Humidity-dependent lubrication of highly loaded contacts by graphite and a structural transition to turbostratic carbon

Morstein, Carina Elisabeth; Klemenz, Andreas; Dienwiebel, Martin; Moseler, Michael

doi:10.1038/s41467-022-33481-9

Cited by 29 publications

(13 citation statements)

References 37 publications

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“…The FF is designed to be compatible with the OPLS FF, which facilitates future extensions, and the description of additional lubricants and/or surface terminations can be based on already existing OPLS parameters, as demonstrated using the example of glycerol. This applies not only to liquid lubricants but also to solid lubricants such as PTFE and graphite . While we show that in many cases, a further optimization of the original OPLS parameters for hydrocarbons and alcohols can improve the description of the passivated a-C surfaces, the original parameters are sufficiently accurate in many of our tests.…”

Section: Discussionmentioning

confidence: 75%

An All-Atom Force Field for Dry and Water-Lubricated Carbon Tribological Interfaces

Reichenbach,

Sylla,

Mayrhofer

et al. 2024

J. Phys. Chem. C

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We present a nonreactive force field for molecular dynamics simulations of interfaces between amorphous carbon surfaces and their interaction with water. The force field is tailored to surfaces with hydrogen, hydroxyl, and aromatic surface passivation and enables large-scale simulations of dry and lubricated tribological contacts. To favor its compatibility with existing force-field parameterizations for liquids and allow a straightforward extension to other types of surface passivation species, we adopt the functional form of the Optimized Potentials for Liquid Simulations. The optimization of the force-field parameters is systematic and follows a protocol that can be reused for other surface−molecule combinations. Reference data are calculated with gradient-and dispersion-corrected density functional theory and include the bonding geometry and elastic deformation of bulk and surface species as well as surface adhesion and water adsorption energy landscapes. The conventions adopted to define the different force-field atom types are based on the hybridization of carbon orbitals and enable a simple and efficient parameter optimization strategy that only requires quantummechanical simulations of crystalline reference structures. After testing the force field on amorphous interfaces, we present two examples of application to tribological problems. Namely, we investigate the relationships between dry friction and the corrugation of the contact potential energy surface and the dependency of friction on the thickness of interface water films. We finally discuss the limitations of the force field and propose strategies for its improvement and extension.

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Section: Discussionmentioning

confidence: 75%

An All-Atom Force Field for Dry and Water-Lubricated Carbon Tribological Interfaces

Reichenbach,

Sylla,

Mayrhofer

et al. 2024

J. Phys. Chem. C

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“…On one hand, the washing effect of water during rotation can take the graphite debris away. On the other hand, water molecules absorbed on the surface [28] prevent the adhesion of graphite debris on the surface of the cemented carbide. Therefore, it can be deduced that the frictional modification of surface textures in water mainly originates from the lubrication effect.…”

Section: Resultsmentioning

confidence: 99%

Frictional performance of surface-textured phenolic resin-impregnated graphite materials under water lubrication

Xu,

Yuan,

Luo

et al. 2023

Mater. Res. Express

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The frictional performance between impregnated graphite materials and YG-8 cemented carbide is investigated on a self-developed rotating-type tribometer. The test configuration is a cemented carbide plate rotating against the graphite surface. Three types of concave-type textures, including linear grooves, circular dimples and isosceles triangular dimples, are fabricated by laser process on the graphite surfaces to improve the tribological properties. The test environments include dry condition and water lubrication. The corresponding friction coefficients, surface micrographs of graphite samples and cemented carbide plates are analyzed. To reveal the underlying mechanism of the frictional modification effect under water lubrication, the formation of graphite transfer film on cemented carbide plates, the water contact angles of graphite surface and the hydrodynamic effect are further discussed. It is verified that the introduction of textures on graphite surfaces can significantly improve the tribological performance of water-lubricated graphite materials.

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“…However, low friction has, to the best of the authors' knowledge, not been reported for carbon-carbon couples in dry nitrogen or hydrogen environments in a at-on-at sliding con guration. Generally, moisture is needed in inert gas environments to promote low friction of graphite or other carbons with sp2 con guration, through passivation of dangling bonds [24,27,28,74]. One paper has been found reporting low friction in argon and helium for sliding graphite couple, however, information about the residual moisture content is inadequate [75].…”

Section: Mechanistic Discussionmentioning

confidence: 99%

Insights of the ultralow wear and low friction of carbon fiber reinforced PTFE in inert trace trace moisture environment

Johansson

Elo

Naeini

et al. 2023

Preprint

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Ultralow wear rates and low friction have been observed for carbon fiber reinforced PTFE (CF/PTFE) when sliding against steel or cast iron in dry gas environments. Although the strong environmental sensitivity of this tribosystem is well known, the origin of the outstanding tribological performance in dry gas remains unanswered. Some researchers attribute the low friction and wear to the formation of carbon-rich surfaces in the absence of oxygen and moisture in the environment. However, low friction between carbon surfaces is generally dependent on moisture. In this paper, extensive analyzes are conducted on the tribofilms formed on the CF/PTFE surface and the steel counterface after sliding in a high-purity nitrogen environment. TEM analysis of a cross-section of the tribofilm on the steel surface reveals that the sliding surface consists mainly of iron (II) fluoride and not carbon, even though a significant amount of carbon was observed near the surface. XPS and TEM analysis further revealed that the tribofilm formed on the worn composite surface consisted of nanoparticle agglomerates, anchored to the PTFE matrix and to each other by carbon with turbostratic structure. Turbostratic carbon also formed an ultrathin and surface-oriented superficial layer on top of the agglomerates. Governing mechanisms of the low friction and wear of the CF/PTFE – steel tribosystem were investigated by complementary tribotests with pure graphite samples and MD simulations of the identified surfaces. These indicated that the low friction between the carbon and iron fluoride in the tribofilms is due to poor adhesion between the distinctly different surfaces.

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Humidity-dependent lubrication of highly loaded contacts by graphite and a structural transition to turbostratic carbon

Cited by 29 publications

References 37 publications

An All-Atom Force Field for Dry and Water-Lubricated Carbon Tribological Interfaces

An All-Atom Force Field for Dry and Water-Lubricated Carbon Tribological Interfaces

Frictional performance of surface-textured phenolic resin-impregnated graphite materials under water lubrication

Insights of the ultralow wear and low friction of carbon fiber reinforced PTFE in inert trace trace moisture environment

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