Anodising
An electrolytic process that thickens the natural protective oxide layer on a metal, especially aluminium.
Formula / equation
2Al + 3H₂O → Al₂O₃ + 6H⁺ + 6e⁻
Unit
μm
In depth
The metal is made the anode in dilute sulfuric acid, growing a porous oxide film tens of micrometres thick. The pores readily absorb dye before being sealed in hot water, which is how coloured aluminium components are produced. The layer greatly improves corrosion and wear resistance.
Examples in the real world
Coloured anodised aluminium on laptop cases, bicycle components and window frames.