Electrical conductivity of salt melts, containing zirconium tetrachloride

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Abstract

The present paper presents an overview of the available experimental data (both our data and provided by other researchers) on the electrical conductivity of ZrCl₄–containing salt melts, for which the saturated vapor pressure of ZrCl₄ above them is P ⩽ 1 atm. These melts have a significant practical application potential. Such mixtures are divided into high‒temperature mixtures with a ZrCl₄ concentration of 0‒30 mol. %, and low‒temperature ones, with a narrower ZrCl₄ content range of 50‒75 mol. %. Based on the obtained experimental data it was found that the electrical conductivity of all molten ZrCl₄–containing mixtures increases as the temperature increases, zirconium tetrachloride concentration decreases, and the molten solvent salt is replaced in the row from CsCl to LiCl. The experimental data obtained are summarized and discussed taking into account the available information on the structure of the molten mixtures. Electrical conductivity of high–temperature MCl‒ZrCl₄ melts (0‒30 mol. % ZrCl₄; M is an alkali metal), is in the range of 0.6–3.1 Cm/cm, which is significantly higher than the electrical conductivity of low–melting molten mixtures of the same chlorides (0.1‒0.5 Cm/cm) with a high content of ZrCl₄ (55‒75 mol. %). It has been found that the use of low‒melting salt solvents, for example, LiCl–KCl eutectic, makes it possible to expand the range of existence of ZrCl₄‒containing melts by hundreds of degrees towards lower temperatures and saturated vapor pressures at sufficiently high values of electrical conductivity (0.9–2.8 Cm/cm). This provides additional advantages for the organization of various technological processes.

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A. B. Salyulev

Institute of High‒Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences

Author for correspondence.
Email: salyulev@mail.ru
Russian Federation, Yekaterinburg

А. M. Potapov

Institute of High‒Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences

Email: salyulev@mail.ru
Russian Federation, Yekaterinburg

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2. Салюлев_статья
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3. Fig. 1. Phase diagram of the NaCl–ZrCl₄ system [7, 13].

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4. Fig. 2. Polytherms of electrical conductivity of melts of pure salts‒solvents (without ZrCl₄ additives) [15, 19–23].

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5. Fig. 3. Polytherms of electrical conductivity of molten and heterogeneous (crystal + melt) mixtures of zirconium tetrachloride with alkali metal chlorides [10, 13, 14] with ZrCl₄ concentrations: 10 mol. % – in LiCl, NaCl–KCl (1:1), KCl and CsCl; 10.5% – in NaCl; 11% – in (LiCl–KCl)eut.

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6. Fig. 4. Polytherms of electrical conductivity of molten and heterogeneous (crystal + melt) mixtures of zirconium tetrachloride with alkali metal chlorides [10, 13, 14] with ZrCl₄ concentrations: 20 mol. % in LiCl, NaCl–KCl (1:1), KCl and CsCl; 20.5% in NaCl; 21% in (LiCl–KCl)eut.

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7. Fig. 5. Polytherms of electrical conductivity of molten and heterogeneous (crystal + melt) mixtures of zirconium tetrachloride with alkali metal chlorides [10, 13, 14] with ZrCl₄ concentrations: 25 mol. % in LiCl, NaCl–KCl (1:1) and KCl; 25.5% in NaCl and (LiCl–KCl)eut.; 30% in CsCl.

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8. Fig. 6. Polytherms of electrical conductivity of low-temperature molten and heterogeneous (crystal + melt) mixtures of zirconium tetrachloride with alkali metal chlorides [11,12,31].

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9. Fig. 7. Isotherms of specific electrical conductivity of ZrCl₄ solutions in molten chlorides of various alkali metals at 700°C [10,13,14] (in molten LiCl at 580°C [10]).

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10. Fig. 8. Isotherms of specific electrical conductivity of molten mixtures of KAlCl₄ – ZrCl₄ [15, 23].

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11. Fig. 9. Isotherms of specific electrical conductivity of molten mixtures of ZnCl2 – ZrCl₄ [38].

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