低濃度クロム酸溶液中での電解時における陰極近傍のｐＨ変化

Abstract

In the previous paper, authors reported that [Cr(H2O)6]3+ ion formed by the resolution of hydrated chromium oxide (Crox) affected the formation of TFS film, which comprised metallic chromium and Crox, in a dilute chromic acid electrolyte containing a small amount of sulfuric acid. The formation and resolution of Crox and hydrogen evolution seemed to be connected with pH of the electrolyte near the cathode because these reactions occurred on the surface of the cathode. An attempt to measure the pH near the cathode during electrolysis was made using an Sb micro-electrode, which was recently applied to the pH measurement near the cathode. The results obtained were as follows: The pH measurement near the cathode during electrolysis in a dilute chromic acid electrolyte was successfully achieved using the Sb micro-electrode, and the pH value near the cathode ascended and the thickness of the cathodic layer increased by adding Cr3+ ion to the electrolyte. The pH value near the cathode ascended and the thickness of the cathodic layer increased with an increase of the current density. The pH value increased rapidly at about 15A/dm2 and gradually at more than 20A/dm2. The difference in the current efficiency of TFS film formation seemed to result from the change of pH near the cathode, of which degree depended on the difference of Cr3+ ion concentration.