When two metals touch each other and water is present, electrolysis occurs.
[2] One well known example is the reaction between zinc (Zn) and iron (Fe).
Zn(s)→Zn2+(aq) +2e (oxidation) The capacity of a sacrificial metal may be calculated from first principle as follows: By similar calculations Zinc and Magnesium have a capacity of 825 and 2206 Amp.Hours per Kg respectively.
[4] Similarly, sacrificial bars of a metal such as aluminium or aluminium alloys can be attached to an oil rig or to the hull of a ship to prevent it from rusting and breaking down.
Magnesium may similarly be used on dry land for installations such as pipelines and oil refineries, where its high driving voltage is better for overcoming the resistance of soils found on dry land.