Assessing Boundary Film Forming Behavior of Phosphonium Ionic Liquids as Engine Lubricant Additives

Abstract

Abstract:The reduction of friction and wear losses in boundary lubrication regime of a piston ring-cylinder liner tribo-system has always been a challenge for engine and lubricant manufacturers. One way is to use lubricant additives, which can form boundary film quickly and reduce the direct contact between asperities. This article focuses on the assessment of boundary film forming behavior of two phosphonium-based ionic liquids (ILs) as additives in engine-aged lubricant to further improve its film forming capabilities and hence reduce friction and wear of contacting surfaces. A reciprocating piston ring segment-on-flat coupon under fully flooded lubrication conditions at room temperature (approx. 25˝C) was employed. The trihexyltetradecyl phosphonium bis(2-ethylhexyl) phosphate and trihexyltetradecyl phosphonium bis(2,4,4-tri-methylpentyl) phosphinate ionic liquids were used as additives in 6 vol. % quantity. Benchmark tests were conducted using fully formulated new lubricant of same grade (with and without ILs). Results revealed that the addition of phosphonium ILs to engine-aged lubricant led to quicker initiation of boundary film forming process. In addition, friction and wear performance of engine-aged lubricant improved by the addition of both ILs and these mixtures outperformed the fresh fully formulated oil. Chemical analysis showed higher concentration of phosphorus element on the worn surface indicating presence of ILs in the formed tribofilms.

Micro- to Nano- and from Surface to Bulk: Influence of Halogen-Free Ionic Liquid Architecture and Dissociation on Green Oil Lubricity

“…32,34,61 Meanwhile, ILs with phosphate anions have shown improved friction and wear when used as additives in various oils. 35,36,65,66,70,71 More recently, orthoborates have attracted attention as a new class of anions for lubrication applications and have been demonstrated to exhibit excellent friction reduction and wear protection, both as neat lubricants and as additives in oils. 58,59 When dispersed in other (more polar) solvents, they have also exhibited high surface activity, providing highly lubricious interfacial structures.…”

“…Moreover, at high temperatures and pressures, halogenated ILs have been demonstrated to readily undergo hydrolysis with ambient water, resulting in the formation of toxic and corrosive halides, , which can shorten the lifetime of machine components and contribute to enhanced wear or system failure. In the past decade, these concerns have driven the development of nonhalogenated ILs for tribological purposes. ,− ,, ILs with phosphate and phosphinate anions have emerged as the popular candidates, largely because of the presence of tribo-active phosphorus and their good miscibility with oils. ,,,− ,,,− ,− Phosphinate-based ILs have been reported to reduce friction on both the nano- and macroscale, in atomic force microscopy (AFM) and pin-on-disk experiments, respectively, when used in very low concentrations in oil. ,, Meanwhile, ILs with phosphate anions have shown improved friction and wear when used as additives in various oils. ,,,,, More recently, orthoborates have attracted attention as a new class of anions for lubrication applications and have been demonstrated to exhibit excellent friction reduction and wear protection, both as neat lubricants and as additives in oils. , When dispersed in other (more polar) solvents, they have also exhibited high surface activity, providing highly lubricious interfacial structures. − …”

Tribological Behaviour of Phosphonium Based Ionic Liquid Blended with ZDDP

“…This is due to the increase in the amount of phosphorous element in the mixture which strengthen the affinity of ILs towards the formation of boundary layer over the metal surfaces as depicted in Figure 3. Thus a boundary layer reduces the plastic deformation and abrasive wear due to the presence of phosphonium based ILs in the engine oil [17].…”

Development of Doped Carbon Quantum Dot-Based Nanomaterials for Lubricant Additive Applications

“…Nowadays, lubricant assists in reducing energy usage and exhaust emissions across the globe. There is no liquid lubricant present to prevent direct interaction between the rubbing surfaces layers [12,13]. Therefore, it is essential to add additional additives to advance the friction-reduction and wear-resistance of the lubricants, and this method is considered to be an effective way to improve the lubricating capacity of lubricants [14].…”