Rust
Rust, in metallurgy, the reddish-brown coating that forms on iron and steel through the action of oxygen and water. Rust does not have a definite chemical composition. It consists mainly of ferric oxide and ferric hydroxide. Rust pits the surface of iron and steel articles, and eats into them, weakening and destroying them. The damage done by rusting is enormously costly. Huge sums of money are spent to remove rust and protect iron and steel from rusting.
Metals can be protected from rust by coating them with paint, varnish, enamel, mineral substances called bitumen, or plastic. Platings of tin, zinc, nickel, and chromium also are used to preserve metals from rusting. Some kinds of steel, known as weathering steels, are protected by rust itself; when they are exposed to the atmosphere, a dense surface coating of rust forms that acts as a barrier to further corrosion. Some articles, such as carpenters' tools, can be protected with a thin film of grease. Silica gel, which removes moisture from air, also is used to protect metals from rusting.
Abrasives and caustic solutions are used to remove rust from metals.