2019 Volume 64 Issue 12 Pages 740-746
The effect of temperature on the lubricity of molybdenum dithiocarbamate(MoDTC) and co-additives was investigated by a ball on disk tribometer at temperatures of 25°C, 40°C, 60°C and 80°C. MoDTC was added in polyalphaolefin(PAO) as base oil. Calcium sulfonate(CaSu), calcium borate dispersed in calcium sulfonate(CaBSu), calcium salicylate(CaSa) and calcium phenate (CaPh) were used as a co-additive. In the test with MoDTC alone, the friction coefficient decreased only at 80°C, and the friction coefficient was not stable and fluctuated during the test at 80°C. The friction coefficient became stable with co-additives. The co-additives were classified in two groups on the basis of friction behavior. When CaSu or CaBSu was used as a co-additive, the friction coefficient decreased even at 60°C and 80°C. On the other hand, the friction coefficient decreased only at 80°C with CaSa or CaPh. The results of XPS analysis and HR-TEM observation revealed that MoS2 was formed clearly when the sulfonates were added to the lubricant oil with MoDTC. The behavior of friction coefficient was closely dependent on the kind of co-additives and the oil temperature. As a role of the sulfonate for the MoS2 layer formation, it is thought that sulfonates act as a S source for MoS2 and a binder for the boundary layer.
