Sacrificial Anode
A block of reactive metal attached to a structure so that it corrodes preferentially and protects the structure.
Unit
Dimensionless
In depth
Because the sacrificial metal is higher in the electrochemical series, it oxidises in place of the protected metal and supplies electrons to it. The anode is consumed over time and must be replaced periodically, which is far cheaper than replacing the structure.
Examples in the real world
Zinc blocks bolted to a ship's hull; magnesium rods inside domestic hot water cylinders.