Lubricant Degradation and Wear II. Antioxidant Capacity and IR-Spectra in Systems Containing Zinc Dialkyldithiophosphates

Abstract

As an extension of earlier work, a systematic study was made of the changes in the antioxidant capacity and infrared spectra of zinc dialkylthiophosphate in model systems and in a fully formulated lubricant aged in laboratory and fleet tests. The reaction of peroxy radicals with a zinc dialkyldithiophosphate in the model systems results in a decay of the P = S absorbance to approximately 40 percent of its initial value. The P=S absorbance is linearly related to the remaining antioxidant capacity of the solutions. For the fully formulated lubricant containing a second ldquo;ashless” antioxidant, the P=S decays to a much lower value approaching zero as the antioxidant capacity approaches a value of about 20 percent of its initial value. A study of the behavior of a zinc dialkyldithiophosphate in admixtures with hindered phenol reveals that the zinc dialkyldithiophosphate was not protected from antioxidant reactions by the hindered phenol, a result which is consistent with results obtained with the fully formulated lubricant.

Presented at the 34th Annual Meeting in St. Louis, Missouri April 30–May 3, 1979

Notes

Presented at the 34th Annual Meeting in St. Louis, Missouri April 30–May 3, 1979