Investigation of tribological properties of two protic ionic liquids as additives in water for steel-steel and alumina-steel contacts

Water-based lubricants are attractive owing to their low cost and eco-friendliness. An appropriate additive package must be considered to use water as a lubricant. Recently, protic ionic liquids (PILs) were emphasized for improving the lubricity of water. Most PILs are nontoxic and biodegradable. In this study, tert-octylamine oleate and diethanolamine oleate PILs were investigated by using them as additives (1% wt.) in water. Their lubrication properties were tested on a ball-on-plate reciprocating tribometer using steel-steel and alumina-steel friction pairs. The investigated PILs improved water's friction and wear reduction ability up to 80%. Both friction pairs performed similarly. However, the alumina-steel friction pair exhibited a more stable friction. The adsorption layer was assumed the most likely friction and wear reduction mechanism.