How is aluminium anodised? - Leaving Cert Chemistry - Question B - 2017

Aluminium anodising is a process where the aluminium object is made the anode (positive electrode) in an electrolytic cell. Here are the steps involved:

1. Preparation of the Aluminium Surface: The aluminium surface must be cleaned and prepared to ensure proper adhesion of the anodised layer.

2. Electrolytic Cell Setup: The aluminium object is immersed in an electrolytic solution, typically a dilute sulfuric acid solution or an acidified water electrolyte.

3. Connection of Electrodes: The aluminium is connected to the positive terminal of the power supply, making it the anode. A cathode, often made from lead or other materials, is also submerged in the electrolyte.

4. Application of Current: When a direct current is passed through the solution, the aluminium begins to oxidize at the surface, forming a layer of aluminium oxide.

5. Control of Conditions: The process is maintained at specific temperatures and voltages to control the thickness and quality of the anodic layer.

6. Finishing: After the desired thickness is achieved, the anodised aluminium is removed from the electrolyte, rinsed, and may be sealed to enhance the protective properties of the oxide layer.