New Functionality of Ionic Liquids as Lubricant Additives: Mitigating Rolling Contact Fatigue

Abstract

Oil-soluble ionic liquids (ILs) have recently been demonstrated as effective lubricant additives of friction reduction and wear protection for sliding contacts. However, their functionality in mitigating rolling contact fatigue (RCF) is little known. Because of the distinct surface damage modes, different types of surface protective additives often are used in lubricants for sliding and rolling contacts. Therefore, the lubricating characteristics and mechanisms of ILs learned in sliding contacts from the earlier work may not be translatable to rolling contacts. This study explores the feasibility of using phosphonium-phosphate, ammonium-phosphate, and phosphonium-carboxylate ILs as candidate additives in rolling–sliding boundary lubrication, and results suggested that an IL could be either beneficial or detrimental on RCF depending on its chemistry. Particularly, the best-performing phosphonium-phosphate IL at 2% addition made a low-viscosity base oil significantly outperform a more viscous commercial gear oil in reducing the RCF surface damage and associated vibration noise. This IL generated a thicker, smoother, and more homogeneous tribofilm compared with commercial additives, which is likely responsible for the superior RCF protection. Results here suggest good potential for using appropriate IL additives to allow the use of low-viscosity gear and axle fluids for improved efficiency and durability.

Applications of carbon quantum dots in lubricant additives: a review

“…Among them, the friction-reducing and anti-wear additives play an indispensable role in alleviating the friction and wear of the contact area by forming a physical adsorption/deposition film and/or tribochemical reaction film on the rubbing surfaces [28][29][30][31][32][33][34]. The traditional friction-reducing and anti-wear additives are usually composed of organic polar materials, such as organic molybdenum compounds [35][36][37], polymers [38], alcohols [39], esters [40][41][42], amine compounds [43], organic salts [44], ionic liquids, and their derivatives [45][46][47][48][49][50]. The strong polarity allows them to form neat adsorption films on the metallic rubbing surfaces to reduce the friction and wear of friction pairs.…”

Using Ionic Liquid Additive to Enhance Lubricating Performance for Low-Viscosity Engine Oil

“…In addition, the ashless phosphonium-organophosphate ILs have shown less adverse impact effects on the emission catalysts compared to the conventional ZDDP and therefore replacing half the amount of ZDDP potentially reduces the exhaust emissions . Our recent study on the effect of ILs on rolling contact fatigue (RCF) revealed suppression of RFC surface damage and associated vibration noise by introducing a phosphonium-organophosphate IL to the gear oil …”

“…20 Our recent study on the effect of ILs on rolling contact fatigue (RCF) revealed suppression of RFC surface damage and associated vibration noise by introducing a phosphonium-organophosphate IL to the gear oil. 21 The objective of this research is to continue to develop ILadditized engine oils by further reducing the oil viscosity grade to SAE 0W-12 and optimizing the oil formulation by understanding the compatibilities between the IL+ZDDP combination and other additives including friction modifiers, detergents, dispersants, and antioxidants. A couple dozen of GF-6 compatible experimental formulations were designed for using the hybrid IL+ZDDP antiwear additives and screened using bench-scale tribological testing and analysis.…”

Competitive Adsorption of Lubricant Base Oil and Ionic Liquid Additives at Air/Liquid and Solid/Liquid Interfaces

“…3 The surface property (wettability) of ILs was evaluated using contact angle measurements, and their evolvement in forming the protective tribofilms has been demonstrated using post-test chemical analysis techniques. 2,3,6,11 However, there is a lack of molecular-level understanding of their adsorption excess behavior at the lubricant oil/solid interface, which is needed to better utilize their capabilities.…”

“…Friction and wear of machines and moving parts pose energy and material loss problems for the global economy. , Lubrication therefore plays an important role in reducing friction and wear, increasing energy efficiency and device reliability. − In practice, base lubricant oils are mixed with various additives such as organic friction modifier, antiwear additive, detergent, antifoam, etc. to improve the lubrication efficiency. − As a new class of additives, ionic liquids (ILs), particularly oil-soluble ones, have been studied recently and demonstrated to significantly improve the tribological performance. ,− Some of them have also shown good synergistic effects with zinc dialkyldithiophosphate (ZDDP), the most commonly used antiwear additive, , as well as with nanoparticles . The surface property (wettability) of ILs was evaluated using contact angle measurements, and their evolvement in forming the protective tribofilms has been demonstrated using post-test chemical analysis techniques. ,,, However, there is a lack of molecular-level understanding of their adsorption excess behavior at the lubricant oil/solid interface, which is needed to better utilize their capabilities.…”