多孔質アルミニウム・アノード酸化皮膜と熱水との反応 ＩＩＩ インピーダンス測定による水和皮膜の酸溶解特性の解析

Abstract

Porous anodic oxide films formed in an oxalic acid solution were hydrated to various extents by allowing them to react with hot water at 99.5°C. The films were then dissolved in a chromic acidphosphoric acid solution and the dissolution was followed by impedance measurements in a neutral borate solution. The results were analyzed by plotting the log of the absolute value of impedance against the log of the frequency. The equivalent circuit of the hydrated film was found to consist of the capacitance of the barrier oxide layer (Cb) combined in series with a parallel combination of the capacitance and resistance components of the hydrous oxide formed in the pores (Ch and Rh). The values of Cb-1, Rh and Ch-1 and the their variation with the dissolution time (td) were determined. It was found for the films filled up with the hydrous oxide that the film-dissolution proceeds uniformly from the outside at a rate controlled by the dissolution of hydrous oxide, the dissolution rate decreases with the time of the reaction with hot water (th). The outermost part of the hydrous oxide formed at th>30min was very resistant to acid-dissolution. It was recognized that the decrease in dissolution rate is always accompanied by an increase in the specific resistance of the hydrous oxide. The barrier oxide layer next to the metal begins to dissolve at the time when the outer part of the film containing the hydrous oxide in the pores is completely dissolved. The dissolution characteristics of the barrier layer itself is little affected by the hot water treatment. These findings agree quite well with the results of a previous investigation conducted by gravimetry.