Preparation and tribological properties of surface-modified calcium borate nanoparticles as additive in lubricating oil

To develop a potential substitute for conventional lubricant additive and improve the oil-solubility of nanoparticles, calcium borate nanoparticles modified by an eco-friendly or “green” modifier lauric acid (CBLA) were prepared. The paper aims to discuss these issues.

The microstructures of the as-obtained samples were characterized by X-ray power diffraction (XRD) transmission electron microscope (TEM) and infrared spectra (IR). The contact angle was also measured. Tribological properties of CBLA used as additive in base oil were evaluated with a four-ball tribotester and compared with a commercial additive. The worn surface was investigated by polarized microscope (PM) and X-ray photoelectron spectroscopy (XPS).

The results indicate that the average size is in the range of 50-100 nm and the surface of calcium borate was altered from hydrophilicity to hydrophobicity. At the same time, the nanoparticles can be dispersed well in the base oil. Tribological results show that CBLA have good antiwear property and friction-reducing property in base oil, and it can be found that during the sliding process, a continuous wear resistance film was formed which containing depositions and the tribochemical reaction products such as B₂O₃, FeB, Fe₂O₃ and CaO.

An eco-friendly or “green” modifier lauric acid could change the surface of calcium borate from hydrophilicity to hydrophobicity, and calcium borate modified by lauric acid has good tribological properties in lubricating oil.