Effects of Molecular Structure of Zinc Dialkyldithiophosphates on Tribological Properties of a Hydrogenated Amorphous Carbon Film under Boundary Lubrication

The effects of the molecular structure of zinc dialkyldithiophosphates (ZDDPs) on the tribological properties of a hydrogenated amorphous carbon (a-C:H) film under boundary lubrication were investigated. Friction tests were performed at a-C:H/a-C:H and steel/steel contacts under lubrication with poly-alpha olefin (PAO) and PAO containing five types of ZDDPs with different alkyl groups (primary-C4 ZDDP, secondary-C4 ZDDP, primary-C6 ZDDP, primary-C8 ZDDP and primary-C12 ZDDP). All our results suggest that the structure of the alkyl chain of ZDDPs strongly influence the tribological properties of the a-C:H/a-C:H and steel/steel tribopairs lubricated with ZDDP solutions.