Effects of Addition of Oxidizing Agents on Anodizing of Aluminum in Alkaline Solutions

Studies on the finishing of aluminum in alkaline media (Part 3)

Abstract

This paper describes the effects of addition of oxidizing agents (KMnO₄, NH₄VO₃, K₂Cr₂O₇, K₂S₂O₈, H₂O₂, and K₃Fe(CN)₆) on AC electrolysis of aluminum in alkaline solutions.
The thickest and hardest film was obtained in 0.1mol NaOH solution containing 0.05mol of KMnO₄.
A bright black film was obtained in the alkaline solution of 0.225mol NaOH containing K₃Fe(CN)₆ and K₂Cr₂O₇.
The optimum conditions were as follows.
pH: 11-12
Current density: 0.8-1amp./dm²
Electrolysis time: 0.5hrs.
Corrosion resistance of the black film was higher than that of anodized film (alumite) in H₂SO₄. Fe, Cr, and Al were found in the film by qualitative analysis.