Hydration numbers pressure effects

As for the volumes of the atoms, the thermal expansion and compressibility is composed of two main terms, the cavity and the hydration. An estimate of the contribution of each factor relies on assumptions that are not easy to check. An estimate of the expansion or compression of the cavities should be possible with positron annihilation lifetime spectroscopy. This approach has proven to be a useful tool for determining the size of cavities and pores in polymers and materials. The lifetime is sensitive to the size of the cavity in which it is localized. A number of empirical relations correlate the distribution of the lifetime and the free volume [33]. Data on the pressure effect on the lifetime are only available for polymers. The results suggest that there may be a considerable contribution of the reduction in cavity size to the compressibility of a protein. 

In the i-Am,NI-H 0 system (figTd) clathrate formation is rapid and occurs at atmospheric pressure P S/, For this reaction dt/dP =4.5 C/kbar (l atm). At 0.26 kbar one more hydrate (h2) forms with a smaller hydrate number, which is shown hy the appearance of the melting effects of water eutectics in the samples in which the salt content slightly e x-ceeds that in the low pressure hydrate. We have managed to identify not only the incongruent melting lines of the hydrates, but also the monovariant equilibrium line The heat effect of this transition is... 

Fig. 3.1. Relationship between the pre-exponential factor

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