Tribochemical reactions of dibenzyl and diphenyl disulphides in boundary lubrication

In this paper we describe our investigation of tribochemical reactions of dibenzyl and diphenyl disulphides in boundary lubrication. We used four-ball wear testing and quantitative analysis of thio byproducts in our studies. We determined the contents of disulphides, thiols, monosulphides, sulphurised hydrocarbons, elemental sulphur, a few phenyl ring thioethers in oil solution and iron sulphide on iron surfaces after wear testing. The tribochemical reactions of these disulphides are very complex. The improvements in wear on using a dibenzyl disulphide additive are probably due mainly to formation of elemental sulphur and its subsequent reaction with iron surfaces to give iron sulphide. With diphenyl disulphide, the load-carrying performance depends probably on the formation of a few phenyl ring thioethers. It seems also that thiooxo species formed by oxidation of additives and organic sulphur byproducts of both disulphides also play an important role in load-carrying action. (C) 1997 Elsevier Science S.A.