The structures and thermophysical properties of molten salts

The salts containing polymeric anions in die solid state melt retain die anion stiiicture, e.g. and on melting, while die phosphates in which die 

The mobilities of ions in molten salts, as reflected in their electrical conductivities, are an order of magnitude larger than Arose in Are conesponding solids. A typical value for diffusion coefficient of cations in molten salts is about 5 X lO cm s which is about one hundred times higher Aran in the solid near the melting point. The diffusion coefficients of cation and anion appear to be about the same in Are alkali halides, wiAr the cation being about 30% higher tlrair Are anion in the carbonates and nitrates. 

The specific conductivities of molten salts are frequently represented, as a function of temperature by an AtTlrenius equation, but it is unlikely that the unit step in diffusion has a constant magnitude, as in the coiTesponding solids and the results for NaCl may be expressed, within experimental eiTor, by the alternative equations 

In view of Swalin s treatment of diffusion in liquid metals. Are latter seems to be a better description. In binaty mixmres such as NaCl-KCl the equivalent conducAvities are a linear manner, but the KCl-CdCla mixture shows a marked negative departure from linear behaviour, probably because of the formation of the complex ion CdCh.  

Molten sulphides are almost invariably semiconductors, and so their conductivities are typically larger than Arose of the average molten electrolyte. For example, the specific conductairce of molten AgaS can be described, as a function of temperature by the equation 

A significant property of the alkali metal halides is the solubility of the metals in their molten halides. Typical values of the consolute temperatures of metal-chloride melts are 1180°C in Na-NaF, 1080°C in Na-NaCl, 790°C 

These facts would suggest that the electrolysis of molten alkali metal salts could lead to the introduction of mobile electrons which can diffuse rapidly through a melt, and any chemical reduction process resulting from a high chemical potential of the alkali metal could occur in the body of the melt, rather than being confined to the cathode volume. This probably explains the failure of attempts to produce the refractory elements, such as titanium, by electrolysis of a molten sodium chloride-titanium chloride melt, in which a metal dust is formed in the bulk of the electrolyte. 

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