Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

Abstract

Metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides. However, in environments that contain aggressive anions such as chloride, Cl − , the passive film becomes unstable and degrades locally causing film breakdown and pitting corrosion. A number of theories describing the initiation of pitting corrosion have been postulated and discussed but to date there is no consensus on the mechanism of breakdown. Since all current mechanisms require Cl − interactions for oxide film breakdown in Cl − containing environments, the question is what is the nature of the interaction of aggressive anions such as Cl − with the passive film, adsorption and/or absorption, leading to pitting? This communication focuses on the interaction of Cl − with the passive oxide film on pure aluminum by reviewing and summarizing the available experimental data concerning Cl − interactions. It should also be noted that the observations for Cl − interactions with Al reviewed and summarized herein might not be applicable to all metals and alloys. Technologically important metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides.1-90 The passive oxides behave as kinetic barriers, which inhibit further oxidation of the underlying thermodynamically reactive metals. However, in environments that contain aggressive anions such as chloride, Cl − , the passive film becomes unstable and degrades locally causing film breakdown and localized corrosion, which in turn decreases the service life of the materials. The consequence of discrete oxide failure is localized corrosion, which occurs in the forms of crevice corrosion in occluded sites and metastable or stable pitting corrosion on open surfaces. It is generally agreed that localized corrosion occurs in two distinct steps: initiation and propagation.A number of theories describing the initiation of pitting corrosion have been postulated and discussed.

Electrochemical treatment of a graphitic forging lubricant effluent: The effect of chloride concentration and current density

“…These super-Faradaic efficiencies are reported in the literature and they may be explained in terms of chemical dissolution of the anode (4), chemical attack of both anode and cathode, which can occur due to acidity and alkalinity produced in the vicinity of the electrodes (31) and pitting corrosion of the anode, caused by chloride ions (32). Figure 6 shows the amount of dissolved aluminum when an aluminum plate was dipped into a NaCl solution for 24 h. One can observe that as the chloride concentration increases, the amount of dissolved aluminum is higher, which is consistent to the literature data that says that the higher the chloride concentration, the higher is the corrosion promoted by Cl-ions over aluminum surface (33)(34)(35)(36)(37)(38)(39). It is also possible to notice that the amount of chemically dissolved aluminum is small.…”

The corrosive influence of chloride ions preference adsorption on α-Al2O3 (0 0 0 1) surface

“…The (2 × 2) Al 2 O 3 slab is used to be the substrate for 1 to 12 Cl − adsorption in one ML plane, and the ML is from 1/28 to 12/28. The experimental and theoretical work [1,5,6,12,17,26,27] have improved that the most stable adsorption sites are Al(1) atop sites which are consistent with our calculations above, then the most stable configurations of ML = 1/28 to 4/28 are Al(1) atop adsorption. Because of the periodic expansion of slab, the most stable configuration in (1 × 1) slab is also the most stable configuration in (2 × 2) slab, this means the most stable configurations of ML = 8/28 and 12/28 are Al(1)B10 and O(5) adsorption.…”

“…However, in environments that contain halogen anions such as chloride ions, the passive film becomes unstable and degrades locally causing film breakdown and pitting corrosion [1][2][3][4][5]. The interaction of chloride ions (Cl − ) on Al 2 O 3 surfaces represents one of the prototype examples of both surface science and electrochemistry [6].…”

Perspective—Localized Corrosion: Passive Film Breakdown vs Pit Growth Stability

“…[3][4][5][6][7][8][9][10][11] After all, localized corrosion can only occur if an otherwise protective passive film is present and undergoes a breakdown event. Studies have focused on linking film breakdown events to the composition and structure of the passive film using techniques such as X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM).…”