X-ray absorption study of tribofilms from ZDDP and overbased salicylate detergents

The interaction of overbased salicylate detergents with zinc dialkyldithiophosphates (ZDDP) and its effect on the formation of tribofilms under boundary lubrication have been studied by means of X-ray absorption near-edge structure spectroscopy. The results show that addition of metallic detergents to neat ZDDP results in the change of surface chemistry of the tribofilm formed from neat ZDDP. Calcium from detergents is digested in the tribofilm. For the high overbased detergents, the deposit of overbasing agent CaCO3 in the tribofilm is also observed along with the formation of calcium phosphate in tribofilms.