Tribological Properties of Dithiophosphorics Acid Imidazolium Salts as Additives in Rapeseed Oil

Rapeseed oil as an environmental friendly lubricant is becoming widely used. Two kinds of dithiophosphorics acid imidazolium salts were synthesized and the tribological properties were tested as anti-wear additive in rapeseed oil. The results of four-ball tests and the wear scar surface morphology analysis show that both the two additives exhibited excellent anti-wear, friction-reduction properties and good extreme pressure property. The friction coefficient decreased from 0.11 to 0.07, the wear scar diameter decreased from 0.82 mm to 0.28 mm and P_B value increased from 490 N to 981 N. The XPS analysis shows the formation of a protective film on the worn surfaces by physical deposition and chemical reaction. Therefore, the synthesized imidazolium salts were excellent anti-friction and anti-wear additives in rapeseed oil and applicable for practice.