| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to increase electrostatic capacity in aluminum foil in an electrode of an electrolytic capacitor, by generating deep etching pits uniformly and increasing an area enlargement ratio surely. SOLUTION: Aluminum has a plurality of primary recessed parts 1 with a diameter d1 of opening of 0.1 to 5μm as a circle on the surface. In this case, the primary recessed part 1 has an inward swelled shape with a maximum inner diameter d2 larger than the opening diameter d1 with a condition; opening diameter d1/maximum inner diameter d2<0.9. In addition, the primary recessed part 1 has one or more secondary inner recessed part 2 and at least one opening diameter d3 of the secondary inner recessed part 2 is not more than one-half the opening diameter of the primary recessed part 1.
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