Abstract
Pure aluminum (99.50%) was electrolyzed with alternating current in alkaline solutions of various concentrations containing glycolic acid, which had been prepared by the reduction of oxalic acid. After that, its surface state was observed.Sodium hydroxide solutions (0.1-0.4% in concentrations) containing 5-14% of sodium glycolate were used as electrolytic solutions.The following results were obtained:(1) When a stainless steel (18-8) was used for the other electrode, a golden film was obtained by the electrolysis for 30-60min. under current density of 3-6amp./dm2.The thickest (9.5μ) and hardest (14.2 by Martens' scratch tester) film was obtained in 0.3- 0.4% solutions of sodium hydroxide containing 12% of sodium glycolate.The maximum reflection absorbance of the colored film was found at 385mμ and the color tone was similar to that of the anodized film from oxalic acid-sulfuric acid soution.(2) When lead was used for the other electrode, a black film was obtained under the same conditions as above (1), and the thickest and hardest film was obtained in 0.1% solution of sodium hydroxide. The degree of coloring was deeper in proportion to the electrolysis time.The color of the film was different according to the kind of the other electrode. However, the coloration would be due to the formation of chelate compounds by theelectrolysis of glycolic acid.
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