Mechanisms and Inhibition of Dealloying in an Alpha Brass.

Dealloying of a single-phase binary alpha brass in pH 4, 0.1M chloride solution was investigated in terms of the operative mechanism. Selective leaching of zinc from the brass was produced under conditions of cathodic polarization. Auger electron spectroscopy was employed to measure composition versus depth profiles of the resulting zinc-depleted surface layers. The selective leaching mechanism was found to be based on enhanced volume diffusion of zinc to the brass surface. Dealloying by dissolution of the brass as a whole, followed by redeposition of the copper, was found to occur exclusively under occluded cell conditions. The mechanism was examined in terms of the copper-chloride equilibria established at the dissolving brass surface. The redeposition of copper was found to proceed by reduction of cuprous chloride near the brass surface. The inhibitive effect of arsenic was determined to be the prevention of the cuprous chloride reduction reaction.