The electrochemical oxidation of silver in chromate solutions

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A study of the electrochemical oxidation of silver in chromate solutions, and the subsequent reduction of the silver chromate formed is described. In the absence of any chromate, only silver dissolution and deposition are observed. In solutions containing 1 × 10−3 M chromate, a shoulder corresponding to silver chromate formation can be observed, but it is largely obscured by c oncurrent silver dissolution. At higher concentrations of chromate, the silver chromate formation peaks are fully resolved. The silver chromate grows as a film which, when formed from solutions with low chromate ion concentration (<10−2 M), does not impede the silver dissolution reaction. However, the dissolution process is suppressed when the film is formed from more concentrated chromate solutions. In 1 M chromate solution, when the anodic potential exceeds about 0.64 V(she), where silver dissolution would have occurred in the absence of any chromate, the silver chromate layer continues to thicken, and a second reduction peak is observed. This second reduction peak is associated with the formation of a powdery layer of silver chromate on the surface of the original compact layer which gives rise to the first reduction peak.