corrosion

thumb|Corrosion on exposed metal, including a bolt (fastener)|bolt and nut

Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion. thumb|left|Riveted connection of elements of the cooling tower of a power plant from 1904. Increased material volume caused by corrosion. In the most common use of the word, this means electrochemical oxidation of a metal reacting with an oxidant such as oxygen (, gaseous or dissolved), or ions (, hydrated protons) present in aqueous solution. Rusting, the formation of red-orange iron oxides, is perhaps the most familiar example of electrochemical corrosion. This type of corrosion typically produces oxides or salts of the original metal and results in a distinctive coloration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although, in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including mechanical strength, appearance, and permeability to liquids and gases.