Electrochemical behavior of antimony and electrodeposition of Mg-Li-Sb alloys from chloride melts

摘要

The electrochemical behavior of Sb(III) ions was investigated in LiCl-KCl molten salt at 673 K. The reaction mechanism and transport parameters of electroactive species were determined by transient electrochemical techniques (such as cyclic voltammetry, square wave voltammetry, chronopotentiometry and chronoamperometry) at a molybdenum electrode. The results showed that electrochemical reduction of Sb(III) in LiCl-KCl melts occurred in a reaction step with an exchange of three electrons. A voltammogram with a different scan rate in LiCl-KCl containing 1.45 × 10~(-4) mol cm~(-3) SbCl_3 showed that the deposition/dissolution reaction of Sb(III) ions was not completely reversible. The diffusion coefficient of Sb(III) ions was 1.65(±0.01) × 10~(-5) cm~(-2) s~(-1) at 673 K. The electroreduction of Sb(III) ions at an Al electrode was also studied by cyclic voltammetry and open circuit chronopotentiometry in the temperature range of 668-742 K. The redox potential of Sb(III)/Sb at an Al electrode was observed at the more positive potentials values than those at an inert electrode. This potential shift due to the formation of intermetallic compound with Al electrode. AlSb alloys were prepared in LiCl-KCl-SbCl_3 melts at 742 K by potentiostatic electrolysis at an Al electrode. The activity of Sb and the Gibbs energy of AlSb formation were also calculated. Mg-Li-Sb alloys were obtained by galvanostatic electrolysis at 673 K and the electrochemical codeposition of Mg, Li and Sb was investigated on a molybdenum electrode in LiCl-KCl containing MgCl_2 and SbCl_3 melts at 673 K by cyclic voltammetry, chronopotentiometry and chronoamperometry. Cyclic voltammograms, chronopotentiometry and chronoamperometry measurements indicated that the electrochemical codeposition of Mg, Li and Sb metal occurred at current densities lower than -0.466 A cm~(-2) or at an applied potential more negative than -2.350V vs. Ag/AgCl. X-ray diffraction (XRD) suggested that Mg_3Sb_2 and Li_3Sb were formed in Mg-Li-Sb alloys. The distribution of Sb element in Mg-Li-Sb alloys from the analysis of scan electron micrograph (SEM) and energy dispersive spectrometry (EDS) indicated that Sb metal showed a distribution which resembled an interlaced network.