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

Thermodynamic properties of water, in various families of hydroxides, oxihy droxides and hydrates (chlorides, chlorates, sulfates and sulfites...), hav e been calculated by using a large number of data available in the literatu re. A phase diagram of water has been used to find the first complete set o f thermodynamic properties at 298 K, 1 bar of 8 ice polymorphs, from Ih (he xagonal ice, the common polymorph) to IX (very low temperature and high pre ssure polymorph). These results are used to illustrate the concept of 'ice- like water' available for a very large number of hydrated phases (noted X.H 2O) in which water is attached to the corresponding anhydrous substrate (no ted X) within a large spectrum of different enthalpies (Delta H-f(degrees)) or Gibbs free energies (Delta (f)G(degrees)), but within a relatively smal l range of others properties. Heat capacity (Cp-degrees), entropy (S degree s), and volume (V degrees) of hydration water (X.H2O-X = H2O) appeared to b e very close to those characterizing ice polymorphs such as ice II or ice V III. This concept allows the authors to propose a classification of mineral s in terms of affinity for water and to predict the relative stability of h ydrated and dehydrated phases under climatic variations. (C) 2000 Elsevier Science Ltd. All rights reserved.