Elastohydrodynamic performance of a bio-based, non-corrosive ionic liquid

To improve performance of machine components, lubrication is one of the most important factors. Especially for use in extreme environments, researchers look for other solutions rather than common lubricant base stocks like mineral oils or vegetable oils. One such example is ionic liquids. Ionic liquids have been defined as molten salts with melting points below 100 ∘ C that are entirely ionic in nature, comprising both cationic and anionic species. The industrial use of ionic liquids is mostly as solvents, electrolytes, extractants and catalysts. In tribological applications, ionic liquids are mainly studied in boundary lubrication and in pure sliding contacts. In this work, the elastohydrodynamic performance of a bio-based, non-corrosive, [choline][l-proline] ionic liquid is evaluated in terms of pressure-viscosity response, film forming capability and friction. The results show a pressure-viscosity coefficient of below 8 GPa − 1 at 25 ∘ C, among the lowest reported for any ionic liquid. The ionic liquid generated up to 70% lower friction than a reference paraffin oil with a calculated difference in film thickness of 11%. It was also shown that this ionic liquid is very hygroscopic, which is believed to explain part of the low friction results, but also has to be considered in practical applications since the water content will influence the properties and thus the performance of the lubricant.

[1]  Mark Hadfield,et al.  Ionic liquids as an additive in fully formulated wind turbine gearbox oils , 2015 .

[2]  Olov Marklund,et al.  Measuring Lubricant Film Thickness with Image Analysis , 1994 .

[3]  R. Larsson,et al.  Boundary and elastohydrodynamic lubrication studies of glycerol aqueous solutions as green lubricants , 2014 .

[4]  Mark Hadfield,et al.  Ionic liquids as a neat lubricant applied to steel–steel contacts , 2014 .

[5]  Tom Welton,et al.  Room-temperature ionic liquids: solvents for synthesis and catalysis. 2. , 1999, Chemical reviews.

[6]  Erik Nyberg,et al.  Formation of Boundary Film from Ionic Liquids Enhanced by Additives , 2017 .

[7]  K. R. Harris,et al.  Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Methyl-3-octylimidazolium Hexafluorophosphate and 1-Methyl-3-octylimidazolium Tetrafluoroborate , 2006 .

[8]  Scott Bair,et al.  High Pressure Rheology for Quantitative Elastohydrodynamics , 2007 .

[9]  D. C. Sun,et al.  Tribological behavior of sialon ceramics sliding against steel lubricated by fluorine-containing oils , 2002 .

[10]  Liping Wang,et al.  A Comparative Study on the Tribological Behavior of Nanocrystalline Nickel and Coarse-grained Nickel Coatings under Ionic Liquid Lubrication , 2008 .

[11]  A. Kornyshev,et al.  Ionic liquids at electrified interfaces. , 2014, Chemical reviews.

[12]  R. Larsson,et al.  Non-corrosive and Biomaterials Protic Ionic Liquids with High Lubricating Performance , 2016, Tribology Letters.

[13]  Faiz Ullah Shah,et al.  Halogen-free pyrrolidinium bis(mandelato)borate ionic liquids : some physicochemical properties and lubrication performance as additives to polyethylene glycol , 2014 .

[14]  Ichiro Minami,et al.  Ionic Liquids in Tribology , 2009, Molecules.

[15]  Jun Qu,et al.  Tribological characteristics of aluminum alloys sliding against steel lubricated by ammonium and imidazolium ionic liquids , 2009 .

[16]  R. Larsson,et al.  Elastohydrodynamic lubrication friction mapping – the influence of lubricant, roughness, speed, and slide-to-roll ratio , 2011 .

[17]  D. Dowson,et al.  Isothermal Elastohydrodynamic Lubrication of Point Contacts: Part III—Fully Flooded Results , 1976 .

[18]  S. Bair,et al.  The Pressure-Viscosity Coefficient for Newtonian EHL Film Thickness With General Piezoviscous Response , 2006 .

[19]  Erik Nyberg,et al.  Molecular design of advanced lubricant base fluids : hydrocarbon-mimicking ionic liquids , 2017 .

[20]  T. Welton.  Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis. , 1999, Chemical reviews.

[21]  Hugh Spikes,et al.  The Measurement and Study of Very Thin Lubricant Films in Concentrated Contacts , 1991 .

[22]  S. Bair,et al.  An improved Yasutomi correlation for viscosity at high pressure , 2013 .

[23]  Marcus Björling,et al.  Film thickness in a ball-on-disc contact lubricated with greases, bleed oils and base oils , 2012 .

[24]  van Hj Harry Leeuwen,et al.  The determination of the pressure—viscosity coefficient of a lubricant through an accurate film thickness formula and accurate film thickness measurements: , 2009 .

[25]  S. Bair.  Pressure–viscosity response in the inlet zone for quantitative elastohydrodynamics , 2016 .

[26]  W. Wakeham,et al.  Viscosity and Density of Five Hydrocarbon Liquids at Pressures up to 200 MPa and Temperatures up to 473 K , 2009 .

[27]  Hugh Spikes,et al.  The Development of a Spacer Layer Imaging Method (SLIM) for Mapping Elastohydrodynamic Contacts , 1996 .

[28]  Philippe Vergne,et al.  Classical EHL Versus Quantitative EHL: A Perspective Part I—Real Viscosity-Pressure Dependence and the Viscosity-Pressure Coefficient for Predicting Film Thickness , 2014, Tribology Letters.

[29]  K. R. Harris,et al.  Temperature and pressure dependence of the viscosity of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate , 2005 .

[30]  A. Goodwin,et al.  Measurement of the Viscosity, Density, and Electrical Conductivity of 1-Hexyl-3-methylimidazolium Bis(trifluorosulfonyl)imide at Temperatures between (288 and 433) K and Pressures below 50 MPa , 2007 .

[31]  Jun Qu,et al.  A low-viscosity ionic liquid demonstrating superior lubricating performance from mixed to boundary lubrication , 2013 .

[32]  A. Pensado,et al.  The Pressure–Viscosity Coefficient of Several Ionic Liquids , 2008 .

[33]  Farrukh Qureshi,et al.  Accurate Measurements of Pressure-Viscosity Behavior in Lubricants , 2002 .

[34]  F. J. Carrión,et al.  Room temperature ionic liquids as lubricant additives in steel–aluminium contacts: Influence of sliding velocity, normal load and temperature , 2006 .

[35]  Long Chen,et al.  Non-corrosive green lubricants: strengthened lignin–[choline][amino acid] ionic liquids interaction via reciprocal hydrogen bonding , 2015 .

[36]  Maria Forsyth,et al.  Ionic liquids as antiwear additives in base oils: influence of structure on miscibility and antiwear performance for steel on aluminum. , 2013, ACS applied materials & interfaces.

[37]  K. Qiao,et al.  Viscosity of 1-Hexyl-3-methylimidazolium Hexafluorophosphate and 1-Octyl-3-methylimidazolium Hexafluorophosphate at High Pressure , 2007 .

[38]  Feng Zhou,et al.  Tribological properties of plasma nitrided stainless steel against SAE52100 steel under ionic liquid lubrication condition , 2006 .

[39]  K. R. Harris,et al.  Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Hexyl-3-methylimidazolium Hexafluorophosphate and 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide , 2007 .

[40]  Kun Qiao,et al.  Viscosity of [bmim][PF6] and [bmim][BF4] at High Pressure , 2006 .

[41]  Ramiro C. Martins,et al.  Torque loss and wear of FZG gears lubricated with wind turbine gear oils using an ionic liquid as additive , 2015 .

[42]  K. R. Harris,et al.  Temperature and Pressure Dependence of the Viscosity of the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate: Viscosity and Density Relationships in Ionic Liquids , 2007 .

[43]  Laigui Yu,et al.  Room-temperature ionic liquids: a novel versatile lubricant. , 2001, Chemical communications.

[44]  Miroslav Liška,et al.  Differential colorimetry: tool for evaluation of chromatic interference patterns , 1997 .

[45]  A. Pensado,et al.  Pressure‐viscosity behaviour and film thickness in elastohydrodynamic regime of lubrication of ionic liquids and other base oils , 2014 .

[46]  Erik Höglund,et al.  Influence of lubricant properties on elastohydrodynamic lubrication , 1999 .

[47]  Josefa Fernández,et al.  Tribological Properties of Two Bis(trifluoromethylsulfonyl)imide–Based Ionic Liquids on Steel–Steel Contact , 2014 .

[48]  S. Bair.  A critical evaluation of film thickness‐derived pressure–viscosity coefficients , 2015 .

[49]  Wassim Habchi,et al.  Towards the true prediction of EHL friction , 2013 .

[50]  J. M. Martin,et al.  Full Film, Boundary Lubrication and Tribochemistry in Steel Circular Contacts Lubricated with Glycerol , 2011 .

[51]  S. Bair.  The high pressure rheology of some simple model hydrocarbons , 2002 .