Electrolytic polishing - Denkaikenma

This is a distortion-free polishing method in which metals or semiconductors are anodically dissolved in a concentrated aqueous solution of phosphoric acid at a relatively high current density to produce a smooth, shiny surface. Electrolytic polishing can be divided into two phenomena: smoothing, or leveling, which removes irregularities of approximately 1 μm or larger, and brightening, which removes irregularities of the order of the wavelength of light, i.e., 0.01 μm. The current-potential (or bath voltage) curve during electrolytic polishing is also called the Jacquet curve, and is divided into an active dissolution region where etching occurs, a limiting current region where polishing occurs, and a polishing region accompanied by oxygen generation. This limiting current is explained by the diffusion of dissolved metal ions or acceptor anions such as _PO43- ^. In fact, a viscous liquid layer of approximately 0.01 cm is observed near the anode during polishing, and since this thickness should be thinner on the convex parts of the surface and thicker on the concave parts, the smoothing phenomenon can be explained by diffusion within this layer. The glossing phenomenon is thought to be due to the diffusion of ions in a thin solid film that forms on the surface.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

金属あるいは半導体などを濃厚なリン酸水溶液などのなかで比較的大電流密度でアノード溶解させ，表面を平滑かつ光沢のある面に仕上げる無ひずみ研磨方法．電解研磨現象は，ほぼ1 μm 以上の凹凸を除去する平滑化(smoothing，leveling)と，光の波長の程度すなわち0.01 μm くらいの凹凸を除く光沢化(brightening)の二つの現象に分けて考えることができる．電解研磨の際の電流-電位(あるいは浴電圧)曲線はJacquet曲線ともよばれ，エッチングの起こる活性溶解領域，研磨の起こる限界電流領域，酸素発生を伴う研磨領域に分けられるが，この限界電流は溶解した金属イオンまたはPO₄^3－のようなアクセプター-アニオンの拡散で説明される．実際，研磨中に陽極近傍には0.01 cm くらいの粘性に富む液層が観察され，その厚さは表面の凸部で薄く，凹部で厚くなっているはずなので，この層中の拡散で平滑化現象は説明できる．光沢化については，表面に生成する薄い固体皮膜中のイオンの拡散にもとづく現象と考えられている．

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