Study of the synergistic effect of di-n-octyl polysulfide with tricresyl phosphate in vegetable oil

A potential good oil-soluble extreme pressure additive-di-n-octyl polysulfide (DOPS) was synthesized at low temperature and under normal atmosphere, its synergistic tribological effect with a traditional additive, tricresyl phosphate (TCP), in rape seed oil was examined by using four-ball machines. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to investigate the worn surfaces of the steel ball. The results show that the load-carrying capacity of the vegetable oil can be improved greatly by the presence of the TCP and/or DOPS; the synergistic system shows a good synergistic effect in improving the tribological performance of vegetable oil when DOPS/TCP mass ratios is 1:9. The addictives reacted with steel interface and generated FeS₂, FeSO₄ and Fe₂(PO₄)₃ boundary lubrication films, which improves the tribological behaviors of vegetable oil.