Abstract
The tribological properties of trifluorotris(pentafluoroethyl) phosphate [(C2F5)3PF −3 , FAP]-derived ionic liquids were evaluated under boundary conditions. The anion is hydrophobic in comparison with bis(trifluoromethylsulfonyl)imide [(CF3SO2)2N−, TFSI]. 1,3-Dialkylimidazolium salts of FAP provided much lower friction than 1,3-dialkylimidazolium salts of TFSI. In addition, the FAP salts exhibit better anti-wear properties than the TFSI salts. Another advantage of the FAP anion is availability of several cations to prepare ionic liquids. For example, tetraalkylphosphonium, N,N-dialkylpyrrolidium, and tetramethylisouronium salts of FAP provided friction coefficient of approximately 0.1. Straight-chain carboxylic acids as model friction-reducing additives improved the tribological properties of the FAP salts. Surface analyses were conducted to study the boundary film formed by rubbing. It was found that the boundary film is composed of adsorbed anion on uppermost surfaces and reacted anion on sub-surfaces. The model friction-reducing additives were found on the rubbed surfaces.
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Abbreviations
- BF4:
-
Tetrafluoroborate
- FAP:
-
Trifluorotris(pentafluoroethyl) phosphate
- PF6:
-
Hexafluorophosphate
- TFSI:
-
bis(Trifluoromethylsulfonyl)imide
- d-C12A:
-
Perdeuteriododecanoic acid, C11D23COOH
- mM:
-
Unit of concentration (mmol kg−1)
- JIS:
-
Japanese Industrial Standards
- m/z:
-
Mass-to-charge ratio
- SUJ2:
-
Bearing steel assigned by JIS
- TOF-SIMS:
-
Time-of-flight secondary ion mass spectroscopy
- XPS:
-
X-ray photoelectron spectroscopy
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Acknowledgments
This research was supported by the grants-in-aid for Scientific Research on Priority Areas, “Science of Ionic Liquids” no. 18045003 from the Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government. The authors are grateful to Merck KGaA (Germany) for supporting the ionic liquids.
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Minami, I., Kita, M., Kubo, T. et al. The Tribological Properties of Ionic Liquids Composed of Trifluorotris(pentafluoroethyl) Phosphate as a Hydrophobic Anion. Tribol Lett 30, 215–223 (2008). https://doi.org/10.1007/s11249-008-9329-y
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DOI: https://doi.org/10.1007/s11249-008-9329-y