Preparation and Tribological Properties of Surface-Capped Copper Nanoparticle as a Water-Based Lubricant Additive

Cu nanoparticle surface-capped by methoxylpolyethyleneglycol xanthate was synthesized using in situ surface-modification technique. The size, morphology and phase structure of as-prepared Cu nanoparticle were analyzed by means of X-ray diffraction and transmission electron microscopy. The tribological properties of as-synthesized Cu nanoparticle as an additive in distilled water were investigated with a four-ball machine, and the morphology and elemental composition of worn steel surfaces were examined using X-ray photoelectron spectroscopy and scanning electron microscope equipped with an energy-dispersive spectrometer attachment. Results show that as-synthesized Cu nanoparticle as a water-based lubricant additive is able to significantly improve the tribological properties and load-carrying capacity of distilled water, which is ascribed to the deposition of Cu nanoparticles on steel sliding surfaces giving rise to a protective and lubricious Cu layer thereon. In the meantime, they may also tribochemically react with rubbing steel surfaces to generate a boundary lubricating film consisting of Cu, FeS and FeSO4 on the rubbed steel surface, which helps to result in greatly improved tribological properties of distilled water, thereby reducing friction and wear of the steel-steel pair.