Molten potassium halides

Papers devoted to the studies of metal-oxide solubilities in molten potassium halides are few. In particular, Guyseva and Khokhlov reported the determination of the solubility product of MgO in molten KC1 in the 1067-1195 K temperature range [374], The study was performed by the potentiometric method using the Pt(02) gas-oxygen electrode. The experimental method consisted of the addition of a known quantity of MgCl2 to the pure melt, and measurements of e.m.f. for the following cell  

The relationship between the equilibrium molality of the oxide ion and the e.m.f. of the cell (equation (3.7.43)) can be expressed by the following equation  

Although the obvious drawback of this work consists of passing 02 through the acidic melt, which leads to oxidation of chloride ions in the excess of the Lux acid, nevertheless, the authors obtained the thermal dependence of MgO solubility in molten KC1 as follows  

From the above-mentioned studies [374, 375] it can be concluded that, up to now, systematic solubility investigations in molten potassium halides have not been performed. This also concerns other alkali-metal halide melts, although these results would be very useful for the estimation of the effect of melt acidity and anion composition on metal-oxide solubilities at 800 °C. 

Recently we have studied the oxide solubilities in molten KC1 at 800 °C [376]. An example of the potentiometric titration curve is depicted in Fig. 3.7.16 (curve 1), and the solubility data obtained by treatment of the titration results are presented in Table 3.7.18. The data collected in this table show that the order of arrangement of oxides according to increase in their 

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What we have said above especially concerns molten potassium halides, since the ionic radii of Ag+ and K+ are close. 

It may be assumed that for all the studied ionic melts, the behaviour of the E-pO calibration—dependence remains unchanged it has two sections with the slopes corresponding to values z — 1 and 2. The inflection point in the E-pO plots obtained in molten potassium halides at 800 °C is located at the pO value equal to 3 the slope values at high pO practically coincide with 1.15R77E (0.106 V), whereas in the strongly basic section the slopes of the dependences are somewhat lower than the theoretical one (2.3RT/F), which is equal to 0.212 V (see Table 2.4.6). 

We have also investigated the solubilities of MgO and CaO in molten potassium halides at 800 °C [197] to elucidate the effect of anion composition of the halide melt on metal-oxide solubility. The MgO was found to be practically insoluble in chloride and bromide melts, and the iodide-melt could not be investigated owing to intense iodine evolution from strongly acidic solutions. In contrast, CaO solubility products were determined successfully in all the potassium halide melts at 800 °C, by the potentiometric titration method. The corresponding potentiometric titration curves are shown in Fig. 3.7.16. 

The obtained solubility data are presented in Table 3.7.19. The oxide-solubility changes in molten potassium halides can be explained successfully in the framework of the HSAB concept. Indeed, Ca2+ ion belongs to the hard acids, whereas chloride ion is a hard base, bromide ion is an intermediate base and iodide ion is a soft base. Therefore, the stability of calcium hahde complexes should reduce in the chloride-bromide-iodide sequence. Since an increase in the halide complex s stability results in the elevation of the oxide solubility in the melts, one should expect a reduction in the solubility of... 

Parameters of Lux acid -base reactions in molten potassium halides at 800 °C (molar fractions)... 

The conception of the formation of hetero-ligand complexes and the nature of anion-anion interactions can be clarified using IR spectra of K2TaF7 - KX mixtures, where X = Cl, Br or I [356, 360]. Fig. 78 shows the spectral transformation due to the dilution of molten K2TaF7 with potassium halide. 

Tantalum powder is produced by reduction of potassium heptafluoro-tantalate, K2TaF7, dissolved in a molten mixture of alkali halides. The reduction is performed at high temperatures using molten sodium. The process and product performance are very sensitive to the melt composition. There is no doubt that effective process control and development of powders with improved properties require an understanding of the complex fluoride chemistry of the melts. For instance, it is very important to take into account that changes both in the concentration of potassium heptafluorotantalate and in the composition of the background melt (molten alkali halides) can initiate cardinal changes in the complex structure of the melt itself. 

Significant improvement of tantalum powder properties was achieved by the application of molten alkali halides as solvents for potassium heptafluorotantalate, K2TaF7. Variation of the initial concentration of K2TaF7 in the melt, stirring and rate of sodium loading enable a well-controllable production of tantalum powder with a wide variety of specific charges. Heller and Martin [590] proposed the use of a reactor equipped with a stirrer in 1960. Fig. 142 shows a typical scheme of the reactor [24, 576]. All metal parts of the reactor are made of nickel or nickel alloy. 

Apart from the fluoride, mercuric halides react explosively with potassium like all analogues of the other metals already mentioned. With mercurous salts, the reaction seems less violent since with mercurous chloride, molten potassium causes the mixture to incandesce without ever combusting. It is likely that other metals react too an extreme violent reaction was mentioned between indium and mercuric bromide. 

When an electrolyte which is without action on vanadium at ordinary temperatures (for example, dilute solutions of mineral acids, of oxalic acid, or of potassium halides) is electrolysed with a vanadium anode, a complex tetravalent vanadium ion is produced. Similarly, electrolysis at 100° C. and in molten chlorides of sodium or zinc gives rise to complex tetravalent vanadium ions. The E.M.F. in each case is found to be independent of the nature of the electrolyte. When, however, solutions of caustic soda or of caustic potash are employed, the vanadium dissolves as a pentavalent ion, irrespective of variations... 

Thermal parameters affecting the crystallization of sorbitol have been studied depending on conditions, two crystalline modifications can arise, and a process for the rapid crystallization of molten sorbitol was proposed. Compression parameters of crystalline xylitol have also been reported. The viscosity of concentrated aqueous solutions of sodium and potassium halides in presence of D-mannitol has been studied the viscosity was related to the structure-making or structure-breaking effect of the salt in solution. ... 

In the second part of the 20th century, the tantalum capacitor industry became a major consumer of tantalum powder. Electrochemically produced tantalum powder, which is characterized by an inconsistent dendrite structure, does not meet the requirements of the tantalum capacitor industry and thus has never been used for this purpose. This is the reason that current production of tantalum powder is performed by sodium reduction of potassium fluorotantalate from molten systems that also contain alkali metal halides. The development of electronics that require smaller sizes and higher capacitances drove the tantalum powder industry to the production of purer and finer powder providing a higher specific charge — CV per gram. This trend initiated the vigorous and rapid development of a sodium reduction process. 

Bismuth phthalocyanines of the type PcBiX can be prepared in solution by the reaction of bismuth(III) halides with PcLi2 or in a molten mixture of phthalonitrile and bismuth(III) halide.166 The sandwich-like complex [Pc2Bi]- can be obtained by slowly adding potassium methoxide to a melt of bismuth(III) oxonitrate and phthalonitrile.167... 

Catalytic elfects on the thermal decomposition and burning under nitrogen of the nitrate were determined for ammonium dichromate, potassium dichromate, potassium chromate, barium chloride, sodium chloride and potassium nitrate. Chromium(VI) salts are most effective in decomposition, and the halides salts during burning of the nitrate [1]. The effect of chromium compounds soluble in the molten nitrate, all of which promote decomposition of the latter, was studied (especially using ammonium dichromate) in kinetic experiments [2],... 

Binary Compounds. The thermodynamics of the formation of HfCl2, of HfCl4, fused sodium and potassium chlorides have been described. The reduction of ZrXj (X = Cl, Br, or I) with metallic Zr or A1 in molten AICI3 has been studied at temperatures from 250 to 360 °C, depending on the halide. The electronic spectra of the initial reaction products were consistent with either a solvated Zr complex or an intervalence Zr "-Zr" species. Further reduction resulted in the precipitation of reduction products which were identified by analysis and i.r., electronic, and X-ray powder diffraction spectra. The stability of the trihalides with respect to disproportionation was observed to increase from chloride to iodide thus ZrC and ZrCl2,0.4AlCl3 were precipitated, whereas only Zrlj was formed. ... 

Hafnium tetrachloride combines with molten sodium chloride, potassium chloride, or other alkali halides to form addition products such as 2NaCl HfCl4, which decompose at higher temperatures. 

As has already been pointed out, the Finkelstein reaction can be conducted in situ in the absence of solvents. For example, alkylations of purine and pyrimidine bases with alkyl halides and dimethyl sulfate have been carried out by solid/liquid phase-transfer catalysis in the absence of any additional solvent [48], as have cyanation of haloalkanes [49] and / -eliminations [50]. Noteworthy is the synthesis of glycosyl isothiocyanates by the reaction of potassium thiocyanate with molten glycosyl bromide at 190 °C [51]. 

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