The catalytically interesting binary system Rb2S2O7-V2O5 has been investiga
ted by means of calorimetric and conductometric methods. Seventeen differen
t compositions of the binary system in the mole fraction range X-V2O5 = 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 cons
tructed in the indicated composition range. The phase diagram exhibits a lo
cal maximum at X-V2O5 = 0.33 and probably also at XV2O5 = 0.5. This corresp
onds to the formation of two compounds Rb-4(VO)(2)O(SO4)(4) and RbVO2SO4, r
espectively, as found previously in the analogous Cs system. Two eutectics
were found at X-V2O5 = 0.175 and X-V2O5 = 0.43, with the temperatures of fu
sion of 348 degrees C and 397 degrees C, respectively. The conductivities o
f each of the 15 molten mixtures investigated have been expressed by polyno
mials of the form kappa = 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 increas
ing mole fraction XV2O5 in the melt, indicating decreasing ionic character
of the melt. A comparison is made with the analogous Na, K, and Cs systems.