Perfluoroalkoxy (PFA)-α-Alumina Composites: Effect of Environment on Tribological Performance

Perfluoroalkoxy polymer (PFA)-alpha-phase alumina (alpha-Al2O3) composites have dramatically (similar to 10,000 x) improved wear resistance compared to unfilled PFA when tested in air. In this study, unfilled PFA and PFA-alpha-Al2O3 composites were tested using a linear reciprocating tribometer in dry nitrogen (< 2.5 ppm O-2 and H2O), humidity-controlled air (15%, 30%, and 45% relative humidity), and submerged water. PFA-alpha-Al2O3 tested in dry nitrogen (N-2) and in submerged water exhibited wear rates that were two to three orders of magnitude higher than those of PFA-alpha-Al2O3 composites tested in humidity-controlled air. Infrared spectra of the worn PFA-alpha-Al2O3 surfaces tested in air exhibited peaks attributed to carboxylate salts. These peaks were severely diminished on the PFA-alpha-Al2O3 sample tested in dry N-2 and not observed for submerged water environments. The high wear rate of PFA-alpha-Al2O3 tested in dry N-2 and submerged water was attributed to the lack of carboxylate salts, which require oxygen and water form. These carboxylate salts bond to the alpha-Al2O3 filler within the PFA matrix which reinforces the polymer wear surface. Additionally, these carboxylate salts form a transfer film on the stainless steel counterface, which protects both the composite and counterface from wear and abrasion.