The tribological behaviors of disulfide-type triazine derivatives as additives in biodegradable lithium grease

Two novel disulfide-type triazine derivatives, 6,6'-disulfanediylbis(4-(dibutylamino)-1,3,5-triazine-2-thiol) (coded DTBT) and 6,6'-disulfanediylbis(4-(bis(2-ethylhexyl)amino)-1,3,5-triazine-2-thiol) (coded DTOT), were prepared. A four-ball tester was used to evaluate their tribological performances as anti-wear and extreme-pressure additives in biodegradable lithium grease. The results show that the disulfide-type triazine derivatives possess good friction-reducing properties and excellent anti-wear, extreme-pressure capacities. For further understanding of their tribological behaviors, X-ray photoelectron spectroscopy and scanning electron microscopy are adopted to analyze the tribofilms generated from these additives in biodegradable lithium grease. The results of X-ray photoelectron spectroscopy analysis illustrate that the prepared compounds as additives in biodegradable lithium grease forms a protective film containing FeS, FeS₂ (or S-containing organic compounds), Fe₂(SO₄)₃, FeSO₄, FeO (or Fe₃O₄), and N-containing organic compounds on the metal surface during the sliding process.