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Thermodynamic model for water and high-pressure ices up to 2.2 GPa and down to the metastable domain.

Choukroun M, Grasset O

UMR-CNRS 6112-Laboratoire de Planétologie et Géodynamique de Nantes, Université de Nantes, 2 rue de la Houssinière, 44322 Nantes Cedex 3, France. mathieu.choukroun@univ-nantes.fr

We propose a thermodynamic model of the properties of liquid water and ices I, III, V, and VI that can be used in the ranges of 0-2200 MPa and 180-360 K. This model is the first to be applicable to all H(2)O phases in these wide ranges, which exceed the stability domain of all phases. Developing empirical or semiempirical expressions for the specific volumes of liquid water or ices has been necessary. The model has been tested on available experimental data sets. The specific volume of liquid water is reproduced with an accuracy better than 1%. The error on the specific volume of ices remains within 2%. The model has also been used to describe the melting curves of high-pressure ice polymorphs and compared with new Simon equations fitting available data. Our calculations suggest a slight revision of the triple point positions in the H(2)O phase diagram. We have ensured the reliability of our model up to 1.5 GPa, and we have shown that it can be used with good confidence up to 2.2 GPa. In order to show the validity of this model in the low-temperature domains, the melting curve of ice Ih in the water-ammonia system has been modeled. This curve is reproduced with good accuracy down to 180 K, at a 1 bar pressure. It shows that this model can be used in further studies for modeling equilibriums involving liquid or solid phases of H(2)O under pressure and for investigating the effect of inhibitors in complex water-rich systems.

Published 1 October 2007 in J Chem Phys, 127(12): 124506.
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