The structure and the formation behavior of porous/barrier composite oxide films formed on aluminum by re-anodizing in a boric acid/ammonium borate solution have been studied by transmission electron microscopy combined with ultramicrotomy. The porous film was formed in an oxalic acid solution. The porous/barrier composite film is amorphous, whereas a crystalline film grows when the porous film is hydrated before the re-anodizing to form hydrous alumina platelets in the pores. The size and the volume of both crystals and voids increase with anodizing time. The thickness of the various types of barrier films formed at a given current density up to 350 V in the borate solution decreases in the order: the amorphous region of the barrier film > the barrier/porous amorphous composite film > the hydrated porous/barrier crystalline composite film > the crystalline region of the barrier film.
|出版ステータス||Published - 1996|
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