Friction and wear are unavoidable phenomena responsible for important energy and lifespan losses in all machines utilizing moving parts. Lubricants can increase the durability and efficiency of machine components by mitigating these losses. However, many of the world’s lubricants are petroleum-based, harmful to the environment, and non-biodegradable. Protic ionic liquids (PILs) are an alternative greener option that may help replace some such lubricants. PILs can be easily synthesized through proton transfer from a Brønsted acid to a Brønsted base and exhibit significant potential as lubricant additives on account of their high thermal stability, non-flammability, low melting points, lack of vapor pressure, low cost, and biodegradability.&nbsp;This research covers the tribological performance of three halogen-free protic ionic liquids, 2-hydroxyethylammonium 2-ethylhexanoate (Eet), 2-hydroxyethylammonium p-toluenesulfonate (Ets), and 2-hydroxyethylammonium 4-dodecylbenzenesulfonate (Eds) which are designed and synthesized using the same base (ethanolamine) but different acids of varying acidity and alkyl chain length. The relationship among their ionicity, molecular structures, and tribological properties are investigated when these protic ionic liquids are used as lubricant additives to water. Each lubricant is synthesized in our lab at the Rochester Institute of Technology and evaluated as a lubricant additive in a 1 wt.% aqueous solution.&nbsp;The PIL solutions are tested using a ball-on-flat reciprocating tribometer under room temperature for steel-ceramic contact. For each trial, a tungsten carbide ball with a diameter of 1.5 mm would slide against the 316 stainless steel disk with a superfinished surface for a total distance of 54 m. Each frictional test is performed under a normal load of 2 N where the maximum Hertz contact pressure is 2.64 GPa and the mean Hertz contact pressure is 1.76 GPa. There are at least three tests performed for each lubricant. The friction coefficient values for each test are recorded over time and are averaged once the test is completed. Both the average frictional coefficient and the coefficient over time are used to compare the PIL solutions. The wear volume of the steel disks is calculated based on wear track measurements through an optical microscope. The surface morphology of the worn ceramic balls and wear tracks on the steel surfaces is observed and obtained by optical microscopy and 3D profilometry.&nbsp; Distilled water is used as a base line lubricant and it is found that even at 1 wt.% concentrations the PILs yielded significant reductions in frictional coefficients and wear volumes.The wear mechanisms and surface interactions are also discussed in terms of PIL-steel surface interactions from SEM and EDX data.

Protic Ionic Liquids as Lubricant Additives

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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