Why does iron rust?
An iron nail left in a damp places will soon be covered by rust. The rusting of iron is an example of oxidation. That is, when iron rusts, it actually “burns up”. But the rusting process is very slow and does not produce heat fast enough to cause a flame.
In this process, the iron metal joins chemically with oxygen dissolved in the moisture in the air. As the iron and oxygen “burn” they form a reddish-brown ash we call rust.
Once started, rust will easily spread. This is because the rough spots of rust help collect whatever moisture there is in the air. The rusting may continue until the iron is rusted away.
Iron objects don’t get rusty if they are covered with something that keeps out oxygen and water. Oil and grease form a thin coat that helps protect iron tools.
Special paints cover such iron things as bicycles, automobiles and ships, and rust never gets a change to start.