Question

Corrosion of metals is useful

Answer 1

Corrosion affects all metals except noble metals (gold, platinum), becausemetals are quite reactive towards oxidation. When iron corrodes, it forms a layer of rust (oxides and hydrous oxides). ... This protects the metalbeneath the outer corroded layer.

Answer 2

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Corrosion is the disintegration of metal through an unintentional chemical or electrochemical action, starting at its surface. All metals exhibit a tendency to be oxidized, some more easily than others. A tabulation of the relative strength of this tendency is called the galvanic series. Knowledge of a metal's location in the series is an important piece of information to have in making decisions about its potential usefulness for structural and other applications.
The driving force that causes metals to corrode is a natural consequence of their temporary existence in metallic form. To reach this metallic state from their occurrence in nature in the form of various chemical compounds (ores), it is necessary for them to absorb and store up for later return by corrosion, the energy required to release the metals from their original compounds. The following pictures illustrate the similarity in color between pale green malachite, a common copper ore mineral, and the corrosion products on a brass plate (70% copper) exposed to a humid environment.
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