Perfluoropolyalkylether Oil Degradation: Inference of FeF3Formation on Steel Surfaces under Boundary Conditions

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Abstract
The formation of iron fluoride (FeF3) through the interaction of perfluoropolyalkylether (PEPE) oil with steel surfaces was investigated under boundary lubrication conditions. Ball-bearing rolling action was simulated by a specially designed wear-test apparatus that incorporated noncoaxial wear members to give a skid/roll ratio of ∼0.16. The contact stress was 8.3 × 108 N·m−2 (∼120 000 psi), and the speed was 1750 rpm. Under these conditions, FeF3 formation on the wear surfaces was inferred using x-ray photoelectron spectroscopic (XPS), Auger electron spectroscopic (AES), and secondary ion mass spectrometric (SIMS) surface analysis techniques. These findings support the hypothesis that, under the low oxygen environment of spacecraft earth orbit, formation of FeF3 and subsequent FeF3 catalyzed degradation of PEPE can constitute an important PFPE degradation pathway under boundary lubrication conditions.