The Tribological Chemistry of the Oil Blends of Zinc Dialkyldithiophosphate with 2-Mercaptobenzothiazole Derivatives

X-ray absorption near-edge spectroscopy at the phosphorous and sulfur edges was used to identify the chemical species in thermal films and antiwear films on the macroscale. For the thermal films, it was found that the introduction of the additive MBTT/MBTA to the base oil, zinc dialkyldithiophosphate (ZDDP), tended to retard the formation of the polyphosphate, and has no effect on the thickness of the films. The topmost surface thermal films may be mainly comprised of some new compounds generated from the interaction of ZDDP with the antiwear additives MBTT/MBTA, along with a small amount of unchanged ZDDP, the sub-surface, and the bulk were mainly comprised of Zn phosphate, along with an amount of ZnS. For the antiwear films, the introduction of the additive MBTT/MBTA to the base oil, ZDDP, reduces the chain length of polyphosphate, which the N-containing decomposed products of 2-mercaptobenzothiazole derivatives are responsible for. It is very clear that MBTT or MBTA has indeed interacted with ZDDP to form new phosphate in the overall antiwear films. The topmost surface antiwear films were mainly comprised of short-chain polyphosphate, the sub-surface and the bulk may be mainly comprised of Zn phosphate and ZnS.