Oxide formation during the selective dissolution of silver from silver-gold alloys in nitric acid

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Abstract
A new phase formed on the surface of silver-gold alloys undergoing selective dissolution of silver in nitric acid has been studied by electron diffraction and dark-field transmission electron microscopy. The results of this analysis together with simple chemical tests suggest that the corrosion phase is gold oxide. It is proposed that the oxidation of gold occurs as a result of a change of chemical environment brought about by the selective dissolution of silver which effectively lowers the oxidation potential for gold. Partial oxidation of residual gold atoms resulting from the selective dissolution of silver might also be important in the growth of gold-rich islands, which are frequently found on the surfaces of corroding alloys, since this probably enhances their surface diffusivity.