Tribological Properties of Pb Nanoparticle in Oil

The solution dispersion method has been successfully used to prepare Pb nanoparticles in a paraffin oilpolyglycol mixed solution by directly dispersing melted Pb granules. In this solution system，paraffin oil was used as reacting media and polyglycol served as an antioxidant to protect Pb nanoparticles from oxidizing. The size and structure of the prepared Pb nanoparticles were characterized by means of the transmission electron microscopy （TEM）and powder X-ray diffraction（XRD）. Their tribological behavior was evaluated with a four-ball tester. The TEM and XRD investigations reveal that the prepared Pb nanoparticles，with the average particle diameter of 70 nm，appear to be of close spherical shape and possess the same crystal structure as the bulk Pb. The tribological results show that the Pb nanoparticles as an oil additive exhibit good friction-reduction and antiwear properties at different additive concentration and applied load. Meanwhile，they can also strikingly improve the load-carrying capacity of the base oil. The rubbed surface was also investigated by the scanning electron microscope（SEM）and energy dispersive spectroscopy（EDS）. However，there was not presence of Pb element on the worn surfaces，which indicated that no chemical reaction occurred between the Pb nanoparticles and the rubbing surfaces. In addition，the tribological mechanism of the formation of the sliding-bearing system was also proposed.