Molten salts fluidity

Why give these liquids special consideration Are not the concepts developed for understanding molten salts adequate for understanding molten oxides The essential features of fused salts ema-ge from models of the liquid state. Tha-e is no doubt that the fluidity of molten salts demands a model with plenty of free space, and a model based on density fluctuations that are constantly occurring in all parts of the liquid seems about the best way to think of the inside of a molten liquid. Is the same dependence on the opening up of temporary vacancies an adequate basis for explaining the behavior of the fused oxides ... 

A portion of the sodium carbonate melt is withdrawn from the molten salt reactor, quenched, and processed in an aqueous recovery system. The recovery system removes the ash and inorganic combustion products (mainly sodium salts such as NaCl and Na2S) retained in the melt. Unreacted sodium carbonate is returned to the molten salt furnace. The ash must be removed when the ash concentration in the melt approaches 20 to 25 wt % in order to preserve the melt fluidity. The inorganic combustion products must be removed before all of the sodium carbonate is completely converted to noncarbonate salts. For the case of a waste containing a valuable mineral resource, the valuable mineral resource is retained in the melt during the gasification process and may be recovered as a by-product of the regeneration process. 

In contrast to inorganic molten salts, the fluidity of ionic hquids at room temperature permits their use as solvents for chemical reactions. Electrostatic properties and charge mobility in ionic hquids can play a distinctive role in chemical reactivity, as compared with neutral solvents. In particular, hydrogen and proton transfer reactions are likely to be sensitive to an ionic environment due to the hydrogen-bond acceptor ability of the anions. Such type of reactions are fundamental in acid-based chemistry and proton transport in solution. 

Molten salt approaches such as the Vogel-Fulcher-Tamman (VFT) equation have been used repeatedly for analyzing the temperature dependence of transport properties W T) such as diffusion, conductance, and fluidity, or of relaxation processes ... 

The fluidity is the reciprocal of the viscosity, 0 = and for molten salts has been related by Marcus [256] to their molar volume V, as both vary with the temperature according to the Hildebrand and Lamoreaux [257] relationship. Fig. 3.6 ... 

The meaning of the B parameters is rather obscure. It is expected that the larger the attractive forces between the ions, the less ready would they be to move in an external force gradient, hence the smaller the fluidity. This expectation is borne out only for the alkali metal fluorides, for which B decreases linearly with their cohesive energy densities. For 51 other molten salts of the 1 1, 1 2, and 1 3 types the B parameters increase linearly with the cohesive energy (that is, with ceti. z ), but with cOTisiderable scatter [256]. 

Table 3.18 The viscosity of molten salts expressed by the and parameters oftj = A,exp(B,/ RT) [214], and their fluidity expressed by the B and I/q parameters of (p = r] = —B + (B/Vo)V [256], The Vo values in parentheses are from Potapov et al. [253], those in italics are the sum of the incompressible ionic volumes from Bockris and Richards [137]...

Fig. 3.6 The fluidities of some molten salts plotted against their molar volumes over a suitable temperature range, limited to that where the viscosity data are available LiF ( ), KF ( ), CaCl2 (A), Na2S04 (T), and CsNOs ( ) (From Marcus [256] by permission of the publisher (Elsevier))...

Another application of the corresponding states approach is that of Abe and Nagashima [259], who used the Tosi-Fumi [112] potential function to obtain the two parameters d = r+ + r for the distance and e for the potential energy. The resulting expression for the fluidity of a molten salts is ... 

Chhabra RP, Hunter RJ (1981) The fluidity of molten salts. Rheol Acta 20 203-208... 

Marcus Y (2014) The fluidity of molten salts re- examined. Fluid Phase Equilib 366 57-60... 

A different approach relates the fluidity of RTlLs to their molar volumes over a large temperature range, based on the Hildebrand-Lamoreaux expression [359], in analogy with its use for molten salts (Sect. 3.4) and many other fluids ... 

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