Study On Tribological Properties Of Ionic Liquids And ZDDP Additives

Excellent tribological performance of Ionic Liquids(ILs)as a new lubricant and lubricant additive has aroused researchers’ attention in recent 10 years.The results show that ionic liquids additives can effectively reduce friction and surface wear,zinc dialkyl dithiophosphate(ZDDP),which has been widely used currently,can also improve wear,but increased friction,it means that the lubrication mechanism of ZDDP and IL additives is different.Unfortunately,the current research on the mechanism of ionic liquid lubrication is not enough thorough,specifically there is few study on the synergetic mechanism of lubrication of ZDDP and IL as lubricant additives.In this work,compared with ZDDP additives,the effect of the two additives on friction and wear,which are oil-soluble quaternary phosphonium ionic liquids with different chain change,were evaluated on four-ball friction and wear tester,simutanously the influence on the film-forming properties were studied the influence of additives on was studied under stavation by means of optical elastohydrodynamic lubrication test rig.the morphology of wear scar was got using surface electron microscopy(SEM)and surface profiler(PGI-800),and the chemical composition of the surface was analyzed by EDS.Our experimental results show that both ZDDP and ionic liquids can improve film-forming of PAO,but the effect of ionic liquid is better than that of ZDDP.Under the condition of boundary lubrication,compared with ZDDP additives,ionic liquid additive is more efficient for anti-wear and reduction of friction especially at higher temperature.Compared with the base oil,the combination of ZDDP and IL can also effectively reduce the wear,and have good temperature stability.For the fresh engine oil,both ZDDP and ionic liquid additives have little impact on the tribological properties as expected;for used base oil,while they can significantly improve tribological properties,which is even close to those of fresh engine oil.The effect of additives may be due to that firstly a very thin physical absorption film can easily appeared on the metal rubbing surface,and then the chemical reaction occurred due to the friction,and then the tribofilm form,this film can protect two contact surfaces by avoiding direct contact,which induce the wear and friction.Besides that,the tribofilm induced by ZDDP is rough and hard,while that of ILs may be softer with low shear strength,which may explain the experimental friction results.Our work is to investigate the effects of ionic liquid additives,ZDDP additives and the composition of both them on the tribological properties.The mechanism of reduction of friction and anti-wear under boundary lubrication conditions was discussed,in order to give some good advice for designing green lubricating oil,simutanously to insure the mechanical parts conduct lubricated by the oil with lower viscosity of as reliable as possible,therefore it is significant for minimizing the energy loss caused by friction and wear.