Aluminium

Aluminium is very useful metal and used as a lightweight construction material eg greenhouse frames.

Aluminium can be made more resistant to corrosion by a process called anodising.

Aluminium is a reactive metal but it is resistant to corrosion. This is because aluminium reacts in air to form a layer of aluminium oxide which then protects the aluminium from further attack.

This is why it appears to be less reactive than its position in the reactivity series of metals would predict.

For some uses of aluminium it is desirable to increase artificially the thickness of the protective oxide layer in a process is called anodising.

This involves removing the oxide layer by treating the aluminium sheet with sodium hydroxide solution.

The aluminium is then placed in dilute sulphuric acid and is made the positive electrode (anode) used in the electrolysis of the acid.

Oxygen forms on the surface of the aluminium and reacts with the aluminium metal to form a thicker protective oxide layer.

Aluminium can be alloyed to make 'Duralumin' by adding copper (and smaller amounts of magnesium, silicon and iron), to make a stronger alloy used in aircraft components (low density = 'lighter'!), greenhouse and window frames (good anti–corrosion properties), overhead power lines (quite a good conductor and 'light'), but steel strands are included to make the 'line' stronger and poorly electrical conducting ceramic materials are used to insulate the wires from the pylons and the ground.