Thermodynamic and Electrochemical Properties of Praseodymium and the Formation of Ni-Pr Intermetallics in LiCl-KCl Melts

Abstract

The electrochemical behavior of Pr(III) was studied on Mo and Ni electrodes in LiCl-KCl melts at different temperatures, respectively. The reduction of Pr(III) on Mo electrode was one-step electrochemical process in this system. The diffusion coefficients of Pr(III) were calculated by the Sand's equation at five different temperatures. The diffusion activation energy of Pr(III) was finally computed to be 34.35 kJmol−1 by the Arrhenius law. The equilibrium potential values of the Pr(III)/Pr(0) system were determined by open circuit chronopotentiometry, and the apparent standard potential E*0Pr(III)/Pr(0) and the Gibbs free energyΔG*0f(PrCl3) were also calculated. With subsequent the subtraction of apparent and standard Gibbs free energies, ΔG*0f(PrCl3)-ΔG0f(PrCl3, SC), the activity coefficients of Pr(III), γPr(III) were obtained. On Ni electrode, seven Ni-Pr alloy formation signals corresponding to all intermetallic compounds in Ni-Pr phase diagram were detected by cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit chronopotentiometry (OCP). According to the electrochemical implantation, PrNi2 films were rapidly formed on Ni electrodes by potentiostatic and galvanostatic electrolysis at different potentials and current densities, respectively. The phase composition and the microstructure of the alloys were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS).