Phase barograms–phase diagrams of vapor pressure: Eutectoid phase formation in binary systems

Abstract Phase barograms are specific representations of conventional ( x , T ) phase diagrams considering the vapor pressure as additional thermodynamic parameter. Thus, the determination of the vapor pressure is complementary to conventional DTA or DSC measurements. A stringent relationship between the phase diagram and the corresponding phase barogram is derived by thermodynamic considerations of phase relations for complex heterogeneous equilibria. For that purpose, a derivative of the three-dimensional Clausius–Clapeyron equation is utilized. As a result, a validation of DTA/DSC measurements becomes feasible by the transformation of characteristic effects of vapor pressure measurements into thermal effects in conventional phase diagrams. The system CsBr/SeO 2 is presented as a case study of systems with a eutectoid phase formation. CsSeO 2 Br is formed from the binaries at ϑ f  = 180(5) °C; the compound decomposes peritectically at ϑ p  = 470(10) °C.