The effect of amine on the tribological properties and hydrolytic stability of borate ester additives

The effect of amine on the tribological properties and hydrolytic stability of borate ester additives was examined by adding different kinds and quantities of amines into borate esters, which formed boron–nitrogen (BN) coordination complex or BN ammonium complex. The results showed that all BN complexes obviously improved the hydrolytic stability of borate ester, and most of them promoted load-carrying abilities, friction-reducing and anti-wear properties. By comparison, BN extra-coordination complexes presented a little stronger hydrolytic stability and tribological properties than BN ammonium complexes. Generally, the hydrolytic stability and tribological properties of BN complexes is promoted with the extension of carbon chain of the added amine. The worn surface analyses revealed B2O3 deposits and adsorbed B- and N-containing organic compounds were responsible for the resulted tribological properties. Our results would provide some guidance to practical application of borate ester additives in lubricants.