A corroded industrial structure outside UCSD's Powell Structural Systems Laboratory.

Corrosion is the breakdown of materials due to chemical reactions. It is usually oxidation with air molecules and often in the presence of water. Corrosion also occurs when an acidic/basic corrosive substance touches another material. When a material corrodes, its physical properties change. Problems with corrosion are mostly with metal, though other materials can corrode. Corrosion is a form of erosion. Some materials, such as stainless steel, are highly resistant to corrosion. Metals that may corrode can be protected by plating, painting, and other means.