Anodised aluminium railings

Anodizing

Many metals are structurally weakened by the oxidation process, but not aluminum. Aluminum is an extremely reactive metal that can actually be made stronger and more durable through a process called ‘anodizing’. Anodizing involves placing a sheet of aluminum into a chemical acid bath, quite often acetone in laboratory experiments. An electric current passes through the acid, causing the surface of the aluminum to oxidize (essentially rust). The oxidized aluminum forms a strong coating as it replaces the original aluminum on the surface. The result is an extremely hard substance called anodized aluminum.

Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than bare metal. Aluminium alloys are anodized to increase corrosion resistance, to increase surface hardness, and to allow dyeing (coloring), improved lubrication, or improved adhesion. Anodized aluminum can be nearly as hard as diamond under the right anodizing process. Many modern buildings use anodized aluminum in places where the metal framework is exposed to the elements. Special dyes can also be used to color the anodized aluminum for decorative uses. Coloured dye seeps into the microscopic pores of the anodized layer and colours it. The layer is then sealed and the colour appears as part of the aluminium metal itself.