Anodic behaviour of Cu, Zr and Cu–Zr alloy in molten LiCl–KCl eutectic

Abstract

The anodic dissolution behaviours of Cu, Zr and Cu–Zr alloy were analysed in LiCl–KCl at 500°C by anode polarization curve and potentiostatic polarization curve. The results show that the initial and fast-dissolving potentials of Cu are −0.50 and −0.29 V, and Zr are −1.0 and −0.88 V, respectively. But, in the Cu–Zr alloy, the initial and fast-dissolving potentials of Cu are −0.52 and −0.41 V, and Zr are −0.96 and −0.92 V, respectively. The potentials satisfy the selection dissolution principle that Zr in the alloy dissolves first, while Cu is left in the anode and is not oxidized. The passivation phenomenon of Zr is observed in the quick dissolution of Zr, while it is not observed in the Cu–Zr alloy. Moreover, from the above anodic dissolution results, potentiostatic electrolysis of Cu–Zr alloy was carried out at −0.8 V for 40 min, and the anodic dissolution mechanism and kinetics of Zr in Cu–Zr alloy were also discussed. In the initial stage, Zr dissolves as Zr 4+ ions from the alloy surface and enters into the molten salt, leaving a Cu layer called ‘dissolving layer’ on the surface of the alloy. After that, another layer between the matrix and ‘dissolving layer’ called ‘diffusion–dissolution layer’ appears. Zr diffuses in the alloy matrix and dissolves as Zr 4+ ions on the surface of the ‘diffusion–dissolution layer’ continuously, and Zr 4+ ions diffuse through the ‘dissolving layer’ and enter into the molten salt finally. In addition, the factors affecting the dissolution of Cu–Zr alloy, such as time and potential, were also investigated. The dissolution loss increases with the increasing dissolution potential and time, while the dissolution rate increases with the increasing dissolution potential and declines with the prolonging dissolution time.