Liquid halide surface energy

This equation shows that the surface energy per atom correlation between the surface energy per atom and the energy of sublimation (or evaporation) is expected provided mi is constant. Such correlations hold well for the solid and liquid surfaces of metallic bodies and also for the liquid surfaces of oxides and halides (see Figures 4.1,4.9 and 4.10). 

Although fused oxides and halides have been less extensively studied than liquid metals, surface energies have been determined for a number of such compounds. In the absence of models for estimating the surface energy of oxide or halide mixtures, this quantity must be determined experimentally. 

The surface energies of liquid halides, e.g. NaCl, are rather low. 

An alternative method for determining the interfacial free energy applies to substances in which the liquid does not wet the crystal at the melting point. In such cases the contact angles, which the liquid drops form with the crystal surface, can be measured and deduced. Zell and Mutaftschiev applied this method first to the (0001) surface of cadmium and more recently to the alkali halides NaCP° and KCP and to mixed alkali halide systems. The number of substances in which the liquid does not wet the solid appears limited, however, so this method cannot be applied in all cases. 

The mobile adsorption state seems to seldom occur in reality. De Boer [12] and other authors present the adsorption of krypton on the surface of liquid mercury as the only good example they do not mention any case of adsorption on solids. The conditions for mobile adsorption can hardly take place in the adsorption of heavy element halides on silica or metallic columns. Doubts can also be cast on the simplest picture of the ideal localized adsorption. An ideal crystal face does show ordered, equally deep potential wells on a map of the adsorption energy moreover, cutting of the crystal by certain planes (perpendicular to the surface) produces sections, which show one-dimensional adsorption wells separated by barriers reaching up to the zero adsorption potential. However, most of the possible sections show barriers, which do not reach the zero potential energy. As a consequence, a molecule can visit many neighboring sites before it is desorbed from the surface. 

Kim et al. [8] examined the migratory motion of Na and Cf ions on ASW surfaces by low energy sputtering (LES). The Na and Cf populations at the surface were measured as a function of the ASW temperature (100 to 140K). The Na intensity decreased in the range 110 to 13OK while the CT intensity remained practically constant. This indicates that the inward migration of Na ions takes place at temperatures where solvent diffusion becomes important, in contrast to surface residence of Cf. This surface propensity of certain halides is characteristic for liquid water [9, 10]. 

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