2. Principle of metal corrosion

A given metal or alloy, in contact with an aqueous medium, can find itself in one of three situations:

• it may be in a state of localized corrosion (rust spots, pitting, cankers) or generalized corrosion (general curling, anodic dissolution). Metal atoms can then leave the crystal lattice;

• it may be in a state of immunity. The metal atoms are locked in and cannot leave the crystal lattice;

• it may be in a passive state. A protective oxide film forms at the metal-electrolyte interface, and may be protective in its own right.

The theoretical aspects relating to these three situations have been examined in the article Corrosion of metals and alloys in aqueous media, which is well worth consulting before turning to the practical applications studied...