Tribological Properties of CaCO₃ Nanoparticles as an Additive in Lithium Grease

CaCO₃ nanoparticles with an average size of 45 nm were synthesized via the carbonation method. The tribological properties of the CaCO₃ nanoparticles as an additive in lithium grease were evaluated with a four-ball tester. The results show that these CaCO₃ nanoparticles exhibit good performance in anti-wear and friction-reduction, load-carrying capacity, and extreme pressure properties. The action mechanism was estimated through analysis of the worn surface with X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The results indicate that a boundary film mainly composed of CaCO₃, CaO, iron oxide, and other organic compounds was formed on the worn surface during the friction process.