Heat capacity and thermodynamic functions of leucite at low temperatures

The heat capacity Cp(T) of leucite with chemical composition (K0.91Na0.04Ca0.01)[Al0.97Si2.03O6]·0.084H2O from Orvieto, Italy was measured in a vacuum adiabatic calorimeter in the temperature range 5.9–310 K. No anomalies were detected in the Cp(T) dependence. Calculated values of heat capacity and thermodynamic functions at standard conditions are as follows: C°p(298.15)=166.4±0.2 J mol−1 K−1; S°(298.15)=182.4±0.3 J mol−1 K−1; H°(298.15)−H°(0)=28120±40 J mol−1; Φ°(298.15)=88.04±0.3 J mol−1 K−1. These results are in good agreement with previous measurements above 51 K [US Bur. Mines Rep. Invest. 4955 (1992) 22]. Recommended values of heat capacity and absolute entropy at standard conditions for stoichiometric leucite KAlSi2O6 are: C°p(298.15)=163.8±1.0 J mol−1 K−1; S°(298.15)=180.0±1.0 J mol−1 K−1.