THERMODYNAMIC PROPERTIES OF SODALITE AT TEMPERATURES FROM 15 K TO 1000 K

The heat capacity of sodalite was measured with a computerized adiabat ic 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 approximate to 250 K associated with fus ion of NaCl(aq) fluid inclusions. The temperature of the spontaneous f reezing of the fluid inclusions was remarkably reproducible, and the m etastable liquid phase persisted from T = 250 K to 200 K upon cooling. The standard molar entropy for the end-member composition: Na-8(Al6Si 6O24)Cl-2 is 102.0 . R at T = 298.15 K. The enthalpy of solution of so dalite was measured in 2PbO . B2O3(I) at T = 973 K with a Calvet-type calorimeter. The value of Delta(sol)H(m) degrees(973 K) is (58.98 +/- 0.71). 10(3) . R . K. The calculated standard molar enthalpy and stand ard molar Gibbs free energy of formation for Na(Al6Si6O24)Cl-2 are -(1 618.6 +/- 1.9) . 10(3) . R . K and -(1527.9 +/- 2.0) . 10(3) . R . K, respectively. (C) 1995 Academic Press Limited