Abstract
The heat of mixing for the binary solid solution diopside–Ca-Tschermak was investigated at T = 980 K by lead borate solution calorimetry. A new statistical technique was applied to overcome the problem of using experimental data of various precisions. A two-parameter Margules model was fitted to the calorimetric data leading to W HCaTs–Di = 31.3 ± 3.4 kJ mol−1 and W H Di–CaTs = 2.4 ± 4.3 kJ mol−1. The results are in good agreement with calorimetric data given in the literature. They agree also with enthalpy data that were extracted from phase equilibrium experiments. With configurational entropy values taken from the literature, the volume and the vibrational entropy, presented in Part I of this work, and the enthalpy data of this study, the activity–composition relationships of the diopside–Ca-Tschermak binary were calculated.
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This work was supported by grant of the Deutsche Forschungsgemeinschaft CE 20/13-1,2 which is gratefully acknowledged. We thank C.A. Geiger for helpful discussions and for proof reading the manuscript and P. Kluge for technical support.
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Benisek, A., Etzel, K. & Cemič, L. Thermodynamic mixing behavior of synthetic Ca-Tschermak–diopside pyroxene solid solutions: II. Heat of mixing and activity–composition relationships. Phys Chem Minerals 34, 747–755 (2007). https://doi.org/10.1007/s00269-007-0192-4
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DOI: https://doi.org/10.1007/s00269-007-0192-4