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.

is the production of irreversible damage of the skin; namely, visible necrosis through the epidermis and into the dermis, following the application of a test substance for up to four hours. Corrosive reactions are typified by ulcers, bleeding, bloody scabs, and, by the end of observation at 14 days, by discoloration due to blanching of the skin, complete areas of alopecia, and scars. Histopathology should be considered to evaluate questionable lesions.

eye corrosion is defined in OECD TG 405 as ”the production of tissue damage in the eye, or serious physical decay of vision, following application of a test substance to the anterior surface of the eye, which is not fully reversible within 21 days of application”. In the EU, this effect is assigned “Xi”, and R41.

Eye irritation is defined in OECD TG 405 as “the production of changes in the eye following application of a test substance to the anterior surface of the eye, which are fully reversible within 21 days of application”.
In the EU this effect is assigned “Xi” and R36.

microbial corrosion, also called microbially induced corrosion (MIC) is corrosion caused or promoted by microorganisms, usually chemoautotroph bacteria. It can apply to both metals and non-metallic materials.

Irritation and corrosion are local effects, i.e. changes occur at the site of first contact of the substance with the skin, eye, or mucous epithelia such as the respiratory tract.

Corrosive substances may destroy living tissues with which they come into contact after single exposure. Irritant substances are non-corrosive substances which, through immediate contact with the tissue under consideration may cause inflammation after single exposure.

Substances that cause irritant effects only after repeated exposure are not classified as irritants. Skin and/or eye irritation refers to the production of fully reversible changes following application of a substance (in the case of eye irritation, when application is performed to the anterior surface of the eye).

Corrosive substances produce irreversible effects such as necrosis through the epidermis and into the dermis, ocular tissue damages or decay of vision.

Chemicals which are classified for respiratory irritation may provoke irritations similar to skin or eye irritations. They may also cause other toxic effects, in relation with interactions with the vegetative nervous system and leading to reflex responses (sneezing, coughing, respiratory symptoms, etc). These effects are reversible. Testing for respiratory irritation is not required under REACH as no validated guidelines are available. Nevertheless, existing and available data that provide evidence of the respiratory irritation potential of a substance should be taken into account.