Pilar Herrera-Fierro

Interfacial chemistry of a perfluoropolyether lubricant studied by X-ray photoelectron spectroscopy and temperature desorption spectroscopy

The interfacial chemistry of Fomblin Z25, a commercial perfluoropolyether used as lubricant for space applications, with different metallic surfaces—440 C steel, gold, and aluminum—was studied. Thin layers of Fomblin Z25 were evaporated onto the oxide‐free substrates and the interfacial chemistry studied using x‐ray photoelectron spectroscopy and temperature desorption spectroscopy. The reactions were induced by heating the substrate and by rubbing the substrate with a steel ball. Gold was found to be completely unreactive towards Fomblin at any temperature. Reaction at room temperature was observed only in the case of the aluminum substrate, the most reactive towards Fomblin Z25 of the substrates studied. It was necessary to heat the 440C steel substrate to 190 °C to induce decomposition of the fluid. The degradation of the fluid was indicated by the formation of a debris layer at the interface. This debris layer, composed of inorganic and organic reaction products, when completely formed, passivated the...

Evaluation of Several Space Lubricants Using a Vacuum Four-Ball Tribometer

The friction and wear behavior of seven space lubricants was investigated under boundary lubrication conditions using a vacuum four-ball tribometer. Three of the lubricants were perfluo-ropolyethers (143AC, S-200, and Z-25). Three were synthetic hydrocarbons (a multiply alkylated cyclopentane, 2001a), and a formulated version with an antiwear and an antioxidant additive (2001). The third hydrocarbon was an unformulated polyal-phaolefin (PAO-100). An unformulated silahydrocarbon (SiHC) was also evaluated. Test conditions included: a pressure <6.7 × 10−4 Pa, a 200N load, a sliding velocity of 28.8 mm/sec (100 rpm), and room temperature (∼23°C). The wear rate for each lubricant was determined from the slope of wear volume as a function of sliding distance. The lowest wear rate (0.033 × 10−9 mm3/mm) was obtained with the silahydrocarbon. The formulated synthetic hydrocarbon had a wear rate of 0.037 × 10−9 mm3/mm, which was a 36 percent reduction compared to the unformulated fluid. The polyalphaolefin had the ...

X‐ray photoelectron spectroscopy study of the stability of Fomblin Z25 on the native oxide of aluminum

Thin films of Fomblin Z25, a perfluoropolyalkylether lubricant, were vapor deposited onto clean, oxidized aluminum, and sapphire surfaces, and their behavior at different temperatures was studied using x‐ray photoelectron spectroscopy and temperature desorption spectroscopy (TDS). It was found that the interfacial fluid molecules decompose on the native oxide at room temperature, and continue to decompose at elevated temperatures, as previous studies had shown to occur on the clean metal. TDS indicated that different degradation mechanisms were operative for clean and oxidized aluminum. On sapphire substrates, no reaction was observed at room temperature. Our conclusion is that the native oxide of aluminum is neither passive nor protective towards Fomblin Z25. At higher temperatures (150 °C) degradation of the polymer on sapphire produced a debris layer at the interface with a chemical composition similar to the one formed on aluminum oxide. Rubbing a Fomblin film on a single crystal sapphire also induced...

Evaluation of Boundary-Enhancement Additives for Perfluoropolyethers

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 ...

A New Antiwear Additive/Surface Pretreatment for PFPE Liquid Lubricants

Pin-on-disk tribology experiments were conducted on a perfluoro-polyalkylelher (PFPE) liquid lubricant with and without a new PFPE lubricant antiwear additive material: a silane. It was found that the silane provided moderate improvement in the antiwear performance of the PFPE lubricant when applied to the metallic surface as a surface coating or when added to the PFPE as a dispersion (emulsion). Slightly belter results were obtained by using the combination of a surface coating and an emulsion of the silane. The silane emulsions or coalings did not affect the friction properties of the lubricant. Micro-Fourier transformation infrared (μFFIR) spectroscopy analysis was performed to study silane transfer films and the degradation of the PFPE. The silane was found to mitigate degradation of the PFPE which may have been the major reason for the improved antiwear performance, observed. Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995