How to prevent corrosion?
Corrosion is a vexed issue. But what is corrosion exactly? How does corrosion occur and how does corrosion protection work?
First of all: Corrosion originates from the Latin word “corrodere” and means being eaten or gnawed away. Corrosion thus describes the disintegration of a material by (electro)-chemical reactions. Metals such as iron or zinc do not start as pure substances but as metallic compounds (ores). To convert such ores into useable materials such as iron, oxygen and other substances are removed in blast furnaces, and this process puts the iron in an unnatural state. The iron tries to regain the removed oxygen from the air to revert to its original state and this reaction is ultimately described as corrosion.
Corrosion protection includes various methods and procedures which are necessary to halt or delay the corrosion process. Corrosion protection can be either active or passive. In the case of passive corrosion protection, steel is protected against the effects of oxygen and water by the application of an organic or inorganic coating system.
Such protection systems can consist of one or more coatings. The number of coating layers and thus ultimately the thickness of the protection layers depend on the required protection duration and the ambient conditions which the structure is subject to. The function of the structure and any optical requirements also need to be considered.
Active corrosion protection is also described as cathodic corrosion protection. This method of corrosion protection involves the use of sacrificial galvanic anodes or protection coatings. Less noble metals such as zinc, aluminium or magnesium act as so-called sacrificial protection anodes which as a result of their electrochemical potential are then corroded instead of the metal.
Another method of passively protecting steel from corrosion is an electro-chemical process. By shifting the equilibrium potential, the metal becomes thermodynamically stable and practically no more metal dissolution takes place.