Preparation and Reaction Mechanism of Nd-Al Alloys by Electrolysis in Molten NaCl-KCl-NdCl3-AlCl3

The electrochemical behaviors of Nd(III) on tungsten electrode and its co-deposition with Al(III) in NaCl-KCl salts at 700 degrees C were investigated by a series of electrochemical techniques such as cyclic voltammetry, square wave voltammetry and open-circuit chronopotentiometry, and then Nd-Al alloy were prepared via direct co-deposition of Nd and Al on the inert electrode. The results show that the reduction of Nd(III) in NaCl-KCl-NdCl3 melts is a one-step process with three electrons exchanging, and the reaction is an irreversible process controlled by diffusion at low scanning rates (0.1 similar to 0.5 V/s) with the calculated diffusion coefficient being approximately 1.2x 10(-5) cm(2).s(-1). After AlCl3 introduced into the NaCl-KCl-NdCl3 melts, the curves of cyclic voltammetry, square wave voltammetry and open-circuit chronopotentiometry indicate that three kinds of Nd-Al intermetallic compounds (Nd3Al11, NdAl3 and NdAl2 ) are formed. It can be deduced that the underpotential deposition of Nd occurs on the tungsten electrode covered with the pre-deposited metal Al from the open circuit chronopotentiometry. Based on the results of open circuit chronopotentiometry, the thermodynamic properties of Nd-Al intermetallic compounds are determined by electromotive force measurement at 700 degrees C, such as the activity of Nd in two-phase coexisting state and relative partial molar Gibbs energies, as well as the standard Gibbs energies of Nd-Al intermetallic compound. Finally, potentiostatic electrolysis was carried out at -2.3 V for 5 h to prepare Nd-Al alloys. X-ray diffraction (XRD) and scan electron micrograph (SEM)-energy dispersive spectrometry (EDS) analysis indicate that the obtained alloys are mainly composed of Nd3Al11, NdAl3, NdAl2 and Al phases.