Cathodic Protection
Definition and meaning of Cathodic Protection in chemistry.
Cathodic protection is a corrosion-control technique that makes a metal structure the cathode of an electrochemical cell, so it gains electrons instead of losing them through oxidation.
In more detail
Corrosion is fundamentally an anodic oxidation reaction in which a metal loses electrons to form metal ions. By forcing the metal to become the cathode, cathodic protection supplies it with a steady flow of electrons that suppresses this oxidation. This is done in two main ways: galvanic (sacrificial anode) protection, where a more easily oxidized metal is electrically connected to the structure and corrodes in its place, or impressed current cathodic protection (ICCP), where an external DC power source drives current through an inert anode to the structure.
Key facts
| Field | Physical Chemistry |
|---|---|
| Common sacrificial anodes | Zinc, magnesium, aluminum |
| Two main methods | Galvanic (sacrificial anode) and impressed current (ICCP) |
| Underlying principle | Suppresses anodic oxidation by supplying electrons to the protected metal |
Steel ship hulls and buried pipelines are commonly fitted with zinc or magnesium blocks; because zinc has a more negative standard reduction potential than iron, it oxidizes preferentially, leaving the steel hull protected as the cathode.
Frequently asked questions
Why does making a metal the cathode stop it from corroding?
Corrosion occurs through oxidation at anodic sites, where the metal loses electrons to form ions. Making the structure the cathode means it receives electrons instead, which suppresses this oxidation reaction.
What is the difference between sacrificial anode and impressed current cathodic protection?
Sacrificial anode protection uses a more reactive metal, such as zinc or magnesium, that corrodes in place of the protected structure with no external power needed. Impressed current cathodic protection uses an external DC power source and typically inert anodes, making it suitable for larger structures needing more current.