TOF-SIMS analysis of boundary film derived from multi-additives

Antagonistic effect on lubricity of overbased calcium sulfonate by zinc dialkyldithiophosphate (ZnDTP) and polybutenyl succinimide (PBSI) was investigated under boundary lubrication conditions by using a block-on-ring type tribo-tester. It was found that overbased calcium sulfonate reduced friction and wear of steel-steel contacts with its single use whereas they increased with multi-additives. Surface analyses of boundary films by means of TOF-SIMS (Time Of Fright Secondary Ion Mass Spectroscopy) revealed that the major component of film derived from calcium sulfonate in single use was calcium oxide, whereas it decreased in multi-additives. Especially in the combination with PBSI, the major component of the film was alkylbenzen sulfonate derived from overbased calcium sulfonate. It suggests that the boundary film composed of calcium oxide play a significant role to reduce friction and wear. On the other hand in combination with PBSI, the adsorption of carbonate micelle was blocked by the adsorbed layer of alkylbenzene sulfonate.