Investigation of the tribological properties of oil-soluble Cu nanoparticles as additive in CD 15W/40 diesel engine oil

Oil-soluble Cu nanoparticles were synthesized by redox method. The effect of the synthetic oil-soluble Cu nanoparticles as an additive on the tribological behavior of commercial diesel engine oil CD 15W/40 was investigated. The tribological behaviors of the CD 15W/40 oil containing various mass fractions of nano-Cu additive were examined on a four-ball machine. The morphology of the nano-Cu was observed by means of transmittance electron microscopy, the worn steel surface morphology and typical elemental distributions thereon were analyzed by means of scanning electron microscopy and energy dispersive spectrometry. The chemical state of the Cu on the worn steel surface was examined on an X-ray photoelectron spectroscope. As the results, Cu nanoparticle as additive contributed to significantly increasing the antiwear ability and load-carrying capacity of the CD 15W/40 oil. This was attributed to the transfer and deposition of the nano-Cu on the worn steel surface.