Corrosion
The gradual destruction of a metal by electrochemical reaction with its environment.
Unit
mm/year
In depth
Corrosion is a spontaneous return of refined metals towards their thermodynamically stable ore forms. It requires an anodic site, a cathodic site, an electrolyte and an electron path, and it is accelerated by salt, acidity, moisture and contact with a less reactive metal.
Examples in the real world
Rusting of iron, green patina on copper roofs, and tarnishing of silver by atmospheric sulfur compounds.