Heat of formation of petalite, LiAlSi4O10

The enthalpy of formation of petalite, LiAlSi4O10, has been measured using high-temperature solution calorimetry. The measurements were carried out in a Calvet-type twin micro calorimeter at 728 degreesC. A 2PbO . B2O3 melt w as used as a solvent. Tabulated heats of formation of the components and ta bulated heat capacities of the reactants and the product (Robie and Hemingw ay 1995) were used to calculate the standard heat of formation of petalite from the measured heats of solution. The calculations yielded a mean value of Delta H-f(298.15)pet = -4872 +/- 5.4 kJ mol(-1). This value may be compa red to the heat of formation of Delta H-f(298.15)pet = -4886.5 +/- 6.3 kJ m ol(-1) determined by the HF solution calorimetry by Bennington et al. (1980 ). Fa ss hauer et al. (1998) combined thermodynamic data with phase-equilib rium results to obtain best-fit thermodynamic results using the Bayes metho d, in order to derive an internally consistent dataset for phases in the Na AlSiO4-LiAlSiO4-Al2O3-SiO2-H2O system. They determined -4865.6 +/- 0.8 kJ m ol(-1) as the enthalpy of formation of petalite, a value that is appreciabl y closer to the enthalpy found in this work.