Effect of Noble Element Alloying on Passivity and Passivity Breakdown of Ni
Welding of stainless steels can generate welding fumes containing carcinogenic hexavalent chromium (Cr^+6). To mitigate this problem, a new Ni-Cu-Pd welding consumable alloy has been developed. The addition of a small amount of Cu and Pd in Ni enhances the galvanic compatibility of Ni with stainless steels and improves its localized corrosion behavior. In this paper, the artificial pit electrode technique and X-ray photoelectron spectroscopy were used to study the benefits of Cu and Pd alloying. The passive film on Ni-10Cu-1Pd alloy mainly consisted of outer Ni-hydroxide and inner oxide, and the noble elements Pd and Cu apparently did not contribute to the formation of the passive film. However, Pd catalyzed the reduction of Cu at the bottom of artificial pits, which enhanced the cathodic reaction and thus ennobled the protection potential, making stable pit growth more difficult. This catalytic effect of Pd also prevented the propagation of deep pits in a test using a thin foil crevice sample.
Cu and Pd alloying, X-ray photoelectron spectroscopy, artificial pit electrode technique
Kim, Yeong Ho; Frankel, G. S. "Effect of Noble Element Alloying on Passivity and Passivity Breakdown of Ni," Journal of The Electrochemical Society, v. 154, no. 1, 2007, pp. C36-C42.