Rust is a brownish-red substance that forms on the surface of iron or steel when it is exposed to damp air. The term used alone means iron rust, which consists mainly of hydrated iron oxide. Rust is formed by the union of the oxygen of the air with the iron by a process called oxidation (see Oxidation).
Rust not only corrodes the surface but also weakens the metal. Long exposure to air and moisture will cause nails to rust off, and rust holes to form in sheet iron. Iron can be alloyed (mixed) with other chemical elements to create rust-resistant metals called stainless steels. Iron and steel that are not rust resistant should be kept dry or coated with some substance, such as chrome or paint, that will resist the action of oxygen. Polished tools may be easily protected if wiped with a cloth soaked in oil. Coating metal objects with heavy greases or spray-on plastics, or wrapping them in special chemically treated paper, also prevents rust.
A coat of rust may be removed by scrubbing in water or using a polishing powder. Removal of a thick coat requires use of an emery wheel, a grindstone, or a file. Acids also dissolve rust.
See also Corrosion; Stainless steel.
