What metal might you fasten to the hull of an aluminium boat to give it cathodic protection in sea water?

Question

Name two metals that you would not use. Explain your choices.

Answer 1

You need to use metals that are higher (than the metal to be protected) on the electrochemical series. Problem is aluminium is near the top & metals above it are very reactive.
The series is K, Na, Ca, Mg, Al, Mn, Zn, Fe, Ni, Sn, Cu, Hg, Ag , Au for some comon metals. So Zinc is used to protect copper propellers and fittings since it is higher on the series. In your example Magnesium, theoretically could be an option as other higher metals will react readily with water. In practice aluminium is protected by a thin film of alum. oxide which forms spontaneously in air , also aluminium boats may be painted.

Answer 2

You might use Mg, but you might not use iron or calcium. Iron is less reactive, and would encourage the Al to corrode, and Ca is too reactive, and would bubble!

Answer 3

Sodium and Lithium