CaCO 3 nanoparticles with an average size of 45 nm were synthesized via the carbonation method. The tribological properties of the CaCO 3 nanoparticles as an additive in lithium grease were evaluated with a four-ball tester. The results show that these CaCO 3 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 CaCO 3 , CaO, iron oxide, and other organic compounds was formed on the worn surface during the friction process.
The tribological behaviors of hydroquinone bis(diphenyl phosphate) (HDP) and tricresyl phosphate (TCP) for polyalkylene glycol (PAG) were evaluated at 200 °C. Results showed that HDP could effectively reduce the friction coefficient and prevent wear of sliding pairs during the test. The best tribological properties of HDP achieves at the concentration of 4 wt %. At this level, the wear volume of the lower disk can be reduced by a factor of 2.4 and the load-carrying capacity can increase from 500 N to 930 N, with respect to pure PAG. Furthermore, HDP exhibited better antiwear (AW) and extreme pressure (EP) properties than TCP, despite the fact that their friction-reducing performances were similar. Boundary lubrication films composed of FeOOH, Fe 2 O 3 , FePO 4 , and polyether compounds were formed on the worn surface, which resulted in excellent friction reduction and AW performance.
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