Determination of Stoichiometry of Solutes in Molten Salt Solvents by Correlations of Relative Raman Band Intensities

Abstract

Raman spectroscopy has been used to determine the stoichiometry of solute complexes in molten salts at high temperatures under static equilibrium conditions. A simple formalism is derived for correlating relative Raman band intensities with stoichiometric coefficients. The experimental procedures and sets of experiments required for establishing the stoichiometry are described. The proposed method was applied for studying the dissolution reactions of V2O5 in molten Cs2S2O7 and of Nb2O5 or MoO3 in molten K2S2O7 at temperatures in the range 430–700 °C: (1) V2O5 + nS2O72- (l) → X2 n- (l); (2) Nb2O5 + nS2O72- (l) → Y2 n- (l); (3) MoO3 + nS2O72- (l) → Z2 n- (l). It is shown that the solute complex species formed in the studied reactions have, respectively, the following stoichiometries: (1) n = 2, (VO)2O(SO4)44-; (2) n = 3, NbO(SO4)33-; (3) n = 1, MoO(SO4)22-.