Chemistry – Metals - Corrosion of metals | e-Consult

The rusting of iron is an electrochemical process, essentially a slow form of electrolysis. Electrolysis involves the movement of ions in a solution driven by an electric current. To prevent rusting, we need to prevent the flow of electrons and ions that drive this process. Several methods achieve this:

• Galvanising: Coating the iron with a layer of zinc. Zinc is more reactive than iron and will corrode preferentially, protecting the iron underneath. This is a barrier method.
• Painting: Applying a protective paint layer to prevent contact between the iron and oxygen and water. This is also a barrier method.
• Alloying: Mixing iron with other metals, such as chromium (to form stainless steel), to create an alloy that is more resistant to corrosion. This alters the electrochemical properties of the iron.
• Sacrificial Protection: Attaching a more reactive metal (e.g., magnesium or zinc) to the iron. The more reactive metal corrodes instead of the iron, protecting it. This is also a barrier method.

Galvanising is a common and effective method. The iron is coated with a layer of zinc. If the paint or zinc coating is scratched, the zinc will corrode first, protecting the iron. This is because zinc is more readily oxidized than iron.