Thermodynamic mixing behavior of synthetic Ca-Tschermak–diopside pyroxene solid solutions: I. Volume and heat capacity of mixing |
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Authors: | Katja Etzel Artur Benisek Edgar Dachs Lado Cemič |
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Affiliation: | 1.Institut für Geowissenschaften, Universit?t Kiel,Kiel,Germany;2.Fachbereich Materialwissenschaften, Abteilung Mineralogie,Universit?t Salzburg,Salzburg,Austria |
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Abstract: | The unite cell parameters and heat capacities of a series of synthetic clinopyroxenes on the join Ca-Tschermak (CaTs)−diopside (Di) were measured using X-ray powder diffraction and calorimetric methods, respectively. The volume of mixing at 298 K shows a negative asymmetric deviation from ideality. A two-parameter Margules fit to the data yields W CaTs−Di V = −0.29 ± 0.11 cm3 mol−1 and W Di−CaTs V = −1.14 ± 0.14 cm3 mol−1. Heat capacities were determined between 5 and 923 K by heat-pulse at 5−302 K and differential-scanning calorimetry at 143−923 K. The precision of the low and high temperature C p data is better than ±1%. Polynomials of the form C p = a + bT −1/2 + cT −2 + dT −3 were fitted to the C p data in the temperature range between 250 and 925 K. Thermal entropy values [S 298 − S 0] and [S 900 −S 0] as well as enthalpies [H 298 − H 0] and [H 900 − H 0] were calculated for all members of the solid solution series. No significant deviation from ideal mixing behavior was observed. |
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Keywords: | Tschermakitic pyroxene Heat capacity Molar volume Entropy Enthalpy |
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