The effect of molecular structure of heterocyclic compounds containing N, O and S on their tribological performance

The friction and wear performance of heterocyclic compounds (2-mercaptobenzoxazole, 2-mercaptobenzothiazole and 2-mercaptobenzimidazole), which have the same cyclic structure except for the one-location atom difference, added to liquid paraffin and synthesized diester were evaluated using a four-ball machine. The results show that there is a ranking of the antiwear performance: 2-mercaptobenzoxazole > 2-mercaptobenzothiazole > 2-mercaptobenzimidazole, but, there is another ranking of the load-carrying capacity: 2-mercaptobenzothiazole > 2-mercaptobenzoxazole > 2-mercaptobenzimidazole. X-ray photoelectron spectroscopy (XPS) was used to examine the binding energy of elements on the rubbed surface in order to determine whether the cyclic compounds remain intact or decompose after rubbing. Finally, the effect of S, N and O elements in the compounds on antiwear properties is discussed according the theory of molecular orbits and electron effect.