PURPOSE: To extend the usable life of etchant by a method wherein the temperature of the etchant is elevated in accordance with the increase of an aluminum content in the etchant.
CONSTITUTION: An aluminum electrode substrate is immersed in etchant composed of hydrochloric acid solution and phosphoric acid ions added to it and etched electrochemically by an AC current and, at the same time, the temperature of the etchant is elevated in accordance with the increase of an aluminum content in the etchant. For instance, 7% hydrochloric acid solution doped with 1.5% phosphoric acid ions is used as the etchant and the aluminum foil is etched by an AC current with a density of 0.15 A/cm2. Then, in accordance with the increase of the aluminum content in the etchant, the etching temperature is elevated as shown by the attached diagram.
KANZAKI NOBUYOSHI
NAKANO KATSUTOSHI
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