Abstract: The surface of calcium borate was modified by stearic acid, oleic acid, ethylenediaminetetraacetic acid and polyethylene glycol, respectively.Various nanometer calcium borate lubricant additives with different hydrophobicity were prepared, and the effect of the modified calcium borate nano-additives on the antiwear and friction-reducing performance of rapeseed oil was systematically investigated by means of SEM, FTIR and tribological test. The results show that the stearic acid-modified calcium borate has the best hydrophobicity, the oleic acid-modified calcium borate has the second hydrophobicity, and ethylenediaminetetraacetic acid modified calcium borate still was hydrophilic, but the calcium borate had not been chemically modified by the polyethylene glycol. It is found that the calcium borate modified with stearic acid shows the best anti-wear and friction-reducing performance in rapeseed oil. When the dosage of calcium borate modified with stearic acid in rapeseed oil was 0.5%, the friction coefficient and the wear scar diameter of the test steel ball were decreased by 22% and 24% than that of rapeseed oil base oil, respectively.

Key words: hydrophobicity, calcium borate, rapeseed oil, tribological performance