Tribochemistry at lubricated interfaces

Abstract

High resolution mass spectrometry is used to monitor in situ gaseous wear products that are generated during sliding of lubricated carbon–carbon interfaces in a vacuum. During the initial stages of sliding, significant amounts of polyperfluoroether lubricant fragments are detected, which resemble the mass patterns of scissioned lubricant in the thermal desorption experiment. The intermediate stage of sliding characterized by lower rate of lubricant fragmentation is followed by higher rate before wear of hydrogenated carbon overcoat occurs, which is accompanied by hydrogen emission and friction increase. Lubricant loss, removal, and alteration are precursors of the wear of solids and are determined by scanning microellipsometry. The amount of altered lubricant that is left on the disk and slider surfaces is quantified by x-ray photoelectron spectroscopy and the chemical structure of altered lubricant is evaluated by time-of-flight mass spectrometry. It is found that the dominant process, before the wear of solids occurs, is tribochemical scission of fluorocarbon polymers. Some fragments desorb from the interface, while others containing carboxylic end groups attach by strong physisorption to solid surfaces.