Lubrication of Ceramics by Tribopolymerization: A Designed Experiment to Determine Effects of Monomer Structure, Load, and Speed on Wear

Abstract

An experimental study of ceramic lubrication by tribopolymerization at high loads and high speeds, using a pin-on-disk (fixed ball-on-flat) machine with alumina-on-alumina, is presented. In order to extend the range of applied loads and sliding velocities beyond those used in previous studies, a three-factor, two-level designed experiment was carried out to determine the effects of monomer structure, load, and speed on wear. Five monomers of widely varying chemical structure were used at one percent concentration in a hydrocarbon carrier fluid, hexadecane. They consisted of (a) one condensation-type monomer, a partial glycol ester of a longchain dimer acid, and (b) four vinyl-type addition monomers. Two levels of load (40 and 160 N) and speed (0.25 and 1.0 m/s) - each varying by a factor of four were used; thus the range of frictional heat generation was 16 to 1. The results of this study were rather surprising and changed our thinking on the mechanism(s) by which monomers can act to reduce ceramic wear. For example, at low speeds — regardless of load — the monomers used were very effective in reducing wear, with reductions ranging from 44 to 98 percent depending on the monomer and load. However, at high speeds, the monomers were generally ineffective; in some cases, increases in wear were observed. This was unexpected. Possible explanations for this behavior — including surface temperature effects and tribochemical reactions — are discussed. Results presented on Fourier Transform Infrared (FTIR) Spectroscopy of worn ceramic surfaces and wear debris show that the film-formation from the monomer solutions is complex, involving a combination of aluminum soap formation as well as evidence of oligomer/polymer formation in some cases, notably diallyl phthalate. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999