Abstract
Dezincification occurs by dissolution of both zinc and copper, followed by redeposition of copper from the oxygen-free cuprous chloride/zinc chloride anolyte. Deposition of copper from such a solution by reduction of Cu+ requires a potentIal below −0·41 V but Cu2+, formed by disproportionation of cuprous chloride, can be reduced to copper at potentials up to −0·16 V. As the potential of film-free beta-brass iS −0·56 V, reduction of copper at the advancing front of dezincification in beta-brass can occur by direct cathodic re~uction of cuprous ions. Alpha-brass, with a potential of −0·38V, can only reduce cupricions; dezincification of alpha-brass therefore depends upon formation of Cu2+ by disproportionation of cuprous chlonde at the advancing front.
Under the conditions existing at the advancing front, disproportionation of cuprous chloride can be suppressed by a small amount of arsenic, acting through reactions in which it cycles between the As3+ and AS(solid)states. Arsenic consequently inhibits dezincification of alpha-brass but the dezincification of beta-brass, which does not require the formation of cupric ions, is unaffected.
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