查看更多>>摘要：? 2022 Elsevier B.V.In industrial applications, it is crucial to characterise the quality of coatings during and after the manufacturing process. It is then relevant to elaborate a reliable procedure allowing for rapid inspection and easy-to-assess quality check. In this paper, we tested a qualitative methodology based on mechanical and visual analyses allowing for easily finding suitable parameters to generate resistant and uniform multi-layered coatings. This qualitative criterion was tested and refined against quantitative measurements. We focussed on carbon-based materials whose remarkable properties could be exploited in many applications, including multilayer coatings as a promising anticorrosion solution in the metal industry and as enhanced surfaces for heat exchange devices. Dip-coating was used to create multilayer coatings on rough 3D objects starting from water solutions of CNT and pure graphene. Visual uniformity and adhesion were chosen as criteria to analyse coatings qualitatively, while samples' roughness and the number of dips were the variable parameters. Different behaviours of the coatings were observed for graphene and CNT. For both, we found a critical number of dips after which the coating loses adhesion and stops to be uniform. The proposed colour maps, summarising the qualitative coatings' assessment, could be used as a methodological reference to issue technological recommendations when using multilayer coatings for specific purposes.
查看更多>>摘要：? 2022 Elsevier B.V.The high hardness, wear resistance and chemical inertness of single crystal diamond makes it challenging to achieve high efficiency and high quality chemical mechanical polishing (CMP) of single crystal diamond with material removal rate MRR higher than 300 nm/h and surface roughness Ra lower than 0.5 nm. The hydroxyl radicals (·OH) produced by the Fenton reaction are strongly oxidizing and can be used for CMP. In this study, ND/LDH catalysts synthesized from nanodiamond (ND) and CuFe-layered double hydroxide (LDH) for visible-light-Fenton reaction were prepared. The dynamics of the ·OH concentration produced by 4 groups of reaction solutions, including hydrogen peroxide and hydrogen peroxide mixed with ferrous sulfate and hydrogen peroxide mixed with ND/LDH and hydrogen peroxide mixed with ND/LDH (visible-light irradiation), were measured. Then, the single crystal diamond was polished with 4 groups of reaction solutions with diamond powder added. The results showed that: hydrogen peroxide mixed with ND/LDH (visible-light irradiation) reaction solution produced the highest ·OH concentration, and achieved high efficiency and high quality polishing of single crystal diamond, with the material removal rate MRR of 370 nm/h and surface roughness Ra of 0.110 nm.
查看更多>>摘要：? 2022 Elsevier B.V.The effect of nanodiamond (ND) content on the microstructures, textures and hot deformation behaviors of ND/ZK60 (Mg-5.1 Zn-0.18 Zr (wt%)) composites were systematically studied. The results showed that the grains size of composites was refined with increasing ND content. The ND particles existed at grain boundaries and formed a ball effect during hot compression, which increased the elongations of composites. The ball effect plays a key role in promoting grain boundary gliding and reducing the textures of composites during hot compression. The ND particles were difficult to disperse evenly when the content of ND exceeds 0.1%, which caused the flow stress of composites first increased and then decreased with increasing ND content.
查看更多>>摘要：? 2022 Elsevier B.V.The effect of the carbon precursor flow rate (CPFR) on the quality and quantity of CNTs is controversial. This study aimed to investigate the effect of the CPFR on the quality and quantity of CNTs at different temperatures. Our results showed that as the CPFR increased, so did the average diameter of the CNTs, indicating an improvement in the decomposition rate of acetylene at a higher CPFR. In general, the height of the CNTs also showed a peak with the CPFR. This was attributed to the competition between the decomposition rate of acetylene and the surface diffusion rate of carbon. Based on the Raman results, the graphite structures of the CNTs increased with temperature. This was ascribed to the increase in the surface diffusion rate of carbon at higher temperatures.
查看更多>>摘要：? 2022 Elsevier B.V.In order to improve the tribological and tribocorrosion performance of Ti-DLC films, a series of Ti-DLC films were prepared by filtered cathodic vacuum arc technique by controlling C2H2 flow rate. The microstructure, mechanical properties, tribological and tribocorrosion performance of Ti-DLC films with different C2H2 flow rates were investigated. As the C2H2 flow rate increased from 10 to 140 sccm, the columnar cross-sectional structure of the Ti-DLC films transformed to dense and uniform structure. The increase in C2H2 flow rate also resulted in an initial increase followed by a decrease in hardness and compressive stress. The results showed that the Ti-DLC films on substrate can significantly improve its tribology, anti-corrosion and anti-tribocorrosion properties. Under dry friction condition, the film prepared at 20 sccm with hardness of 49.1 GPa showed low wear rate at a reciprocating frequency of 1 Hz under a load of 2 N (2 N/1 Hz), however, the film was worn through due to the high compression stress at 10 N/5 Hz. The film at 140 sccm showed great tribology performance with the lowest coefficient of friction of 0.017 and the lowest wear rate of 5.91 × 10?8 mm3/N·m at 10 N/5 Hz, which was attributed mainly to the formation of sp2-carbon rich transfer layers on the counterpart. The tribocorrosion properties test demonstrated that the coating prepared at 140 sccm exhibited the best tribocorrosion resistance with the lowest coefficient of friction of 0.055, the lowest wear rate of 3.56 × 10?7 mm3/N·m and high stable value of OCP of 0.116 V under the synergistic action of corrosion and friction.
查看更多>>摘要：? 2022 Elsevier B.V.First-principle density functional theory (DFT) is employed to investigate the hydrogen separation performance of porous carbon nanotubes (PCNTs). The calculation results indicate that PCNTs are an excellent material for H2 purification. The reaction path of the gas penetration through PCNTs demonstrates that the diffusion barriers of gas inside or outside the tube are various, 0.413 eV and 0.328 eV, respectively, indicating that the gas located outside the nanotubes is relatively easy to diffuse into the tube. Additionally, PCNTs are more selective to H2 than other gas molecules, up to 1031, superior to porous silicon and porous phosphorene, and making potential material for gas separation.
查看更多>>摘要：? 2022 Elsevier B.V.This study employs a modified Rapoport apparatus to measure sodium expansion during aluminum electrolysis to elucidate the role of titanium carbide (TiC) in the graphitization of TiB2?carbon composite cathodes comprising a TiB2-rich bottom layer, a functional TiB2/C middle layer, and a graphite (carbon base) top layer. The results indicate that TiC crystallites catalyze the graphitization of TiB2?carbon composite cathodes during aluminum electrolysis. Transmission electron microscopy (TEM) analyses reveal three types of residual TiC in the TiB2?carbon composite cathodes after aluminum electrolysis; these TiC particles indicate two distinct catalytic graphitization mechanisms. The regular morphology of TiC is a result of the dissolution-precipitation mechanism, whereas the eroded TiC corresponds to a carbide formation-decomposition mechanism. The voltage drop in the TiB2?carbon composite cathodes was reduced by approximately 120 mV compared with that observed using simple carbon cathodes. This work provides key insights regarding the mechanism that hinders Na penetration into the carbon/TiB2 cathodes during aluminum electrolysis.
查看更多>>摘要：? 2022Polycrystalline diamond (PCD) is widely used in drill bits and bearings of downhole tools for oil drilling because of its excellent tribological properties. However, the graphitization of PCD caused by downhole high temperature and the reduction of wear resistance are urgent problems that need to be solved. Cobalt at high temperature is the main factor leading to graphitization. Therefore, this experiment improves the tribological properties of PCD at high temperatures by leaching Co treatment. An annealing experiment was conducted in a box-type resistance furnace, and the PCD after high-temperature annealing for Co leaching was studied by X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, and Raman spectroscopy. Results of Raman spectroscopy show that Co leaching is conducive to the significant reduction of graphitization. The results show that the area of the transfer films increases with the increase of the annealing temperature, and the formation of the transfer films may result from the complex chemical reaction or the combined effect of the transfer film mechanism, passivation mechanism, and graphitization mechanism of the friction pairs in the flash temperature state. Thus, the tribological properties of PCD annealed at high temperatures with the Co leaching are greatly improved.
查看更多>>摘要：? 2022Polyacrylonitrile precursor was obtained by one-step method of polymerization and spinning. After conventional pre-oxidation at 180–280 °C in air, the polyacrylonitrile pre-oxidized fiber was carbonized at 600–1000 °C by microwave heating and conventional heating in nitrogen. An infrared thermometer is used to detect the surface temperature of the fiber in real time. The dielectric loss tangent (tanδ) increases first and then decreases with increasing temperature. The intensity of the A line of the MCF-1000 sample increases, the G line gradually separates from the D line, and the ID/IG value decreases. Compared with CCF-700, the tensile strength of MCF-700 is increased by 10.06%. The microwave carbonization method creates excellent carbon fiber tensile strength at a temperature of 200 °C lower than the conventional carbonization temperature. The initial modulus of MCF-700 is 51.33% higher than that of CCF-700. Microwave carbonization can obtain carbon fiber with a higher initial modulus at a lower carbonization temperature.
查看更多>>摘要：? 2022In this paper, the free vibration of hybrid carbon boron-nitride heteronanotubes (CBNNTs) is analyzed through molecular dynamics (MD) simulations. In the vibration analysis, various CBNNTs (Cx ∣ (BN)y and C-BN models) according to two geometrical arrangements of constituent segments are considered. By introducing vacancy defects in nanotubes, the influence of defects on the vibrational response is studied in terms of the weight percentage and distribution pattern. The highest vibration frequency is reported and CBNNTs' results are compared with those of carbon nanotubes (CNTs) and boron-nitride nanotubes (BNNTs). It is observed that CBNNTs possess natural frequencies which lie between the values for CNTs and BNNTs. The natural frequency is found to be reduced by increasing the defect percentage. At each defect percentage, the defective C-(BN) model I and C1.5 ∣ (BN)1.5 experience almost the same natural frequency in both distribution patterns. Vibration frequencies of defective C-(BN) model II and C4.5 ∣ (BN)4.5 are nearly close together at a defined percentage of defects. Despite the minor differences between natural frequencies in either distribution pattern, regularly defected CNTs tend to have a bit higher frequency than randomly defected CNTs, however, the results are opposite in the regularly and randomly defected BNNTs. Moreover, the C-(BN) model II vibrates at a higher natural frequency than that of the C-(BN) model I. It is found that the vibrational behavior of the C-(BN) model I is mostly affected by the BN segment than the C segment. Further, the natural frequency's drop in the defected C1.5 ∣ (BN)4.5 is found to be more significant than other CBNNTs by rising the defect percentage. C-(BN) model I and defective C-(BN) model I experience higher deformations in comparison with the Cx ∣ (BN)y configurations when vibrating at their natural frequency.
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