Hydrolytic stability and tribological properties of N-containing heterocyclic borate esters as lubricant additives in rapeseed oil

Borate ester compounds are emerging as promising materials for lubricating systems. The main drawback of borate esters however, is the susceptiblity to hydrolysis. In this work, two kinds of N-containing heterocyclic borate esters were synthesized. Their hydrolytic stability and tribological properties as lubricant additives in rapeseed oil were evaluated. The results showed that these borate esters not only possessed promising tribological properties, but also had high hydrolytic stability. Thermal films and tribofilms were investigated by using X-ray absorption near-edge structure (XANES) spectroscopy. Surface analysis indicated that thermal films were mainly composed of adsorbed films and thermo-chemical reaction products. Tribofilms were mainly constituted by BN, B2O3 and organic B.