Corrosion

Corrosion is a natural aging process for metals. Corrosion is generally initiated when residues or atmospheric moisture settles on the surface of metals. 

In nature, iron can only be found in a stable form as iron ore or iron oxide.

In blast-furnace process iron ore is reduced to iron by adding carbon. This is done because oxygen has higher affinity for carbon than for iron. This “reduced” state of iron is thermodynamically instable. As a result, the iron attempts to return to its energetically more stable state as an iron oxide. In other words, iron oxidises.

Corrosion is metal-specific, i.e. it depends on the composition of the metal and its surface texture. Consequently, to achieve effective corrosion protection it is necessary to match the protective mechanism to the metal to be protected.