This paper aims to investigate the tribological properties of CeO2 and La2O3 in different vegetable oil–based lithium greases.
Lithium greases were prepared with rapeseed oil and waste vegetable oil as base oils as well as nano-rare earth oxides additives which were added before the saponification. The structure of the lithium greases was analyzed by Fourier transform infrared spectroscopy and scanning electron microscopy. Its thermal stability was evaluated by thermogravimetric analysis. The tribological properties of lithium greases were assessed via a four-ball friction and wear test. The morphology of the worn surfaces of test balls was characterized by scanning electron microscopy equipped with an energy-dispersive spectrometer and three-dimensional profilometry.
The results showed that the extreme pressure value, thermal stability and anti-wear ability of the lithium greases were improved after the addition of nano-rare earth oxides. The introduction of 0.05 Wt.% CeO2 or 0.01 Wt.% La2O3 in lithium greases exhibit good anti-wear ability, especially in waste vegetable oil–based lithium grease, with 15.3% and 20.4% reduction in wear scar diameter, respectively. The significant improvement in anti-wear performance is mainly due to the stable physical adsorption films and chemical tribo-film generated onto the friction surface during the friction process.
This work serves as a reference for the preparation of lithium grease with different base oils using nanomaterials as additives and enriches the study of nano-rare earth oxides as lubricant additives.
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