Elucidation of the Antiwear Performance of Several Organic Phosphates Used with Different Polyol Ester Base Oils from the Aspect of Interaction between Additive and Base Oil

Abstract

The antiwear performance of organic phosphates, such as tricresylphosphate (TCP), tributylphosphate (TBP) and diphenylhydrogen-phosphate (DPHP), dissolved in several polyol esters is studied. Several trimethylolpropane esters (TMP) and pentaerythritol esters (PE) having different carbon chains were used as base oils. A four-ball tribometer was used to determine the antiwear performance of oils, using commercially available bearing steel balls as test specimens. Although the wear of steel was drastically reduced with low-concentration solutions of these phosphates, the wear increased with increasing concentration in the higher-concentration region. All of the phosphates showed characteristics of an optimum concentration for minimizing wear. This behavior can be attributed to the effective adsorption/reaction of phosphates in the low concentration region and the reaction forming excess inorganic phosphates on the surface that causes corrosive-like wear in the high-concentration region. Different polyol esters showed different optimum concentrations of the additive. The order of optimum concentration among the polyol esters was different with different phosphates. Although the wear rate absolute values at the optimum concentration did not show clear correlation, it is shown that the effect of the concentration of additives on the antiwear performance can be explained by the interaction between additives and base oils using the solubility parameter.

Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

KEY WORDS:

• Synthetic Lubricants
• Polyesters
• Wear and Failure

Notes

Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998