The Effects of Antioxidant Reactions on the Wear Behavior of a Zinc Dialkyldithiophosphate

A systematic study of the wear behavior of a synthetic hydrocarbon bare oil as a function of time and concentration of added zinc di-n-octyldithiophosphate, ZDTP, has been carried out utilizing the 4-ball apparatus. A comparative study was made using ZDTP which had been reacted with a known concentration of peroxy radical species. Wear rates manifested, by the reacted, ZDTP at concentrations near 10−4 M total ZDTP were considerably higher than those observed with unreacted ZDTP at the same concentrations. Moreover, the observed wear rates were found to be quantitatively related to amounts of unreacted ZDTP as measured by a new peroxy radical litration method. These findings are consistent with the view that the products derived from the anti-oxidant reactions of ZDTP in lubricants are ineffective as antiwear agents.