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Effects of Alkyl Chain Length of Sulfate and Phosphate Anion-Based Ionic Liquids on Tribochemical Reactions
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
2018 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 66, no 1, 8Article in journal (Refereed) Published
Abstract [en]

Ionic liquids are expected to become increasingly popular lubricants as they feature a number of attractive properties. This investigation focused on sulfate and phosphate anion-based ionic liquids and the improvement in lubricating performance with the addition of these anions. However, the detailed lubricating mechanism and effect of alkyl chain length on tribochemical reactions are unclear. This study investigates tribochemical reaction processes using a quadrupole mass spectrometer (Q-MS) and X-ray photoelectron spectroscopy. Seven types of ionic liquids: 1-ethyl-3-methylimidazolium hydrogensulfate ([EMIM][HSO4]), 1-ethyl-3-methylimidazolium methylsulfate ([EMIM][MSU]), 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][ESU]), 1-ethyl-3-methylimidazolium n-octylsulfate ([EMIM][OSU]), 1-ethyl-3-methylimidazolium dimethyl phosphate ([EMIM][DMP]), 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][DEP]), and 1-ethyl-3-methylimidazolium dibutyl phosphate ([EMIM][DBP]), were selected as lubricants. The friction coefficient of sulfate anion-based ionic liquids increased as their alkyl chain lengthened. However, wear scar diameter in this case showed the opposite tendency. The friction coefficient and wear scar diameter of phosphate anion-based ionic liquids increased with an increase in the alkyl chain length. Q-MS results indicated that the main outgassing components during sliding were the cation components, whereas the anion remained on the sliding surface and formed a tribofilm. The ionic liquids with short alkyl chains reacted with the sliding surface easily and led to very low friction. However, corrosive wear occurred in the case of the sulfate anion. On the other hand, anions with long alkyl chains underwent gradual tribochemical reactions because that led the mitigation of contact with nascent surface. The phosphate-based ionic liquids with long alkyl chains were unable to cause the lubricating effect due to low reactivity.

Place, publisher, year, edition, pages
Springer-Verlag New York, 2018. Vol. 66, no 1, 8
Keyword [en]
Ionic liquids, Phosphate, Quadrupole mass spectrometer, Sulfate, Tribochemical reaction
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
URN: urn:nbn:se:kth:diva-220192DOI: 10.1007/s11249-017-0962-1Scopus ID: 2-s2.0-85037054268OAI: oai:DiVA.org:kth-220192DiVA: diva2:1167090
Note

QC 20171218

Available from: 2017-12-18 Created: 2017-12-18 Last updated: 2018-01-13Bibliographically approved

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Watanabe, Seiya

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