On the Mechanism of Pitting of Aluminum

Corrosive effect of lithium nitrate trihydrate on common heat exchanger materials

“…It has been previously discussed that the corrosion of aluminum in alkaline solution with sodium nitrate present follows a reaction pathway leading to aluminum being oxidized and nitrate ions being reduced to ammonia . In the case of dissolved Br − , the reaction which leads to the initiation of pitting on the surface of aluminum in low pH solutions has been shown to proceed according to 1) adsorption of Br − onto oxide film; 2) reaction: Al 3+ + 4 Br − ⇋ AlBr 4 − ; and 3) dissolution of AlBr 4 − leading to the thinning of the oxide layer . This process will continue until the film is dissolved, allowing the bulk metal to have direct contact with the solution leading to further dissolution and the formation of deep pits.…”

“…[27] In the case of dissolved Br − , the reaction which leads to the initiation of pitting on the surface of aluminum in low pH solutions has been shown to proceed according to 1) adsorption of Br − onto oxide film; 2) reaction: Al 3+ + 4 Br − ⇋ AlBr 4 − ; and 3) dissolution of AlBr 4 − leading to the thinning of the oxide layer. [28] This process will continue until the film is dissolved, allowing the bulk metal to have direct contact with the solution leading to further dissolution and the formation of deep pits. Taking this information into consideration and combining our observations via EDS and XRD, it is suggested that the reaction occurring in our system, which is acidic (pH ∼4) and has Li + and NO 3 − ions present, is likely to follow general oxidation/reduction reactions (1) through (4), followed by precipitation of insoluble corrosion products LiAl 2 (OH) 7 · 2H 2 O, potentially accompanied by Al(OH) 3 .…”

The role of indium in the activation of aluminum alloy galvanic anodes

“…The dilution by bulk electrolyte of the solution in the pits to the pH range of oxide stability (4 < pH < 9) is responsible for suppressing the propagation of the pits . The Pourbaix diagram for aluminum shows that the aluminum oxide film is stable in the near neutral 4–9 pH range only. It dissolves in acidic environments (pH < 4) to form Al 3+ ions, and in alkaline environments (pH > 9) to form AlO 2 − .…”

Atmospheric corrosion comparison of antirust aluminum exposed to industrial and coastal atmospheres

“…It is generally acknowledged that the chloride ion is a significant cause of aluminum surface degradation under exposure condition. As shown in Figure 7a, the presence of the intermediate compound [AlCl(OH) 2 · 2H 2 O] in corrosion products shows proof that Cl − will react with Al 3+ to form aluminum chloride through a stepwise chlorination of aluminum hydroxide: [30,31] Al OH ð Þ 3 þ Cl À → Al OH ð Þ 2 Cl þ OH À ð6Þ…”