Oxide solubilities in ionic melts

1 METHODS USED FOR SOLUBILITY ESTIMATIONS IN IONIC MELTS 

Processes of the dissolution of metal oxides in ionic melts are accompanied by interactions between ions of dissolved substance with ions of the melt (solvation). The superimposition of the mentioned processes results in the formation of metal complexes with the melt anions and cation complexes with oxide-ions. Therewithal, the definite part of the oxide passes into the solution without dissociation as uncharged particles. Thus, in saturated solution of oxide the following equilibria take place  

Since at the dissolution of any oxide in melts a degree of interaetion Kt - O should be the same and the complexation with melt anions for eations of oxide may be assumed as closed, therefore, it can be believed that oxide solubilities depend mainly on the degree of interactions [21.3.1] and [21.3.2], latter may be eonsideredas an acid-base interactions as proposed by Lux. The constant of [21.3.2] 

The mentioned method seems to have no wide usage for studying behavior of oxides in molten salts, solubility studies by isothermal saturation and potentiometric titration methods are more precise and informative. 

From the listed above scheme of equilibria [21.3.1-21.3.4] it follows that the fixation of oxide ions by metal cations is in common case a heterogeneous process resulting in the formation of a new phase and cation acidity may have no connection with the completeness of interaction Me - O in molten salts. 

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Our consideration of the data on metal-oxide solubilities in ionic melts based on alkali-metal halides shows that there is much experimental material, and an attempt at systematizing it is made in this book. Some regularities of metal-oxide solubilities in different melts and over a wide temperature range are obtained. 

V.L. Cherginets, Oxide Solubilities in Ionic Melts, in Handbook of Solvents, ed G. Wypych (Chemtec Publishing, Toronto, NY, 2001) pp. 1484-1495. 

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