Melts LiCl/KCl

For preparation of alloys nickel by cleanliness of 99.99 %, magnesium by cleanliness of 99.95 %, lanthanum by cleanliness of 99.79 %, and mishmetall (industrial mixture of rare-earth metals (REM) Ce - 50, La - 27, Nd - 16, Pr - 5, others REM - 2wt. %) were used. The melting of metal charge was carried out in the vacuum-induction furnace under fluxing agent from eutectic melt LiCl-KCl. The composition of alloys was supervised by the chemical analysis and the X-ray testing. 

Previously [7, 8] it was shown that, during precipitation of lanthanide phosphates from alkali chloride melts (LiCl-KCl and NaCl-KCl), up to fivefold molar excess of the precipitant is required for complete conversion of the lanthanide chloride into phosphate. In the present work in the first series of the experiments rare earth phosphates were precipitated from NaCl-CsCl-based melts at various initial phosphate to lanthanide mole ratios. The initial Na3P04 RECl3 mole ratio varied from 0.4 up to nearly 8.0. The results obtained are presented in Figure 6.10.2. 

Lithium hydride is perhaps the most usehil of the other metal hydrides. The principal limitation is poor solubiUty, which essentially limits reaction media to such solvents as dioxane and dibutyl ether. Sodium hydride, which is too insoluble to function efficiently in solvents, is an effective reducing agent for the production of silane when dissolved in a LiCl—KCl eutectic at 348°C (63—65). Magnesium hydride has also been shown to be effective in the reduction of chloro- and fluorosilanes in solvent systems (66) and eutectic melts (67). 

Fig. 5.25. The shock temperature in LiCl KCl electrolytes is controlled with the use of eleetrolytes with initial densities as shown. The cirele represents the shock conditions. Upon release of pressure the final temperature is expected to cross the melt eurve for certain initial conditions.

The blue color of 83 has been observed in numerous experiments. For example, a brilliant blue color occurs if a potassium thiocyanate melt is heated to temperatures above 300 °C [132] or if eutectic melts of LiCl-KCl (containing some sulfide) are in contact with elemental sulfur [132, 133], if aqueous sodium tetrasulfide is heated to temperatures above 100 °C [134], if alkali polysulfides are dissolved in boiling ethanol or in polar aprotic solvents (see above), or if borate glasses are doped with elemental sulfur [132]. In most of these cases mixtures of much 83 and little 82 will have been present demonstrating the ubiquitous nature of these radicals [12]. 

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. 

However, there are no known SB systems with Mg in aqueous solutions. The Mg anode s irreversibility in aqueous solutions is thought to be due, in part to the existence of monovalent Mg ions during the electrochemical discharge, in part to the selfcorrosion and film formation, and in part caused by other factors (136,140). All attempts to deposit this metal on the negative electrode from aqueous electrolytes have failed. It is claimed that the Mg cell with molten salt electrolyte, LiCl-KCl eut., is reversible (141) it operates at temperatures above the eutectic melting point, i.e. about 400°C. Small amounts of water might decrease the operating temperature. 

Several investigations have been made of the reduction of cobalt(II) to cobalt(O) in molten salt media. Eor a eutectic melt of LiCl-KCl at 450°C[10], a 1 1 NaCl-KCl melt at 450°C[11], and a MgCh-NaCl-KCl (50 30 20 mol%) mixture at 475 °C [12], the apparent standard potentials for the cobalt(II)-cobalt(0) couple have been deduced to be —1.207 V, — 1.277 V, and—1.046 V, respectively, each with respect to a chlorine-chloride ion reference electrode. 

Recent studies on the electrochemical behavior of plutonium in molten salts have mainly been performed in LiCl— KCl based melts. The electrorefining step in a pyroprocessing procedure for the recycling of nuclear fuel from the Integral Fast Reactor (IFR) Program has been... 

Uozumi, lizuka, and coauthors have published several studies on the electrochemical behavior of Pu at liquid cadmium cathodes in LiCl—KCl eutectic melts [128-130]. In one account [130] the authors studied the reduction of Pu " " to Pu° at the LiCl— KCl melt and liquid Cd interface and compared the results to those obtained at a solid Mo cathode surface. The electrode reaction at liquid Cd was found to be close to fully reversible with rapid. 

Electrochemical studies of plutonium in NaCl-based melts are less common than that in LiCl—KCl mixtures. In a recent paper by Lambertin etal. the standard potentials for the Pu(III)/Pu(0) couple were determined from cyclic voltammetry data in equimolar NaCl—KCl and CaCl2... 

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 ... 

An excellent procedure for purification of the LiCl-KCl melt has been summarized by Levy and Reinhardt [11]. To apply this procedure the melt is maintained under an atmosphere of dry HC1 gas at 400°C while HC1 is passed through the melt to convert hydroxide impurities to H20 ... 

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 and ion-exchange properties of ceric tungstate have been investigated.521 The acidic properties of WOa in a KCl-NaCl melt have been studied.522" and the reduction characteristics of Mo042- in fused LiCl-KCl reported.5226... 

The kinetics of the electrodeposition and electrocrystallization of titanium were studied in alkali chloride melts by Haarberg et al. [140], The cathodic reduction Ti(III)/Ti(II) was very irreversible, and the Ti(II)/Ti reduction was found to be quasi-reversible, as shown in the voltammogram in Figure 14. In LiCl-KCl... 

The use of other electrolyte compositions with a low melting point and higher electrical conductivity was also tried. The following electrolytes were tested the eutectics LiCl-KCl, LiCl-LiBr-KBr and LiF-LiCl-LiBr and also a LiCl-rich composition 34 mol% LiCl-32.5 mol% LiBr-33.5 mol% KBr. 

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