What is Rust?
{{unreferenced|date=August 2010}} [[File:Rust.rost.JPG|thumb|right|250px|Rust, the most familiar example of corrosion, on an old train. It becomes brown or red.]] '''Rust''' is a type of [[corrosion]]. It happens to [[iron]] and its alloys when it is [[wikt:exposed|exposed]] to [[air]] or [[water]] for a long time. Rust slowly [[wikt:decompose|decomposes]] iron into other [[chemicals]], because of a [[chemical reaction|reaction]] with the [[oxygen]] [[molecule]]s. Both [[air]] and [[water]] are needed for rust. Almost all metals corrode but they can be protected by covering with [[paint]], a coating of oil or grease or even plastic. Sacrificial protection or industrial [[galvanizing]] can also work. [[Alloy]]s (mixes of metals) such as [[stainless steel]], rust more slowly than pure [[iron]]. When iron rusts, it becomes [[red]] or [[brown]], and the metal eventually [[wikt:decay|decays]]. Rust appears on metal if it is left outside in the [[humidity|damp air]]. For example, rust occurs mostly in cracks of alloys or metals. [[Rain]] water can enter the cracks and stay in the cracks, and cause the metal to [[Corrosion|corrode]]. Eventually it becomes rust. Iron is not strong after it rusts. Some metals, such as [[aluminium]], [[titanium]], and [[stainless steel]] form a very thin [[wikt:coat|coating]] of tough corrosion on the metal. The metal cannot continue corroding because the coating isolates the rest of the metal from the source of oxygen. This is why aluminium keeps its [[wikt:shine|shine]]. It also makes aluminium seem very [[chemical reaction|unreactive]], even though it can react with water. Rusting iron makes [[iron oxide]]s that are not tough, so air and water continue to get in and the iron continues to rust. [[File:Bruine roest op tarwe (Puccinia recondita f.sp. tritici on Triticum aestivum).jpg|thumb|basidiomycete [[fungus]] on a plant]] Some types of basidiomycete [[fungi]] can be [[wikt:mistake|mistaken]] for rust because they are similar to rust in [[color]] and [[texture]] and sometimes