Water vacancies

In this model, the water molecules occupy specific crystallographic positions, and some of those positions are not occupied, thus constituting water vacancies. In the most usual case of associated defects q and q, the quasi-chemical equilibrium is written as follows ... 

If the indices I and 2 are assigned, respectively, to the relative values of the water vacancies and the normal elements of water, it is easy to show that the molar fractions of those entities are given... 

Figure 31 Calculated free energy barrier for the hopping of a carbon dioxide molecule between clathrate hydrate cages (a) containing no water defects (b) water vacancy present between the cages (c) through the shared hexagonal water face and (d) through the shared pentagonal water face. Adapted from Ref. 129.

Table 6 CO2 Hopping and Diffusion Rates and Between Clathrate Hydrate Cages with a Water Vacancy Between them at 273 K Determined from Monte Carlo ...

A. Peters, N. E. Zimmermann, G. T. Backham, J. W. Tester, and B. L. Trout,/. Am. Chem. Soc., 130,17342 (2008). Path Sampling Calculation of Methane Diffusivity in Natural Gas Hydrates from a Water-Vacancy Assisted Mechanism. 

Non-stoichiometric hydrates with water vacancies The equilibrium is now written as ... 

For example, the nucleation of an anhydrous salt starting from the corresponding hydrated salt needs the creation of water vacancies according to the following... 

Nucleation is modeled by the creation of associated water vacancies. It is assumed that an elementary step of association, [18.R.i], merges only one vacancy with a polymer of / -1 alreacfy associated vacaiKies. 

The first step is the creation of a water vacancy. For that, a molecule of water leaves the hydrate phase and takes place onto the surface on an adsorbed site ... 

Then the following steps involve the condensation of the water vacancies, we assume that they are polymerized one after the other. So, we will have, for the first condensation step,... 

The formation of an anhydrous salt from its hydrated form will pass via the formation of water vacancies, for example, according to the following process ... 

Ice(cmc) with one water vacancy in two different locations, (b) QM and ReaxFF water energies of Ice(cmc) as a function of density. 

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