Corrosion and Its Prevention

1677 WordsAug 6, 20107 Pages
CORROSION Corrosion is defined as the involuntary destruction of substances such as metals and mineral building material by surrounding media, which are usually liquid (i.e. corrosive agents)." Most metals corrode. During corrosion, they change into metallic ions. In some cases, the product of corrosion itself forms a protective coating. "For example, aluminium forms a thin protective oxide layer which is impervious to air and water. In other cases (e.g. iron), however, the coating either flakes off or is pervious to both air and water. So the whole piece of metal can corrode right through." The most common forms of metallic corrosion are caused by electrochemical reactions, wherein two metallic phases (e.g., iron oxide and iron) react…show more content…
Applying a Protective Layer Both air and water are necessary for rusting to occur. Any method which can keep out one or both of them from iron will prevent rusting. The most obvious way is to apply a protective layer. 1) Coating with paint, oil or grease Objects that are unlikely to be scratched can be coated with paint (or lacquer, or enamel). For example, bridges, ships and car bodies are painted. Moving parts of a machine are protected by applying oil or grease. 2) Coating with another metal Iron can be coated with a thin layer of another metal which is resistant to corrosion. Galvanized iron is iron coated with zinc. Some roofs, buckets and dustbins are made from galvanized iron. Tin -plate is iron coated with tin. 3) Using Alloys Of Iron An alloy is a partial or complete solid solution of one or more elements in a metallic matrix.Alloys usually have different properties from those of the component elements. Alloys are sometimes made to stop corrosion of metals and at the same time make it stronger. For example Steel, Carbon steel. Steel is produced form iron by carefully controlling the amount of carbon present (0 - 1%). To fight against corrosion, steel can be alloyed with other metals such as chromium and nickel to produce stainless steels. Cathodic Protection Rusting is a redox reaction in which iron loses electrons. If iron is connected to a more reactive metal, the other metal will lose electrons in preference, preventing the formation of Fe2+
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