Abstract
Anthracite sheets were coated by sorbitol fatty acid ester (span80) through ball-milling process. The tribological properties of the span80-coated anthracite sheets as the additive in polyalpha olefin were evaluated through a series of friction tests using a four ball machine. The results revealed that the span80-coated anthracite sheets exhibited excellent dispersion stability in base oil. In addition, compared with base oil, the average coefficient of friction, wear scar diameter, and wear volume of modified oil at a mass fraction of 0.03% span80-coated anthracite sheets decreased by 45.39%, 60.13%, and 95.95%, respectively. The oil containing span80-coated anthracite sheets achieved good friction-reducing and anti-wear effects over a wide range of applied loads, temperatures, or rotating speeds. Control experiments were performed as well. The results obtained using span80-coated anthracite sheets were superior to those obtained using pure anthracite. The lubrication mechanism was attributed to the synergistic action of the crystalline and amorphous carbon in anthracite sheets as they formed a protective film and played a mitigative role on the surface of friction pair, which mitigated the wear extent of the friction pair.
Highlights
Studies have revealed that approximately 30% of all primary energy is lost through friction, 50% of accidents involving mechanical equipment are caused by lubrication failure and/or excessive lubrication, and 60% of machine parts fail because of wear every year [1]
The X-ray powder diffraction (XRD) pattern of the anthracite revealed that it has a higher background strength, which indicates that the anthracite contains a large amount of amorphous carbon (Fig. 2(e))
Span80-coated anthracite sheets fabricated by a simple ball milling method effectively enhanced the dispersion stability of anthracite in the base oil
Summary
Studies have revealed that approximately 30% of all primary energy is lost through friction, 50% of accidents involving mechanical equipment are caused by lubrication failure and/or excessive lubrication, and 60% of machine parts fail because of wear every year [1]. Considerable research has been conducted on lubricating oil additives, and the results have revealed that nano-elements, such as oxides, sulfides, nitrides, and complexes, nitrogen-containing heterocyclic compounds, and ionic liquids have antiwear (AW), friction-reducing (FR), and anti-corrosion (AC) properties. These carbon-based materials have better anti-wear and anti-friction performances, their disadvantages such as high cost or complex preparation processes limit their development for industrial applications. It is crucial to find other lubricating oil additives with excellent anti-wear and friction-reducing properties that can overcome the shortcomings of the aforementioned materials. Studies on the utilization of anthracite as a lubricant additive, its effect on the tribological behavior of base oil, remain very limited. Anthracite contains many polar functional groups, such as phenolic hydroxyl, carboxy, and methoxyl groups, which make it susceptible to agglomeration in non-polar oil, thereforem, it is difficult to directly use it as an additive for oil-based lubricants
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