Molten salts expression

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]...

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... 

As in die case of die diffusion properties, die viscous properties of die molten salts and slags, which play an important role in die movement of bulk phases, are also very stiiicture-seiisitive, and will be refeiTed to in specific examples. For example, die viscosity of liquid silicates are in die range 1-100 poise. The viscosities of molten metals are very similar from one metal to anodier, but die numerical value is usually in die range 1-10 centipoise. This range should be compared widi die familiar case of water at room temperature, which has a viscosity of one centipoise. An empirical relationship which has been proposed for die temperature dependence of die viscosity of liquids as an AiTlienius expression is... 

The phenomenological constants can be expressed in terms of experimental quantities. The Ly represents the interaction of component i with other particles of component/ In molten salts no component seems particularly suitable for serving as a solvent. The use of a volume fixed frame of reference for defining the fluxes gives a more symmetrical representation. The equations for the phenomenological constants are given by Sund-heim. ... 

Wave-front shearing interferometry has been applied to transparent molten salt systems by Gustafsson et al. " The optical path of a light beam traversing the cell at an arbitrary level x is expressed by... 

The symbols appearing in this equation are defined in Chapter 3. At 25°C, Equation 17.20 simplifies to Equation 3.18. (However, in molten salt experiments it is extremely rare for this equation to be employed at such a low temperature ) The reversibility of an experimental system is often judged by comparing the experimental values of Ep - Ep/21, Ep/2 - E and AEp to the theoretical values calculated from these equations in the case of a reversible redox system. Therefore, it is important to point out that these parameters are temperature dependent and that they increase with increasing temperature. The complete theoretical expressions for these parameters are given in Equations 17.21 to 17.23, respectively [67]. 

The same choice of using component or species is also met in the study of binary systems of molten salts. We could choose to deal solely with components, but because of the concept of the ionic nature of the melts we choose to express the chemical potential of the component in terms of the chemical potential of the species. Equation (8.202) gives the relation for the chemical potential of the general salt Mv+Av in terms of the chemical potentials of the ions. The discussion given in Section 8.18 results in the more convenient equation for the chemical potential of the salt (Eq. (8.208))... 

Around 1995, Seddon realized that the expression room-temperature molten salts was counter-productive. The expression molten salt was always associated with high temperature , as also the editors (and many authors) of this book had... 

Another approach has been developed by Bruno and Della Monica [24-26], This work takes the Vogel-Tamman-Fulcher (VTF) equation, which has been used to rationalize transport properties in molten salts and glassy electrolytes, and modifies it for nonaqueous solutions. The work follows the development of Angell and co-workers [27,28], who carried out a similar development for aqueous solutions. The expression used is... 

The situation is less arbitrary in molten salt mixtures. In that case, the migration of two or more different ions can be defined relative to another ion, often a common ion, in order to avoid the arbitrary reference to a porous plug. That transport number is designated as internal. In a binary mixture of molten salts MX + NX, the internal mobilities of the cations M+ and N+ are referred to the mobility of X and are given by the expressions [39]... 

The electrical conductivity of molten salts can be expressed in two ways equivalent conductivity A (ohm-1 cm2 cquiv ) and specific conductivity k (ohm-1 cm-1), and between these terms there is the relation... 

Ionic liquids are sometimes, especially in the older literature, also referred to as molten salts, non-aqueous ionic liquids or room temperature molten salts. While all of these names are entirely valid, their meaning has somewhat changed over the years. The term molten salt is now used less frequently in the field of ionic liquids and generally refers to salts with melting points greater than 100°C. The expression non-aqueous ionic liquid was originally coined to differentiate synthetic ionic liquids from water, since... 

In experiments involving radiotracer measurements of diffusion in molten salt, the Stokes-Einstein equation has been found to be roughly applicable. For a series of ions, in molten salts it was found that the product D /T = 10 dyn mol . From this information, find whether the best form of the coefficient in this expression for this case is nearer to 6 or 4. 

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.,... 

In the Fiirth hole model for molten salts, the primary attraction is that it allows a rationalization of the empirical expression = 3.741 r p. In this model, fluctuations of the structure allow openings (holes) to occur and to exist for a short time. The mean hole size turns out to be about the size of ions in the molten salt. For the distribution function of the theory (the probability of having a hole of any size), calculate the probability of finding a hole two times the average (thereby allowing paired-vacancy diffusion), compared with that of finding the most probable hole size. 

It is a pleasure for me to express my thanks to my teachers Professor Milan Malinovsky, who taught me the theory of molten salts, Professor Kamil Matiasovsky, who taught me his experimental skills, and Dr. Ivo Proks, who helped me to understand a little of thermodynamics. Professor Pavel Fellner of the Slovak Technical University is greatly acknowledged for his advice and comments which helped improve this book. 

It is obvious that the expression enclosed in the brackets by the author of the present book is nothing but the primary medium effect of O2- expressed via the difference in the values of the equilibrium constants of equation (1.3.6) for the media compared the molten equimolar KCl-NaCl mixture, which was chosen as a reference melt, and for which pKHa/H20 was found to be 14 at 700 °C, and the melt studied. As to the physical sense of the common acidity function Cl, this is equal to the pO of the solution in the molten equimolar KCl-NaCl mixture, whose acidic properties (oxide ion activity) are similar to those of the solution studied. Moreover, from equation (1.3.7) it follows that solutions in different melts possess the same acidic properties (f ) if they are in equilibrium with the atmosphere containing HC1 and H20 and Phc/Ph2o — constant. This explanation confirms that the f function is similar to the Hammett function. Therefore, Cl values measured for standard solutions of strong bases in molten salts allow the prediction of the equilibrium constants on the background of other ionic solvents from the known shift of the acidity scales or the f value for the standard solution of a strong Lux base in the solvent in question. According to the assumption made in Refs. [169, 170] this value may be obtained if we know the equilibrium constant of the acid-base reaction (1.3.6) in the solvent studied. 

Nuclear industry participation early in the development is a requirement to address the many engineering aspects of the design, and to provide a long-term path forward. Interest in the AHTR has already been expressed by two reactor vendors, and these need to be pursued. Also, international interest in the AHTR, and molten salt (fueled) reactors in general, has been expressed by France and other countries. Collaborations should be pursued through the Generation IV International Forum to leverage the investments of these other countries. 

At very high electrolyte concentrations, where a large fraction of the solvent is expected to be bound to the ions in their solvation shells, a different approach applies, namely one that considers the solvent to be adsorbed on the ionic sites of the electrolyte, according to the BET method. This was suggested by Stokes and Robinson [14] and recently taken up by Marcus [19] as applying to molten salt hydrates. The terms adsorption and binding sites, taken over from the BET method for sorption of neutral small molecules on solid surfaces, should not be taken too literally. The operative expression is ... 

Diffusivities in molten salts and metals are even more difficult to predict and here we often resort to an Arrhenius-type relation to express the strong temperature dependence of the diffusion coefficienf, which is concealed in the viscosity of Equation 3.2 and Equation 3.3 ... 

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