Galvanic Sacrificial Anodes

Galvanic anodes should exhibit as low a polarizability as possible. The extent of their polarization is important in practice for their current output. A further anode 

For application in flowing media (e.g., for ships) it is also necessary that the usable current content be as large as possible not only per unit of mass but also per unit of volume, so that the volume of the installed anodes becomes as small as possible. 

The cathodic protection of plain carbon and low-alloy steels can be achieved with galvanic anodes of zinc, aluminum or magnesium. For materials with relatively more positive protection potentials (e.g., stainless steels, copper, nickel or tin alloys), galvanic anodes of iron or of activated lead can be used. 

The anodes are generally not of pure metals but of alloys. Certain alloying elements serve to give a fine-grained structure, leading to a relatively uniform metal loss from the surface. Others serve to reduce the self-corrosion and raise the current yield. Finally, alloying elements can prevent or reduce the tendency to surface film formation or passivation. Such activating additions are necessary with aluminum. 

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