Thermal and Conductometric Investigations and Phase Diagram of the Rb2S2O7-V2O5 System

The catalytically interesting binary system Rb2S2O7−V2O5 has been investigated by means of calorimetric and conductometric methods. Seventeen different compositions of the binary system in the mole fraction range XV2O5 = 0−0.45 have been investigated, and the phase transition temperatures obtained. Based on these, the phase diagram of the Rb2S2O7−V2O5 system has been constructed in the indicated composition range. The phase diagram exhibits a local maximum at XV2O5 = 0.33 and probably also at XV2O5 = 0.5. This corresponds to the formation of two compounds Rb4(VO)2O(SO4)4 and RbVO2SO4, respectively, as found previously in the analogous Cs system. Two eutectics were found at XV2O5 = 0.175 and XV2O5 = 0.43, with the temperatures of fusion of 348 °C and 397 °C, respectively. The conductivities of each of the 15 molten mixtures investigated have been expressed by polynomials of the form κ = A(X) + B(X)(t − 470) + C(X)(t − 470)2 + D(X)(t − 470)3. The conductivity of the Rb2S2O7−V2O5 system decreases by increasi...