Study on tribological properties of the complex of rare earth dialkyldithiocarbamate and phenanthroline in lubricating grease

Three complexes of rare earth dialkyldithiocarbamate (DTC) and phenanthroline (Phen) were synthesized. Their tribological properties as additives in lithium grease were evaluated using a four-ball machine and a SRV machine. As a comparison, the tribological properties of molybdenum dialkyldithiocarbamate (MoDTC) as an additive in lithium grease were also investigated. The thermal stabilities of rare earth complexes were also investigated with a thermal gravity analyzer. The results indicate that these rare earth complexes possess excellent load-carrying capacity, antiwear and friction reduction properties, and high thermal stability. Their extreme pressure properties are superior to that of MoDTC. At lower concentration and lower load, the antiwear properties of lanthanum and neodymium complexes are superior to those of MoDTC. At lower concentration and higher load, the antiwear properties of the these rare earth complexes are inferior to those of MoDTC. But the wear increases, as the increase of concentration of rare earth complex. The results of Auger electron spectroscopy and X-ray photoelectron spectroscopy analyses indicate that these rare earth complexes as additives in lithium grease can form a protective film containing rare earth oxide, sulfate and an organic compound containing sulphur and nitrogen on a rubbed surface. Especially, the lubricating film rich in rare earth and sulphur contributed largely to the excellent tribological properties of EDTC·Ln·Phen.