Carbon最新文献

Strength-ductility synergy has long been a challenge in the development of advanced metallic materials. In this study, we fabricated a novel bimodal-structured nickel matrix composite, which features in-situ synthesized three-dimensional graphene networks (3DGN) strengthening the hetero-interfaces between coarse-grained and fine-grained zones (CGZ and FGZ). Compared to the bimodal matrix, this 3DGN-reinforced composite exhibits remarkable enhancements of 30 % in yield strength, 40 % in ultimate tensile strength, and 40 % in uniform elongation, respectively, representing the highest comprehensive performance among nickel matrix composites and pure nickel obtained through cold rolling, severe plastic deformation, and dynamic plastic deformation as reported in the previous literature. The superior strength-ductility combination originates from the incorporation of 3DGN, which enables multiple strengthening and toughening mechanisms. Specially, the strength and strain hardening capability have been enhanced through improved dislocation storage capacity, a stronger hetero-deformation induced (HDI) hardening effect, and the activation of numerous stacking fault ribbons. Moreover, high-density dispersed microcracks in the FGZ relieve strain/stress concentrations while being constrained within the CGZ, further enhancing tensile ductility. This study provides new insights into addressing the inherent strength-ductility paradox in metal matrix composites.

In this study, amorphous carbon (a-C) films were modified using different process sequences—H passivation followed by graphitization (a-C@H@G2000K) and graphitization followed by H passivation (a-C@G2000K@H). The friction dependence on the surface H content and the processing priority was comparatively investigated at the atomic scale, with a focus on the coupling mechanism for achieving low friction. The results indicated that the friction properties closely depended on the H content of the contacted a-C surfaces. An appropriate H content significantly improved the friction property through the coupling effect of the lubrication between surface graphitized structures and the repulsion between H atoms, resulting in a rapid decrease in the friction coefficient; however, the graphitization mechanism remained dominant. Excessive H reduced the repulsion between the contacted graphitized structures and hindered the sliding of these structures (shear susceptible), resulting in a slow increase in the friction coefficient. Most importantly, compared with the a-C@H@G2000K systems, the a-C@G2000K@H system exhibited higher effectiveness in reducing the friction coefficient, achieving a lower friction coefficient under the same surface H content; this was attributed not only to the small surface roughness and the low fraction of unsaturated bonds but also to the well stress distribution of the surface H atoms.

The elaborate construction of multi-component composites has been deemed as a promising strategy to enhance dielectric polarization response capability in the preparation of highly efficient microwave absorbers. However, the rational design and integration of homogeneous composites with diverse components continues to pose a great challenge. Herein, we propose a straightforward self-assembly-carbonization strategy for fabricating Co/MnO@NC ternary composites derived from CoMn-Prussian Blue Analogous precursors, featuring enriched heterogeneous interfaces and balanced magneto-electric coupling synergy. The ternary composites effectively introduce diverse dissipation mechanisms, including interfacial polarization behavior originated from the constructed heterogeneous interfaces, dipole polarization relaxation triggered by atomic defects, and optimized magnetic loss ability from well-dispersed metallic Co species. Benefiting from these advantages, the Co/MnO@NC composites demonstrate superior electromagnetic wave absorption performances, with a minimum reflection loss value of −61.37 dB at the thickness of 3.5 mm and effective frequency absorption bandwidth of 6.32 GHz, covering the full Ku-band. Furthermore, power loss density and radar cross-section simulations validate that the Co/MnO@NC ternary composites possess exceptional microwave signal attenuation abilities, with a maximum radar cross-section reduction value of up to 27.98 dBm² at 0°. Such outstanding absorption properties exceed those of most currently reported ternary composites and exhibit significant potential to replace conventional ferromagnetic-based absorbers. This work offers a straightforward strategy to fabricate ternary composites with excellent electromagnetic wave attenuation properties and sheds novel insights into the dissipation mechanisms.

The diamond inner wall of drawing die is crucial for the precise formation of ultra-fine wires during the drawing process. Unexpectedly, when drawing soft metal wire, a significant wear occurs on hard-phase diamond surface, resulting in increased friction at the drawing interface, which leads to the wire cross-section distortion, uneven wire diameter, surface scratches and burrs. In this study, the interface interaction and friction products between diamond and iron were investigated, focusing on the primary factors influencing diamond phase transitions by adjusting friction atmosphere. Whether in air or nitrogen, the friction coefficient (CoF) decreases with the increase of load, but CoF value is relatively lower in nitrogen environment. The friction curve of diamond against iron stabilized after an initial downward trend, reaching a minimum CoF of 0.08 in nitrogen under a load of 15 N. The friction mechanism is explained through material transfer, friction products, phase transition, tribolayer formation, and interfaces interactions. It is speculated that in nitrogen, even if a small amount of oxide forms on iron surface, iron remains in contact with diamond, generating a large amount of iron carbide and inducing the graphitization of diamond, which would act as a lubricating role. In contrast, in air, oxygen atoms continuously interact with iron, forming a dense oxide film at the friction interface, which prevents carbon from continuous contacting iron atoms and limits the formation of iron carbide. Overall, the discovery provides new insights into the interaction between metals and diamonds, and offers theoretical guidance for the drawing of iron wires.

Two-dimensional MXene has structural advantages in electromagnetic wave scattering due to its layered structure, but MXene materials can lead to impedance mismatch problems due to their high dielectric constants, so it is still a challenge to design highly efficient wave-absorbing materials based on MXene with low reflection loss, thin thickness, and wide absorption frequency. In this study, composite wave-absorbing materials were fabricated from Co–Co PBA precursors and MXene using liquid nitrogen flash freezing and freeze-drying techniques. By treating MXene and the PBA precursor at a high temperature of 750 °C, a rich heterogeneous interface was formed between Co@C and MXene (CCM7), and the impedance matching was optimized to improve the reflection loss capability. The optimized sample has an effective absorption bandwidth of 4.1 GHz at 2.5 mm covering the entire X-band with a minimum reflection loss of −61.42 dB. It is also demonstrated that CCM7 is satisfactory for Radar Cross-Section of flat panels and unmanned aerial vehicles by CST calculations, and this work provides a fresh perspective on the use of effective MXene composites for microwave absorption.

Aiming to attain porous carbon nitride photocatalysts with high specific surface area, abundant active sites, broad absorption range and effective electron-hole separation, we remove carbon rings from graphene and replace all the edge carbon atoms of the cavity with nitrogen atoms. The accurate electronic structures and exciton properties of the proposed materials are revealed by the ab initio many-body Green's function theory. Computational results show that the absorption of the designed materials can cover both the visible and the near-infrared light region. The exciton binding energies of the materials are one order of magnitude lower than those of the typical two-dimensional photocatalyst graphitic carbon nitride. Due to the formation of hydrogen bonds between pyridinic nitrogen atoms and water molecules during water splitting, the key excited-state proton-coupled electron transfer reactions are barrierless. These findings could serve as guidelines for the realization of high-performance metal-free two-dimensional photocatalysts.

This study examines the effects of heat and fire on the physical, mechanical and electrical properties of carbon fibre and those in carbon fibre reinforced composites (CFRCs). Carbon fibres were exposed to controlled heating (thermogravimetric analysis (TGA) and a tube furnace) in inert and air (oxygenated) environments and simulated fire (cone calorimetry at 35–75 kW m⁻² and jet fire (propane burner) of 116 kW m⁻²) atmospheres. In inert atmospheres there was a minimal effect on the properties of carbon fibres, but in an oxygenated environment, significant oxidation began at temperatures ≥550 °C, resulting in a reduction in fibre diameter, which reduced further with increasing temperature and exposure duration. Tensile strength and electrical conductivity of carbon fibre decreased with reduction in fibre diameter. CFRCs exposed to 75 kW m⁻² in a cone calorimeter and direct flame in a propane burner (116 kW m⁻²) showed varying degrees of oxidation in CFRC plies, with surface ply fibres experiencing more oxidation and consequent reductions in fibre diameter and tensile properties compared to fibres in underlying plies, where oxidation was limited due to restricted oxygen availability. Fibres exposed to the propane burner exhibited notable damage, including pitting and internal oxidation. Despite this, the overall electrical properties of residual carbon fibres did not significantly decrease, indicating that they still pose an electrical hazard if exposed during a high heat or fire event.

Graphene is an excellent support film for high-resolution transmission electron microscopy (TEM) but its use with biological samples, notably in cryo-TEM, is hindered by its inherent hydrophobicity. Whereas surface treatments have been proposed to render graphene hydrophilic, they are often difficult to reproduce due to a lack of information on the structural changes that modify the wetting properties of graphene. This study aims to correlate the atomic structure of graphene with its wetting properties to allow a reproducible protocol to advance its application in cryo-TEM. We follow the change in the atomic structure of graphene as a function of low-energy hydrogen plasma treatment duration on monolayer graphene transferred onto TEM grids. With finely controlled plasma exposure, partial hydrogenation, monoatomic vacancies, and pores of a few nanometers are realized in the graphene. The introduction of defects (vacancies and pores) enables the formation of continuous layers of vitreous ice on TEM grids. Grids with defect-integrated graphene are reproduced and used in the vitrification of the mouse serotonin 5-HT₃ receptor, a membrane protein. Single particle analysis of the membrane protein on graphene compared to conventional holey carbon film give insight into the strengths and discretions in using graphene membrane for protein structural studies.