Underpotential Deposition of Zn in Presence of Iron-group Metals.

在水溶液中电沉积锌镍合金的过程中发现了锌的欠电位沉积，其中锌在比其平衡电位更正的电位下共沉积。与以往报道的“欠电位沉积”不同，本研究所讨论的锌的欠电位沉积是以相当高的速率持续进行的。这一现象仅在锌-镍、锌-钴、锌-铁等锌铁族金属体系的异常共沉积中观察到，而在正常的锌-铜、锌-镉体系的共沉积中没有出现。用X射线光电子能谱(XPS)、X射线光电子能谱(XPS)、X射线光电子能谱(XPS)和X射线光电子能谱(XPS)研究了合金成分的化学状态，发现在欠电位区得到的电沉积层中电还原为金属态。在铁族金属存在下，锌的欠电势沉积随着温度的升高、镀液中In的金属浓度比的降低以及镀液中氯离子的加入而增强。由于这些操作条件的改变降低了铁族金属的固有过电位，锌的欠电位沉积与铁族金属在合金沉积过程中的极化行为有关，并用X射线衍射技术研究了在欠电位区沉积的合金的组织结构。锌的欠电位沉积机制很难用合金中金属锌的活性降低来解释，因此，由于锌铁系金属合金的异常共沉积中存在锌的欠电位沉积，因此应结合异常共沉积的机理来探讨锌的欠电位沉积机理。

Underpotential deposition of Zn in which Zn was codeposited at the potentials more positive than its equilibrium potential was found in the electrodeposition of Zn-Ni alloys from aqueous solutions. The underpotential deposition of Zn discussed in this study proceeded continuously with appreciable high rate, which was different from the so-called "underpotential deposition" reported in the previous papers. This phenomenon was observed only in the anomalous codeposition of Zniron-group metal systems such as Zn-Ni, Zn-Co and Zn-Fe but did not appear in the normal codeposition of Zn-Cu and Zn-Cd systems. The chemical states of the alloy constituents were investigated by XPS and Zn as well as Ni in the electrodeposits obtained in the underpotential region was found to be electroreduced to metallicstate.The underpotential deposition of Zn in the presence of iron-group metals was enhanced with an increase in temperature, a decrease in metal concentration ratio of in in the bath and the addition of chloride ion to the baths. Since it was known that these changes in the operating conditions diminished the inherent overpotential of iron-group metals, the underpotential deposition of Zn was related to the polarization behavior of iron-group metals during alloy deposition.Further, the microstructure of the alloys deposited at the underpotential region was investigated by X-ray diffraction technique. It was difficult that the mechanism of the underpotential deposition of Zn was explained in terms of the decrease in the activity of metallic Zn in the alloys.Consequently, since the underpotential deposition of Zn is observed in the anomalous codeposition of Zn-iron-group metal alloys, the mechanism of the underpotential deposition should be discussed in connection with that of the anomalous codeposition.