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[Display omitted] Hierarchically cellular, stiff, and lightweight niobium carbide (NbC)-pyrolytic carbon (PyC) monolithic foam composites possessing excellent electromagnetic interference shielding effectiveness (EMI SE) were developed via a natural wood template-based method. Pyrolytic carbon derived from the decomposed cellulose in the wood worked as the carbon source for the growth of NbC phase, and the NbC-PyC heterogeneous nano-interface formed between the residual PyC and the freshly formed NbC. Multi-loss mechanisms (e.g. conductive loss, dipole polarization loss, and especially interface polarization loss) were established by controlling the NbC content and residual PyC phase in the NbC-PyC foams, which significantly improved the absorption capability. Compared to 28.0 dB of PyC monolith, the EMI SE of NbC-PyC foam can reach 54.8 dB when the thickness is 0.5 mm, which outperforms the other porous-based shielding materials. Due to the highly porous structure of pristine wood, the resulting NbC-PyC foam exhibited a low density of 0.48 g/cm3, which is ~ 1/16 of dense NbC (7.78 g/cm3). Generally, this work introduces innovative ideas for designing novel and advanced transition metal carbide–carbon composite materials. [ABSTRACT FROM AUTHOR]

In this study, a novel sensor with high sensitivity and linear was prepared based on two-dimensional (2D) material (MXene) and ink, which can be used for deformation and damage monitoring of structural composites. The MXene was efficiently prepared by etching Ti3AlC2 powder with LiF–HCl solution and subsequent vacuum drying. The viscosity and adhesion of MXene/ink composites were controlled by changing the ratio of solvent (dimethyl sulfoxide) to ink. The MXene/ink was printed on the surface of the composite material to avoid forming defects in the composite material. The percolation threshold of the MXene/ink nanocomposite was relatively low, 3.6wt%. In this paper, MXene/ink composites with different contents were selected as the sensor, and the characteristics of the sensor were verified through monotone stretch and cyclic load-and-unload tests. When the MXene content just exceeds the percolation threshold (4wt%), the gauge factor (GF) of the sensor is higher, the results of monotonic tensile experiment show that there are two different sensitive stages of linear change (0 ~ 0.477%) and (0.477 ~ 1.37%), and the range GF is116.6 and 554.3, respectively. In addition, the linear relationship and sensitivity of the sensor remained stable after loading and unloading tensile tests. MXene/ink sensor has a broad application prospect in damage monitoring of aerospace structural composites. [ABSTRACT FROM AUTHOR]

Novel single-source-precursors (SSPs), namely carbon nanotube modified poly (methylvinyl) silazane (CNTs-HTT 1800), were synthesized via amidation reaction of poly (methylvinyl) silazane (HTT 1800) with carboxylic acid functionalized carbon nanotubes (CNTs-COOH) at the assistance of ZnCl2 catalyst, which was confirmed by means of Fourier transform infrared spectra ( FT IR) and transmission electron microscopy ( TEM). Besides, the TEM results unambiguously show the homogeneous distribution of the CNTs in the matrix of SSPs while serious aggregation of the CNTs in the matrix of physically-blended-precursor. Crack-free monolithic silicon carbonitride modified by carbon nanotubes ceramic nanocomposites ( CNTs-Si CN) were prepared through pyrolysis of the obtained SSP green bodies at 1000°C. Due to the strong influence of polymer structure on the microstructure of final ceramics, the SSP-derived CNTs-Si CN nanocomposites clearly show the homogeneous distribution of the CNTs in the Si CN matrix while the physically-blended-precursor derived CNTs-Si CN nanocomposites exhibit serious aggregation and entangling of the CNTs in the Si CN matrix. With the same CNT content in the feed, the SSP-derived CNTs-Si CN nanocomposites possess significant improvements of electromagnetic ( EM) absorbing properties compared to those from physically-blended-precursors, due to the quality of the dispersion of CNTs in the ceramic matrices. [ABSTRACT FROM AUTHOR]

Abstract: In order to enhance the dielectric and electromagnetic interference shielding (EMI) properties, the SiC/C composite ceramics were fabricated by pyrolysis of ferrocene-modified polycarbosilane. The microstructure evolutions, dielectric properties, EMI and microwave absorption properties of SiC/C composite ceramics were investigated. The increases of both ferrocene contents and annealing temperatures led to the increases of crystallizations of SiC and carbons. Crystallized carbons including carbon nanowires, turbostratic carbons, onion-like carbons and graphene-like carbons were obtained in the materials. The carbon nanowires were longest when the 5wt.% ferrocene-modified polycarbosilane was annealed at 1250°C. These carbons played a more important role than SiC in the increases of dielectric and EMI properties. The average real and imaginary permittivities of materials increased from 4.4 and 0.7 to 38.9 and 39.6, respectively. The materials exhibited high total shielding effectiveness, high absorption shielding effectiveness and low reflection shielding effectiveness, which were 36.6, 30.1 and 6.5dB, respectively. [Copyright &y& Elsevier]

Abstract: Porous Si3N4–SiC composite ceramic was fabricated by infiltrating SiC coating with nano-scale crystals into porous β-Si3N4 ceramic via chemical vapor infiltration (CVI). Silica (SiO2) film was formed on the surface of rod-like Si3N4–SiC grains during oxidation at 1100°C in air. The as-received Si3N4–SiC/SiO2 composite ceramic attains a multi-shell microstructure, and exhibits reduced impedance mismatch, leading to excellent electromagnetic (EM) absorbing properties. The Si3N4–SiC/SiO2 fabricated by oxidation of Si3N4–SiC for 10h in air can achieve a reflection loss of −30dB (>99.9% absorption) at 8.7GHz when the sample thickness is 3.8mm. When the sample thickness is 3.5mm, reflection loss of Si3N4–SiC/SiO2 is lower than −10dB (>90% absorption) in the frequency range 8.3–12.4GHz, the effective absorption bandwidth is 4.1GHz. [Copyright &y& Elsevier]