The matted and pitted surface of metals had conventionally been utilized as decoration. But, recently, it has become to be used for optical, and precision instruments, etc.
Pitting on metals is practically formed by sand blasting, wire wheel scratching, chemical etching methods, etc. These methods, however, affect the quality of material, and some pre-treatments such as leveling, polishing, cleaning, etc., and post-treatments such as bright finishing etc. are required. Pitting frequently formed during chemical and electropolishing is considered deteriorate brightness, however, these would be good methods to be utilized to get desired matt surface.
The author compared the shape of the pit by the said ordinary method, with that by electropolishing method, and observed the mechanism of formation of pits by the latter.
The summerized results are as followes;
(1) The shape of the pit by the ordinary methods is complicated, but that by the electropolishing method is of almost complete circle.
(2) The surface besides the pits by electropolishing is smooth and even, which will make possible to do without pre- and post-treatments.
(3) The shape of the pit formed under the anode current density and bath voltage for bright surface, is of circlet, but that for rough surface, is complicated due to selective dissolving by local attack of the electrlyte.
(4) The size and distribution of the pit formed under the condition of smooth surface, are affected by the state of bubbling oxygen from anode, i.e. by anode current density and bath voltage.
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