Mechanism of Aluminium Electrochemical Oxidation and Alumina Deposition Using a Carbon Sphere Electrode

Using electromagnetic and electrochemical theories as a framework, this study examines the influence of carbon sphere electrodes on the distribution patterns of anodic oxidation and deposition current densities in metallic aluminium and porous anodic alumina. Theoretical calculations show that the current density symmetrically decreases from the centre outward under the effect of carbon sphere electrodes. Increasing the electrode distance improves the uniformity of the current distribution across the film, while decreasing the distance increases the rate of gradient change in current density. Simulation results reveal that at electrode spacings of 15 cm and 1 cm, the oxidation current density at the film centre is 1333 A/m2 and 2.9 × 105 A/m2, respectively. The current density gradually decreases outward along the radius, reaching 1330 A/m2 and 1.8 × 105 A/m2 at the edges, with observed current density gradient change rates of 500 A/m3 and 1.83 × 107 A/m3, respectively. Experimental results confirm that carbon sphere counter electrodes can create non-uniform oxidation and deposition electric fields. Microstructures with gradually varying symmetry can be generated by adjusting the electrode spacing, resulting in porous anodic alumina and composite films exhibiting iridescent, ring-like structural colours. The experimental findings align well with theoretical calculations and simulation results.