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Heat-capacity measurements and absolute entropy of ɛ-Mg2PO4OH

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Abstract

The low-temperature heat capacity of ɛ-Mg2PO4OH was measured between 10 and 400 K by adiabatic calorimetry. No phase transition was observed over this temperature range. A relative enthalpy increment of 22,119 J mol−1 and an absolute entropy value of 127.13±0.25 J mol−1 K−1 at 298.15 K are derived from the results. The low-temperature heat-capacity data are compared with the DSC data obtained from 143 K to 775 K and show marginal differences in the common temperature range. The latter data are fitted by the polynomial

$$ C_p = \left\{ {316.62 - 2957\,T^{ - 0.5} - 563350\,T^{ - 2} + 955.55 \times 10^5 \,T^{ - 3} } \right\}{\text{J}}\,{\text{K}}^{ - 1} \,{\text{mol}}^{ - 1} , $$

which allows extrapolation to high temperatures.

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Acknowledgements

We thank Mrs Kluge, Kiel, for the DSC measurements, Fabrice Brunet and Peter Schmid-Beurmann for numerous discussions, Gunnar Raade and the anonymous referee for their careful reviews.

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Authors and Affiliations

  1. Laboratoire de Géologie, UMR 8538 du CNRS, Ecole normale supérieure, 24 rue Lhomond, 75005, Paris, France

    Catherine Leyx & Christian Chopin

  2. Chemical Thermodynamics Group, State University of Utrecht, Padualaan 8, Utrecht, 3508 TB, The Netherlands

    J. Cornelis Van Miltenburg

  3. Institut für Geowissenschaften der Christian-Albrechts-Universität Kiel, Olshausenstrasse 40, Kiel, 24098, Germany

    Lado Cemič

Authors
  1. Catherine Leyx
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  2. J. Cornelis Van Miltenburg
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  3. Christian Chopin
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  4. Lado Cemič
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Correspondence to Christian Chopin.

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Leyx, C., Van Miltenburg, J.C., Chopin, C. et al. Heat-capacity measurements and absolute entropy of ɛ-Mg2PO4OH. Phys Chem Minerals 32, 13–18 (2005). https://doi.org/10.1007/s00269-004-0432-9

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  • DOI: https://doi.org/10.1007/s00269-004-0432-9

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