing electromagnetic absorbing capability and decreasing the thickness. The atomically ...thin layers of two-dimensional (2D) transition-metal carbides (MXenes) make them a convenient precursor for synthesis of other 2D and layered structures. Here, laminated carbon/TiO2 hybrid materials composed of well-aligned 2D carbon sheets with embedded TiO2 nanoparticles were synthesized and showed excellent microwave absorption. Disordered 2D carbon layers with an unusual structure were obtained by annealing multilayer Ti3C2 MXene in a CO2 atmosphere. The minimum reflection coefficient of laminated carbon/TiO2 composites reaches −36 dB, and the effective absorption bandwidth ranges from 3.6 to 18 GHz with the tunable thickness from 1.7 to 5 mm. The effective absorption bandwidth covers the whole Ku band (12.4–18 GHz) when the thickness of carbon/TiO2/paraffin composite is 1.7 mm. This study is expected to pave the way to the synthesis of carbon-supported absorbing materials using a large family of 2D carbides.
By using a catalytic growth procedure, carbon nanotubes (CNTs) are in situ formed on reduced graphene oxide (RGO) sheet at 600°C. CNTs growing on RGO planes through covalent C–C bond possess lower ...interfacial contact electrical resistance. As a hybrid structure, the CNTs/graphene (CNT/G) are well dispersed into poly (dimethyl siloxane). The hybrid combining electrically lossy CNTs and RGO, which disperses in electrically insulating matrix, constructs an electromagnetic wave (EM) absorbing material with ternary hierarchical architecture. The interfacial polarization in heterogeneous interface plays an important role in absorbing EM power. When the filler loading is 5wt.% and thickness of absorber is 2.75mm, the minimum value of reflection coefficient and the corresponding frequency are −55dB and 10.1GHz, and the effective absorption bandwidth reaches 3.5GHz. Therefore, combining the CNTs and graphene sheet into three-dimensional structures produces CNT/G hybrids that can be considered as an effective route to design light weight and high-performance EM absorbing material, while the effective EM absorption frequency can be designed.
Materials with an ultralow density and ultrahigh electromagnetic‐interference (EMI)‐shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical ...work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT–multilayered graphene edge plane (MLGEP) core–shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X‐band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm−3, respectively, which far surpasses the best values of reported carbon‐based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT–MLGEP hybrids also exhibit a great potential as nano‐reinforcements for fabricating high‐strength polymer‐based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials.
Carbon nanotube–multilayered graphene edge plane core–shell hybrid foams are fabricated by chemical vapor deposition methods for the first time. The seamless junctions of multilayered graphene edge planes on the carbon nanotubes endow the hybrids with potential applications as high‐performance nanocomposites and ultrahigh‐performance lightweight electromagnetic‐interference shielding materials.
Carbon fiber reinforced SiC matrix composites (Cf/SiC) were fabricated through chemical vapor infiltration. Effects of SiC content on the mechanical and electromagnetic properties of the as-prepared ...materials were studied systematically. The high volume fraction of SiC matrix is beneficial to the transfer of load to carbon fiber. With the increase of SiC content from 21.5 to 42.2 vol.%, the total porosity decreases from 38.5 to 17.8 vol.%, the flexural strength and fracture toughness of Cf/SiC increase from 38 ± 4 to 375 ± 10 MPa and from 6.2 ± 0.7 to 21 ± 0.3 MPa m1/2. The electromagnetic interference shielding effectiveness of as-prepared Cf/SiC decreases from 43 ± 1.4 to 31 ± 1.1 dB over the frequency range of 8.2–12.4 GHz with the increase of SiC content. The decease of electromagnetic interference shielding effectiveness is mainly attributed to the decline of absorption loss. With the increase of SiC content, the electrical conductivity of Cf/SiC diminishes, leading to the conspicuous drop of the conductive loss, which plays the key role in lowering the absorption loss of electromagnetic waves.
Graphene is highly desirable as an electromagnetic wave (EM) absorber because of its large interface, high dielectric loss, and low density. Nevertheless, the conductive and electromagnetic ...parameters of pure graphene are too high to meet the requirement of impedance match, which results in strong reflection and weak absorption. In this paper, we report a facile solvothermal route to synthesize reduced graphene oxide (RGO) nanosheets combined with surface-modified γ-Fe2O3 colloidal nanoparticle clusters. The obtained two-dimensional hybrids exhibit a relatively low EM reflection coefficient (RC) and wide effective absorption bandwidth, which are mainly attributed to the unique microstructure of colloidal nanoparticle clusters assembled on RGO. The nanoparticle clusters have more interfaces. The interfacial polarization within nanoparticle clusters and conductivity loss of RGO plays an important role in absorbing EM power. The minimum RC reaches −59.65 dB at 10.09 GHz with a matching thickness of 2.5 mm. The special integration of some metal oxide semiconductor crystals assembled on RGO sheets provides an effective avenue to design metal oxide semiconductor/carbon hybrids as EM absorbing materials.
Due to the unique properties of femtosecond laser in precision machining, femtosecond laser was utilized for irradiation on SiC/SiC composites. Effects of different processing parameters, including ...the spot overlap ratio, helical line overlap ratio, laser processing power, as well as processing steps, were discussed in detail. The results indicated that the parameters above had significant effect on machining of SiC/SiC composites. The surface morphology and geometry of the micro-holes were investigated under different parameters, and the corresponding formation mechanism was discussed in detail. It was believed that both the spot and helical line overlap ratio had great effect on the quality of the micro-holes and would be responsible to the depth of micro-holes. Besides, it is indicated that the higher processing power will lead to a better quality of surface morphology and machining results. In micro-hole drilling process, debris and fragments were observed within the micro-holes, and XPS analysis showed that there existed Si-O bonds and Si-C bonds, indicating that the oxidation during processing was incomplete. In addition, the effect of feeding speeds on geometry and depth of the micro-holes were discussed as well.
A dense carbon fiber reinforced silicon carbide matrix composites modified by SiBC matrix (C/SiC-SiBC) was prepared by a joint process of chemical vapor infiltration, slurry infiltration and liquid ...silicon infiltration. The effects of pyrolytic carbon (PyC) interphase thickness on mechanical properties and oxidation behaviors of C/SiC-SiBC composites were evaluated. The results showed that C/SiC-SiBC composites with an optimal PyC interphase thickness of 450nm exhibited flexural strength of 412MPa and fracture toughness of 24MPam1/2, which obtained 235% and 300% improvement compared with the one with 50nm-thick PyC interphase. The enhanced mechanical properties of C/SiC-SiBC composites with the increase of interphase thickness was due to the weakened interfacial bonding strength and the decrease of matrix micro-crack amount associated with the reduction of thermal residual stress. With the decrease in matrix porosity and micro-crack density, C/SiC-SiBC composites with 450nm-thick interphase exhibited excellent oxidation resistance. The residual flexural strength after oxidized at 800, 1000 and 1200°C in air for 10h was 490, 500 and 480MPa, which increased by 206%, 130% and 108% compared with those of C/SiC composites.
Considering the widespread presence of electromagnetic interferences (EMI), it is necessary to develop new electromagnetic wave (EM) absorbing materials with low reflection coefficient and large ...operating frequency band. The well-known EM absorbing materials have a microstructure combining a low permittivity phase with a high electrical conductivity phase. In the present work, a phase in nanoscale with medium permittivity is added into the well-known EM absorption materials to obtain an EM absorption material with low EM reflection coefficient and wide absorption band. Composite powders with special microstructure have been synthesized via sol–gel process, which are composed of submicrometer-sized ZnO acting as electrically lossy phase and ZnAl2O4 nanograins acting as a medium permittivity phase. When the composite powders are mixed with paraffin, the as-received materials exhibit appropriate permittivity and electrical conductivity, which can be attributed to the high carrier concentration and mobility at the interfaces in nanoscale. The high absorption coefficient, small reflection coefficient, and wide absorption band can be obtained. Absorption coefficient per unit thickness increases from 0.01 to 0.13/mm, the minimum reflection coefficient reaches −25 dB, and the effective absorption bandwidth covers the whole X-band (8.2–12.4 GHz). The ZnO/ZnAl2O4 composite materials exhibit excellent EM absorption properties.
The TiC nanowires with high specific surface areas were prepared by a chloride-assisted carbothermal reduction. The 30wt% loaded sample shows strong EM wave absorption capability in X-band, due to ...the good impedance match degree and destructive interference at the air–material interface. TiC nanowires show a potential as a new-type of stealth materials.
•TiC nanowires with high surface areas were prepared by a carbothermal reduction.•The TiC nanowire/paraffin sample had good electromagnetic loss abilities in X-band.•The matching thickness was determined by the quarter-wavelength law and impedance match.
TiC nanowires were synthesized by chloride-assisted carbothermal reaction, using sucrose, TiO2 and NaCl as precursors and Ni(NO3)2·6H2O as a catalyst. The TiC nanowires have specific surface areas of 186.7m2g−1 with a diameter of 200–400nm and length of dozens micrometers. The hybrids of TiC nanowires/paraffin exhibited distinct electromagnetic wave absorbing ability in X-band (8.2–12.4GHz). The optimal reflection loss (RL) of −51dB at 11.8GHz and the bandwidth of 3.0GHz (RL<−10dB) was achieved when the thickness is 1.7mm. The optimal reflection loss and matching thickness were determined by the impedance match and quarter-wavelength law.
Carbon nanotube reinforced carbon fiber/pyrolytic carbon composites were fabricated by precursor infiltration and pyrolysis method and their electromagnetic interference shielding effectiveness (EMI ...SE) was investigated over the frequency range of 8.2–12.4GHz (X-band). Carbon nanotubes (CNTs) were in situ formed through catalyzing hydrocarbon gases evaporating out of phenolic resin with nano-scaled Ni particles. The content of CNTs increased with the increase of Ni loadings (0.00, 0.50, 0.75 and 1.25wt.%) in phenolic resin. Thermal gravimetrical analysis results showed that the carbon yield of phenolic resin increased with the addition of Ni catalyst. With the formation of CNTs, the EMI SE increased from 28.3 to 75.2dB in X-band. The composite containing 5.0wt.% CNTs showed an SE higher than 70dB in the whole X-band.
