Abstract
The electrochemical behaviour of aluminium alloyed with small amounts (up to 0.2%) of indium, gallium and thallium has been investigated. It has been found that these additions result in: (a) A considerable shift of the rest potential in the negative direction (to 1.4–1.7 V versus SCE), (b) A significant increase of the passivating current density (up to 0.1–1 Acm−2) and (c) A considerable decrease in the negative difference effect (increase of the faradaic efficiency to 99.5%) compared to the behaviour of pure aluminium. Except for the gallium alloy, the rate of corrosion of the alloys in neutral salt solutions is also decreased compared to that of pure aluminium. A ternary alloy, Al-0.01 In-0.01 Ga, exhibited a more negative rest potential than the Al-In alloy and a corrosion stability superior to that of the Al-Ga alloy. The negative difference effect was found to depend on the cation of the neutral salt in solution. The lowest effect was obtained in ammonium chloride solutions.
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