We have performed a surface characterization study in attempts to identify the chemical species that constitute the iron fluoride-based passivation film in the anhydrous HF/carbon steel system. Relative to untreated carbon steel, anhydrous HF-exposed samples have a homogeneous surface with an unaltered overall morphology. X-ray photoelectron spectroscopic (XPS) data have provided detailed fundamental insight into the chemical nature of the surface passivation film. We have discovered that, upon exposure to anhydrous HF media, carbon steel passivates by forming an FeF2-based film (> 1000 Å), with a terminating Fe(III) fluoride overlayer (< 50 Å). The proposed fluoride film structure is discussed in context of published surface science literature and known metal oxide passivation chemistry.

Subject
Films, Thin films, Steel surfaces, Fluorides, Metal surfaces, Autoclaves, Oxide films, Iron, X-ray spectroscopy, Oxide surfaces, Film formation, Passivation, Carbon steel
Keywords:
hydrofluoric acid, carbon steel, iron fluoride, surface film, alkylation
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1995
Association for Materials Protection and Performance (AMPP)
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