Reversible Potentials of Alloys

Unless the standard potentials of the alloy components are very close to each other, an alloy can be electrochemically equilibrated only in solutions of ions corresponding to the less noble component (having a more negative value of the standard potential). In adverse cases, precipitation of the more noble component on account of dissolution of the less noble one (cementation) would occur until the surface is completely and tightly covered by the former. 

If only ions of the less noble component are present, the reversible potential of the alloy electrode will be determined basically by the free-energy change of the less noble component in the alloy. 

The possible cases reflect the variety of possibilities existing in solid phase formation by alloying. 

In an ideal case, the free energy of the less noble metal in the alloy, G, relative to that of a pure metal, G, taken as the standard state, is given by the common thermodynamic relationship 

Since this implies the absence of any free energy of mixing, few alloys follow this relationship. Some dilute amalgams in aqueous solutions of corresponding ions at temperatures at which they are liquid do show linear relation- 

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