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Phosphonium Ionic Liquids in Lubrication

Part 3: CYPHOS® IL 109

In the previous blogs [1-2] we briefly reviewed some literature on the applications of room-temperature ionic liquid (RTIL) trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide 1 aka CYPHOS® IL 109 (CAS # 460092-03-9, Strem: 15-6370, 96-6520, Ionic Liquid Kit 3: CYPHOS® IL Phosphonium Salt Kit) in lubrication:

This blog is the final installment in the series describing the use of ionic liquids (ILs) in lubrication. In the work [3], the lubricating ability and physicochemical properties of three ionic liquids with TFSI-anion (including 1), but based on three different cations (ammonium, imidazolium and phosphonium) were studied for steel-steel contact. The three ILs studied presented very similar values of thermal stability, density, and surface tension. No significant differences in friction coefficients of the three lubricants were observed at low frequency for any of the surface finishes. However, at the highest frequency studied, and only when the steel disk had a machine finish, a friction reduction of 90% was observed when 1 was used.

The examples reviewed so far have mostly concerned the lubrication of steel-on-steel and steel-on-aluminum contacts. However, 1 was shown to be a promising candidate also for other challenging areas such as lubrication of nickel (Ni)-based alloys and titanium (Ti).

Thus, Ni-based alloys are widely used in tribological pairs as hardfacing coatings owing to their anti-wear and anticorrosion behavior. The NiCrBSi alloys provide coatings with high tenacities, hardness’s, and protection against corrosion, depending on the Cr content. In the publication [4] 1 and trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate ([P6,6,6,14][BEHP]) were used as neat lubricants in Ni-based coatings reinforced with spherical WC (tungsten carbide) particles. The wear was not related to the WC content for [P6,6,6,14][BEHP]. However, the wear decreased with the increase in WC content when 1 was used. The authors thought that it could be related to the higher viscosity of [P6,6,6,14][BEHP] in comparison with 1.

Ti is an attractive candidate to replace steel in automobiles, aircrafts, and watercrafts due to its unique characteristics. However, a critical drawback of Ti is its poor lubrication [5]. In this study, the lubricity of four phosphonium ionic liquids, including 1, was studied (three-ball-on-disk macrotribology and AFM nanotribology) under various conditions. The lower viscosity of 1 coupled with its good boundary lubrication made it the most effective IL for the macrotribological measurements, which were in the mixed lubrication regime. It was concluded that the results reiterated the importance of carefully selecting IL lubricants based on the lubrication regime of the sliding surfaces.

The reviews could be continued, but it is evident that the interest in 1 in lubrication (and other areas) remains unabated due to its unique characteristics [6].

And “Phosphonium ILs clearly offer, in some cases, several advantages over other types of ILs, including, in specific cases and applications, higher thermal stability, lower viscosity, and higher stability in strongly basic or strongly reducing conditions” [7]. Thus, the readers can expect to see more blogs on the fascinating phosphonium ionic liquids and their use in different applications. Stay tuned!

References:

Related products

15-6370 Trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide, min. 97% CYPHOS® IL 109 (460092-03-9)

96-6520 Ionic Liquid Kit 3: CYPHOS® IL Phosphonium Salt Kit

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