Passivation of stainless steels in hydrochloric acid

Journal Article · Thu Apr 01 04:00:00 EST 1999 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.1391777· OSTI ID:345328

Wegrelius, L; Falkenberg, F; Olefjord, I ^[1]

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1. Chalmers Univ. of Technology, Goeteborg (Sweden). Dept. of Engineering Metals

High alloyed stainless steels (Fe20Cr20Ni, Fe20Cr20Ni6Mo, and Fe20Cr20Ni6Mo0.2N) were polarized in 0.1 M HCl + 0.4 M NaCl solution for 10 min and 2 h between {minus}75 and 800 mV vs. saturated calomel electrode (SCE). The composition of the passive films was analyzed by angle-resolved X-ray photoelectron spectroscopy, and showed that oxide particles are formed during the initial stage of the passivation process. It is suggested that they are formed by deprotonation of hydroxide. For prolonged exposure, a uniform oxide film is developed under the hydroxide layer. The composition of the film is strongly dependent on the potential. Molybdenum decreases while Cr, Fe, and Ni increase with the potential. The content of Cr in the hydroxide layer decreases with the potential. {beta}-MoCl{sub 2} is identified in the film on the Mo-containing steels. Chloride is present in both the oxide and hydroxide layers. The film forced at {minus}75 mV(SCE) on the Mo-free alloy contains over 50% more Cl{sup {minus}} compared to the film formed on Mo-containing steels. It is suggested that one of the beneficial effects of Mo in stainless steels is that it forms soluble oxochloro complexes, which thereby lower the amount of Cl{sup {minus}} in the film and makes the steel more resistant to pitting.

• OSTI ID: 345328
• Journal Information: Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 4 Vol. 146; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHEMICAL COMPOSITION
CORROSION PRODUCTS
CORROSIVE EFFECTS
HYDROCHLORIC ACID
PASSIVATION
STAINLESS STEELS