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Abstract
The tribological properties of steel surfaces lubricated with blends consisting of base oil, some secondary zinc dialkyl dithiophosphate (ZDDP), and salicylate, sulphonate, or overbased phenate detergent were examined experimentally. Sliding experiments were performed in the temperature range of 106–124°C using a ball-on-disk tribometer equipped with a contact voltage circuit. The boundary lubrication efficacy of the tribofilms formed from these blends was evaluated in light of coefficient of friction, contact voltage, and wear volume measurements. The chemical compositions of the produced tribofilms and associated wear mechanisms were analyzed by X-ray photoelectron spectroscopy and scanning electron microscopy. The critical load for equal tribofilm formation and removal rates was determined from the variation of the wear rate with the applied normal load. The best antiwear performance was demonstrated by the tribofilm formed from the blend containing sulphonate detergent, presumably due to the presence of a hard borate glassy phase in the tribofilm, followed by that of the tribofilms produced from the blends containing overbased phenate and salicylate detergents. The results provide insight into synergistic and antagonistic effects between ZDDP and detergents that affect the tribofilm antiwear performance.
ACKNOWLEDGMENT
This research was supported by Chevron Oronite Company, LLC, Richmond, California.
Review led by Cyril Migdal