Molten salts parameter

The three principal electrochemical methods are described by which fluorine can be directly introduced into organic compounds, namely electrolysis in molten salts or fluoride ion solutions, electrolysis in molten potassium fluoride/hydrogen fluoride melts at porous anodes, and electrolysis in anhydrous hydrogen fluoride at nickel anodes. Using examples from the past decade, it is aimed to demonstrate that electrofluorination in its various forms has proved to be an increasingly versatile tool in the repertoire of the synthetic chemist. Each method is described in terms of its essential characteristics, reaction parameters, synthetic utility, advantages and disadvantages, patent protection, and potential for commercial exploitation. The different mechanisms proposed to explain each process are critically reviewed. 

We are forced to reflect that the failure of so many attempts to improve on the DH theory can be attributed to a premature rejection of the DH approach, and a tendency to include extra parameters without proper theoretical foundation. It is surprising that although ionic polarization is emphasized in studies of solvation (36), molten salts (37), and chemistry in general (38), the phenomenon has received little attention in interionic theory. In particular, our attention is drawn to the early work of Fajans and co-workers (39), who first noted the effects of concentration on the ionic molar refractivities of solutions, which were interpreted in terms of a distorting effect on the ions. For various reasons the significance of this work has not been appreciated in the field of electrochemistry. 

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]. 

Bredig [21] presumed that in a mixture of molten salts the variation of the interaction parameter X [see Eq. (8)] makes evident the formation of complex ions. Thus, in the KCl-CdCl2 and RbCl-MgCl2 systems it is observed variations of the X parameter and with the composition of the melt, and the minimum points of those variations correspond to the composition of complex ions. However, the most convincing data on the formation of complex ions can be obtained from measurements of the enthalpy of mixing [22],... 

By using the pair potentials of one of the pioneer works in the modeling of molten salts (Woodcock and Singer) as well as the corresponding parameters in this work, calculate the equilibrium distance for Li and Cl ions j ust above the... 

If the answer in the above question is no, what parameter is needed to describe the distribution of the hole size Is there validity to the statement that all holes are of the same size in molten salts Using data in Table 5.15, find the above distribution for KCl molten salt at 1170 K. 

One of the most important technological parameters in molten salt chemistry is surface tension, as the majority of important reactions take place at the interface of electrolytes or molten reacting media. In aluminum electrolysis, for instance, this parameter influences the penetration of the electrolyte into the carbon lining, the separation of carbon particles from the electrolyte, the coalescence of aluminum droplets and fog in the electrolyte, the dissolution rate of aluminum oxide in the electrolyte, etc. Similar is the effect of interface in aluminum recovery. 

Direct calibration is the simplest investigational method and is used widely for molten salts. Subsequent calculations of the equilibrium parameters of the... 

Since there are no well-developed and generally accepted methods for the determination of the activity coefficients and of their dependence on the concentration of the corresponding particles in molten salts, practical investigations of solubility usually result in the corresponding parameters being obtained based on the concentration, but not on the ion activities. 

From the dependence shown in Fig. 3.7.15 it can be concluded that the growth of the parameter a of the cubic crystalline lattice of the oxide increases its solubility in ionic melts based on alkali- and alkaline-earth metal halides. This may be explained by the fact that the increase in the parameter a of the crystalline lattice results in the weakening of the interaction between ions and molecules in oxide crystals, which favours dissolution of these oxide crystals in molten salts. The solubilities of ZnO and PbO are not shown in Fig. 3.7.15, since at the temperature of the experiment both oxides possess hexagonal crystalline lattices. 

Although Eq. 9.10-19 has a large number of parameters, especially for mixed electrolyte solutions, it has been useful in representing the thermodynamic behavior of electrolyte solutions all the way from dilute solutions to molten salts. 

Table 11 Dispersion (/), Polarity (s), Polarizability (f), Basicity (h), and Acidity (a) Solvation Parameters for Polymers, Molten Salts, and Conventional Liquid Stationary Phases... 

The ORNL analysis of the void coefficient used a core geometry that modeled individual prismatic fuel elements as depicted in Fig. 2.4. Table 3.2 lists the key parameters for the detailed ORNL fuel assembly model. The fuel assemblies were formed into a 102-column annular core corresponding to the GT-MHR core model, but with molten salt (Flibe) coolant. The core contained 78 fuel columns and 24 control columns. The focus of the analysis was to explore options for reducing the void coefficient through the use of burnable poisons (BPs) placed either in discrete rods within the fuel assembly or distributed in the graphite blocks. Because the presence of the BP lowers the overall reactivity of the core, the fuel enrichment was increased to 14 wt % for all cases. 

The proposed General Atomics GT-MHR," with a direct recuperative gas-turbine cycle, has an efficiency of 48% with an exit gas temperature of 850°C. The AHTR, with an indirect recuperative multireheat gas-turbine cycle (Fig. 2.11), has an efficiency of 54%—assuming the same temperatures and turbomachinery parameters. Current materials may allow molten salt temperatures of 750°C. At these temperatures, the AHTR matches the efficiency of the GT-MHR with its exit helium temperature of 850°C. At 1000°C turbine inlet temperature that might be obtained with advanced materials, using the same fuel that currently limits the GT-MHR to an exit heliiun gas temperature of 850°C, and taking advantage of the improved heat transfer properties of the molten salt (see above), the efficiency of the AHTR can exceed 59%. 

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