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Microstructure and Wear Behavior of Cold-Sprayed Cu-BNNSs Composite Coating
No full textCu-boron nitride nanosheets (BNNSs) composite coating was fabricated by mechanical alloying and then cold spray. The microstructure, mechanical properties and tribological performance of the composite coating were investigated. The addition of BNNSs into Cu leads to a decrease in the deposition efficiency and microhardness of the coating. However, the introduction of BNNSs reduces the coefficient of friction evidently and improves the wear resistance significantly (by 34%) due to the sliding and lubricating effects of the BNNSs. Hence, the Cu-BNNSs composite coatings could be excellent candidates for low friction and high wear-resistance applications
Fluid-like graphene oxide organic hybrid materials as efficient anti-wear and friction-reducing additive of polyethylene glycol
No full textAchieving graphene-based lubricants with simultaneous excellent dispersibility and tribological performance remains challenging as graphene tends to agglomerate in lubricating oils. Herein, a fluid-like graphene oxide (FLGO) was developed based on covalent grafting and epoxide ring-opening reactions, which exhibited obviously improved dispersion ability and tribological behaviors in polyethylene glycol (PEG). The dispersion stability of FL-GO was demonstrated by sedimentation experiment and the 0.5% of FL-GO reduced wear volume of 91.1% and friction coefficient of 43.7%. This well-dispersed graphene helps continue to generate an uneven lubricating film on the rubbing surface, thereby improving the friction and wear performance of the lubricating oils
Tribological mechanism of (Cr, V)N coating in the temperature range of 500?900?C
No full textAiming to study the influence of temperature on the wear mechanism, we fabricated (Cr, V)N coating by cathodic arc ion-plated and conducted tribological experiments at 500?900 ?C. The results indicated that there were two tribological behaviors, depending on the temperature. Below 600 ?C, the (Cr, V)N coatings exhibited a high friction coefficient, but generated a mild wear because of the slight oxidation. Above 700 ?C, the increased oxidation degree reduced adhesion of asperity contacts. However, the wear rate enhanced significantly with the temperature increasing from 700 to 900 ?C due to the fast oxidation accompanied by the decrease in both hardness and adhesion strength
Near-Ambient-Temperature Dehydrogenative Synthesis of the Amide Bond: Mechanistic Insight and Applications
No full textThe current existing methods for the amide bond synthesis via acceptorless dehydrogenative coupling of amines and alcohols all require high reaction temperatures for effective catalysis, typically involving reflux in toluene, limiting their potential practical applications. Herein, we report a system for this reaction that proceeds under mild conditions (reflux in diethyl ether, boiling point 34.6 degrees C) using ruthenium PNNH complexes. The low-temperature activity stems from the ability of Ru-PNNH complexes to activate alcohol and hemiaminals at near-ambient temperatures through the assistance of the terminal N-H proton. Mechanistic studies reveal the presence of an unexpected aldehyde-bound ruthenium species during the reaction, which is also the catalytic resting state. We further utilize the low-temperature activity to synthesize several simple amide bond-containing commercially available pharmaceutical drugs from the corresponding amines and alcohols via the dehydrogenative coupling method
Viscous Oil De-Wetting Surfaces Based on Robust Superhydrophilic Barium Sulfate Nanocoating
No full textViscous oil adherence onto solid surfaces is ubiquitous and has caused intractable fouling problems, impairing the function of solid surfaces in various areas such as optics and separation membranes. Materials with superhydrophilicity and underwater superoleophobicity are very effective in elimination of oil fouling. However, most of them cannot dewet viscous oils and may malfunction without prehydration treatment. Herein, we report a facile and environmental strategy to prepare barium sulfate (BaSO4) nanocoating to dewet viscous oils on dry surfaces. Abundant surface polar groups (surface hydroxyl) on BaSO4 nanocoating enhance both hydrophilicity after oil fouling (underoil water contact angle 155 degrees) and then facilitate oil dewetting ability. Different oils with viscosity up to 900 mPas can be easily eliminated after immersion into water. The results and force analysis also demonstrate that small surface roughness and ultrahydrophilicity under oil are beneficial to achieve oil dewetting property on dry surfaces. Furthermore, BaSO4 nanocoating displays excellent mechanical, thermal and chemical stability and can maintain oil repellency through various harsh conditions. Outstanding antioil fouling ability also enables the fabric coated by BaSO4 nanocoating to separate crude oil/water with flux higher than 28 000 Lm(2-)h(-1) and separation efficiency larger than 99.9% and maintain effective separation performance even after 100 times of separation. Thus, the robust superhydrophilic BaSO4 nanocoating is potential in oil dewetting and waste oil remediation
Bimetallic Metal-Organic Framework with High-Adsorption Capacity toward Lithium Polysulfides for Lithium-sulfur Batteries
No full textThe practical application of Li-S batteries is largely impeded by the shuttle effect generated at the cathode which results in a short life cycle of the battery. To address this issue, this work discloses a bimetallic metal-organic framework (MOF) as a sulfur host material based on Al-MOF, commonly called (Al)MIL-53. To obtain a high-adsorption capacity to lithium polysulfides (Li2Sx, 4 <= x <= 8), we present an effective strategy to incorporate sulfiphilic metal ion (Cu2+) with high-binding energy to Li2Sx into the framework. Through a one-step hydrothermal method, Cu2+ is homogeneously dispersed in Al-MOF, producing a bimetallic Al/Cu-MOF as advanced cathode material. The macroscopic Li2S4 solution permeation test indicates that the Al/Cu-MOF has better adsorption capacity to lithium polysulfides than monometallic Al-MOF. The sulfur-transfusing process is executed via a melt-diffusion method to obtain the sulfur-containing Al/Cu-MOF (Al/Cu-MOF-S). The assembled Li-S batteries with Al/Cu-MOF-S yield improved cyclic performance, much better than that of monometallic Al-MOF as sulfur host. It is shown that chemical immobilization is an effective method for polysulfide adsorption than physical confinement and the bimetallic Al/Cu-MOF, formed by incorporation of sulfiphilic Cu2+ into porous MOF, will provide a novel and powerful approach for efficient sulfur host materials
Effect of nickel electroplating followed by a further copper electroplating on the micro-structure and mechanical properties of high modulus carbon fibers
No full textThe nickel electroplating followed by a further copper electroplating process was conducted on high modulus carbon fibers (HMCFs), and the HMCFs were oxidized in nitric acid prior to the Ni-plating process. Effect of the electroplating process on the microstructure and mechanical properties of HMCFs was investigated. Uniform nickel particles were observed on the surfaces of Ni-plated HMCFs and fiber diameter increased from 5.0 mu m to 6.1 mu m. With a further Cu-electroplating process, the fiber diameter continued increasing to 7.5 mu m. The Niplating process resulted in increased surface roughness, whereas the surface RMS and Ra values dropped significantly after the Cu-plating process. Owing to the Ni-plating treatment, the relative content of carbon element on fiber surfaces decreased from 96.54 % to 36.74 %. After a further Cu-plating process, the relative content of Cu element on HMCF surfaces was as high as 54.01 %. The electroplating process resulted in decreased tensile modulus from 415.71 GPa to 407.71 GPa. By contrast, the tensile strength of electroplated HMCFs increased by 1.1 % due to the reduction of fiber defects and stress concentration. Results also showed that both the Ni-plating and Cu-plating process could lead to significant decreases in the values of electrical resistance and resistivity
Electrodeposition Mechanism of La3+ on Al, Ga and Al-Ga Alloy Cathodes in LiCl-KCl Eutectic Salt
No full textStudying the electrodeposition mechanism of La3+ in LiCl-KCl salt is extremely important for understanding the main characteristics of the deposition of An/Ln in the pyrochemical reprocessing of spent nuclear fuels. In this work, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel methods were employed to investigate the electrodeposition mechanism and kinetic processes of La3+ on Al, Ga and Al-Ga alloy cathodes in LiCl-KCl eutectic salt at the temperature range of 723-873 K. The EIS spectra were measured by applying a minimum overpotential near the equilibrium potential, and the suitable equivalent circuits were fitted. The values of exchange current density (i (0)) calculated by EIS ranged from 0.078 to 0.42 A cm(-2). Finally, Al2Ga2La ternary and Al3La, Ga6La binary alloys were obtained by the potentiostatic electrolysis, which were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS)
Constructing zebra skin structured graphene/copper composites with ultrahigh thermal conductivity
No full textHeat sink materials with superior thermal conductivity and excellent mechanical strength with low cost, are desirable for electronic packaging and thermal management in electronic and electrical engineering systems. In this work, the graphene paper (GP)/copper (Cu) composites were prepared by using a vacuum hot pressing. A zebra skin structure was constructed for improving the thermal transportation performance of GP/Cu composites. In virtue to its unique zebra skin structure, the ultrahigh thermal conductivity of 968 W m-1 K-1 was achieved for the GP/Cu composite at 70 vol% graphene loading. Furthermore, the GP/Cu composite retains high flexural strength (88 MPa) due to the good interface compatibility between the surface chemical treated GP and Cu paper. Our work provides a new method to significantly improve the in-plane thermal conductivity of thermal management materials
Sodium alginate fasten cellulose nanocrystal Ag@AgCl ternary nanocomposites for the synthesis of antibacterial hydrogels
No full textSodium alginate (SA) hydrogel has broad prospects in medical dressings due to its good biocompatibility and non-toxicity. However, the shortcomings of a single SA hydrogel, such as insufficient toughness and poor antibacterial properties, limit its large-scale application. In this study, SA/CNC-Ag@AgCl/TA (SACT) hydrogels were prepared using CNC-Ag@AgCl and tannic acid (TA) with different contents into SA. The results show that the addition of CNC-Ag@AgCl improves the toughness of the gel, and the addition of TA, and the fracture strain is further improved, and get to 128% form 8% of SA and 78% of SAC. Simultaneously, the antibacterial analysis using the zone-inhibition and colony-counting method shows that the composite hydrogel has decent antibacterial effects on both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This work demonstrates a new method for improving the toughness and antibacterial properties of SA hydrogel, which is expected to be used in medical dressings and other relevant fields