Cyclic voltammograms of Cu-30Ni-1.5 Al alloy were traced in stirred and non-stirred solutions of 3.5% sodium chloride containing 100 ppm sodium sulphide. The surface film was analyzed using electron dispersive X-ray (EDX) and IR whereas the soluble cations were measured by atomic absorption technique. It was found that in chloride solutions free from sulphide ions, a passive film which composed mainly of Cu20 and Cu2(OH)3CI is formed through the first two oxidation steps. The passive film obtained in non-stirred solution has appeared somewhat more stable than that obtained in stirred solution. In the presence of sulphide ions, the formation of sulphide compounds came on the expense of the formation of the passive film. Consequently, the corrosion rate was highly increased due to the presence of sulphide ions. It was found that in addition to the anodic dissolution of the alloy during negative-to-positive potential sweep, there is also a reductive dissolution during the positive-to-negative potential sweep. |
