Enemies of metals

The causes of rust? Oxygen, moisture and saltiness.

Rust is a spontaneous compound generated by the corrosion of ferrous materials. The substances present in the material (iron oxides, hydrates and carbonates), in contact with oxygen in the air, atmospheric humidity, rain and salt, give rise to a real electrochemical reaction that causes oxidation.

The noble metals (gold, silver, platinum) are those that resist oxidation, the base metals (iron, lead, zinc), on the other hand, are the easiest to oxidise and corrode. Rust occurs differently in the base metals.

In iron, for example, oxidation occurs on the surface layer: the part crumbles until it falls off, leaving the part underneath exposed, which can still be attacked again until complete deterioration.

Other metals such as aluminium, nickel, tin, for example, undergo the passivation process: the oxide layer adheres perfectly to the surface, preventing or slowing down the corrosion reaction. Below is the galvanic scale, the list of materials from the most oxidisable to the most noble:

  1. Lithium 
  2. Sodium
  3. Magnesium
  4. Aluminium
  5. Manganese
  6. Zinc
  7. Chrome
  8. Iron
  9. Cadmio
  10. Nichel
  11. Pond
  12. Lead
  13. Copper
  14. Stainless steel
  15. Titanium
  16. Silver
  17. Mercure
  18. Platinum
  19. Gold

It is important to bear in mind that even steel (an alloy of iron and carbon), the most widely used material in industrial and civil applications, considered by all to be eternal, is instead subject to deterioration caused by rust.

Rust forms on unprotected materials.

To counteract its formation, it is important to protect metals by coating processes that are essential during production and useful for proper maintenance.

To check the durability and maintenance requirements of a metal, it is essential to verify that it has at least one of the following rust protection processes:

  • Zinc plating, nickel plating, chrome plating: application of a surface layer of zinc, nickel or chrome.
  • Anodising: the surface of the metal (mainly aluminium, nickel, cobalt) is coated with an oxide layer.
  • Cathodic protection: connection with a metal to an electrolyte solution or with corrosion-absorbing materials to keep corrosion away from the artefact