Evaluation of Boundary-Enhancement Additives for Perfluoropolyethers

Abstract

Six additives were synthesized and evaluated as boundary lubrication enhancers for perfluoropolyalkylethers. These additives included a phosphate, a thiophosphate, a β-diketone, a benzothiazole, an amide/thiol and a sulfite. These additives were evaluated in a vacuum four-ball apparatus, at a one weight percent concentration in a perfluoropolyalkylether based on hexafluoropropene oxide. Tests were performed in vacuum (<6.7 × 10⁻⁴ Pa), at room temperature (∼23°C), at an initial Hertzian stress of 3.5 GPa (200N load), and a sliding velocity of 28.8 mm/sec (100 rpm). Infrared (IR) and Raman spectroscopies were used to analyze the steel (AISI 52100) specimens after testing. Wear rates for each formulation were determined from the slope of wear volume as a function of sliding distance. All additives 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 percent. IR and Raman analysis indicated the severity of wear can be correlated to the amount of surface fluorinated polymeric acid species (R_fCOOH) and graphitic amorphous carbon, in and around the wear scar.

Presented as a Sociey of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997

KEY WORDS:

• Perfluoropolyethers
• Boundary Lubrication
• Additives

Notes

Presented as a Sociey of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997