STUDY OF TRIBOLOGICAL PROPERTIES OF BIS(DIMETHYL SULFOXIDE) TRI(N,N-DIMETHYLDITHIOCARBAMATE) RARE-EARTH IN LUBRICATING GREASE

Four complexes of bis(dimethyl sulfoxide) -- tri(N,N-dimethyldithiocar bamate) rare earth (MDTC.Ln.DMSO) were synthesized and their thermal s tabilities were investigated with a thermal gravity analyzer (TGA). Fr iction and wear behaviors of the complexes were evaluated as additives in lithium grease using a four-ball machine and a Timken Tester. As a comparison, the tribological properties of molybdenum dialkyldithioca rbamate (MoDTC) as an additive in lithium grease were also investigate d. Electron Probe Microanalyzer (EPMA), Auger Electron Spectroscopy (A ES) and X-ray Photoelectron Spectroscopy (XPS) were employed to elucid ate the lubricating mechanism of these rare earth complexes as additiv es in lithium grease. Friction and wear tests indicated that these rar e earth complexes possess excellent load-carrying capacity and good an tiwear property at concentrations up to 3 wt%. Their extreme-pressure properties were much superior to that of MoDTC at concentrations from 1 wt% to 5 wt%., but the antiwear properties were inferior to that of MoDTC. Results of EPMA analyses revealed the existence of rare earth m etals and sulfur on the rubbed surfaces, whereas the results of AES an d XPS analyses indicated that these rare earth complexes had formed a protective film containing a rare earth oxide, sulfate and organic com pounds containing sulfur and nitrogen on rubbed surfaces. The lubricat ing film rich in rare earth and sulfur especially seem to contribute t o the good tribological properties of bis(dimethyl sulfoxide) -- tri(N ,N-dimethyldithiocarbamate) rare earth (MDTC.Ln.DMSO).