LiCl-KCl eutectic molten salt

A series of experiments have been undertaken to evaluate the relevant thermodynamic properties of a number of binary lithium alloy systems. The early work was directed towards determination of their behavior at about 400 °C because of interest in their potential use as components in molten salt batteries operating in that general temperature range. Data for a number of binary lithium alloy systems at about 400 °C are presented in Table 1. These were mostly obtained by the use of an experimental arrangement employing the LiCl-KCl eutectic molten salt as a lithiumconducting electrolyte. 

The flux method is a well-known method used for single erystal growth as discussed below. It has not been applied to the synthesis of fine powders because usually high temperature heating is necessary to obtain molten salts. However, nanosized Ce02 particles have been synthesized by the flux method at relatively low temperature (873 K), utilizing tetravalent cerium salt and three different eutectic mixtures of KOH/NaOH, NaNOs/KNOs, and LiCl/KCl as molten salts [99]. Well-crystallized Ce02 powders with very fine size (14-20 nm), narrow size distribution, and a clearly spherical shape are obtained. 

Methods have been developed (75) to prepare actinide metals directly from actinide oxides or oxycompounds by electrolysis in molten salts (e.g., LiCl/KCl eutectic). Indeed, the purest U, Np, and Pu metals have been obtained (19, 24) by oxidation of the less pure metal into a molten salt and reduction to purer metal (electrorefining. Section III,D). 

If an actinide metal is available in sufficient quantity to form a rod or an electrode, very efficient methods of purification are applicable electrorefining, zone melting, and electrotransport. Thorium, uranium, neptunium, and plutonium metals have been refined by electrolysis in molten salts (84). An electrode of impure metal is dissolved anodically in a molten salt bath (e.g., in LiCl/KCl eutectic) the metal is deposited electrochemically on the cathode as a solid or a liquid (19, 24). To date, the purest Np and Pu metals have been produced by this technique. 

During the electrorefining of uranium metal in a molten salt eutectic, a low current density favors the formation of large single crystals. Up to 5-cm single crystals of uranium metal have resulted from the large-scale (100 kg of U) electrorefining of uranium metal in molten LiCl/KCl eutectic (17). 

Li-Al electrodes behave well in molten salt electrolytes such as the LiCl-KCl eutectic, showing low polarization and good reversibility, with... 

The classification system described earlier is limited to the simplest kinds of individual melts and is not intended to include mixtures. However, molten mixtures of these different classes of compounds are often more practical solvents than the melts of the individual compounds, due to their much lower melting points and other favorable properties, and this system of classification can usually be extended to these mixtures. For example, the very popular molten LiCl-KCl eutectic mixture is simply a binary ionic melt, whereas molten NaN03-KN03-LiN03 is a ternary polyanionic melt. Interestingly, the equimolar molten mixture of the simple ionic salt NaCl (a) and the molecular compound A1C13 (d) produces a simple polyanionic salt melt (b) composed of Na+ and A1C14 ions ... 

The production of the light actinide metals is usually accomplished through the reduction of tri- or tetrafluorides with an electropositive metal, for example, Ca, Zn, or Mg. The heavy actinides are typically made through the direct reduction of oxide phases. An alternative method to access the actinide metals is through pyrochemical methods. In this technique, actinides in high-temperature molten salts, for example, NaCl-KCl or LiCl-KCl eutectics, are electrolyzed... 

There is a relatively large volume of electrochemical data on americium in molten-salt media, specifically LiCl—KCl eutectic at solid (W, Mo, Ta) and liquid (Cd, Bi) electrodes. Lambertin etal. studied the electrochemical reduction of AmCb in LiCl—KCl at 470 °C at a tungsten working electrode [144]. It was determined from the cyclic voltammetric data that Am(III) is first reduced to Am(II) and subsequently reduced in a second step to Am(0). The voltammetry data were used to estimate the standard potential for the Am(III)/Am(II) couple as —2.84 V versus CI-/CI2 and —2.945 V versus Cl /Cl2 for Am(II)/Am(0). These results are in very good agreement with an earlier study by Fusselman and coauthors [105,145]. They determined standard potentials for the Am(III)/Am(II) couple as —2.83 V versus Cl /Cl2 and —2.852 V versus Cl /Cl2 for the Am(II)/Am(0) couple at 450 °C. More recently Lambertin etal. extended their studies with a report on the stability of Am ions in molten LiCl—KCl in the presence of fluoride ions [146]. They found that Am(III) undergoes a direct three-electron reduction to Am(0) in the presence of fluoride at —2.91 V versus CI-/CI2 without voltammetric evidence... 

Two long-term tests have been performed with copper sulfide electrodes, one in a small investigative cell of the type shown in Figure 1, the other in a sealed 25-W-hr cell which will be described later. The starting active material in both cells was CuS. In both cases, the lithium electrodes consisted of porous metal plates impregnated with molten lithium metal. The electrolyte was the LiCl-KCl eutectic salt mixture, saturated with Li2S and maintained at 380-400°C. 

The aim of this work was to deposit molybdenum on a steel substrate at temperatures sufficiently low (< 650°C) in order to avoid structural modifications of the substrate. This is why the LiCl-KCl eutectic was selected as the solvent. A literature survey shows that molybdenum deposits have already been obtained from molten chlorides, fluorides, oxides, and mixed fluoride-oxide media, and that many questions concerning the chemistry of the molybdenum solutions and the reduction mechanism remain unanswered. In this paper, we will talk about the preparation of the molybdenum salt used as a solute, then describe the electrochemical kinetic investigation performed, and finally briefly outline a practical application of the knowledge gained during this work. 

---