Abstract
The initial repassivation processes of anodic reaction on newly created surfaces of high nickel alloys containing 0-30 mass% chromium were investigated by a rapid straining electrode technique in a 10%Na2SO4+H2SO4 (pH at room temperature=3.0) solution at 553 K at constant anodic potentials. The results obtained are as follows:(1) The decrease in current density with time after rapid straining was stopped consists of two stages. Namely, current density in a short period (within around 20 ms) after rapid straining was stopped decays to the formula of i∝exp (−tn) (i: current density, t: time, n: constant), and then the density at least up to 1000 ms decays to the formula of i∝t−n.(2) The repassivation rate increased with increasing chromium content, and so the amounts of charge caused by the metal dissolution decreased with increasing chromium content.(3) It was considered that the reason for which nickel-base alloys containing high chromium content such as Alloy 690 (60%Ni-30%Cr-10%Fe) had high SCC resistance in a high temperature acidic solution containing sulfate ions is due to both the promotion of the repassivation and the suppression of the film dissolution by the formation of the chromium oxide film.
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