Melts molar conductivity

Such a model of the melt structure does not contradict conductivity data [324], if plotted against the composition of the KF - TaF5 system. Fig. 63 presents isotherms of molar conductivity, in which molar conductivity of the ideal system was calculated using Markov s Equation [315], and extrapolation... 

As a whole, the KF — TaF5 system forms melts that are characterized by a decrease in molar volume and increase in molar conductivity, as demonstrated in Fig. 64. This behavior enables classification of the system as a lib-type... 

Table 8.2 lists the conductivities, transport numbers and molar conductivities of the electrolyte A = olc, and ions Xj = t+A for a number of melts as weU as for 0.1 M KCl solution. Melt conductivities are high, but the ionic mobilities are much lower in ionic liquids than in aqueous solutions the high concentrations of the ions evidently give rise to difficulties in their mutual displacement. 

TABLE 8.2 Conductivities, o, Cationic Transport Numbers, Molar Conductivities of the Electrolyte (A) and Cation (X+), and Activation Energies of Conduction, A, for a Number of Melts and Aqueous KCl Solution... 

Figure 1.3 Molar conductivity of various alkali halides atT = 1100 K (fluorites atT = 1270 K) versus the ratio of the bond energy of individual and complex ions A U to the internal energy of the melt AU (according to Khokhlov ). (Reproduced with permission from Ref. [18], 1998 by Trans Tech Publications.)...

BIAN, = bis(imino)acenaphtene DiPP, 2,6-diisopropylphenyl Xyl, 2,6-dimetylphenyl A, elemental analysis m/d melting or decomposition point Am molar conductivity MS, mass spectrum UV, ultraviolet-visible IR, infrared H, C, p, isp, Li NMR spectra XR X-ray diffraction CV, cyclic voltammetry dec, decomposition temperature. 

The polarization free resistance of the melt was measured with an ac Wheatstone type bridge using an input frequency from 0.5 to 10 kHz. The schematic diagram of the apparatus and the experimental procedure were described in detail elsewhere [13,14]. The electrical conductivity k was calculated by use of the cell constant and the real electrolytic impedance. The molar conductivity A of the mixture melt was evaluated from the following equation [15] ... 

Some structural information is obtained from models that relate bulk properties to the structures. An early attempt to apply this approach was that of Lind et al. [35], who dealt with the Walden product of the molar conductivity A and the viscosity // of molten ILiN BF4, -PFg , and -BPh4 (R = C3 to Cg). This product is rather insensitive to the temperature and was applied to the melts at 250 °C. The hard-sphere model predicted the product At] to be proportional to where r is the radius of the cation. However, only for the R = C3 salts with BF4 and PFg were the predicted values commensurate with the experimental ones, for the other salts the prediction overestimated the product. For such melts with small globular ions the structure is determined mainly by the coulomb forces as for high-melting salts, but with alkyl chains longer than propyl (C3) the thermal movements of these chains clog the interstices in the liquid and obstruct the movement of the ions. 

Fig. 60. Isotherms (800°C) of molar volume (top) (after Agulyansky et al. [322]) and specific conductivity (bottom) (after Agulyansky et al. [3241) of the melts KF- K2TaF7 (I) andKCl - K2TaF7 (2).

The formation of complex ions is an important problem for the study of the structure and properties of molten salts. Several physicochemical measurements give evidence of the presence of complex ions in melts. The most direct methods are the spectroscopic methods which obtain absorption, vibration and nuclear magnetic resonance spectra. Also, the formation of complex ions can be demonstrated, without establishing the quantitative formula of the complexes, by the variation of various physicochemical properties with the composition. These properties are electrical conductivity, viscosity, molecular refraction, diffusion and thermodynamic properties like molar volume, compressibility, heat of mixing, thermodynamic activity, surface tension. 

Equivalent conductivities (and ionic mobilities) of the melts are similar to that of aqueous solutions. Very high specific conductivities are typical for molten salts, as seen in Table 1 [49], The reason for this is the fact that molten salts are very concentrated solutions (for example, the concentration of molten LiF is about 65 molar the concentration of molten KC1 is about 20 molar, etc.). The electrical conductivities of various molten salts cannot be compared at constant temperature because of their different melting points. Therefore, in Table 1 the values of conductivities were selected at 50° above the melting point of each salt. 

In this chapter it is demonstrated that the heat conductivity of amorphous polymers (and polymer melts) can be calculated by means of additive quantities (Rao function, molar heat capacity and molar volume). Empirical rules then also permit the calculation of the heat conductivity of crystalline and semi-crystalline polymers. 

Thermal Conductivity and Thermal Expansion. Thermal conductivity of liquids (and gases to some extent) is still an empirical subject in any but the broadest sense. Kowalczyk (1144) reviewed the subject and the equations which relate thermal conductivity to viscosity, molar volume, melting point, and sound conductivity. Sakiadis and Goates (1776, 1777) tabulate values for a number of compounds and present correlation functions for thermal and sound conduction. 

Fluorine is manufactured electrochemically from a salt melt, which consists of a mixture of potassium fluoride and hydrofluoric acid in a molar ratio of 1 2.0 to 1 2.2. The temperature of the salt melt is ca. 70 to 130°C. Potassium fluoride provides the necessary melt conductivity, the hydrogen fluoride consumed being continuously replenished during the electrolysis. 

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