NaCl-KCl-NaF

HM>9) Gray amorphous powder or crystals. Corrosion-resistant to molten metals such as Al, Pb, Zn, Cd, Bi, Rb, and Sn, and molten salts NaCl-KCl, NaF, and sihcate glasses. Corroded by molten Mg, Ti, V, Cr, Fe, Co, cryolite, KOH, and NaaO. Silicon nitride (Nitrasil )... 

Derivative molten salts are the mixtures of chloride and fluoride like KCl-KF and NaCl-KCl-NaF. In these molten salts, both K2SiFg and Si02 can be used as the silicon source [28, 29]. Electroreflning of MG-Si was also reported in molten KCl-NaF at 800 °C [30]. 

Cai Z, Li Y, He X, Liang J (2010) Electrochemical behavior of Silicon in the (NaCl-KCl-NaF-Si02) molten salt. Metall Mater TransB 41 1033-1037... 

In this paper, the mechanism of cathodic discharge of titanium in the NaCl-KCl-NaF system with K2T1F6 dissolved therein, is studied in the temperature range 700-800 °C. Cyclic voltammetry (CV) and chronopo-tentiometry (CP) are employed, as previously done for Ti in NaCl-KCl melts [19,20]. 

In previous studies of the cathodic reduction of K2T1F6 in molten salts, we chose an equimolar NaCl-KCl mixture as the solvent. Then, in some of the electrochemical runs performed, a change of the electrolyte colour from colourless (specific to tetravalent titanium) to pink (specific to trivalent titanium) was noted. To avoid instability of this melt and ensure data reproducibility, it was decided to add fluoride ions to the solvent, as proposed by Polyakova et al. [11]. Accordingly, in the present paper, a NaCl-KCl-NaF melt (42.25-42.25-15.5 mol% or 197-251-52 g, m.p. 602 °C) is chosen as solvent, and the solute added (K2TiFg) varied its concentration from 0.1 to 0.5mol% (0.034-0.17 mol 1 ). 

A sample of NaCl-KCl-NaF powder was placed in a graphite crucible, which was then located on a firebrick on the bottom of the cell envelope. The furnace temperature was subsequently raised slowly up to 700 °C and the salts became molten. The cell was then filled with dry argon, the temperature adjusted to its final value and the electrodes inserted into the melt. K2TiFg was added to the fused mixture via a long silica tube which had a funnel attached at the top. 

In order to further determine where the products of the reduction waves are soluble or insoluble, inverse chronopotentiometric runs were performed for the two waves. It was shown that the first step proceeds reversibly giving a product which is soluble in the temperature range 700-800 °C. Figure 4.7.1 shows a chronopotentiogram with current inversion, typical of the behaviour of the Pt/NaCl-KCl-NaF-K2TiF6 interface in the potential range corresponding to the second reduction step. 

The cyclic voltammogram of Ti" " " in NaCl-KCl-NaF-K2TiF6 melts, for the studied K2TiFg concentrations and working temperatures, showed two well defined peaks as illustrated in Figure 4.7.2, for... 

In summary, the CV and CP techniques gave complementary results, which elucidated the behaviour of titanium in molten NaCl-KCl-NaF melts with KjTiFg, and led to results and conclusions in agreement with previous literature data [11, 15, 19, 20]. 

The mechanism of the reduction of Ti" " " in molten NaCl-KCl-NaF-K2TiF6 was studied using CV and CP over a Ti" concentration range of 0.1 -0.5 mol%, at temperatures varying from 700 to 800 °C. Two reduction and two oxidation steps were observed, which established that Ti" + is reduced to Ti + (soluble) followed by a three-electron reduction of Ti + to Ti (Pt alloy). The first step is the reversible reduction of Ti" + to give a soluble product, and the second step is the reduction to Ti metal, and its reversibility may be restricted by chemical/electrochemical complications. 

Miscellaneous Impurities. Iribarne et al. (75) and Levi and Lubart 106) measured d.c. conductivities of ice doped with LiOH, NaOH, NH4OH, LiF, NaF, LiCl, NaCl, KCl, RbCl, CsCl, and NH4CI as a function of concentration at — 10°C. For the salts, they did not obtain a clear concentration dependence of the conductivity. In any event, the interpretation of such measurements is complicated by differential ion incorporation, not taken into account by the authors. They did, however. 

Expressions for the force constant, i.r. absorption frequency, Debye temperature, cohesive energy, and atomization energy of alkali-metal halide crystals have been obtained. Gaussian and modified Gaussian interatomic functions were used as a basis the potential parameters were evaluated, using molecular force constants and interatomic distances. A linear dependence between spectroscopically determined values of crystal ionicity and crystal parameters (e.g. interatomic distances, atomic vibrations) has been observed. Such a correlation permits quantitative prediction of coefficients of thermal expansion and amplitude of thermal vibrations of the atoms. The temperature dependence (295—773 K) of the atomic vibrations for NaF, NaCl, KCl, and KBr has been determined, and molecular dynamics calculations have been performed on Lil and NaCl. Empirical values for free ion polarizabilities of alkali-metal, alkaline-earth-metal, and halide ions have been obtained from static crystal polarizabilities the results for the cations are in agreement with recent experimental and theoretical work. 

NaF, KF, KHF2, CsF LiCl, NaCl, KCl, CsCl LiBr, NaBr, KBr Alkali iodides, Lil,... 

The melts chosen for this study were NaCl-KCl(50-50mol%)-NaF-KBF4-K2MeF6 (Me-Ti, Zr, Hf). The chloro-fluoride melt was chosen, as the pure fluoride melt is more aggressive, and, on the other hand, the oxo-fluoride melt gives a lower current efficiency. Also, the cathodic product is easier to wash from the quenched salt if the chloro-fluoride melt is used for the synthesis. 

Voltammetric experiments in the system NaCl-KCl-K2TiF6-KBF4-NaF have been performed [6, 7], also in the systems NaCl-KCl-K2ZrF6-KBF4-NaF [7, 8], and NaCl-KCl-K2HfF6-KBF4-NaF [5, 9]. 

In the system NaCl-KCl-KBF4-NaF one process, more electropositive than the discharge of the alkali metals has been observed (Figure 1.). This process corresponds to a three electron irreversible change transfer with formation of insoluble product ... 

In the system NaCl-KCl-K2TiF6-KBF4-NaF of a one-electron reversible change transfer Ti(IV)/Ti(III) occurs more positive than the HTES of TiB2. Therefore in order to obtain a TiB2 coating, metallic Ti was used as an anode to produce low-valent titanium ions in the melt ... 

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