A thermodynamic analysis of the system LiAlSiO4-NaAlSiO4-Al2O3-SiO2-H2O based on new heat capacity, thermal expansion, and compressibility data for selected phases

Abstract

Heat capacity, thermal expansion, and compressibility data have been obtained for a number of selected phases of the system NaAlSiO4-LiAlSiO4-Al2O3-SiO2-H2O. All Cp measurements have been executed by DSC in the temperature range 133–823 K. The data for T ≥ 223 K have been fitted to the function Cp(T) = a + cT −2 + dT −0.5 + fT −3, the fit parameters being The thermal expansion data (up to 525 °C) have been fitted to the function V0(T) = V0(T) [1 + v1 (T−T0) + v2 (T−T0)2], with T0 = 298.15 K. The room-temperature compressibility data (up to 6 GPa) have been smoothed by the Murnaghan equation of state. The resulting parameters are These data, along with other phase property and reaction reversal data from the literature, have been simultaneously processed by the Bayes method to derive an internally consistent thermodynamic dataset (see Tables 6 and 7) for the NaAlSiO4-LiAlSiO4-Al2O3-SiO2-H2O quinary. Phase diagrams generated from this dataset are compatible with cookeite-, ephesite-, and paragonite-bearing assemblages observed in metabauxites and common metasediments. Phase diagrams obtained from the same database are also in agreement with the cookeite-free, petalite-, spodumene-, eucryptite-, and bikitaite-bearing assemblages known to develop in the subsolidus phase of recrystallization of␣lithium-bearing pegmatites. It is gratifying to note that the cookeite phase relations predicted earlier by Vidal and Goffe (1991) in the context of the system Li2O-Al2O3-SiO2-H2O agree with our results in a general way.