No abstract

A fiber-based Raman spectroscopy system was commissioned in an inert atmosphere for in situ analysis of high temperature molten salts. Speciation of samarium chloride was studied in the LiCl-KCl eutectic system at 500 °C. Raman spectra indicated trivalent samarium forms an octahedral SmCl63- complex with two detectable vibration modes. Chemical reduction experiments were conducted to investigate the coordination of divalent samarium in the same eutectic salt. The resulting spectra are reported and discussed in terms of complex formation and behavior of divalent samarium ions. Trivalent samarium was electrochemically reduced in situ and Raman spectra obtained were compared with those resulting from chemical reduction experiments. The spectra suggest divalent samarium ions form in LiCl-KCl only temporarily and spontaneously disproportionate into a mixture of trivalent samarium ions and metallic samarium.

Cyclic voltammetry (CV) was used to investigate the electrochemical behavior of SmCl3 when it is solvated in the molten LiCl-KCl eutectic at 773 K. An experimental method obtained from the literature was adjusted to produce repeatable current responses attributed to the Sm3+/Sm2+ reaction couple and to determine working electrode surface area. The effect of solvating SmCl3 at high concentration was investigated as it relates to electrochemical reversibility and diffusion coefficient analysis. An electrochemically reversible region was identified using correlations between the current response and the scan rate along with peak current ratio measurements. In these, the reversibility was unaffected by increasing concentration. The correlation between current response and concentration was less linear than expected, suggesting the effects of additional modes of diffusion, solution resistance, and charge transfer kinetics may be contributing more at high concentrations. The measurement errors associated with peak current response, working electrode surface area, and melt temperature were used to estimate the associated uncertainties of the reported diffusion coefficients of Sm3+ in the molten LiCl-KCl eutectic. These diffusion coefficient values were found to be relatively consistent with values for Sm3+ reported in the literature for lower concentrations.

The spectroscopic and electrochemical properties of synthesized samarium oxychloride were investigated in molten LiCl-KCl salt of eutectic composition.