Abstract
The pit growth behavior of high purity aluminum foil in electrolytic capacitors used for DC etching in a hot HCl solution has been studied using grained foil. Hemispherical patterns with diameters of about 1∼3μm and cubic patterns with widths and lengths of 7∼15μm were formed by electrolytic grainings in HNO3 and HNO3/HCl solutions, respectively. By using cubic or hemispherical patterns, uniform distributions of pits were obtained for a surface that was untreated and one that was pre-treated during the early stage of DC etching. Tunnel pits were distributed most uniformly on hemispherical patterns grained at 1C/cm2. Surface dissolution occurred as clusters of tunnel pits at the intersection of hemispherical patterns above a graining charge of 10C/cm2. For cubic patterns grained at up to 30C/cm2, the distribution of tunnel pits became uniform with an increase in the charge for graining. As a result, grainings affected the expansion of the surface area as measured by capacitance after DC etching. Cubic patterns are more effective for an increase in capacitance than hemispherical patterns.
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