1,720,972 research outputs found
Barrier mechanism of multilayers graphene coated copper against atomic oxygen irradiation
No full textGraphene has been demonstrated as a protective coating for Cu under ambient condition because of its high impermeability and light-weight oxidation barrier. However, it lacks the research of graphene as a protective coating in space environment. Here, we experimentally and theoretically study the oxidation behavior of graphene-coated Cu in vacuum atomic oxygen (AO) condition. After AO irradiation, the experimental results show multilayer graphene has better anti-oxidation than monolayer graphene. Meanwhile, the calculation results show the oxidation appeared on the graphene's grain boundaries or the film's vacancy defects for the monolayer graphene coated Cu foil. Moreover, the calculation results show the oxidation process proceeds slowly in multilayers because of the matched defects overlaps each other to form a steric hindrance to suppress the O atom diffusion in the vertical direction, and the mismatched defects generates potential energy barriers for interlayer to suppress the O atom diffusion in the horizontal direction. Hence, multilayer graphene films could serve as protection coatings to prevent diffusion of O atom. (C) 2018 Elsevier B.V. All rights reserved
Barrier mechanism of multilayers graphene coated copper against atomic oxygen irradiation
No full textGraphene has been demonstrated as a protective coating for Cu under ambient condition because of its high impermeability and light-weight oxidation barrier. However, it lacks the research of graphene as a protective coating in space environment. Here, we experimentally and theoretically study the oxidation behavior of graphene-coated Cu in vacuum atomic oxygen (AO) condition. After AO irradiation, the experimental results show multilayer graphene has better anti-oxidation than monolayer graphene. Meanwhile, the calculation results show the oxidation appeared on the graphene's grain boundaries or the film's vacancy defects for the monolayer graphene coated Cu foil. Moreover, the calculation results show the oxidation process proceeds slowly in multilayers because of the matched defects overlaps each other to form a steric hindrance to suppress the O atom diffusion in the vertical direction, and the mismatched defects generates potential energy barriers for interlayer to suppress the O atom diffusion in the horizontal direction. Hence, multilayer graphene films could serve as protection coatings to prevent diffusion of O atom. (C) 2018 Elsevier B.V. All rights reserved
Corrosion Behavior of Epoxy Coating Containing Poly-dopamine Modified Hexagonal Boron Nitride
No full textIn order to improve the dispersion of hexagonal boron nitride (h-BN) in the solvents and organic matrix, and to investigate the effect of h-BN on the corrosion resistance of epoxy coating, polydopamine was modified on the h-BN to achieve the well dispersion stability of h-BN in the solvents and epoxy coating. The corresponding morphology, chemical composition and thermal stability were characterized by SEM, TEM, XPS, Raman spectrum and TG. In addition, the corrosion behavior of the epoxy coating and h-BN@PDA/epoxy coating was investigated in 3.5%NaCl solution by electrochemical measurements. The results indicate that h-BN@PDA/epoxy composite coating exhibites nobler open circuit potential (-0.1 V), higher impedance modulus and coating resistance (~10~(10)Omega·cm~2), lower breakpoint frequency (~0.1 Hz) than those of the epoxy coating during long time immersion in 3.5 % NaCl solution. Furthmore, very little corrosion is found at the substrate surface coated with h-BN@PDA/epoxy composite coating, indicating the outstanding corrosion resistance of the composite coating. Addition of h-BN nanosheets can reduce the coatings porosity and inhibit the penetration of corrosive medium, which helps to improve the corrosion resistance of the composite coating
Improved adaptability of polyaryl-ether-ether-ketone with texture pattern and graphite-like carbon film for bio-tribological applications
No full textWith the development of surface treatment technology, an increasing number of bearings, seals, dynamic friction drive or even biomedical devices involve a textured surface to improve lubrication and anti-wear. The present investigation has been conducted in order to evaluate the friction and wear behaviours of textured polyaryl-ether-ether-ketone (PEEK) coated with a graphite-like carbon (GLC) film sliding against stainless steel pin in biological medium. Compared with pure PEEK, the PEEK coated with GLC film shows excellent tribological performance with a low friction of 0.08 and long lifetime (wear volumes are about 3.78 x 10(-4) mm(3) for un-textured one and 2.60 x 10(-4) mm(3) for textured GLC film after 36,000 s of sliding) under physiological saline solution. In particular, the GLC film with appropriate dimple area density is effective to improve friction reduction and wear resistance properties of PEEK substrate under biological solution, which is attributed to the entrapment of wear debris in the dimples to inhibit the graphitization and the fluid dynamic pressure effect derived from the texture surface to increase the thickness in elastohydrodynamic lubrication (EHL) film during sliding motions. Moreover, the friction coefficient of GLC film under physiological saline solution decreases with the increase in the applied load. With the increasing applied load, the texture surface is responsible for accounting the improved wear resistance and a much lower graphitization of the GLC film during whole test. (C) 2016 Elsevier B.V. All rights reserved
Functional regulation of Pb-Ti/MoS2 composite coatings for environmentally adaptive solid lubrication
No full textThe lubrication of molybdenum disulfide coatings has commonly been limited by the application environments, for instance, the crystal MoS2 are easily affected by water to form MoO3 that causes a higher friction coefficient and short lifetime. Therefore, to improve the tribolgical performance of MoS2 in high humidity condition, the co-doped Pb-Ti/MoS2 composite coatings are deposited by unbalanced magnetron sputtering system. The design of the co-doping elements in MoS2-based coatings can not only maintain the characteristic of low humidity-sensitivity as the Ti/MoS2 coating but also improve the mechanical properties and tribological performance of coatings as a comparison with single-doped ones. Moreover, the ultra-low friction coefficient with a minimum value of 0.006 under the vacuum condition is achieved for Pb-Ti/MoS2 composite coating containing about 4.6 at.% Pb, depending on the densification structure of coating. Intriguingly, the wear behaviours of Pb-Ti/MoS2 composite coatings are in accordance with the variation in H/E (hardness to the elastic modulus) ratio that the coating with higher H/E exhibits lower wear rate. These results demonstrate that the lubricating properties of MoS2 coatings in both humid environment and vacuum condition can be achieved through the Pb and Ti co-doped, which is of great significant for developing MoS2 coatings as the environmentally adaptive lubricants. (C) 2017 Elsevier B.V. All rights reserved
Polydopamine coated graphene oxide for anticorrosive reinforcement of water-borne epoxy coating
No full textThis study reports an eco-friendly water-borne epoxy (EP) with enhanced corrosion protection performance by embedding graphene oxide (GO). For this purpose, the dispersion of the GO in ethanol is improved by modifying the GO nanosheets with hydrophilic dopamine (DA), owing to the p-p interactions between the GO and selfpolymerized polydopamine (PDA) as well as the covalent bonding between DA and GO. Results obtained from transmittance electron microscopy (TEM), scanning probe microscopy (SPM) Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, UV-vis absorbance spectroscopy and X-ray photoelectron spectroscopy (XPS) reveal the successful modification of PDA on the surface of GO nanosheets. Besides, the GO/ EP and GOPDA/ EP coatings are applied on the steel substrates and their corrosion protection performance is investigated via electrochemical measurements, scanning electron microscopy (SEM) and scanning vibration electrochemical technology (SVET). Results demonstrate that inclusion of well-dispersed GO-PDA nanosheets leads to the remarkable improvement in the corrosion protection performance of water-borne EP coating
Novel nitrogen doped carbon dots for corrosion inhibition of carbon steel in 1 M HCl solution
No full textNitrogen doped carbon dots (NCDs) were synthesized and used for inhibiting the corrosion of Q235 carbon steel in hydrochloric acid (HCl) solution. Inhibition effectiveness in short-and long-term immersion was examined using electrochemical measurements, weight loss and surface analysis. Results revealed the inhibition efficiency was improved significantly after adding NCDs and strongly dependent on the concentration of NCDs. SVET results showed that the sample immersed in HCl solution with NCDs showed lower anodic current density mapping than that in blank HCl solution. According to the data extracted from the Langmuir adsorption, the absorption of NCDs involved both chemisorption and physisorption. (C) 2018 Elsevier B.V. All rights reserved
Novel nitrogen doped carbon dots for corrosion inhibition of carbon steel in 1 M HCl solution
No full textNitrogen doped carbon dots (NCDs) were synthesized and used for inhibiting the corrosion of Q235 carbon steel in hydrochloric acid (HCl) solution. Inhibition effectiveness in short-and long-term immersion was examined using electrochemical measurements, weight loss and surface analysis. Results revealed the inhibition efficiency was improved significantly after adding NCDs and strongly dependent on the concentration of NCDs. SVET results showed that the sample immersed in HCl solution with NCDs showed lower anodic current density mapping than that in blank HCl solution. According to the data extracted from the Langmuir adsorption, the absorption of NCDs involved both chemisorption and physisorption. (C) 2018 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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