Cyclic alkyl disulphides as tribological additives

Abstract

The use of sulphurized natural oils, fats, hydrocarbons, terpenes and aromatic sulphides, disulphides and polysulphides, as antiwear and extreme-pressure lubricant additives, has already been established. However, the potential of cyclic disulphides merits attention. The present paper describes the synthesis and evaluation of 0.5% solutions of certain cyclic disulphides as tribological additives, namely 3-alkylimino-5-(N-methylphenyl)amino-1,2,4-dithiazolines, in paraffin oil, on a four-ball test rig with 12.7 mm diameter steel bearing balls as test specimens. All the additives in general, and 3-propylimino-5-(N-methylphenyl)amino-1,2,4-dithiazoline in particular, exhibited remarkably good antifriction and EP activity, showing a decrease in the coefficient of friction and an appreciable increase in the load-carrying capacity of the lubricant as indicated by a higher load wear index. The wear surface topography of the used test specimen was studied using scanning electron microscopy.