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Thermodynamic properties of chlorite CCa-2. Heat capacities, heat contents and entropies |
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| Authors: | H. Gailhanou J. Rogez A.C.G. van Genderen C. Gilles N. Michau P. Blanc |
| Affiliation: | a BRGM, 3 av. Claude Guillemin, BP 6009, 45060 Orléans Cedex 2, France b IM2NP-CNRS, Faculté des Sciences et Techniques de Saint-Jérôme, Case 251, 13397 Marseille Cedex 20, France c Chemical Thermodynamics Group, State University of Utrecht, Padualaan 8, 3508 TB Utrecht, The Netherlands d LPEC, UMR CNRS 6087, Université du Maine, 72085 Le Mans Cedex 9, France e Centre de Microscopie Electronique, Université d’Orléans, 45071 Orléans Cedex 2, France f ANDRA, 1/7 rue Jean Monnet, 92298 Châtenay-Malabry Cedex, France |
| Abstract: | The heat capacities of the international reference clay mineral chlorite CCa-2 from Flagstaff Hill, California, were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 5 to 520 K (at 1 bar). The studied chlorite is a Fe-bearing trioctahedral chlorite with an intermediary composition between ideal clinochlore (Si3Al)(Mg5Al)O10(OH)8 and chamosite (Si3Al)(Fe5Al)O10(OH)8. Only few TiO2 impurities were detected in the natural chlorite sample CCa-2. Its structural formula, obtained after subtracting the remaining TiO2 impurities, is (Si2.633Al1.367)(Al1.116 Mg2.952 Mn0.012Ca0.011)O10(OH)8. From the heat capacity results, the entropy, standard entropy of formation and heat content of the chlorite were deduced. At 298.15 K, the heat capacity of the chlorite is 547.02 (±0.27) J mol−1 K−1 and the molar entropy is 469.4 (±2.9) J mol−1 K−1. The standard molar entropy of formation of the clay mineral from the elements is −2169.4 (±4.0) J mol−1 K−1. |
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