Warning: in order to watch properly this Flash animation you should have downloaded the last version of Flash Player, which is available for free at the www.adobe.com website.

Anodic oxidation

Aluminum is a silvery metal which, under treatment, can modify its structure to form a porous and transparent aluminum oxide layer. This is not as prone to peeling as iron (rust); on the contrary, it is hard, compact, it can be dyed and it is virtually untouched by atmospheric corrosion.

The electrochemical transformation process of the aluminum surface is called “anodizing”, since the material is connected to the anode (the positive electrode) of an electrochemical device.
Anodizing differs from other processes like painting, chrome- plating, painting. While in these processes a layer of a different material is laid on a base material, anodizing is a proper modification of the metal surface.

The anodized material is usually formed by “aluminum alloys”: this allows to combine the corrosion resistance of pure aluminum to the mechanical characteristics of other chemical elements (alloying elements). Alloying elements (magnesium, silicon, manganese, zinc, copper,…) must not exceed the maximum percentages allowed for anodizing.

Some of the characteristics of the oxide:

  • Specific weight: 4
  • Apparent density : 2,8 - 3,2, according to its porosity
  • Melting point: 2000° C (compared to 660° C for aluminum)
  • Dielectric constant:8.