Chemistry – Metals - Corrosion of metals | e-Consult

While a barrier method like galvanising effectively prevents corrosion, it's not always sufficient because barriers can be damaged. If the barrier is scratched, chipped, or otherwise compromised, the underlying metal is exposed to the environment and corrosion can begin. For example, consider a galvanised iron fence that is repeatedly scratched by balls or weather. The zinc coating will be damaged, exposing the iron to moisture and oxygen, leading to rust formation.

Sacrificial protection overcomes this limitation. By using a more reactive metal like zinc, the zinc will corrode preferentially to the iron, even if the coating is damaged. The zinc will continue to protect the iron as long as it remains in electrical contact with the iron. This is particularly useful in situations where the barrier coating is likely to be damaged, such as underwater pipelines or ship hulls. The sacrificial anode (zinc) is regularly inspected and replaced as it corrodes, ensuring continued protection of the iron structure.