What is the primary purpose of a sacrificial anode in cathodic protection?

The primary purpose of a sacrificial anode in cathodic protection is to prevent corrosion of a more valuable metal structure by acting as the anode in an electrochemical cell, corroding in place of the protected metal. Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. Corrosion is an electrochemical process where metal atoms lose electrons and become ions, leading to material degradation. A sacrificial anode, typically made of a more electrochemically active metal like zinc, aluminum, or magnesium, is electrically connected to the structure being protected, such as a steel offshore platform or pipeline. Because the sacrificial anode has a more negative electrochemical potential than the steel, it readily gives up electrons and corrodes, while the steel structure receives these electrons and is thus prevented from corroding. The term "sacrificial" indicates that the anode is intentionally designed to corrode, thereby "sacrificing" itself to protect the more valuable structure. For example, zinc anodes are commonly attached to steel ship hulls; the zinc corrodes preferentially, extending the lifespan of the hull by preventing it from rusting. The process relies on the natural flow of electrons from the more active (anode) to the less active (cathode) metal in a conductive environment like seawater. This electron flow effectively suppresses the oxidation reaction on the protected structure, stopping or significantly slowing down corrosion.