Halides alkaline earth metals

Based on the concept of mixed-framework lattices, we have reported a novel class of hybrid solids that were discovered via salt-inclusion synthesis [4—7]. These new compounds exhibit composite frameworks of covalent and ionic lattices made of transition-metal oxides and alkali and alkaline-earth metal halides, respectively [4]. It has been demonstrated that the covalent frameworks can be tailored by changing the size and concentration of the incorporated salt. The interaction at the interface of these two chemically dissimilar lattices varies depending upon the relative strength of covalent vs. ionic interaction of the corresponding components. In some cases, the weak interaction facilitates an easy... 

Salt-inclusion solids described herein were synthesized at high temperature (>500°C) in the presence of reactive alkali and alkaline-earth metal halide salt media. For single crystal growth, an extra amount of molten salt is used, typically 3 5 times by weight of oxides. The reaction mixtures were placed in a carbon-coated silica ampoule, which was then sealed under vacuum. The reaction temperature was typically set at 100-150 °C above the melting point of employed salt. As shown in the schematic drawing in Fig. 16.2, the corresponding metal oxides were first dissolved conceivably via decomposition because of cor-... 

The auxiliary electrolyte is generally an alkali metal or an alkaline earth metal halide or a mixture of these. Such halides have high decomposition potentials, relatively low vapor pressures at the operating bath temperatures, good electrolytic conductivities, and high solubilities for metal salts, or in other words, for the functional component of the electrolyte that acts as the source of the metal in the electrolytic process. Between the alkali metal halides and the alkaline earth metal halides, the former are preferred because the latter are difficult to obtain in a pure anhydrous state. In situations where a metal oxide is used as the functional electrolyte, fluorides are preferable as auxiliary electrolytes because they have high solubilities for oxide compounds. The physical properties of some of the salts used as electrolytes are given in Table 6.17. 

Normal glass will only transmit radiation between about 350 nm and 3 /rm and, as a result, its use is restricted to the visible and near infrared regions of the spectrum. Materials suitable for the ultraviolet region include quartz and fused silica (Figure 2.28). The choice of materials for use in the infrared region presents some problems and most are alkali metal halides or alkaline earth metal halides, which are soft and susceptible to attack by water, e.g. rock salt and potassium bromide. Samples are often dissolved in suitable organic solvents, e.g. carbon tetrachloride or carbon disulphide, but when this is not possible or convenient, a mixture of the solid sample with potassium bromide is prepared and pressed into a disc-shaped pellet which is placed in the light path. 

Goldberg, R. N. Nuttall, R. L. "Evaluated Activity and Osmotic Coefficients for Aqueous Solutions The Alkaline Earth Metal Halides" J. Phys. Chem. Ref. Data, 1978, 7,... 

TABLE 1.16 Lattice energies of some alkali and alkaline earth metal halides at 0 K... 

Goldberg, R. N., and R. L. Nuttall. 1978. Evaluated activity and osmotic coefficients for aqueous solutions The alkaline earth metal halides. J. Phvs. Chem. Ref. Data 7(1) 263-310. 

TABLE 9.1 Lattice Energies and Melting Points of Some Alkali Metal and Alkaline Earth Metal Halides and Oxides... 

OXOACIDITY SCALES FOR MELTS BASED ON ALKALI- AND ALKALINE-EARTH METAL HALIDES... 

Oxoacidity scales for melts based on alkali- and alkaline-earth metal halides 119... 

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. 

All the above-said concerns alkali-metal carbonates dissolved in melts based on alkaline- and alkaline-earth metal halides. It should be mentioned that there is a lack of data on the behaviour of alkaline-earth carbonates, in high-temperature alkaline halide melts. Nevertheless, these data are necessary, in particular, for the purification of halide melts. For example, it is known that alkaline-earth oxides possess appreciable solubilities in molten alkaline halides, and that they can be used for precipitation of less soluble transition metal-oxides. After such a precipitation, the excess of alkaline-earth oxide remains in the dissolved state. The question arises, therefore, whether it can be removed from the halide melt by passing C02 according to the conventional reaction... 

For oxides of the type MeO, there exists a linear dependence of the solubility product index of the oxide against the inverse-squared radius of the metal cation. The slopes of these plots in the melts based on alkali-metal halides and alkaline-earth metal halides are stated to be approximately the same. This can give evidence that, at high temperatures in the order of 1000 K, the changes in solvation ability of the ionic melts, proceeding from one melt to another, are close for different cations with radii in the order of 0.1 nm (from 0.74 nm for Mg2+ to 1.38 nm for Ba2+). An increase in the melt temperature... 

Mishchenko and co-workers ° and Krestov and Klopov have measured heats of solution for several alkali and alkaline earth metal halides and nitrates in water-methanol mixtures. The data, which are given only in graphical form, indicate the same functional dependence upon alcohol concentrations as those reported by Slansky, and Moss and Wolfenden. ... 

Scattered data for several other aprotic amides exist. Pistoia and Scrosati have reported the solubilities for several alkali and alkaline earth metal halides and transition metal halides in JV,JV-dimethylacet-amide. The solubilities increase in the order Cl < Br < I. Alexander and co-workers have reported solubility product values for numerous silver salts in DMA. They have also reported values for silver salts, KBr and NaCl in hexamethylphosphorotriamide (HMPT). The solubilities of the silver halides in both these solvents follow the same trend as they do in water. Coleman has measured the solubilities and activity coefficients of sodium and potassium chlorides in several dialkylamides containing water. Distribution coefficients of the salt between water and amide have also been calculated. 

TABLE 4.5 Lattice Energies of Some Alkali and Alkaline Earth Metal Halides at OK (kJ/mol) ... 

Molten salts may be classified (1) into simple ionic salts (e.g. the alkali and alkaline earth metal halides), simple and polymeric oxyanionic salts (e.g. metal nitrates, carbonates, phosphates. 

Evaluated Activity and Osmotic Coefficients for Aqueous Solutions The Alkaline Earth Metal Halides... 

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