Tribological performance of phosphonium-based halogen-free ionic liquids as lubricant additives

Abstract

In recent years, ionic liquids have shown great potential as an additive in lubricants. However, most of the explored ionic liquids for machining applications contain halogen-based anions, which are sensitive to moisture and have a tendency to produce harmful halogen acids (HX) after reacting with water/moisture. These acids are harmful to the environment and can corrode the working surfaces. This study investigates the effectiveness of halogen-free ionic liquids as potential additives to vegetable oil (canola oil). Two halogen-based ionic liquids (1-methyl 3-butylimidazolium tetrafluoroborate [BMIM BF4] and 1-methyl 3-butylimidazolium hexafluorophosphate [BMIM PF6]) and one halogen-free ionic liquids (trihexyl tetradecyl phosphonium bis (24,4-trimethylpentyl) phosphinate P6,6,6,14 [i(C8)2PO2]) were blended individually with canola oil. The percentage ratio of ionic liquid to canola oil is 1:99. Dynamic viscosity and contact angles of different lubricants were measured. Sliding tests were conducted in various conditions; dry, canola oil, and three different blends of ionic liquid with canola oil. Further, to connect tool-chip tribology with machining, turning experiments were carried out under similar lubricating conditions. Results show that the sliding friction, pin surface temperature, and wear were reduced by 48.1%, 44%, and 69.6%, respectively, due to better lubricating ability and spreading tendency of halogen-free ionic liquid blended with canola oil. The microscopic analyses of pin surfaces and the morphology of counter disc surfaces further supported better lubrication between the sliding pair. For P6,6,6,14 [i(C8)2PO2] ionic liquid blended with canola oil, the average cutting temperature and machined workpiece surface roughness reduces by 43.6% and 62.4% compared to dry machining.

Evaluation of tribological properties of vegetable oil–based ionanolubricants: An experimental study

“…A decrease of 48.1% in sliding friction, a reduction of 44% in pin surface temperature and a reduction of 69.6% in wear were found. 26 Rohlmann et al examined the lubrication properties of imidazolium and phosphonium bis(oxalato)borate ILs in a reciprocating sliding contact. Only phosphonium-based ILs reduced wear, however, imidazolium ILs demonstrated lower friction than phosphonium ILs.…”

Enhancing the Performance of Rapeseed Oil Lubricant for Machinery Component Applications through Hybrid Blends of Nanoadditives

“…Bambam et al [24] compared the tribological behavior of three types of ILs added to canola oil each with 1 wt.% to be used in machining operations. They used two halogenbased ILs of BMIM PF4 and BMIM PF6 and one halogen-free IL of P6,6,6,14 [(C8)2 PO2].…”

Evaluation of tribological behavior of a circulation oil with ionic liquid and hybrid additives

“…Numerous theoretical and experimental studies have proved that ILs exhibit good lubricating properties when they are used as neat lubricants or additives in various types of lubricants for different friction pairs. [15][16][17][18][19][20][21][22][23][24][25][26][27] When used as neat lubricants, the interaction between ILs and metal surfaces depends on materials of friction pairs and the composition of cations and anions in ILs. 16,17 The increase in the length of alkyl chains of ILs can prevent direct metal-to-metal contact, resulting in low friction and wear.…”

“…28 The concentration of ILs in lubricants plays a significant role in determining their tribological performance. 21–27 For instance, a recent study by Kreivaitis 23 showed excellent tribological characteristics of two protic ILs when used as 1.0 wt% additives in water for different metal contacts. Singh and Sharma 24 observed that the inclusion of pyrrolidinium cation-based and hexafluoro-phosphate anion-based ILs, at a concentration of 1.0 wt%, improved the thermophysical properties and tribological performance of rice bran oil.…”

“…Singh and Sharma 24 observed that the inclusion of pyrrolidinium cation-based and hexafluoro-phosphate anion-based ILs, at a concentration of 1.0 wt%, improved the thermophysical properties and tribological performance of rice bran oil. Bambam et al 25,26 demonstrated that blending 1.0% of phosphonium-based halogen-free ILs to canola oil yielded notable enhancements in machining and tribological performances. Similarly, Kumar and Garg 27 found that the addition of a halogen-free IL at a concentration of 2.0 wt% in canola oil resulted in the lowest friction coefficient and wear.…”