Abstract
A magnetic ionic liquid (abridged as MIL) [C6mim]5[Dy(SCN)8] was prepared and used as the magnetic lubricant of a steel-steel sliding pair. The tribological properties of the as-prepared MIL were evaluated with a commercially obtained magnetic fluid lubricant (abridged as MF; the mixture of dioctyl sebacate and Fe3O4, denoted as DIOS-Fe3O4) as a control. The lubrication mechanisms of the two types of magnetic lubricants were discussed in relation to worn surface analyses by SEM-EDS, XPS, and profilometry, as well as measurement of the electric contact resistance of the rubbed steel surfaces. The results revealed that the MIL exhibits better friction-reducing and antiwear performances than the as-received MF under varying test temperatures and loads. This is because the MIL participates in tribochemical reactions during the sliding process, and forms a boundary lubrication film composed of Dy2O3, FeS, FeSO4, nitrogen-containing organics, and thioether on the rubbed disk surface, thereby reducing the friction and wear of the frictional pair. However, the MF is unable to form a lubricating film on the surface of the rubbed steel at 25 °C, though it can form a boundary film consisting of Fe3O4 and a small amount of organics under high temperature. Furthermore, the excessive Fe3O4 particulates that accumulate in the sliding zone may lead to enhanced abrasive wear of the sliding pair.
Highlights
With the continuous progress of industrial technology, newly developed lubricants need to meet more and more stringent requirements for mechanical properties and lubricating performance [1,2,3]
It can be seen that the Magnetic ionic liquids (MILs) performs significantly better than the magnetic fluids (MFs) in reducing friction
The coefficients of friction of the steelsteel sliding pair lubricated by the MIL at 100 and 200 N at 25 °C are 0.17 and 0.18, respectively, much lower than those obtained under MF lubrication (0.27 and 0.26)
Summary
With the continuous progress of industrial technology, newly developed lubricants need to meet more and more stringent requirements for mechanical properties and lubricating performance [1,2,3]. Besides excellent load-bearing capacities, good friction-reducing, and antiwear abilities, they need to exhibit self-repairing capabilities and environmental acceptance In this respect, magnetic lubricants as novel lubricants could be of special significance, because they can fill up the scratches and grooves on rubbed surfaces under an external magnetic field to achieve continuous lubrication, and they can counteract the effect of gravity and the centripetal force during the lubrication process, thereby preventing leakage and external pollution [4,5,6]. Bombard et al [28] prepared and investigated the tribological properties of ionic liquids, ionic liquidbased MFs (ionic liquids + carbonynyl iron particles), and PAO-based MF (PAO + carbonyl iron particles; PAO refers to poly-alpha olefin) They found that ionic liquids exhibit optimal antiwear effects for the steelsteel tribopair and polyformaldehyde-polyformaldehyde tribopair, and all ionic liquid-based MFs exhibit a much better friction-reducing ability than traditional. DIOS is used as the base stock for formulating the MFs, because, as an ideal carrier for preparing MFs widely used in mechanical sealing, lubrication, and other fields, it has excellent chemical stability and a good viscosity-temperature characteristic
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