The Structure of Metal Deposits Obtained by Electrochemical Displacement upon Zinc

Abstract

An attempt is made to identify the composition and the structure of nonadherent immersion deposits of noble metals on zinc. For this purpose Cu, Au, Ni, and Ag deposits, obtained by electrochemical displacement from their salt solutions in 1N sulfuric acid, were examined by x‐rays. All of them contained redeposited Zn. Cu deposits contained approximately 9 to 13 atom per cent in solid solution, and Ni deposits contained 17 to 20 per cent in solid solution; Au deposits large amounts and Ag deposits below 0.5 atom per cent. The grain size of the deposits was very small because their growth was hampered by codeposited Zn. During the displacement of Ag, zinc deposited mostly as a very thin layer on the surface of the grains. The other three metals absorbed Zn readily, forming α‐phases. The displacement of the noble metal occurs because of the activity of the local cells; Zn acts as anode and the noble metal forms very small cathodes. The redeposition of Zn on these cathodes is possible because it is deposited in form of a solid solution, the free energy of which is reduced.