Science

Corrosion

Corrosion is a chemical or electrochemical transformation of a material caused by its environment. Rusting iron is the best-known example, but corrosion is much broader than rust.

What is happening?

For iron to rust, water and oxygen are normally involved. Different areas on the metal surface can act as tiny electrochemical sites where iron is oxidised and oxygen is reduced. The products evolve into hydrated iron oxides and related compounds we call rust.

Where do we see it?

Salt can accelerate corrosion because dissolved ions make water conduct electricity better. Acidity, temperature and contact with other metals can also change the rate.

Protection can work in several ways: paint blocks water and oxygen, zinc coatings can protect steel, and stainless steel relies on chromium to form a thin passive surface layer.

Worth rememberingRust is one form of corrosion; corrosion is the broader phenomenon.

Corrosion is more than rust

Aluminium, copper, zinc and stainless steel can also corrode. Some of them form surface layers that strongly slow further attack.

Go one step further

A useful way to understand this phenomenon is to separate the driving force from the visible result. Temperature, pressure, concentration, surface area and the nature of the materials can each change the rate or the final state. In real systems, several of these factors often act at the same time.

That is why the same phenomenon can look different in a laboratory, in the kitchen or outdoors. The underlying chemistry or physics stays the same, but the conditions change the balance.