Question

How are redox reactions involved in corrosion?

Answer 1

The simple answer is `"intimately"`, in that corrosion is simply a redox reaction involving oxidation of a metal, which is usually iron.

Explanation:

It is trivial to write the oxidation of iron metal to iron (II) oxide:

`Fe + 1/2O_2 rarr FeO`,

And this is quite clearly an oxidation reaction. More, and more complex oxidation products are accessible, as iron has a particularly rich redox chemistry. Hydrous oxides of iron(III) are all known: `Fe_2O_3*(OH_2)_n`, iron(III) hydroxide oxides, `FeO(OH)`, and iron(III) hydroxides, `Fe(OH)_3`. Mixed oxidation state hydrous oxides are also known. Iron oxide (rust) chemistry, is a very broad church, and I know that a significant proportion of our budget goes into rust prevention and control. It is a losing battle, because iron oxidation is thermodynamically downhill.

We've all seen pictures of monumental bridges around the world, in Sydney Harbour, and San Francisco bay, or the Hell Gate bridge in NY. To this day, there would be huge teams of dedicated corrosion engineers inspecting the rust that inevitably develops, and trying to control it.