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1. Macroscale Superlubricity Accomplished by Sb2O3-MSH/C Under High Temperature

   https://doi.org/10.3389/fchem.2021.667878  

   Gao, Kai; Wang, Bin; Shirani, Asghar; Chang, Qiuying; Berman, Diana (April 2021, Frontiers in Chemistry)

   null (Ed.)

   Here, we report the high-temperature superlubricity phenomenon accomplished in coatings produced by burnishing powders of antimony trioxide (Sb 2 O 3 ) and magnesium silicate hydroxide coated with carbon (MSH/C) onto the nickel superalloy substrate. The tribological analysis performed in an open-air experimental setup revealed that with the increase of testing temperature, the coefficient of friction (COF) of the coating gradually decreases, finally reaching the superlubricity regime (the COF of 0.008) at 300°C. The analysis of worn surfaces using in-situ Raman spectroscopy suggested the synergistic effect of the inner Sb 2 O 3 adhesion layer and the top MSH/C layer, which do not only isolate the substrate from the direct exposure to sliding but also protect it from oxidation. The cross-sectional transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results indicated the tribochemically-activated formation of an amorphous carbon layer on the surface of the coating during sliding. Formation of the film enables the high-temperature macroscale superlubricity behavior of the material system. 

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2. Growth of Highly Transparent Amorphous Carbon Films Using Beam Plasma Source

   https://doi.org/10.3390/coatings12081159  

   Kim, Youngsuk; Baule, Nina; Shrestha, Maheshwar; Fan, Qi Hua (August 2022, Coatings)

   A single beam plasma source was used to deposit hydrogenated amorphous carbon (a-C:H) coatings at room temperature. Using methane source gas, a-C:H coatings were deposited at different radio frequency (RF) power to fabricate transparent and durable coatings. The film deposition rate was almost linearly proportional to the ion source power. Hydrogenated amorphous carbon films of ~100 nm thickness appeared to be highly transparent from UV to the infrared range with a transmittance of ~90% and optical bandgap of ~3.7 eV. The coatings also possess desirable mechanical properties with Young’s modulus of ~78 GPa and density of ~1.9 g/cm3. The combined material properties of high transmittance and high durability make the ion-source-deposited a-C:H coatings attractive for many applications. 

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3. Tribocatalytically-activated formation of protective friction and wear reducing carbon coatings from alkane environment

   https://doi.org/10.1038/s41598-021-00044-9  

   Shirani, Asghar; Li, Yuzhe; Eryilmaz, Osman Levent; Berman, Diana (December 2021, Scientific Reports)

   Abstract Minimizing the wear of the surfaces exposed to mechanical shear stresses is a critical challenge for maximizing the lifespan of rotary mechanical parts. In this study, we have discovered the anti-wear capability of a series of metal nitride-copper nanocomposite coatings tested in a liquid hydrocarbon environment. The results indicate substantial reduction of the wear in comparison to the uncoated steel substrate. Analysis of the wear tracks indicates the formation of carbon-based protective films directly at the sliding interface during the tribological tests. Raman spectroscopy mapping of the wear track suggests the amorphous carbon (a-C) nature of the formed tribofilm. Further analysis of the tribocatalytic activity of the best coating candidate, MoN-Cu, as a function of load (0.25–1 N) and temperature (25 °C and 50 °C) was performed in three alkane solutions, decane, dodecane, and hexadecane. Results indicated that elevated temperature and high contact pressure lead to different tribological characteristics of the coating tested in different environments. The elemental energy dispersive x-ray spectroscopy analysis and Raman analysis revealed formation of the amorphous carbon film that facilitates easy shearing at the contact interface thus enabling more stable friction behavior and lower wear of the tribocatalytic coating. These findings provide new insights into the tribocatalysis mechanism that enables the formation of zero-wear coatings. 

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4. Emerging superlubricity: A review of the state of the art and perspectives on future research

   https://doi.org/10.1063/1.5051445  

   Baykara, Mehmet_Z; Vazirisereshk, Mohammad_R; Martini, Ashlie (October 2018, Applied Physics Reviews)

   We present a review of superlubricity: the state of ultra-low friction between surfaces in relative motion. Various approaches to achieving this state are considered in a broad sense, including structural superlubricity, superlubricity via normal force control, and contact actuation, as well as thermolubricity, liquid superlubricity, and quantum lubricity. An overview of the physical fundamentals associated with each approach is presented, with particular emphasis on recent theoretical and experimental developments that constitute milestones in our scientific understanding. The review also includes a discussion of perspectives on future research in the context of existing challenges. It is projected that interest in superlubricity from the basic science and engineering communities will continue to accelerate in the near future, accompanied by a transition from fundamental studies to technologically relevant applications. 

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5. Fabrication of Porous Carbon Films and Their Impact on Carbon/Polypropylene Interfacial Bonding

   https://doi.org/10.3390/jcs5040108  

   Peng, Yucheng; Burtovyy, Ruslan; Bordia, Rajendra; Luzinov, Igor (April 2021, Journal of Composites Science)

   null (Ed.)

   Porous carbon films were generated by thermal treatment of polymer films made from poly(acrylonitrile-co-methyl acrylate)/polyethylene terephthalate (PAN/PET) blend. The precursor films were fabricated by a dip-coating process using PAN/PET solutions in hexafluoro-2-propanol (HFIP). A two-step process, including stabilization and carbonization, was employed to produce the carbon films. PET functioned as a pore former. Specifically, porous carbon films with thicknesses from 0.38–1.83 μm and pore diameters between 0.1–10 μm were obtained. The higher concentrations of PET in the PAN/PET mixture and the higher withdrawal speed during dip-coating caused the formation of larger pores. The thickness of the carbon films can be regulated using the withdrawal speed used in the dip-coating deposition. We determined that the deposition of the porous carbon film on graphite substrate significantly increases the value of the interfacial shear strength between graphite plates and thermoplastic PP. This study has shown the feasibility of fabrication of 3D porous carbon structure on the surface of carbon materials for increasing the interfacial strength. We expect that this approach can be employed for the fabrication of high-performance carbon fiber-thermoplastic composites. 

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