Abstract
Because of the wide use of galvanised steel pipes for conveying a variety of aqueous solutions a study has been made of the effects of the presence of chloride, nitrate and carbonate-bicarbonate ions on the relative potentials of zinc and steel. In the majority of solutions used, the potential of steel fell to an approximately steady value between −550 and −700 m V SCE, presumably due to anodic depolarisation. However, the behaviour of the zinc potential was irregular and depended on the type of solution employed. In particular, chloride ions were found to reduce the tendency towards ennoblement while the presence of nitrate and carbonate-bicarbonate ions raised the zinc potential sufficiently to produce a reversal of the potential of the zinc-steel couple.
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