Why Does Iron Rust?
The metal iron combines chemically with oxygen when there is moisture in the air, and the result is the reddish substance we call rust. Iron and steel rust when they come into contact with water and oxygen. Both water and oxygen are needed for rusting to occur.
If you leave a nail in a damp place, a scaly, red-brown coat will form over it. When the nail first gets wet, a chemical action known as oxidation takes place.
Oxygen dissolved in the water joins with the iron in the nail to produce a new substance — rust.
Iron objects don’t rust if they are protected by something that keeps out oxygen and water. Paint, for example, forms a coating that protects iron objects from rust.