Lexikon

materially damaging, or even destroying metals by chemical action of a substance or a mixture. The corrosion resistance of metals and alloys is a basic property related to the easiness with which these materials react with a given environment.

Most common corrosion is a natural electrochemical process, that seeks to reduce the binding energy in metals. In the presence of oxigen the end result of corrosion involves a metal atom being oxidised, whereby it loses one or more electrons and leaves the bulk metal.

Corrosion of metals can be a chemical process or a biological process, as well as the combination of the two.

Some metals are more intrinsically resistant to corrosion than others, either due to the fundamental nature of the electrochemical processes involved or due to the details of how reaction products form. The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. Any corrosion products of gold or platinum tend to decompose spontaneously into pure metal, which is why these elements can be found in metallic form on Earth, and is a large part of their intrinsic value. Some metals have naturally slow reaction kinetics, even though their corrosion is thermodynamically favorable. These include such metals as zinc, magnesium, and cadmium: their corrosion is very slow. Metals, such as iron are very reactive, and corrosive in the presence of oxigen.

Microbial corrosion, is caused or promoted by microorganisms, usually chemoautotrophs. Sulfate-reducing bacteria are common in lack of oxygen; they produce hydrogen sulfide, causing sulfide stress cracking. In presence of oxygen, some bacteria directly oxidize iron to iron oxides and hydroxides, other bacteria oxidize sulfur and produce sulfuric acid causing biogenic sulfide corrosion. Concentration cells can form in the deposits of corrosion products, causing and enhancing galvanic corrosion.

The prevention of metals from corrosion may happen by passivation, coating, cathodic protection, or by using corrosion inhibitors, which are chemical compounds that, when added to a liquid or gas, decreases the corrosion rate of a metal or and alloy.

Indirectly biocides also are abel to prevent metal corrosion by killing the microorganisms responsible for it.