Critical assessment of thermodynamic properties of CsI solid, liquid and gas phases
Résumé
Thermodynamic data for the CsI compound, including solid, liquid and are important for the calculation of iodine release in the case of severe nuclear accident: - (i) for accurate evaluation of the nature of iodine containing volatile compounds, and - (ii) for scaling kinetic data that are important in the calculations of intermediate states at short release time. The present study is a critical analysis of thermochemical data for the CsI compound based on available literature data. Revised values of the heat capacity for the liquid phase are proposed within the range of available experimental thermodynamic determinations. Vapor pressure data are assessed and accurate values of the standard enthalpies of formation of the gaseous monomer CsI(g) and dimer Cs2I2(g) are proposed: Delta H-f degrees (CsI, g,298.15 K) = -153.3 +/- 1.8 kJ . mol(-1), Delta H-f degrees (Cs2I2, g,298.15 K) = -469.2 +/- 5 kJ . mol(-1). The trimer Cs3I3(g) also exists as well as tetramer species in smaller amounts, less than 0.1% up to 1500 K.