In Situ Synthesis of Graphene Nitride Nanolayers on Glycerol-Lubricated Si₃N₄ for Superlubricity Applications

Abstract

The increasing demand for sustainable tribology has accelerated the development of environmentally friendly lubrication solutions such as water or water-related lubricants. Earlier works have reported on water-lubricated sliding of silicon nitride (Si 3 N 4 ) at high speeds, which can result in a superlow friction (μ < 0.01) owing to the formation of hydrodynamic water films on hydrophilic surface layers. Here, combined boundary-lubrication experiments at low sliding speeds and atomistic simulations reveal an alternative superlubricity mechanism for glycerol-lubricated Si 3 N 4 . X-ray photoelectron and time-of-flight secondary ion mass spectrometry performed inside and outside the wear track as well as high-resolution mass spectroscopy of the used lubricant strongly suggest that sub-nanometerthick graphene nitride layers form at the very top of Si 3 N 4 . In the accompanying atomistic simulations, glycerol molecules undergo tribochemical decomposition and react with surface-bound nitrogen atoms to form carbon nitrides. Further shearing promotes the formation of 2D graphene nitrides that passivate the ceramic surfaces and induce a superlow friction under boundary lubrication. Thus, glycerol-lubricated Si 3 N 4 has a high potential for use in green superlubricity enabled by in situ synthesis of disordered graphene nitride species.

Superlow Friction of a-C:H Coatings in Vacuum: Passivation Regimes and Structural Characterization of the Sliding Interfaces

“…Analogous, tribologically-induced sp 3 -to-sp 2 transitions were observed in our previous atomistic simulations, revealing shear-induced aromatic surface reconstructions on diamond (111) surfaces lubricated with water [10,11] and ta-C surfaces lubricated with glycerol [12]. The delocalization of π-electrons on the graphenoid surfaces makes them chemically inert and, thus, shields them from cold welding, even at high contact pressures [10,13].…”

Nitrogen-Doped Carbon Dot as a Lubricant Additive in Polar and Non-polar Oils for Superior Tribological Properties via Condensation Reaction

“…The N 1s spectrum (Figure b) shows peaks with binding energies of about 398.6, 399.4, and 400.1 eV, which was attributed to the C–N and −NH groups in the carbonitrides after carbamide-assisted carbonization . It can be seen in Figure c that the characteristic peaks appear when the binding energies were 706.4, 709.1, 714.0, 717.0, and 720.1 eV, which confirms the existence of metal oxides Fe 2 O 3 and Fe 3 O 4 . − Similarly, the Fe–O (528.4 eV) peak also appears in the O 1s fine spectrum (Figure d) of the worn surface lubricated by 0.12 wt % NCD PAO10 dispersion, corresponding to the peaks of Fe 2 O 3 and Fe 3 O 4 in the Fe 2p fine spectrum (Figure f). The formation of carbonitrides can also be inferred from the three characteristic peaks in the N 1s fine structure spectrum (Figure e).…”

Effect of the Graphitization Mechanism on the Friction and Wear Behavior of DLC Films Based on Molecular Dynamics Simulations

“…Moreover, in the late friction stage, continuous sliding makes the amorphous graphite area expand (Figure 11c). Meanwhile, although the N sp 2 of the two models is increasing and the N sp 3 is decreasing (Figure S2), their F f does not decline with the increase in sp 2 , which indicates that the number of hybrid carbon atoms cannot completely determine the F f change. In other words, the amorphous graphitization area formed by sliding cannot effectively reduce the F f .…”

“…1 Effectively reducing the energy consumed by friction has profound significance for sustainable development. 2,3 Diamond-like carbon (DLC) films have excellent physical and chemical properties, low-friction coefficients, and high wear resistance, which have already been widely used in industry fields. 4−8 However, the related friction and wear mechanisms are still controversial at present, especially the effect of the graphitization mechanism on the low-friction behavior of the DLC film, and there are diametrically opposed views.…”

“…Since the industrial revolution, a large part of the energy generated by increasing industrial activities has been consumed by friction within the mechanical system . Effectively reducing the energy consumed by friction has profound significance for sustainable development. , Diamond-like carbon (DLC) films have excellent physical and chemical properties, low-friction coefficients, and high wear resistance, which have already been widely used in industry fields. − However, the related friction and wear mechanisms are still controversial at present, especially the effect of the graphitization mechanism on the low-friction behavior of the DLC film, and there are diametrically opposed views. Therefore, it is very meaningful to further study how the graphitization mechanism controls the influence of friction and the wear behavior of the DLC film.…”