Effect of Ashless Dispersant on Deterioration of Antiwear Characteristics of ZnDTP due to Decomposition during the Oxidation Inhibition Process

Abstract

A study of the antiwear characteristics of intentionally deteriorated zinc dialkyldithiophosphate (ZnDTP) was carried out. ZnDTPs were degraded to simulate used engine oil by reacting with cumenehydroperoxide (CHP), which models the hydroperoxide present in combustion gas. Sample oils were analyzed by ³¹ P-NMR, showing that ZnDTP produces various kinds of phosphorus-containing oil-soluble compounds after reacting with CHP. It was found that the antiwear characteristic of ZnDTP deteriorated due to the degradation, and an acceleration of wear was observed in the highly degraded regions. The effect of the ashless dispersant on the antiwear characteristics of both the degraded and the nondegraded ZnDTP was studied. It was found that the dispersant reduced wear in the low-degradation region. The addition of the dispersant, however, had no effect on wear with further degradation, where the dispersant was almost entirely consumed in dispersing Zn-containing solids when the dispersant concentration was low. When the concentration was high, the dispersant showed wear reduction in the region of greater degradation. The antiwear action of the dispersant was discussed herein, based on its adsorption characteristics and micelle formation.

KEY WORDS:

• Antiwear Additive
• Antioxidant Additive
• Dispersant
• Additive Degradation

ACKNOWLEDGEMENTS

The authors would like to express their appreciation to Dr. J. Igarashi and Mr. K. Yagishita, the Central Research Laboratory of Nippon Oil Co., for the supply of the oil and for their valuable discussions.

Presented at the STLE/ASME International Joint Tribology Conference in San Antonio, Taxas October 23-25, 2006, Review led by Elaine Yamaguchi