Thermodynamic properties of the calcium zeolites stilbite and stellerite

The thermodynamic properties of natural stilbite and stellerite were determ ined by the methods of high-temperature Calvet calorimetry. The standard en thalpies of formation from oxides and elements are 232.0 +/- 8.3 and -11 01 7.9 +/- 10.9 kJ/mol, respectively for stilbite of the Ca1.01Na0.12Al2.12Si6 .88O18 . 7.27H(2)O composition and -200.1 +/- 7.5 and -10909.1 +/- 10.9 kJ/ mol, respectively for stellerite of the Ca1.02Al2.01Si6.98O18 . 7.04H(2)O c omposition. The enthalpy of dehydration at 298.15 K is 229.2 +/- 7.4 kJ/mol for stilbite and 214.5 +/- 2.2 kJ/mol for stellerite; these values corresp ond to an endothermic effect of similar to 30 kJ/mol at the removal of one mole of water from the framework of zeolite. The enthalpy values obtained w ere extrapolated to the ideal stoichiometric compositions; all thermodynami c characteristics for stilbite and stellerite of theoretical compositions w ere calculated taking into account experimental data from the literature.