Metal-molten salt systems

Molecular dynamics calculations in metal-molten salt systems which could lead to diffusion and conduction values were first made by Parinello and Rahman in 1984. They have been used particularly by Malescio to examine the degree of delocalization of the electrons, which increases with the radii of the metal atoms. 

The most obvious and frequently used route to sub-valent species in molten halide solution is the reduction of a normal-valent halide with its parent metal, i.e. sym-proportionation reactions such as (2). This methodology is natural, since it disfavors disproportionation of the sub-valent compound to the zero-valent state according to (1). In addition, the methodology minimizes the number of components in the system. Post-transition metal-molten salt systems from which solid, sub-valent compounds have been isolated through symproportionation reactions are summarized in Table 1. 

Table 1. Metal-molten salt systems in which solid, sub-valent compounds with metal-metal bonds have been synthesized by symproportionation or similar reactions. The many sub-halides of gallium and indium have been omitted. These compounds contain either sub-valent monoatomic cations e.Lj. (Ga )(GaCl4 )l > and (In )(Cl )] " and/or ligand-stabilized metal-metal bonded anions (Ga+)2(Ga2X6- ), X = Br, For a review of the sub-valent chemistry of the group...

Metal-molten salt system Isolated solid phases Ref. 

In conclusion, it appears that few metal-molten salt systems behave in the ideally polarizable sense generally associated with the mercury/aqueous solution interface at 298 K. Possible exceptions include some noble liquid metal/melt systems such as mercury/molten nitrates and lead/molten halides at low temperatures (<773 K), but only when the molten electrolyte is extensively purified. Otherwise, systems need to be analyzed as complex impedances, using ac or pulse techniques, to determine whether the minimum interfacial capacitance is affected by extensive factors, leading to parallel pseudocapacitances and Faradaic components. The range of potentials and measuring frequencies for which the interface approaches ideally polarizable behavior also needs to be established. It now seems clear that the multilayer ionic model of charge distribution at the metal/melt interface is more pertinent to molten media than the familiar double layer associated with aqueous solutions. However, the quantitative theories derived for the former model will have to be revised if it is confirmed that the interfacial capacitance is, indeed, independent of temperature in the ideally polarizable region. 

Alternatively, the TiCl may be reduced using hydrogen, sodium, or magnesium. It follows that TiCl2 is the first stage in the KroU process for the production of titanium metal from titanium tetrachloride. A process for recovery of scrap titanium involving the reaction of scrap metal with titanium tetrachloride at >800° C to form titanium dichloride, collected in a molten salt system, and followed by reaction of the dichloride with magnesium to produce pure titanium metal, has been patented (122,123). 

Electrolysis. Electrowinning of zirconium has long been considered as an alternative to the KroU process, and at one time zirconium was produced electrolyticaHy in a prototype production cell (70). Electrolysis of an aH-chloride molten-salt system is inefficient because of the stabiUty of lower chlorides in these melts. The presence of fluoride salts in the melt increases the stabiUty of in solution, decreasing the concentration of lower valence zirconium ions, and results in much higher current efficiencies. The chloride—electrolyte systems and electrolysis approaches are reviewed in References 71 and 72. The recovery of zirconium metal by electrolysis of aqueous solutions in not thermodynamically feasible, although efforts in this direction persist. 

Electrochemically, the system metal/molten salt is somewhat similar to the system metal/aqueous solution, although there are important differences, arising largely from differences in temperature and in electrical conductivity. Most fused salts are predominantly ionic, but contain a proportion of molecular constituents, while pure water is predominantly molecular, containing very low activities of hydrogen and hydroxyl ions. Since the aqueous system has been extensively studied, it may be instructive to point out some analogues in fused-salt systems. 

Other Pyrochemical Processes. The chemistry of pyrochemi-cal separation processes is another fertile area of research e.g., new molten salt systems, scrub alloys, etc. and the behavior of plutonium in these systems. Studies of liquid plutonium metal processes should also be explored, such as filtration methods to remove impurities. Since Rocky Flats uses plutonium in the metal form, methods to convert plutonium compounds to metal and purify the metal directly are high-priority research projects. 

Chlorostannate and chloroferrate [110] systems have been characterized but these metals are of little use for electrodeposition and hence no concerted studies have been made of their electrochemical properties. The electrochemical windows of the Lewis acidic mixtures of FeCh and SnCh have been characterized with ChCl (both in a 2 1 molar ratio) and it was found that the potential windows were similar to those predicted from the standard aqueous reduction potentials [110]. The ferric chloride system was studied by Katayama et al. for battery application [111], The redox reaction between divalent and trivalent iron species in binary and ternary molten salt systems consisting of 1-ethyl-3-methylimidazolium chloride ([EMIMJC1) with iron chlorides, FeCb and FeCl j, was investigated as possible half-cell reactions for novel rechargeable redox batteries. A reversible one-electron redox reaction was observed on a platinum electrode at 130 °C. 

The fact that a concentration of about 1 mol% of an alkali metal in a molten salt system can cause a considerable specific conductance demands some kind of explanation. At 1 %, the electrons are about 2 nm apart, on the limit for tunneling site to site. What is the mechanism of their easy passage through the molten salt ... 

Calculate the relaxation time for an electron conducting in a metal-molten salt mixture. (The mobility for such systems is about 0.2 cm V s . )... 

In this section we present some applications of the LAND-map approach for computing time correlation functions and time dependent quantum expectation values for realistic model condensed phase systems. These representative applications demonstrate how the methodology can be implemented in general and provide challenging tests of the approach. The first test application is the spin-boson model where exact results are known from numerical path integral calculations [59-62]. The second system we study is a fully atomistic model for excess electronic transport in metal - molten salt solutions. Here the potentials are sufficiently reliable that findings from our calculations can be compared with experimental results. 

The behavior of an excess electron in dilute metal-molten salt solutions has been the subject of many experimental and theoretical studies [69-72]. The details of the model we employ are exactly the same as the early calculations of Selloni and coworkers [71,72]. Specifically, our simulations have been performed on a periodically repeated system of 32 K+ cations, 31 CP anions, and 1 electron. The mass density was set to p = 1.52 x 10 kg/m. The temperature we use here is T = 1800 K. 

In general, the ionic composition of molten salt systems depends on the solvent used for the dissolution of the compound, which contains the metal to be deposited, and the chemical nature of this compound. Usually, chemical reactions take place between this compound and the solvent. At these chemical reactions, new complex anions are formed, atomic composition and stability of which depend on the electronic state of the central metallic atom and the polarization ability of the alkali metal cations. The chemical nature of the anions present also plays a non-negligible role. The above-mentioned phenomena will be explained in the following chapters. 

Divalent metal halides and their mixtures with alkali metal halides have been among the first molten salt systems to be investigated by Raman spectroscopy. Studies of molten mixtures of the type MeX2-MX (X = Cl, Br, I) have provided means of identifying and characterizing the species that may exist in the mixture and have information regarding the liquid structure of the MeX2 component. 

In 1963 Dr. Danbk joined the Institute of Inorganic Chemistry of the Slovak Academy of Sciences in Bratislava, of which he was the director in the period 1991-1995. His main field of interest was the physical chemistry of molten salts systems in particular the study of the relations between the composition, properties, and structure of inorganic melts. He developed a method to measure the electrical conductivity of molten fluorides. He proposed the thermodynamic model of silicate melts and applied it to a number of two- and three-component silicate systems. He also developed the dissociation model of molten salts mixtures and applied it to different types of inorganic systems. More recently his work was in the field of chemical synthesis of double oxides from fused salts and the investigation of the physicochemical properties of molten systems of interest as electrolytes for the electrochemical deposition of metals from natural minerals, molybdenum, the synthesis of transition metal borides, and for aluminium production. 

This book includes selected topics on the measurement and evaluation of physicochemical properties of molten electrolytes. It describes the features, properties, and experimental measurement of different physico-chemical properties of molten salt systems used as electrolytes for the production of different metals, metallic layer deposition, as a medium for reactions in molten salts, e.g. precipitation of double oxide powders used for functional and construction ceramics, special parts for steel and copper production, etc. 

This is of course not the case when working with room temperature ionic liquid systems. Electrochemical and spectroscopic studies of cobalt, copper, and nickel, have been carried out in the AlClj-butylpyridinium chloride molten salt system. The direct current and pulsed current electrodeposition of Ni-Al alloys has also been shown in acidic AlCls-butylpyridinium chloride ionic liquids. This particular alloy has also been shown to be successful in AlCl3-[C2-mim]Cl ashave Co-Al andCu-Al. Electrochemical techniques can also be used to calculate the diffusion coefficients of metal ions. Table 21.2.6 shows the calculated diffusion coefficients and stokes-Einstein products of cobalt(II), copper(I), nickel(II) and zinc(II) in the 40-60 mol% [Cj-mimlCl-AlClj ionic liquid. 

He has carried out researches in various fields of inorganic chemistry (coordination chemistry of 3d-metals, high-temperature chemistry of molten fluorides), physical chemistry (phase equilibria in molten salt systems), electrochemistry (thermodynamics of metal-electrolyte interface, electrodeposition of refractory and other metals from molten salts, lithium batteries and active materials for them) and, more recently, nanochemistry of inorganic oxide materials. 

Several fluid-fueled reactors have been built and operated as experiments. The concept is that fuel is contained within the coolant. Systems of this type include aqueous fuel systems, liquid metal-fueled systems, molten salt systems, and gaseous suspension systems. The homogeneous reactor experiment was constructed and operated at Oak Ridge Nahonal Laboratory, as was the Molten-Salt Reactor experiment. A liquid metal fuel reactor experiment was operated at Brookhaven National Laboratory. Power reactors of this type have not been built. 

Coulometry represents a simple method of quantitative additions to molten salt systems once the electrochemical processes have been established. For example, Laitinen and Liu (14) studied the Nernst equation behavior of a number of metals against their ions by generating the ions coulometrically to form a series of solutions of increasing concentration. 

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