Abstract
It is not yet cleared whether the electrostatic capacity and leakage current of dielectric film is influenced or not by the grain size of high-purity aluminium foil which are used for anode of electrolytic condenser. The investigation was carried out with foils of 99.99% and 99.9% purities. Various grain sizes were obtained by the following methods. (1) After rolling with a heavy reduction from 1 mm to 0.1 mm (90%), the specimens 0.1 mm thick were annealed at various temperatures (250∼550°). (2) Initial sheets (0.125, 0.20, 0.40 mm) were rolled down to 0.1 mm in thickness. All the specimens were then annealed at 380° for 2 hrs and were etched electrolytically so that their weight was reduced by 24% each. Then it was found that the foil annealed at the end temperature of recrystallization (300∼320°), i,e, the foil of minimum grain size, has the maximum capacity in the experiment using the specimens of method (1). With the specimens of method (2), it was also ascertained that the foil with smaller grain size has the larger capacity, and the larger the capacity, the higher the leakage current is. If the grain size of 99.99% aluminium foils made by method (2), is so small as 0.1 mmφ, it would have a superior dielectric property with not less capacity and lower leakage current than 99.9% aluminium foil.
