Abstract
Due to the widespread use of nanocarbon materials (NCMs), more researchers are studying their tribological performances. In this work, the tribological behaviors of the following five types of NCMs with different geometric shapes were evaluated in a novel oil-in-water system: spherical fullerenes (C60, 0D), tubular multi-walled carbon nanotubes (MWCNT, 1D), sheet graphene oxide (GO, 2D), sheet graphene oxide derivative (Oct-O-GO, 2D), and lamellar graphite (G, 3D). Among these, GO with two types of oxidation degrees, i.e., GO(1), GO(2), and Oct-O-GO(1) were synthesized and characterized using Fourier-transform infrared spectroscopy, Raman spectroscopy, x-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and contact angle measurements. The load-carrying capacity of the NCM emulsions were evaluated using a four-ball test machine, and the lubrication performances were investigated using a high-frequency reciprocating friction and wear tester with a sliding distance of 1,800 mm under different loads (50 N and 100 N) at 0.5 Hz. The results revealed that the Oct-O-GO(1) emulsion exhibited the best load-carrying capacity, and the best friction-reducing and anti-wear properties compared to other emulsions. Moreover, the anti-wear advantage was more prominent under high load conditions, whereas the other emulsions exhibited a certain degree of abrasive or adhesive wear. The lubrication mechanism was determined through the analysis of worn surfaces using scanning electron microscopy/energy-dispersive x-ray spectroscopy, micro-Raman spectroscopy, and x-ray photoelectron spectroscopy. The results revealed that during frictional sliding, the ingredients in the emulsion can absorb and react with the freshly exposed metal surface to form surface-active films to protect the surfaces from abrasion. Moreover, it was found that the higher the amount of ingredients that contain alkyl and O-H/C=O, the better was the lubrication performance in addition to an increase in the carbon residue in the tribofilm generated on the meal surface.
Highlights
Graphene has attracted significant attention in recent years
Other nanocarbon materials (NCMs) with the same skeleton structures, such as fullerene (C60), multi-walled carbon nanotubes (MWCNTs), graphite (G) and graphene oxide (GO) exhibit remarkably low friction and wear [5−9]; they demonstrate a high potential for application as lubricant additives
The FTIR spectra were obtained by a Paragon 1000 FTIR spectroscope (Perkin Elmer, Inc., USA) with the attenuated total reflectance (ATR) attachment scanning from 650–4,000 cm−1
Summary
Graphene has attracted significant attention in recent years. One of its most desirable properties is its superlow-friction characteristic, which expands the concept of zero wear [1−4]. Other nanocarbon materials (NCMs) with the same skeleton structures, such as fullerene (C60), multi-walled carbon nanotubes (MWCNTs), graphite (G) and graphene oxide (GO) exhibit remarkably low friction and wear [5−9]; they demonstrate a high potential for application as lubricant additives. When used as oil additives, alkylated C60 exhibits a remarkable anti-wear property by reducing the areas of the worn surfaces and smoothing the scuffing. The results revealed that the addition of the alkylated C60 reduces the friction coefficient both at 25 °C and 90 °C, where it exists as aggregates and monomers, respectively This can be attributed to the presence of the aliphatic chains, leading to an improved solubility and dispersibility of the target compound in lubricating oils. Graphene-based additives in the lubrication medium can effectively reduce the friction and improve the wear resistance of the contacting surfaces [36−38]. The corresponding tribological properties were evaluated, and the worn surfaces were analyzed to clarify their lubricating mechanisms
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