engleski

The Behaviour of Cu-xNi (x=10-40wt%) Alloys in Alkaline Solutions Containing Chloride Ions

It is well known that in the presence of chloride ions the Cu-10Ni alloy is susceptible to pitting attack (1). Based on the literature daia (2), it was expected that the Ni addition has a beneficial effect on the resistance towards localized corrosion. The results were, however, unexpected and rather interesting, as summarized in Fig. 1. Evidently, constants a and b from the general relationship E_b= a + b log c_NaCl are dependent not only on the material investigated, but also on the chloride concentration. Although the resitance of the alloy is somewhat better copper and Cu-10Ni alloy show a very similar behaviour. For chloride concentrations higher than 0.5 M no fiirther shift of critical breakdown potential is observed. In the lower chloride range both Cu and Cu-10Ni alloy are superior to Ni metal, however, the situation becomes reversed for > 0.1 M. The addition of higher nickel contents to copper does indeed improve the resistance towards localized corrosion, however, only for chloride concentrations higher than a certain critical concentration, c_crit. An example is given in Fig. 1 for the Cu-40Ni alloy. In the lower chloride concentration range (c < c_crit which is in this case 0.05 M), constant b for Cu-40Ni is similar to those for Cu and Cu-10Ni alloy. However, at c_crit the straightline changes its slope and now follows that of nickel metal. With increasing content of Ni in the alloy from 10 to 40 wt.% the critical chloride concentration above which the alloy behaves similar to Ni, and therefore shows an improved resistance towards localized corrosion, inereases. References: (I) I. Milošev, Metikoš-Huković, M.; J. Electrochem. Soc., 138 (1991) 6l. (2) R.G. Blundy, M.J. Pryor, Cor. Sci., 12 (1972) 65; A.-M. Beccaria, J. Crousier, Br. Corros. J., 24 (1989) 49.

Cu-xNi alloys; cyclic voltammetry; Ni incorporation; pitting corrosion

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