Extreme Pressure Lubrication and Wear. The Chemical Reactivity and the Extreme Pressure Action of Two Aliphatic Disulfides

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Abstract
Reaction rates were studied for the action of di-tert-octyl disulfide and di-n-cetyl disulfide in white oil on iron powder over the temperature range 165–250 C. The data were fitted to the Arrhenius equation, and the tertiary disulfide was found to be 1500 times as reactive as the normal disulfide. White oil solutions of the two disulfides were subjected to the Falex test and to the four-ball extreme-pressure test, and the tertiary disulfide was found to be the more effective lubricant additive in these tests. Wear studies were carried out with a pin and disk apparatus under conditions which approximated the above bench tests as regards specimen material, rubbing speed and pressure. The complex nature of the course of wear made it difficult to compare the two disulfides quantitatively. It was found that the tertiary disulfide was 2 to 20 times as efficacious as the normal disulfide in reducing the terminal steady-state wear rate. By treating the additive action of the disulfides as a competition between the rate of metallic adhesion and the rate of chemical reaction with iron, it is possible to reconcile the wide discrepancy between the relative chemical reactivity and the relative additive action of the two disulfides in a quantitative fashion.