Density Functional Theory Study of Influence of Oxide Thickness and Surface Alloying on Cl Migration within α-Al₂O₃

Abstract

Insertion and migration of chlorine atoms (Cl) in α-Al2O3 were studied by density functional theory calculations focusing on the influence of oxide thickness and doping by Mg, Cu and Si. Work function, electronic band gap, and insertion energy were calculated to explore thermodynamics of Cl migration. Partial density of state (PDOS) calculations revealed the role of dopants in the electronic character of metal–O and Al–Cl bonds. Work function data showed the effect of Cl insertion into the oxide film on the corrosion resistance. Cl can locate at an O vacancy ( V O ) with a large exothermic insertion energy, independent of oxide thickness, but can only locate at superficial Al vacancy ( V A l ) exothermically. The energy barrier for Cl migration via neighboring V O increases with oxide thickness, and is 2 ∼2.5 eV for thicker oxides. Cl insertion causes a work function reduction exceeding 2 eV, implying a decreased corrosion resistance. The inhibition of Cl migration by Si-doping can be explained by a more intense hybridization peak of Si–O over Al–O in the PDOS profile, while the reduction of energy barrier by Mg–/Cu-doping probably is due to the deviation of metal-s state from the Fermi energy, thus facilitating Cl movement within the oxide.

Cerium and aluminum molybdates as inhibitors of the aluminum AA1050 corrosion process in aqueous NaCl solutions

“…According to the mechanism of oxide film destabilization by Cl − suggested in the literature, [31,32] these anions adsorb on the oxide surface, migrate through the film and catalyze the dissolution of aluminum through the formation of oxochloride complexes. Soluble aluminum species (including hydrolyzed species and chloride complexes) migrate to the metal/electrolyte interface and subsequently form solid corrosion products such as hydroxides, oxyhydroxides, and basic aluminum chlorides, developing a loose, porous passive layer on the metal surface.…”

Analysis of the elemental effects on the surface potential of aluminum alloy using machine learning

“…3) However, when exposed to acid or solutions containing Cl − , the passive layer is destroyed and corrosion occurs. [4][5][6][7][8][9][10][11] One of the forms of corrosion of aluminum alloy is pitting corrosion, which causes localized corrosion to form pits. Pitting corrosion can lead to various corrosion behavior such as filiform corrosion (FFC), 12,13) intergranular corrosion (IGC) [14][15][16][17][18][19] and stress corrosion cracking (SCC), 20) so it is important to prevent it.…”

First Principles Determination of the Potential-of-Zero-Charge in an Alumina-coated Aluminum/Water Interface Model for Corrosion Applications

“…In particular, Density Functional Theory (DFT) predictions of PZC's will help establish voltage-function relationships which have been largely lacking in current DFT modeling of explicit metal|oxide interfaces. 6,[14][15][16][17][18][19] For example, Ref. 6 predicted that uncharged oxygen vacancies (V 0 O ) give way to charged V 2+ O upon applying a sufficient electric field via adding a negative charge at the outer oxide surface.…”