Tribological studies of highly hydrolytically stable N-containing long chain alkyl phenylborate esters in mineral oil

Abstract

The tribological properties and hydrolytic stabilities of two novel N-containing long chain alkyl phenylborate esters, 2-(4-dodecylphenyl)-6-octadecyl-1,3,6,2-dioxazaborate (DBDB), and bis(2-(2-((E)-heptadec-8-enyl)-4,5-dihydro-1H-imidazol-1-yl) ethyl)-4-dodecylphenylborate (OMDB), as lubricating additives in mineral oil (HVI WH150) were evaluated. The results confirm that the two additives possess good anti-wear property and excellent hydrolytic stability, which demonstrates that the new approach by introducing long chain alkyl phenyl group is an effective way to improve the hydrolytic stability of borate esters. X-ray absorption near edge structure (XANES) spectroscopy was adopted to analyze the thermo-oxidative films and tribofilms generated from the synthesized additives in base oil to further understand their tribological behaviors on the metal surfaces. The XANES spectra reveal that the thermal films are mainly composed of trigonal coordination boron, while the tribofilms consist of trigonal and tetrahedral coordination borons in comparison with the model compounds, which suggests that the additive can generate the tetrahedral boron species or the trigonal boron species partially undergoing transformation to produce tetrahedral boron species during the vigorous condition of rubbing process.