Tribological properties of borate ionic liquids with low corrosion grade and excellent thermal stability in 500 N base oil

Two borate ionic liquids 1-Butyl-3-(2-methoxy-2-oxoethyl)-imidazole bis(mandelato)-borate [MABIM][BMB]) and 1,3-Dioctylbenzotriazole bis(mandelato)-borate ([DOBI][BMB]) were synthesised and utilised as the lubricating additives. Their corrosion degrees were measured and the results show that [DOBI][BMB] and [MABIM][BMB] exhibit remarkable anti-corrosion properties ([DOBI][BMB]: 1a, [MABIM][BMB]: 1b). The 4-ball machine was employed to evaluate their tribological properties in 500 N base oil. When [DOBI][BMB] and [MABIM][BMB] were added at the concentration of 3.0 wt%, the friction coefficient of 500 N was reduced by 37.5% and 29.5%. It can be concluded from the results of XPS and SEM that a lubricating film containing iron oxide, B2O3 and organic N-containing compounds have formed. And a model is proposed so as to describe the lubricating mechanism.