What is cathodic protection and give a basic mechanism?

• A. A method that uses insulating coatings to block metal contact.
• B. A process to strengthen metal by alloying with another metal.
• C. A corrosion prevention method where a more easily oxidized sacrificial anode protects a structure by preferential oxidation, preserving the protected metal.
• D. A protective technique using a controlled external current to maintain a protective potential.

Answer: (C)

Cathodic protection works by making the protected metal act as a cathode in its electrochemical environment. This is achieved by attaching a more active metal, a sacrificial anode, to the structure. The sacrificial metal is more prone to oxidation, so it corrodes first, while electrons flow from the sacrificial anode to the protected metal. That transfer pushes the protected surface to a more noble potential, suppressing its tendency to oxidize, and thus preventing corrosion of the protected metal. Over time the sacrificial anode is consumed and must be replaced, while the structure remains preserved. A common example is zinc or magnesium anodes protecting steel in seawater.

There is also a related form, impressed-current cathodic protection, where an external power source provides the protective current to the structure. The basic idea—driving the protected metal to remain a cathode and resist oxidation—remains the same, even though the source of the protective current differs.