Thermodynamics of ice polymorphs and 'ice-like' water in hydrates and hydroxides

Thermodynamic properties of water, in various families of hydroxides, oxihydroxides and hydrates (chlorides, chlorates, sulfates and sulfites...), have been calculated by using a large number of data available in the literature. A phase diagram of water has been used to find the first complete set of thermodynamic properties at 298 K, 1 bar of 8 ice polymorphs, from Ih (hexagonal ice, the common polymorph) to IX (very low temperature and high pressure polymorph). These results are used to illustrate the concept of 'ice-like water' available for a very large number of hydrated phases (noted X.H2O) in which water is attached to the corresponding anhydrous substrate (noted X) within a large spectrum of different enthalpies (Delta H-f(degrees)) or Gibbs free energies (Delta (f)G(degrees)), but within a relatively small range of others properties. Heat capacity (Cp-degrees), entropy (S degrees), and volume (V degrees) of hydration water (X.H2O-X = H2O) appeared to be very close to those characterizing ice polymorphs such as ice II or ice VIII. This concept allows the authors to propose a classification of minerals in terms of affinity for water and to predict the relative stability of hydrated and dehydrated phases under climatic variations. (C) 2000 Elsevier Science Ltd. All rights reserved.