Sacrificial anodes are used in cathodic protection because they are...

• A. More electrochemically active (less noble) and corrode preferentially to protect the structure.
• B. More noble than the protected structure
• C. Inert
• D. Non-conductive

Answer: (A)

In cathodic protection, the sacrificial anode must be more electrochemically active (less noble) than the metal it protects so that it will corrode first. This lets the sacrificial metal act as the anode in a galvanic cell, delivering electrons to the protected structure and keeping it as the cathode. By preferentially oxidizing, the sacrificial anode sacrifices itself to prevent the protected metal from oxidizing, greatly reducing its corrosion rate. If the anode were more noble, it wouldn’t corrode to supply electrons; if it were inert or non-conductive, it wouldn’t participate in the electrical circuit or carry current, and protection wouldn’t occur.