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Lubricants 2016, 4(2), 22; doi:10.3390/lubricants4020022

Towards Phosphorus Free Ionic Liquid Anti-Wear Lubricant Additives

1
Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
2
CIC Energigune, Albert Einstein 48, 01510 Miñano, Álava, Spain
3
School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
*
Author to whom correspondence should be addressed.
Academic Editors: Antolin Hernández Battez and Rubén González Rodríguez
Received: 15 April 2016 / Revised: 15 June 2016 / Accepted: 16 June 2016 / Published: 22 June 2016
(This article belongs to the Special Issue Nanoparticles and Ionic Liquids in Lubrication)
View Full-Text   |   Download PDF [4222 KB, uploaded 22 June 2016]   |  

Abstract

The development of improved anti-wear additives would enable the use of lower viscosity oils that would lead to improved efficiency. Ionic liquids have the potential to be this type of new anti-wear additive. However, currently the best performing ionic liquids that are miscible in non-polar base oils, the phosphonium phosphates, contain phosphorus on both the cation and anion. Manufacturers are seeking to reduce the presence of phosphorus in oils. Here, as a first step towards phosphorus-free anti-wear additives, we have investigated ionic liquids similar to the phosphonium phosphates but having either a phosphorus-free cation or anion. Two quaternary ammonium phosphates (N6,6,6,14)(BEHP) and (N8,8,8,8)(BEHP) and a phosphonium silyl-sulfonate (P6,6,6,14)(SSi) were compared to a phosphonium phosphate (P6,6,6,14)(BEHP) and a traditional zinc dithiophosphate (ZDDP) as anti-wear additives in mineral oil. The change from a phosphonium to a quaternary ammonium cation drastically reduced the miscibility of the Ionic liquid (IL) in the oil, while the change to a smaller silicon containing anion also resulted in limited miscibility. For the pin-on-disk wear test conditions used here none of the ionic liquids outperformed the ZDDP except the (P6,6,6,14)(BEHP) at a relatively high loading of 0.10 mol·kg−1 (approximately 8 wt%). At a more moderate loading of 0.025 mol·kg−1 the (P6,6,6,14)(SSi) was the best performing ionic liquid by a significant amount, reducing the wear to 44% of the neat mineral oil, while the ZDDP reduced the wear to 25% of the mineral oil value. Electron microscopy and energy dispersive X-ray spectroscopy showed that the presence of a silicon containing tribofilm was responsible for this protective behaviour, suggesting that silicon containing ionic liquids should be further investigated as anti-wear additives for oils. View Full-Text
Keywords: anti-wear additive; miscibility; ionic liquid; wear test; phosphorus free; boundary lubricant anti-wear additive; miscibility; ionic liquid; wear test; phosphorus free; boundary lubricant
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Somers, A.E.; Yunis, R.; Armand, M.B.; Pringle, J.M.; MacFarlane, D.R.; Forsyth, M. Towards Phosphorus Free Ionic Liquid Anti-Wear Lubricant Additives. Lubricants 2016, 4, 22.

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