HCl溶液中の交流エッチングで生ずるアルミニウム表面皮膜の検討

概要

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The AC etching process of aluminum in HCl solutions was examined by capacitance measurement and galvano-dynamic voltammetry. It was found that the electrostatic capacitance of the etched specimens showed a maximum depending on the electrolytic conditions such as current density and frequency. The phenomenon is explained in terms of the change in the distribution of cubic pits reflected by the change of the protective behavior of the films formed on the pits surface in the etching. Scanning electron microscope examination of the films stripped from etched specimen revealed that they replicate the cubic pit propagation in the metal and that they have a duplex structure consisting of an inner anodic film formed during the anodic cycles and an outer film of hydrous oxide (the etch film), precipitated during the cathodic cycles. The anodic film next to the metal is thin and compact, while the etch film is thicker and shows granular structure. Film thicknesses for etching with 3.6%HCl solution (303K) at 0.3A/cm2 and 5Hz were about 4nm for the anodic film and about 16nm for the etch film determined using electron microscope by transmission of ultramicrotomed sectional specimens. It is concluded that whether or not the porous layer develops deeply into the metal by the etching depends upon largely the formation and local breakdown behavior of an anodic film covering the cubic pits at the propagation tips.
社団法人表面技術協会の論文