Pulsed-Potential Electrodeposition of Zirconium in a Molten LiCl–KCl Salt: Improvements in the Selectivity and Adhesion Strength

Abstract

This study demonstrates the pulsed-potential electrodeposition of reduced Zr species (ZrCl and Zr) in a molten LiCl–KCl salt. We report, for the first time, a new reduction reaction of Zr species (−1.90 V vs. Ag/AgCl 10 wt%) in molten LiCl–KCl salt, characterized by cyclic-voltammetry experiments using W and Zr electrodes. The pulsed-potential electrodeposition experiments were performed using an inert W-foil electrode in a molten ZrCl4–LiCl–KCl salt. Three cathodic-pulse potentials (−1.30, −1.60, and −1.90 V) were applied, and the chemical and structural characteristics of respective deposits were compared. The deposits were characterized by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and Raman spectroscopy. Additionally, we accomplished the pulsed-potential electrodeposition (>103 A/m2) of α-Zr metal with a practical ZrCl4 concentration (2.6 wt%). The results confirm that pulsed-potential electrodeposition can be employed for the selective deposition of the α-Zr metal by minimizing the co-production of ZrCl in molten LiCl–KCl salt while achieving excellent adhesion to the inert W electrode.

Optical monitoring of the anodic dissolution of zirconium and the agglomeration of potassium hexachlorozirconate during transpassive dissolution in molten LiCl–KCl salt

“…2(b)). According to our previous work, 27 the reduction product of R4 is Zr metal. Hence, we conclude that the oxidizing reactant of O2 is also Zr metal.…”

“…and a cylindrical tungsten rod ( ϕ = 1.5 mm, 99.95%, Nilaco) as the counter electrode. Elemental analysis of the Zr wire 27 showed that the proportion of Hf in it is less than 0.8 at%. Only a negligible amount of Hf was therefore dissolved into the electrolyte during the anodic dissolution processes.…”

“…Recall that the experimental procedures remained the same for all the samples (except ZrCl (ref. 27)). Therefore, the absolute intensity of the background noise should be identical for each sample.…”

“…2(a)) once the peak characteristics of the redox reactions had stabilized during multiple potential sweeps. 27 Fig. 2(b)-(i) summarize the optical monitoring results during CV with the Zr electrode in molten LiCl-KCl salt.…”

“…2(c)-(f)). 27,28 The first oxidation reaction (O1) is well known as the reaction in which insoluble ZrCl is oxidized to yield Zr(IV) ions. 7 The reaction mechanism of O1 can also be confirmed by visual changes on the inert tungsten electrode surface during CV in molten ZrCl 4 -LiCl-KCl salt (Fig.…”