Molecular Behavior of Room-temperature Ionic Liquids under Lubricating Condition
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ORIGINAL PAPER
Molecular Behavior of Room-temperature Ionic Liquids under Lubricating Condition Seiya Watanabe • Koji Takiwatari • Miki Nakano • Koji Miyake • Ryo Tsuboi Shinya Sasaki
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Received: 14 November 2012 / Accepted: 10 March 2013 / Published online: 22 March 2013 Ó Springer Science+Business Media New York 2013
Abstract The molecular behavior of room-temperature ionic liquids (RTILs) under lubricating condition was analyzed using fourier transform infrared spectroscopy equipped with a pin-on-disk tribometer to simultaneously measure the friction force, normal load, and IR spectrum. When 1-metyl-3butylimidazolium trifluoromethanesulfonate ([BMIM]OTf), which is miscible with water, was used as a lubricant, the water content increased with time, and the ratio of water to cation remained constant even though the film thickness reduced under the lubricating condition at a load of ~25 N. When 1-metyl-3-butylimidazolium tetrafluorophosphate ([BMIM]PF6), which is water-insoluble, was used as a lubricant, the water content was quite small and increased slightly with time, and the ratio of water to cation also remained constant even when a normal load of ~25 N was applied. The SUJ2 pin surface showed oxidative discoloration after the friction test using [BMIM]OTf, but there was little change in color when[BMIM]PF6 was used. XPS results indicated that iron oxide, chromium oxide and sulfate were observed on the worn pin surface using [BMIM]OTf and the CaF2 disk. However, iron oxide and iron phosphate were observed for the
S. Watanabe R. Tsuboi S. Sasaki (&) Tokyo University of Science, 6-3-1 Niijyuku, Katsushika-ku, Tokyo 125-8585, Japan e-mail: [email protected]; [email protected] K. Takiwatari M. Nakano K. Miyake Advanced Manufacturing Research Institute (AMRI), National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan Present Address: K. Takiwatari Department of Chemical Engineering, Ichinoseki National College of technology, Takanashi, Hagisho, Ichinoseki, Iwate 021-8511, Japan
worn pin surface using [BMIM]PF6 and the CaF2 disk. These results suggest that the amount of water contained in the RTILs as well as window materials have a significant effect on the tribo-chemical reaction of RTILs. Keywords Imidazolium-based room-temperature ionic liquids FT-IR XPS Water Corrosion
1 Introduction Room-temperature ionic liquids (RTILs) based on imidazolium cations have been extensively investigated over the last 20 years in the field of electrochemistry [1–3]. They are finding potential for utilization in more wideranging areas of technology. RTILs have properties such as high thermal stability, low volatility, non-flammability, low melting point, and broad liquid range, which are applicable to superior lubricants and additives [4–7]. Previous research on RTILs as a lubricant have mainly focused on the characterization of various types of RTILs and synthesizing novel functionalized RTILs. Tetrafluoro-borate (BF4) and hexafluoro-ph
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