Cl-induced passivity breakdown in α-Fe2O3 (0001), α-Cr2O3 (0001), and their interface: A DFT study. (1st December 2022)

• Record Type: Journal Article
• Authors: Yin, Xiaoran; Wang, Haitao; Han, En-Hou
• Is Part Of: Journal of materials science & technology. Volume 129(2022)
• Page Start: 70
• Page End: 78
• Publication Date: 2022-12-01
• Subjects: Hematite -- Chromia -- DFT+U -- Interface -- Cl-induced depassivation; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2022.03.034
• Languages: English
• ISSNs: 1005-0302

Abstract

Highlights: Interactions between Cl and α-Fe2 O3 (0001) surface, α-Cr2 O3 (0001) surface, along with their interface were systematically studied by density functional theory. Vacancy acts as the favorite channel for Cl penetration, which is in agreement with the ion exchange model. Cr2 O3 has stronger resistance to Cl corrosion than Fe2 O3, for its higher vacancy formation energy and Cl diffusion barrier. The interface region is proved to be the weak point of the α-Fe2 O3 /α-Cr2 O3 bilayer. Abstract: The presence of chloride ions is the critical factor of passivity breakdown of the protective film and eventually leads to localized corrosion. However, the mechanism and the role of chlorides in these processes are still controversial. Hematite and chromia are generally believed to be the major components of outer and inner oxide layers on stainless steels. In the present paper, a comparative study of Cl ingress into pristine and defective α-Fe2 O3 (0001) surface, α-Cr2 O3 (0001) surface, along with their interface, was conducted using density functional theory. Vacancy formation energy calculation confirms good stability of α-Cr2 O3 and high reactive activity of the interface region. Cl inserts into an O vacancy is energetically more favorable than Fe vacancy and interstitial site, demonstrating Cl-induced degradation complies with the ion exchange model. Transition state search for Cl diffusion through O vacancies shows α-Cr2 O3 is more protective than α-Fe2 O3, while the interface region is the weak point of the duplex passive film.