Film Formation of Non-Phosphorus Wear Inhibitors

Abstract

The time-dependent film formation of two potential non-phosphorus supplemental wear inhibitors in the presence of secondary zinc dialkyldithiophosphate (ZnDTP) was studied by electrical contact resistance (ECR), auger, and X-ray photoelectron (XPS) spectroscopy. One weight percent of a molybdenum dithiocarbamate or an ashless dithiocarbamate was blended with a secondary ZnDTP, sufficient in quantity to yield 0.05 wt% phosphorus at blend level. A thorough surface examination by auger and XPS, coupled with the ECR results, detailed the deleterious effects that these supplemental antiwear additives had on ZnDTP antiwear film formation. Both carbamates interfered with antiwear film formation by secondary ZnDTP. It is speculated that MoDTC generated a competing molybdenum sulfide film that oxidized over time to form MoO ₃ , which promotes wear in the ECR bench test based on literature insight. Ashless DTC also formed a competing antiwear film but not as good a film as from ZnDTP alone.

KEY WORDS:

• Wear Inhibitors
• XPS
• Auger
• ECR

Acknowledgments

Review led by Cyril Migdal

Notes

*Mo-containing organic species.

^aThe presence of carbide is uncertain. See text for details.