Thermodynamic properties of sodalite at temperatures from 15 K to 1000 K

The heat capacity of sodalite was measured with a computerized adiabatic calorimetric system at temperatures from 15 K to 350 K and with a d.s.c. from 340 K to 1000 K. No anomalies were observed over the entire range except for a peak at T≈250 K associated with fusion of NaCl(aq) fluid inclusions. The temperature of the spontaneous freezing of the fluid inclusions was remarkably reproducible, and the metastable liquid phase persisted from T=250 K to 200 K upon cooling. The standard molar entropy for the end-member composition: Na 8(Al 6Si 6O 24)Cl 2is 102.0· Rat T=298.15 K. The enthalpy of solution of sodalite was measured in 2PbO·B 2O 3(l) at T=973 K with a Calvet-type calorimeter. The value of Δ sol H° m(973 K) is (58.98±0.71)·10 3· R·K. The calculated standard molar enthalpy and standard molar Gibbs free energy of formation for Na(Al 6Si 6O 24)Cl 2are −(1618.6±1.9)·10 3· R·K and −(1527.9±2.0)·10 3· R·K, respectively.