Introduction and Principles of Corrosion

The term corrosion has its origin in Latin. The Latin term rodere means gnawing and corrodere means gnawing to pieces . It is rather interesting to examine the historical aspects of the developments of corrosion. Metallic corrosion has no doubt been a problem since common metals were first put to use. Most metals occur in nature as compounds, such as oxides, sulfides, silicates or carbonates (very few metals occur in native form). The obvious reason is the thermodynamic stability of the compounds as opposed to the metals. The process of extraction of a metal from the ore is reduction. 

In the extraction of iron, the oxide is reduced to metallic iron. On the other hand, the oxidation of iron to produce the brown iron oxide commonly known as rust is the opposite reaction to the production of the metal from the oxide. The extraction of iron from the oxide, must be conducted with utmost careful control of the conditions, such that the backward reaction is prevented. 

During the Gupta Dynasty (320—480 A.D.) the production of iron in India achieved a remarkable degree of sophistication as attested by the Dhar Pillar, a seven-tonne, one-piece iron column made in the fourth century A.D. This implies that the production of metallic iron from the ores was a well-established process, and the people involved at that time were aware of the reverse reaction involving the oxidation of iron to produce the oxide (the familiar rusting of iron). 

Other examples involve the use of copper nails coated with lead by the Greeks in the construction of lead-covered decks for ships.1 They probably realized that metallic couples of common metals are undesirable in seawater. Protection of iron by bitumen, tar, etc., was known and practiced by the Romans. 

The earliest published accounts of the causes of corrosion are the two publications by Robert Boyle (1627-1691) entitled Of the Mechanical Origin of Corrosiveness and 

---