Evaluation of boundary-enhancement additives for perfluoropolyethers

Six additives were synthesized and evaluated as boundary lubrication enhanc ers for perfluoropolyalkylethers. These additives included a phosphate, a t hiophosphate, a beta-diketone, a benzothiazole, an amide/thiol and a sulfit e. These additives were evaluated in a vacuum four-ball apparatus, at a one weight percent concentration ill a perfluoropolyalkylether based on hexafl uroopropene oxide. Tests were performed in vacuum (< 6.7x 10(-4) Pa), at ro om temperature (similar to 23 degrees C), at an initial Hertzian stress of 3.5 GPa (200N load), and a sliding velocity of 28.8 mm/sec (100 rpm), Infra red (IR) and Raman spectroscopies were used to analyze the steel (AISI 5210 0) specimens after testing. Wear rates for each formulation were determined from the slope of wear volume as a function of sliding distance. All addit ives yielded reductions in mean wear rates of at least 50 percent, with the exception of the benzothiazole which had no effect. Two of the additives, an amide/thiol and a sulfite, reduced the mean,wear rate by at least 80 per cent. IR and Raman analysis indicated the severity of wear call be correlat ed to rite amount of surface fluorinated polymeric ic acid species (RfCOOH) and graphitic amorphous carbon, in and around the wear scar.