Halide melts

Bep2 melts are strong liquids, with relatively low viscosities. Addition of alkali fluorides decreases the viscosity of these melts and increases the fragility of the melt. 

An important feature of oxide solubilities was the essential difference of solubility values of powdered (added as powder) and prepared in situ oxide solubilities. Solubilities of latter samples have been found to be considerably greater (CaO, CdO), although there was no explanation to this observation. Quantitative characteristics of oxides solubilities in KCl-LiCl were not presented.  

The important fact found was the relatively high PtO solubility, therefore, platinum gas oxygen electrode, sometimes considered as metal-oxide one, cannot be used for measurement of pO in strongly acidic media because of complete dissolution of the oxide film over its surface. Pt PtO electrode was attempted for pO index measurements in buffer solutions NP/NiO.  

Stabilities of iron (II) and (III) oxides in the chloride melt at 470 C have been investigated. Oxide precipitation by carbonate CO/ =0 has been shown by potentiometric and diffractometric data to result in formation of FeO from Fe° solutions. Fe precipitation led to formation of solid solutions LiFeOj-LiyFei.yO. Solubility products in molarity scale have been determined as FeO-10 Fe3O4-10 , FejOj-lO . Cations Fe have been found to oxidize chloride melt with chlorine evolution, that is in good agreement wifli the results of other studies.Carbonate ion as oxide donor had its dissociation to essentially incomplete and, therefore, obtained solubility products gave systematic error. -  

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Silver chloride crystals are face-centered cubic (fee), having a distance of 0.28 nm between each ion in the lattice. Silver chloride, the most ionic of the halides, melts at 455°C and boils at 1550°C. Silver chloride is very ductile and can be roUed into large sheets. Individual crystals weighing up to 22 kg have been prepared (10). 

The only significant difference between halide melts and oxyhalide melts is that oxyfluoride complexes have a tendency to dissociate at relatively high concentrations yielding polyanion groups. This phenomenon is related with the need to achieve coordination saturation. 

G. J. Janz, R. P. T. Tomkins, and C. B. Allen, J. Rhys. Chem. Ref Data 8 (1979) 125 Molten Salts, Vol. 4, Part 4 Mixed Halide Melts, American Chemical Society-American Institute of Physics-National Bureau of Standards, Washington, DC, 1979. 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

Tumanova N., Babenkov E., Chemuhin S. and others. Electrochemical properties of carbamide-halide melts. Ukr. Chim. J., 2000 66 35-9 (in Russian). 

Cycloheptatrienylium bromide, instead of having the properties of a typical covalent organic halide, melts at 203°, is strongly deliquescent, miscible with water, and insoluble in the less polar organic solvents. The infrared spectrum is a simple one consistent with the high degree of symmetry postulated for the ion. 

Organic molten salts such as tris-n-butyl-dodecylphosphonium halides (melting point below 40°C) have been used as reaction media for nucleophilic aromatic substitution of aryl tosylates by halide ions (Fry and Pienta, 1985). 

White [7] gives a general review that includes information about the preparation and purification of a variety of alkali and alkaline earth halide melts. Information about fluorides can also be found in an earlier review article by Bamberger [8]. Many different halide melts have been used as solvents for electrochemistry, and a complete discussion of all of these melts is outside the scope of this chapter. However, two systems that have generated continuous interest over the years are the LiCl-KC1 eutectic (58.8-41.2 mol%, mp = 352°C) [9] and the LiF-NaF-KF (46.5-11.5-42.0 mol%, mp = 454°C) also known as FLINAK [10]. The former is an electrolyte commonly used in thermal batteries, whereas the latter molten salt is of interest for refractory metal plating. 

At a platinum electrode, highly purified FLINAK has a voltammetric window extending from about +1.5 to -2.0 V vs. the nickel reference electrode [7]. The positive limits of the alkali halide melts discussed herein arise from the oxidation of halide ions, whereas the negative limits are due to reduction of the alkali metal ions. Because chloride ion is substantially easier to oxidize than fluoride ion, the potential window of the LiCl-KCl melt is approximately 1.5 V smaller than that for FLINAK. 

The synthesis of the title compositions has been selected as representative of compounds that can readily be prepared by the flux-reaction technique. In this technique, a halide melt serves both as a flux and as a constituent component of the basic reaction. The procedure has been described in the literature1 and has served for the preparation of a variety of ternary oxides, usually in the form of small, well-defined, single crystals. The halide phosphates and vanadates of strontium represent the apatite and spodiosite structures, both interesting compositions from a biochemical and solid-state point of view. 

The aim of the present work is the fulfillment of the complex studying (a) -investigation of peculiarities of carbon solid phase electrodeposition from halide melts, saturated by carbon dioxide under excessive pressure up to 1.5 MPa in temperatures range 500 - 800 °C (b) - elucidation of electrode processes mechanism (c) - characterization of produced carbon powders (d) - establishment of correlation between product structure and yield against electrolysis conditions and regimes. 

The hexahalorhenate(IV) anions have been the subjects of extensive electronic absorption spectra studies. Their spectra have been recorded in aqueous and non-aqueous solvents, in halide melts, in the solid state and doped into other crystal hosts (e.g. K2PtCl[Pg.172]

Scattering by Alkali Halides Melts A Comparison of Shell-Model and Rigid-Ion Computer Simulation Results. 

The IR and Raman spectra of MLnI2, where M = Ni, n = 4 M = Zn or Cd, n = 2, L = m-methylaniline, gave quite detailed ligand mode vibrational assignments.197 The IR spectra of platinum(II) complexes in carbamide and carbamide-halide melts show the formation of Pt(NH3)42+ on dissolution of (NH4)2[PtCl4], as well as Pt(NH3)X3 in the presence of NH4+X, where X = Cl or Br.198 Picosecond-scale TRIR spectroscopy was used to probe the dynamics of the lowest excited state of Pt(bipy)(4-CN-C6F4-S)2.199... 

In every pure alkali metal halide or earth alkali metal halide melt, the cation is surrounded by anions in the first coordination sphere and has cations in the second coordination sphere. This arrangement is caused by the coulombic forces between cations and anions. 

Alkali metal halide melts are characterized by a quasi-crystalline structure originating by dilatation of the crystal structure and by the occurrence of different kinds of positional disordering. Cations and anions are preferably surrounded by ions of the opposite charge... 

The changes in coulomb energy, when substituting one alkali metal cation by another one in a binary alkali metal-earth alkali metal halide melt, will tend to give negative k versus 512 plot slopes, which are decreasing when the size of the common alkali metal cation is increasing. 

Tungsten dissolved in a NaCl/NaF halide melt, which is used to extract tungsten from ore concentrates, can be crystallized as WC by sparkling the melt with carbon monoxide. The advantage in comparison to the above-described method is that no acid is necessary to dissolve the auxiliary bath material. Only water is needed. 

Examinations of the interactions of ionic halide melts-solvents with gaseous reagents of acidic or basic character, which include high-temperature hydrolysis of molten alkali-metal halides, their purification from oxygen-containing admixtures, and studies of the dissociation of strong and weak Lux bases (such as COf-, OH-, 0 ) in melts of different acidity. 

Pure oxygen-less melts contain no oxide ions in any form, and, therefore, such pure melts cannot serve as donors of O2-. The melts, which are solvents of the second kind, can affect acid-base interaction on their background in two manners by fixation of oxide ions entering in the melt and by solvation of the conjugate acid or base. However, the ionic solvents of the second kind, used in practice for different measurements and applied purposes, contain admixtures of oxide-ion donors, which are formed in the melt from initial admixtures of oxo-anions such as SO4-, COf- or OH-. The second way of appearance of oxide ion admixtures in molten media is characteristic of the melts based on alkali metal halides the process of high-temperature hydrolysis of the said halide melts results in the formation of hydroxide ions and, after their dissociation, of oxide ions ... 

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