Zinc dialkyl dithiophosphate (ZDDP) is routinely used as an antiwear additive in engine lubricants and is activated by heat and rubbing experienced in tribological contacts<i>. In the contact ZDDP forms a protective tribofilm which can be more than 100 nanometers thick. Many other mechanically activated reactions have been studied using classical mechanochemical methods[ii] but have not been compared to the tribochemistry of ZDDP. This study investigates the relationship between ZDDP tribochemistry in a lubricated contact and the mechanochemistry of ZDDP in a traditional ball mill grinder to determine the role of mechanical activation on ZDDP reactivity and wear protection. ZDDP was shaken at room temperature under typical mechanochemical reaction conditions in a mechanical ball mill. The intermittent mechanical contact in a ball mill is significantly different than the continuous frictional sliding and rolling contact encountered in a lubricant wear experiment. Analysis by x-ray photoelectron spectroscopy (XPS), auger emission spectroscopy (AES) and infrared spectromicroscopy demonstrate that under traditional mechanochemical conditions ZDDP is reactive and undergoes a chemical transformation. ZDDP reaction product produced in the ball mill is chemically related to the composition of the tribofilm formed in lubricant wear tests. These results suggest that ZDDP antiwear activity can be understood in terms of classical mechanochemical reaction chemistry.<i> Spikes, H., Tribol. Lett., 17(3), 2004 , 469.[ii] Takacs, L., Chem. Soc. Rev., 42, 2013  , 7649.

Mechanochemical activation of zinc dialkyl dithiophosphate

248th National Meeting (2014)

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