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

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 + nS₂O₇^2- (l) → X^2n- (l); (2) Nb₂O₅ + nS₂O₇^2- (l) → Y^2n- (l); (3) MoO₃ + nS₂O₇^2- (l) → Z^2n- (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)₄^4-; (2) n = 3, NbO(SO₄)₃^3-; (3) n = 1, MoO(SO₄)₂^2-.