Abstract
The structure and the coloring of unsealed films of aluminum oxide, which had been anodized in various acid baths, were investigated by means of electron diffraction, electron probe X-ray microanalysis, single crystal X-ray diffraction, gas chromatogrphy, and infrared absorption spectrum analysis.The following results were obtained:(1) The structures of aluminum oxide films, which had been anodized in sulfuric, oxalic, and sulfo-salicylic acid baths, were identified as an amorphous alumina mixed with a small part of more crystalline or less crystalline γ-Al2O3.(2) AlKα in sulfosalicylic acid film showed a chemical shift due to heat produced by electron irradiation during the observation with electron probe X-ray microanalyzer and electron microscope.(3) Carbon in oxalic acid film formed to CO2 at about 900°C, at which the color of film disappeared.On the other hand, the colors of sulfosalicylic acid film and of p-phenolsulfonic acid film faded at about 700°C.The difference in these temperatures for decolorization would be due to the effects of sulfur in the films.(4) Carbon, included in oxalic acid film or in the film obtained from Ematal solution, would probably be present at ionized carboxyl group (COO-).Sulfur, included in sulfuric, sulfamic, sulfosalicylic, and p-phenolsulfonic acid films, would probably be present as sulfate ion (SO42-).(5) An oxide film, which had been anodized in aqueous solution of H2SO4-(COOH)2 mixed acid, was divided into two layers according to the distribution of sulfur content; and single crystals of γ-Al2O3 were found in the outer layer of the film.
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