Tribological Properties of Three S-Alkyl-N,N-dicarboxymethyl Dithiocarbamates as Additives in Water–Glycol Hydraulic Fluid

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.

KEY WORDS:

• S-Alkyl-N,N-dicarboxymethyl Dithiocarbamate
• Water-Soluble Lubricant Additive
• Tribological Behaviors
• Water– Glycol Hydraulic Fluid

ACKNOWLEDGEMENT

This work was supported by the Major State Basic Research Development Program of China (973 Program, Grant No. 2007CB607606).