抄録
In order to establish the mechanism of coloring process, the anodic oxide film obtained in a mixture of maleic acid and sulfuric acid was investigated by utilizing visible and infrared spectra, E.S.R. spectrum and E.P.M.A. The film obtained in a bath containing 250g/l maleic acid and 0.8g/l H2SO4 included a variety of organic compounds derived from maleic acid, and also presented a dark amber tone from the initial period of anodizing. If the content of H2SO4 increased to 1.8-4.4g, the color turned darker as the anodizing proceeded, because the organic compounds incorporated into the film increased as the bath voltage rose. In a bath of 6.0g/l H2SO4 and maleic acid, on the other hand, the anodic oxide film was almost colorless like the oxide film obtained by sulfuric acid anodizing. From these facts the following mechanism has been proposed. (1) Coloring of the anodic oxide film is caused by the organic compounds produced by polymerization or complicated reactions of maleic acid incorporated into the film. This is the same process as the conventional oxalic acid film is colored. (2) Increase of negative bisulfate ion in the bath prevents the negative ion from migrating into the film, because bisulfate ion migrates into the film more easily than ion and, therefore, the color tone of the film tends to be lighter.
