Investigation of the interactions between a novel, organic anti-wear additive, ZDDP and overbased calcium sulphonate

The use of zinc dialkyldithiophosphate (ZDDP) in automotive lubricants is being questioned due to its detrimental effect to the efficiency of catalytic converters. In an effort to determine an effective replacement, a novel, organic anti-wear additive (OAW) was tested to examine its tribological properties and interactions with ZDDP and a deposit control additive (DCA), overbased calcium sulphonate (OBCS). Tribological tests were performed that found OAW to be beneficial to the anti-wear performance of the lubricant, through synergism with OBCS. Surface analysis techniques were employed to analyse the subsequent tribofilms that were found to be composed of CaCO3 and Ca polyphosphates.

► Organic anti-wear additive produces anti-wear tribofilms of comparative performance to ZDDP.
► Organic anti-wear (OAW) interacts with ZDDP film and removes Zn from Zn polyphosphate.
► OAW improves coalescence of overbased detergent cores on the rubbed surfaces.
► Combination of interactions produces tribofilm of Ca polyphosphates and CaCO3—an effective film.