Synergistic effect between a novel S-N style additive and tricresyl phosphate in 500 N hydrogenated base oil

A novel potential S-N style ashless additive DBTT was synthesized. The tribological properties of the DBTT, commercial additive tricresyl phosphate (TCP ) and the mixtures of DBTT and TCP with different mass ratios as additives in 500 N hydrogenated base oil were examined with four-ball machines. Thus the worn surfaces of the steel ball lubricated with the additive-containing base oil were analyzed by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Results indicated that DBTT has good solubility in 500 N hydrogenated base oil, DBTT, TCP, and their mixture of various mass ratios as additives all greatly increased the load-carrying capacity of the base oil. Both DBTT and TCP improved the friction-reducing and antiwear ability of the base oil under certain conditions. The combined additive of DBTT and TCP showed synergistic effect in increasing the antiwear ability but antagonistic effect in improving the friction-reducing ability. The additives reacted with counterface metal and generated a boundary lubricating and protecting film that contributed to improve the tribological properties of the hydrogenated base oil.