Abstract: The study of rare earth compounds as lubricant additives has become one of the most interested research topics. With C8H17OH, La2O3 and P2S5, an new oil-soluble lanthanum dialkldithiophate (LaDDP) is prepared as an antiwear are extreme pressure additive, and its tribological performances are evaluated. In addition, tribochemical characteristics of the additive under boundary lubrication conditions are studied by means of AES, XPS and SEM. The results indicated that LaDDP possesses better lubrication ability than ZDDP. This can mainly be attributed to the formation of boundary film containing La, La2O3, FeS, sulphate, phosphate and lanthanum diffused layer. The tribological decomposition reactions of LaDDP are simulated through mass spectroscopy. Its tribochemical mechanism is suggested.

Key words: Lubrication film, Rare earth, Tribochemistry Diffused layer