硫酸塩浴からの卑金属(Zn, Cd, Mn)電析の臨界電流密度

Abstract

Zn、Cd、Mnのような卑金属の電析の臨界電流密度を、硫酸塩浴を用いて測定した。結果は以下の通りである。(1)水素イオンの大きな拡散過電圧により陰極電位がMnの平衡電位に移行して、Mnの電析が起こる。(2)ZnとCdの臨界電流密度は、水素イオンの限界電流密度よりも小さかった。(3)Znの電析中、陰極界面のpHは水酸化亜鉛形成の臨界pHに達した。そして、陰極上に吸着された水酸化亜鉛は、更に過電圧を上げ、陰極電位をZnの平衡電位にまで移行させた。(4)Cdの電析では、水酸化カドミウム形成の臨界pHより陰極界面のpHはずっと低く、電析挙動は水酸化物抑制機構では説明できなかった。

The critical current densities for the electrodeposition of less noble metals such as Zn, Cd and Mn were measured using sulfate baths. The results obtained are as follows: (1) for Mn deposition, the cathode potential was shifted to the equilibrium potential of Mn to occur its deposition by a significant diffusion overpotential of hydrogen ion; (2) the critical current densities of Zn and Cd were smaller than the limiting current density of hydrogen ion; (3) during the deposition of Zn, the pH in the cathode layer was reached to the critical pH for Zn hydroxide formation and the Zn hydroxide adsorbed on the cathode brought about an extraoverpotential to shift the cathode potential to the equilibrium potential of Zn; and (4) the pH in the cathode layer was much lower than the critical pH for Cd hydroxide formation during its deposition and the deposition behavior was not able to be explained by the hydroxide suppression mechanism.