To develop a potential substitute for conventional lubricant additive, lanthanum borate nanoparticles modified by triethanolamine monooleate (TEMO-LaB) were prepared. The composition and microstructures of the samples were characterized by inductively coupled plasma optical emission spectroscopy, X-ray power diffraction, infrared spectra, transmission electron microscope, and thermogravimetric analysis. The results indicate that TEMO-LaB with the size around 50 nm is amorphous and the composition is La2[B4O5(OH)4]3. Tribological properties of the prepared nanoparticles were evaluated using a four-ball tribometer and compared with a commercial borate ester (Vanlube 289). The results show that TEMO-LaB has better friction-reducing property in base oil than Vanlube 289. A three-dimensional non-contact surface profilometer was used to explore the morphology of the worn surface and X-ray photoelectron spectroscopy analysis was carried out. Based on the results of surface analysis, the action mechanism of nanoparticles during the friction process was preliminarily discussed.

A new method of improving the hydrolytic stability of borate esters is proposed based on ‘stable benzylic cation’ theory. In accordance with this strategy, phenyl-borated hydroxyalkyldithiocarbamate as a multi-functional additive is designed and synthesized. Its tribological properties are evaluated using four-ball friction and wear tester. Results show the additive possesses outstanding load-carrying and friction-reducing properties, compared with MoDTC, and can improve anti-wear properties of rapeseed oil (RSO) dramatically. Moreover, it is surprisingly found that PBDTC has prominent effect in controlling the oxidation of RSO. The worn surface of the steel ball is investigated by X-ray photoelectron spectroscopy and the anti-wear mechanism of the additive is preliminarily discussed.