The role of organics in metallic passivation

Organic substances are known to affect electrochemical reactions. The passivation characteristics of iron have been shown to be drastically altered in the presence of certain ions. Since passivation must occur to preserve the physical integrity of some materials in vivo, a study was initiated to determine the effect of alanine, bovine plasma albumin, and cystine on this phenomenon for nickel and copper. The procedure was as follows: (1) potential pH diagrams which show stable metal‐containing forms with respect to pH and electrical potential were constructed to interpret anodic dissolution data; (2) measurements were made to determine potential ranges in which organic adsorption occurs; and (3) data on electrical potential of the metal and associated current were taken for construction of anodic dissolution curves. The results showed that the presence of cystine inhibited the passivation of nickel and improved the passivation tendency of copper. The other organic substances had little or no effect on passivation. A possible mechanism for these effects is proposed. Further, the results showed a relationship between the onset of passivation and the potentials where metal‐containing solid substances become thermodynamically stable, as determined from the potential pH diagrams.