Synergistic lubricating effect of several ashless dithiocarbamates with Mo-donor additives

Several kinds of alkylenebis(dialkyldithiocarbamates) were synthesized and the tribological properties as additives in base oil (100N) and Li-soap greases were evaluated using 4-ball tester and SRV tester (Schwingreibverschleissprüfung für Schmierstoffe). The results show that all additives reduce wear. Especially, when Mo(Zn)-donor additives such as Mo-DTC, Zn-DTP, and a vegetable oil modified organomolybdenum complex were blended in base oil containing methylenebisdibutyldithiocarbamate as sulfur donor, synergism was seen both in terms of oxidation stability through thermo gravimetric analysis (TGA) and wear properties using a 4-ball tester. TGA showed that oils containing sulfur-donor and Mo(Zn)-donor additive mixtures possess improved oxidation stabilities. Also, these oils have good antiwear properties under mild pressure conditions. The elemental composition of the antiwear films generated on steel counterfaces were investigated with scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). It was found that sulfur-donor and Mo-donor additives reacted with the counterface metal and generated a surface protective film consisting of FeS and MoS2.