Study on phosphorous-free triazinyl disulfides as additives in combustion engine base oil

Purpose - This paper seeks to study the tribological properties, corrosion inhibition properties and action mechanism of two triazine-containing disulfides, TOSS and TOMA, as additives in combustion engine base oil (5CST); those properties of an alkyl disulfide dodecyl disulfide and zinc dialkyldithiophosphate (ZDDP) were also evaluated for comparison to discover whether these additives could be used as potential substitute candidates for ZDDP. Design/methodology/approach - Their tribological performances were evaluated using a four-ball machine. The worn surfaces were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) Findings - The three additives have good load-carrying capacity and corrosion inhibition properties comparable with those of ZDDP. The anti-wear properties of the triazine-containing disulfides TOSS and TOMA are good but a little inferior to those of ZDDP. The friction-reducing performances of the additives are better than those of ZDDP. The XPS results show that absorption and tribochemical reactions occur to generate a complex boundary lubrication films comprising inorganic sulfate, sulfide, iron oxide and organic nitrogen, and sulfur-containing compounds. Research limitations/implications - The anti-oxidation properties are still to be estimated, and the synergistic effectiveness with other additives could be demonstrated. Practical implications - These additives are good extreme pressure and anti-wear additives in combustion engine base oil and, through further modification of molecular structure or combination with other additives, they may be a potential replacement for ZDDP. Originality/value - To reduce the cost, the products synthesized were not finely separated. Their tribological properties as additives in the widely used combustion engine base oil were first investigated and results indicate that they show excellent performances.