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Nickel acetyl acetonate (Ni(acac)2), a metal-organic compound, was directly dispersed in base oils alkylated naphthalene (AN-5), diisooctyl sebacate (DIOS), poly-α-olefin (PAO6), and mineral oil (liquid hydrocarbon mixtures:150 N) in the presence of commercial dispersant RF1151 (monoallyl poly(isobutylene succinimide). The tribological properties of the lubricants were tested with a four-ball friction and wear tester. The friction-induced in-situ formation of carbon films on rubbed steel surfaces under the catalysis of Ni(acac)2 was investigated, and the as-formed carbon films were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results show that Ni(acac)2 added in the base oils can decompose to form metallic nickel to form nickel layer on the rubbed metal sub-surfaces and catalyze the degradation of the base oil molecules adsorbed to form carbon-based tribofilms. The carbon film formed from AN-5 with aromatic ring structure has a high degree of graphitization and the best friction-reducing and antiwear abilities, and those formed from PAO6 and 150 N with linear structure have a low degree of graphitization as well as good tribological properties. Under the lubrication of DIOS with Ni(acac)2, however, there is no carbon film formation while the tribological properties of the lubricant are relatively poor, due to the absence of the catalytic metallic nickel and nickel oxide layer on the rubbed metal sub-surface. Thanks to the catalytic effect of metallic nickel released from Ni(acac)2 for the degradation of various base oils with different molecular structure, the present approach could provide a rational pathway to tune the in-situ formation of carbon-based tribofilm on rubbed steel surfaces so as to effectively reduce the friction and wear of steel-steel sliding pair. [ABSTRACT FROM AUTHOR]

Nickel (Ni) nanoparticles can be enriched on the surface of iron-based frictional pairs, which provides the possibility to get rid of the competitive adsorption between the polar species of vegetable oil and the surface-active nano-additives thereon. In this paper, nickel acetylacetonate was used as a precursor to in-situ synthesize nickel nanoparticles with an average diameter of about 12 nm in rapeseed oil (RO) as the reducing agent, surface modifier, and solvent as well. The tribological properties of the as-synthesized Ni nanoparticles were evaluated with a four-ball tribometer, and their tribomechanism was investigated based on the characterizations of the tribofilm on rubbed steel surfaces by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that the Ni nanoparticles in-situ prepared in the RO with a mass fraction of 0.3% can reduce the wear scar diameter (WSD) of the steel ball by 36%. This is because, on the one hand, the Ni nanoparticles are adsorbed on the rubbed steel surfaces to repair or fill up the micro-pits and grooves thereon. On the other hand, Ni nanoparticles participate in tribochemical reactions with atmospheric O and steel substrate to form the tribochemical reaction film on the rubbed steel surfaces with the assistance of friction-induced heat and applied normal load. In addition, an amorphous carbon film is formed on the rubbed surface via the carbonization of base oil under the catalysis of Ni nanoparticles. The adsorbed Ni layer, the tribochemical reaction film, and the carbon layer comprise a composite tribofilm composed of amorphous carbon, polar fatty acid, metallic nickel, iron oxides, and nickel oxides on the rubbed steel surfaces, which contributes to significantly improving the antiwear ability and load-carrying capacity of the RO for the steel–steel sliding pair. [ABSTRACT FROM AUTHOR]

Oleic acid-modified lanthanum borate nanosheets (OA-LBNs) were prepared by simple surface modification technology combined with precipitation method. The structure of the as-prepared light yellow transparent nanofluid of OA-LBNs was analyzed by Fourier transform infrared spectroscopy and transmission electron microscopy, and its thermal stability was evaluated by thermogravimetric analysis. Moreover, the tribological properties of OA-LBNs nanofluid as the lubricant additive in diisooctylsebacate (DIOS), poly-α-olefin (PAO4), and rapeseed oil (RO) were evaluated with a four-ball friction and wear tester, and its tribomechanisms in the three kinds of base oils were also discussed. The results show that OA-LBNs nanofluid exhibits good antiwear ability in the three kinds of base oils; in particularly, OA-LBNs nanofluid added in PAO4 shows the best antiwear ability. The tribological properties of the OA-LBNs nanofluid as the lubricant additive are dependent on the nature of the base oils. Namely, the polarity of the base oil influences the adsorption of the OA-LBNs nanofluid on the rubbed steel surface, thereby affecting the composition of the tribofilm formed on the rubbed steel surface and resulting in changes in tribological properties. [ABSTRACT FROM AUTHOR]