Study of preparation and tribological properties of rare earth nanoparticles in lubricating oil

Surface-modified mixed rare earth nanoparticles are prepared and their tribological performances as lubrication additives are evaluated using a four-ball friction and wear tester. The analytical results show that the average size of the particles is less than 30 nm and they exhibit excellent anti-wear, load-carrying and good friction-reducing capacities in base stock. Auger electron spectroscopy (AES) and X-ray photoelectron spectrometry (XPS) are performed to investigate their tribochemical mechanism and the results indicate that there is a boundary film composed with ferrous oxides, organic acid, rare earth oxides and complex of rare earth metals formed on the rubbed surface. The high concentration of ferrous oxides in the friction surface, which attributes to the oxidation catalysis of nano rare earth particles during the friction process, may be the main reason that leads to their excellent tribological properties.