Three things are required for rust to develop: iron, water and oxygen. Rust, also known as iron oxide, occurs when water begins to react with carbon dioxide in the air to form a very weak carbonic acid, which causes the iron to dissolve and bond with oxygen.
Although all metals can oxidize, only iron or other iron alloys can actually form rust. To prevent oxidation and rust, iron that is exposed to air and water typically is protected. Painting, galvanizing or coating the iron with a rust-resistant alloy are all common techniques used to prevent the iron from reacting with the air and water by forming a protective layer over the iron.