Abstract
Three S-alkyl-N,N-dicarboxymethyl dithiocarbamates with different alkyl chain lengths were synthesized and their tribological properties as additives for a water–glycol hydraulic fluid were evaluated with four-ball machines and an Optimol SRV-IV oscillating friction and wear tester. The influence of the alkyl chain length on their lubricating abilities was also studied. The results demonstrated that all three S-alkyl-N,N-dicarboxymethyl dithiocarbamates can improve the extreme-pressure, antiwear, and friction-reducing properties of the water–glycol hydraulic fluid to different degrees; that is, the additive with the longest alkyl chain exhibited the best tribological properties, especially at high loads. The worn surfaces were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The analytical results of typical elements on the worn surfaces demonstrated that these additives reacted with the steel surfaces during the friction processes and generated a protective film mainly composed of iron sulfides, iron oxides, and organic amines, which played an important role in improving the tribological properties of the base liquid.
ACKNOWLEDGEMENT
This work was supported by the Major State Basic Research Development Program of China (973 Program, Grant No. 2007CB607606).