Corrosion

Corrosion costs the civil aircraft industry many millions of pounds each year. With care and good husbandry, this figure can be reduced. The more that aircraft can be manufactured, operated and maintained with the short/long-term considerations of the effects of corrosion in mind, the more those maintenance costs will be reduced.

Metallic elements are usually compounded with other elements in the ground, before they are mined and (compared to the actual metals into which they are subsequently formed) they are relatively stable. Corrosion is the tendency of metals to revert to the thermodynamically more stable and oxidised state. This occurs when they react with dry air to form metal oxides or with acids and alkalis to form metallic salts. Some metals, such as gold and platinum, strongly resist corrosion.

Reactions, between metals and their environments, can occur in either of two (often simultaneous) ways:

• Chemical (oxidation)
• Electrochemical (galvanic)

In both cases, the metal is converted into metal compounds such as carbonates, hydroxides, oxides or sulphates.

The corrosion process involves two concurrent changes. The metal that is attacked, suffers an anodic change while the corrosive agent undergoes a cathodic change. The result is that material is lost from the Anode and gained by the Cathode, forming an ionic bond.