Viscosity, molten salt transport properties

Some 30 years ago, transport properties of molten salts were reviewed by Janz and Reeves, who described classical experimental techniques for measuring density, electrical conductance, viscosity, transport number, and self-diffusion coefficient. 

Janz, G. J., Thermodynamic and Transport Properties for Molten Salts Correlation Equations for Critically Evaluated Density, Surface Tension, Electrical Conductance, and Viscosity Data. 1988, New York American Institute of Physics. 

There are some density data for solid salts above ambient temperature which are given in the form of thermal expansion coefficients. These have been listed when they seemed reliable. Above the melting point, density data are scarce. Most are available for alkali halides but those available for salts are taken from the critically evaluated compilation Janz, G.J., Thermodynamics and transport properties for molten salts, correlation equations for critically evaluated density, surface tension, electrical conductance, and viscosity data,./. Phys. Chem. Reference Data, 17, Suppl. 2, 1988. 

Some facts about transport processes in molten salts have been mentioned (Section 5.6). Whether a hole model (Section 5.4) can provide an interpretation of these must now be examined. First it is necessary to cast the model into a form suitable for the prediction of transport properties. The starting point is the molecular-kinetic expression (Appendix 5.3) for the viscosity ij of a fluid, i.e.,... 

There are two kinds of polymer material that used in quasi-solid/solid state DSSCs. For quasi-solid electrolytes, polyionic liquids have been proposed as solvent and redox couple as solute. They appear in molten salts and present many promising properties, such as, high chemical and thermal stability and high ionic conductivity Their main drawback is related to its high viscosity, which makes the ions diffusion rather slow. As the transport of ions to the counter electrode in an ionic liquid matrix represents a rate-limiting step in DSSC (Bella, 2015), the performance of quasi-solid electrolytes based solar cell is imsatisfled. 

References (i) Janz, G.J. (1967) Molten Salts Handbook. Academic Press, New York (ii) Lovering, D.G and Gale, R.J. (1983,1984, and 1990) Molten Salts Techniques, Vol. 1, 2, i and 4. Plenum Press, New York, (iii) Janz, G.J. (1988) Thermodynamic and Transport Properties for Molten Salts Correlation equations for critically evaluated density, surface tension, electrical conductance and viscosity data. Journal of Physical and Chemical Refrence Data. Vol. 17, Supplement 2, Published jointly by the American Chemical Society (ACS), the American Institute of Physics (AIP), and the National Bureau of Standards (NBS) and (iv) Barin, I., and Knacke, O. (1973) Thermodynamical Properties of Inorganic Substances. 

Melts of these fluorides have satisfactory values of heat capacity, thermal conductivity, and viscosity in the 500-1000°C temperature range and provide an efficient removal of heat when they are used as the coolant over a wide range of compositions. Transport properties of molten salt coolants ensure efficient cooling with natural circulation the salt—waU heat transfer coefficient is close to the same coefficient for water. The thermal diffiisivity of the salt is 300 times smaller than that of sodium. Therefore, all other things being equal, the characteristic solidification time for a volume of the fluoride melt is 300 times longer than that of sodium [2]. 

Janz GJ (1988) Thermodynamic and transport properties for molten salts correlation equations for critically evaluated density, surface tension, electrical conductance, and viscosity data. J Phys Chem Ref Data 17(Suppl 2) 1-325... 

The transport properties of molten salt hydrates are rather scarce too, and the values that could be obtained for the dynamic viscosity, t], and the molar conductivity, A, at the corresponding temperature of F= l.ir , are shown in Table. 5.6. 

Molten (Li,K,Cs)TFSA (TFSA bis(trifluoromethylsulfonyl)amide, Li K Cs = 20 10 70 in molar ratio) was selected as an electrolyte of a rechargeable lithium metal battery taking account of the melting temperature [1] and physical properties. The viscosity, conductivity, and electrochemical window of this salt mixture at 170 °C are 36.5 cP, 22.5 mS cm , and 5.0 V, respectively [2]. The transport number of the lithium ion is 0.15 at this temperature [3]. 

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