Showa Aluminum Kabushiki Kaisha

Tadao Fujihira

Kozo Arai

Tatsuhiko Ejima

Eizo Isoyama

A process for treating the surface of aluminum foil for use as an electrode of electrolytic capacitors to increase the surface area of the foil to the greatest possible extent includes the three steps of pre-etching treatment, intermediate nitric acid treatment and post-etching treatment. The pre-etching treatment is conducted electrolytically in an aqueous solution of chromic acid and at least one of chromic acid and chromates. The intermediate nitric acid treatment is carried out by immersing the pre-etched foil in an aqueous solution of nitric acid to remove a chromate film formed by the pre-etching from the foil surface, especially from the interior of the resulting pits. The post-etching treatment is conducted electrolytically in an aqueous solution of hydrochloric acid, or hydrochloric acid and an oxidizing acid.

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Sakaishi, Japan

Tadao Fujihira