Abstract
Ammonium hydroxide solution (2.3mol) containing ammonium tartrate (0.1mol), ammonium carbonate (0.1mol), and ammonium fluoride (0.27M mol) was used as an electrolyte for anodizing aluminum in alkaline solution.A thick film (about 15μ) was formed on an aluminum specimen by electrolysis for 30min. under current density of 2Amp/dm2 in this solution.It was found by chemical analysis that the film contained about 1.2% of F- and its density (10μ:1.8mg/cm2) was lower than that of the anodized film in H2SO4 (10μ:2.1mg/cm2). It had a high corrosion resistance to acid (H2SO4 10%) and base (NaOH 10%), but its hardness was not so high.It was supposed by electron microscopic examination of the surface and cross-section that the film had larger pores and cells as compared with the anodized film in H2SO4.The double anodized film, which had been anodized in sulfuric acid after the electrolysis in alkaline solution, had higher corrosion resistance as compared with a double anodized film, which had been electrolyzed in reverse order. It was clearly observed by microscopy that the layer of 2ry oxide film was formed beneath that of 1ry oxide film.
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