The designation corrosion is used for a process during which a metal loses its characteristic (metallic) properties. Corrosion processes are usually chemical reduction-oxidation reactions where metal atoms give up electrons to a corrosive medium, which can be a non-metal (e.g., oxygen) or a chemical compound (e.g., water). A metal corrodes because the reductionoxidation reaction leads to a gain in free energy. The rate of the reaction is highly dependent upon a series of different external factors, e.g. the temperature and the surface characteristicsof the metal. To control the corrosion rate one has to know how the external factors influence the chemical processes at the atomic level.