Surface films and soluble degradation products formed in a PFPAE fluid and their implications to the wear of steel

The soluble degradation products were generated in a linear perfluoropolyalkylether (PFPAE) fluid in boundary lubrication. Perfluoropolyalkylether carboxylic acid species were found in the residual fluids from the sliding tests by vibration spectroscopy. Surface-bound organic and inorganic reaction products were identified by vibration microspectroscopy with a grazing angle objective attachment and X-ray photoelectron spectroscopy (XPS), respectively. Inorganic surface films were found to be composed primarily of FeF3. A monodentate perfluorocarboxylate surface species was found on the sliding surfaces in 50 degrees and 100 degrees C tests but not found in 150 degrees C tests. The higher friction and wear in 150 degrees C tests as compared to 50 degrees and 100 degrees C tests were attributed to the absence of the perfluorocarboxylate species over the sliding surfaces at high temperatures.