マレイン酸‐硫酸混合浴による自然発色アノード酸化

Abstract

For the purpose of obtaining integral color films in a mixture of malefic acid-sulfuric acid, studies have been made on electrolyte composition, electrolyte temperature, current density, electric wave form and also conditions for the initial two-step current control method. Under the anodizing conditions of 200 to 250g/l malefic acid and 3 to 6g/l sulfuric acid concentration, 20 to 40°C electrolyte temperature and 1 to 3A/dm2 current density, unifom integral color anodic films of dark amber to light gold were obtained on commercially pure aluminum and Al-Mg, Al-Mg-Si and Al-Zn alloys. In addition, it was found that the initial two-step current control method, in which anodizing is carried out at a low current density for the initial stage of anodizing and at a specified current density thereafter, was very effective to prevent the formation of pittings on the film surface. With respect to the applied electric wave form, it was found that low ripple waves such as direct current or three-phase full waves were effective to obtain colored films of uniform thickness. The electron microscopic observation of the anodic films revealed that the addition of sulfuric acid caused the cell to be small in size and more like the regular hexagonal structure, with an indication that the pore diameter also became small. The anions incorporated in the colored film were studied by using chemical analysis, IMA, IR and ESR, and it was revealed that coloring of the anodic film depended greatly on the amount of SO42- from sulfuric acid and corresponded to the amount of organic compounds, incorporated into the film from maleic acid as well. As the result, it was assumed that coloring has a close correlation to the behavior of organic anion radicals. Further, it was shown that when the colored films, were heated, the decoloration of the films, began at about 500°C or over, but by means of DTA and TGMS, it was found that the organic compounds in films were decomposed into CO2 at about 875°C, while SO42- decomposed into SO2 at about 950°C. This decoloring process corresponds to the variation of ESR spectra of the anodic oxide films.