Tribochemistry of the Antiwear Action of a Dimer Acid/Glycol Monoester on Alumina

In pin-on-disk tests using alumina-on-alumina, it was found that the monoester of C 36 dimer acid and ethylene glycol was effective in reducing wear. For example, the addition of 1% of this monoester to hexadecane reduced the volumetric wear of alumina by over 40%. The monoester, originally designed to function through a process of tribopolymerization, has been found in previous studies to be effective in reducing wear in steel systems under severe conditions of boundary lubrication. Using alumina test specimens from pin-on-disk experiments, studies of the wear scars and tracks were made in an effort to understand the detailed surface chemical and tribochemical reactions that might be occurring. The techniques included photomacrography, scanning electron microscopy and Fourier transform infrared microspectroscopy. The results of this study showed evidence of a surface reaction between the monoester and alumina substrate as well as tribopolymerization. Based on these findings, a possible new mechanism of antiwear action is suggested-one that involves an initial chemical reaction with the surface followed by the formation and growth of oligomer/polymer chains somewhat similar in structure to a Langmuir-Blodgett multilayer. Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17-20, 1993