Corrosion
The corrosion indicates the deterioration of an object by reaction with an oxidant (dioxygene and the H+ proton in majority). It is necessary to exclude from it the effects purely Mécanique S (that does not concern, for example, the Rupture under the effect of Choc S) but corrosion intervenes in certain forms of wear of surfaces whose causes are at the same time physico-chemical and Mécanique S.
The most known examples are the chemical weatherings of the metals in water, such rust of the Fer and the Acier or the formation of Vert-de-gris on the Cuivre and its alloys (Bronze, Laiton). However, corrosion is a field much wider which touches all kinds of materials (metals, Céramique S, Polymère S) in variable environments (aqueous medium, atmosphere, high Température S).
The fundamental study of the phenomena of corrosion concerns the electrochemistry primarily. The study applied of the phenomena of corrosion is a field of the Science of the materials, which comprises at the same time concepts of Chimie and Physique (physicochemistry). Corrosion is an industrial problem important because at the origin of accidents (rupture of a part). In addition, it represents high costs (it is estimated that each second, 5 tons of steel are lost in the world, which represents an annual cost of 2% of the produces gross world).
Corrosion of metals
The corrosion of metals is a natural phenomenon. Indeed, except for some rare exceptions (the Gold and more generally all metals of the family of the Platinum than one finds in a native state naturally, Cuivre, Argent, meteoritic Fer of source ), the Métal is present on Ground in the form of Oxyde, in the Minerai S (Bauxite for the Aluminum, Hématite for iron). Since the Prehistory, the work of Métallurgie consisted in reducing these oxides in Low-furnace X then blast furnaces to manufacture metal. Corrosion is only one return to the natural oxide state.
The corrosion of metals is in the large majority of the cases an electrochemical reaction (a Oxydo-réduction) which utilizes the manufactured part and the environment.
Examples of contact corrosion (in connection with this phenomenon, to see the page of discussion): . Indeed, chromium in itself did not corrode, therefore protected the part, but the least stripe was catastrophic because the part then played the part of sacrificial anode for chromium and corroded very quickly. Anti-corrosion paintings with the Plomb were also abandoned because of their environmental impact.
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