Ternary Molten Salt Systems Research Articles

First‐Principles Molecular Dynamics Study on Ionic Structure and Transport Properties of NaCl‐MgCl2‐CaCl2 Ternary Molten Salt System

AbstractThe carbochlorination in molten salt is an effective method for titanium extraction form low‐grade titanium slag with a high calcium and magnesium content. However, in industrial practice, the fluidity of molten salt will gradually decrease with the increase of CaCl2 content. It is important to elucidate the influencing mechanism of CaCl2 content on the microstructure and diffusion properties of molten salt for the rational selection of a molten salt system and clean utilization of titanium slag. In this study, the densities of molten salt systems with different CaCl2 contents are measured according to the Archimedes principle. Then, using the first‐principles molecular dynamics (FPMD) method, the ionic structure and transport properties of NaCl‐MgCl2‐CaCl2 ternary molten salt systems under different CaCl2 contents are qualitatively and quantitatively described by determining the partial radial distribution functions (PRDF), coordination number (CN), angular distribution functions (ADF), and diffusion coefficient (DC). The results show that with the addition of CaCl2, Ca2+ ion complexed with Cl− ion to form larger ionic clusters, which reduced the proportion of free Cl− ion and restricted the diffusion of Cl− ion.

Electrochemical preparation of W coatings in Na2WO4-WO3-ZrO2 molten salt

In this paper, the flat tungsten coatings with uniform grains were prepared via electrolytic tungsten at 1173 K in ternary molten salt system formed by tungstate, tungsten oxide and different mass fractions of ZrO2. Dense tungsten coatings containing the second phase of ZrO2 were obtained by constant direct current electrodeposition in molten salt, and the coatings have preferential growth orientation along the (2 1 1) crystal plane. These coatings were characterized via X–ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and laser scanning confocal microscope (LSCM). The results show that W-ZrO2 coating obtained at Na2WO4-WO3-ZrO2. In addition, the existence of zirconia in molten salt reduced the coating roughness from 13.567 μm to 3.017 μm, the current efficiency was lost from 84.15% to 70.76%, and the grains became fine and uniform. What’s more, the mechanical properties and thermal cycle performance of the coating have been effectively improved. To further illustrate the electrochemical process, the electrochemical behavior of tungsten ions and zirconium ions during the electrodeposition was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). The results indicated that the reduction reactions of tungsten ions and zirconium ions are divided into two steps, and the reaction processes are as follows: W(VI) → W(IV) → W, Zr(IV) → Zr(II) → Zr.

Improvement of Electrochemical Stability Using the Eutectic Composition of a Ternary Molten Salt System for Highly Concentrated Electrolytes for Na-Ion Batteries.

The increase in the concentration of electrolytes for secondary batteries has significant advantages in terms of physicochemical and electrochemical performance. This study aims to explore a highly concentrated electrolyte for Na-ion batteries using a ternary salt system. The eutectic composition of the Na[N(SO2F)2]-Na[N(SO2F)(SO2CF3)]-Na[SO3CF3] ternary molten salt system increases solubility into an organic solvent, enabling the use of highly concentrated electrolytes for Na-ion batteries. The ternary salt system achieved concentrations of 5.0 m (m = mol kg-1) with propylene carbonate (PC), 2.9 m with dimethoxyethane, 2.0 m with ethylene carbonate/dimethyl carbonate, and 3.9 m with ethylene carbonate/diethyl carbonate. The highly concentrated electrolyte of 5.0 m in PC suppressed Al corrosion and exhibited better oxidative stability. Stable electrochemical performance using hard carbon/NaCrO2 in the full-cell configuration introduces a new strategy to explore highly concentrated electrolytes for secondary batteries.

Application of geometric models for calculation of viscosity and density of LiNO3 and CsNO3 based ternary nitrate salt systems

Determining the thermophysical properties of ternary molten salt systems accurately is a challenging task as it incorporates experimentation at high temperatures, cost of running the experiments, and complexity due to material interactions. Modelling of these properties can overcome most of these difficulties. In this paper, various geometric models were used for determining the density and viscosity of two ternary nitrate salt systems viz. LiNO3–NaNO3–KNO3 and CsNO3–NaNO3–KNO3. On comparison, it was observed that the General Solution Model (GSM) developed by K.C. Chou predicts better results for both density and viscosity of the salts. The density prediction of the salt systems using GSM recorded an error less than 2%, while the prediction of viscosity showed a variation of 17–20%.

Preparation of Two-dimensional Ti2CTx by Molten Fluorinated Salt Method

We prepared a two-dimensional transition metal carbide Ti2CTx by treatment of Ti2AlC in molten fluoride salt. Two fluorinated salt systems were used to etch Al from Ti2AlC powder precursor under the argon atmosphere, and then the resulting MXene was delaminated with TBAOH to produce few-layered nanosheets of Ti2CTx. The reaction was undergone at different temperatures to study the effect of temperature. The results show that the optimal reaction temperature is 600 °C in LiF-NaF-KF system, and 850 °C in NaFKF system. The molten salt treated products are delaminated and quasi-2D MXene sheets can be obtained. The thickness of the MXene sheets prepared from the binary molten salt system is smaller than that of the ternary molten salt system.

Discharge behavior of Li-Mg-B alloy/MnO2 couples with LiNO3-KNO3-Mg(OH)NO3 eutectic electrolyte

A novel LiNO3-KNO3-Mg(OH)NO3 ternary molten salt system is used as electrolyte with Li-Mg-B alloy/MnO2 couples for possible use as a power source for geothermal borehole applications. Chemical-compatibility studies of these materials are conducted using simultaneous differential thermal analysis (DTA) and thermo gravimetric analysis (TGA). The ionic conductivity of the new electrolyte has been evaluated by electrochemical impedance spectroscopy (EIS) and its value range from 0.107 to 0.457 Scm−1 in the temperature range from 150 to 300°C. The discharge behavior of the system is studied over a temperature range of 150 to 300°C at current densities from 10 to 30mAcm−2. At 200 to 300°C, discharge behavior seems unaffected by discharge rate. However, the system has some specific restrictions associated with temperature.

Thermodynamic performance of the NaNO3–NaCl–NaNO2 ternary system

Calculations of phase diagram for additive ternary molten salt system are carried out by the conformal ionic solution theory. The liquidus temperatures of the system NaNO3–NaCl–NaNO2 are determined according to different types of solid–liquid equilibrium and different values of the binary interaction coefficients. For the system NaNO3–NaCl–NaNO2, the calculated and experimental temperatures differ are very small below 673 K, but the oxidation and decomposition of the mixed salts are found when the temperature is higher than 673 K. Meanwhile, the eutectic point is obtained from calculated phase diagram and the eutectic temperature is 507 K. Thermal stability of this eutectic mixture is investigated by thermo-gravimetric analysis device. Experimental results show this kind of molten salt has a lower melting point (501.28 K), similar to solar salt (493 K). It is thermally stable at temperatures up to 819 K, and may be used up to 827 K for short periods.

Evaluation of Static Thermophysical Properties of the Ternary Molten Salt System Li, Na and Be/F Based on the Modified Peng-Robinson Equation

Evaluation of Static Thermophysical Properties of the Ternary Molten Salt System Li, Na and Be/F Based on the Modified Peng-Robinson Equation

Estimation of thermodynamic properties of the ternary molten salt system, LiF-NaF-BeF2, by the modified Peng-Robinson equation

The molten salt reactor (MSR), which is one of the generation IV reactors, can meet the demand of transmutation and breeding. The thermodynamic properties of the molten salt system like LiF-NaF-BeF2 influence the design and construction of the fuel salt and coolant in the MSR for the new generation. In this paper, the equation of state of the ternary system 15%LiF-58%NaF-27%BeF2, over the temperature range from 873.15 to 1 073.15 K at one atmosphere pressure, is described using a modified Peng-Robinson (PR) equation. The densities of the ternary system and its components are estimated by this equation directly, and compared with the experimental data. Based on the equation of state, the other thermodynamic properties such as the enthalpy, entropy and heat capacity at constant pressure are estimated by the residual function method and the fugacity coefficient method respectively. The densities calculated by PR equation are highly in agreement with the experimental data, and the enthalpy, entropy and heat capacity evaluated by the two different methods are consistent with each other. It can be concluded that the modified PR equation can be applied to evaluate the density of the molten salt system, and it is recommended that it be used as the basis to estimate the enthalpy, entropy and heat capacity of the molten salt system.

Redox reaction in 1-ethyl-3-methylimidazolium–iron chlorides molten salt system for battery application

The redox reaction between divalent and trivalent iron species in binary and ternary molten salt systems consisting of 1-ethyl-3-methylimidazolium chloride (EMICl) with iron chlorides, FeCl 2 and FeCl 3, was investigated as a candidate of the half-cell reactions of novel rechargeable redox batteries based on low temperature molten salt systems. A reversible one-electron redox reaction between divalent and trivalent iron species was observed on a platinum electrode in EMICl–FeCl 2–FeCl 3 system at 130 °C. The voltammetric data indicated that divalent and trivalent iron species were FeCl 3 − and FeCl 4 − complex anions, respectively. Combined with another proper redox couple, this molten salt system can be utilized in a rechargeable redox battery on account of its low melting temperature and reversible redox reaction.

Thermodynamic Properties of MgCl2 ‐ NaCl ‐ LiCl Melts by EMF Measurements

The ternary molten salt system has been accurately studied by EMF measurements of a reversible electrochemical formation cell. The corresponding thermodynamic properties were fit to empirical power series as functions of composition. The data compare well with a model which assumes the existence of the complex in the melt.

Molar Volume and Electrical Conductivity Measurements in the Ternary Molten Salt System NaCl ‐ CsCl ‐ MnCl2: II . Electrical Conductivities

Electrical conductivities in the ternary molten salt system have been measured in U‐tube capillary‐type cells over the entire ternary composition range and at temperatures varying between 510° and 1054°C. Molar conductivity and apparent activation energies for the process have been calculated. The relationship obeyed by some of the thermodynamic properties for this system (10) is not applicable to electrical conductivities. The concentration dependence of the molar conductivity indicates the presence of complex species in this system.

Charge Asymmetrical Ternary Molten Salt Systems: Theory of Dilute Solutions

The thermodynamic properties of dilute solutions of in the ternary system have been investigated by the measurement of the reversible emf of the formation cellThe partial molar properties of have been found to be in good agreement with values predicted by the complex‐ion model reported in previous publications from this laboratory (1–3). In the present paper it is shown that these rather involved expressions reduce to useful, simple equations of the formwhere represents either an integral or a partial molar property. The ternary solution is denoted by the subscripts 1,2,3, while the two binaries, each containing the reactive‐metal chloride, are denoted by 1,2 and 1,3; is a concentration variable. It is also shown that the following expression applies to the activity of the reactive‐metal chloride (component 1) in solutionFor dilute solutions obeying Henry's law, the activity coefficients are given bywhere is the Henrian activity coefficient in the binary i,k and is the mole fraction of present in the ternary solution, providing that in the ternary 1,2,3 is the same as that in the two binary solutions 1,2 and 1,3.

Additive Ternary Molten Salt Systems—Calculation of Phase Diagrams from Thermodynamic Data of Lower Order Systems

Calculations of the liquidus temperatures of additive ternary molten salt systems are carried out from the conformal ionic solution theory (up to second order terms). The comparison between measured and calculated phase diagrams is made for five systems chosen according to different types of liquidus and different values of the binary interaction coefficients. For most cases, and in particular when solid solutions are not reported, the agreement between measurements and calculations is found to be very good. In the search for low melting electrolytes for electrochemical applications, these equations should prove useful in predicting the range of compositions where low liquidus temperatures are most likely.

Theory of Enthalpy of Mixing in Reactive Charge Asymmetrical Molten Salt Systems. Part II. Ternary Solutions

The enthalpies of mixing for a reacting charge asymmetrical ternary molten salt system have been calculated on the basis of an extension of a previously developed model for binary systems. The enthalpy of mixing is considered to consist of a reaction term and a mixing term; the former results from the formation of the tetrahedrally coordinated complex species [Formula: see text] and the latter from the mixing of the products of reaction according to quasichemical theory modified to account for charge asymmetry.The ternary model enables the prediction of the integral enthalpies from a knowledge of the interaction parameters determined for the two charge asymmetrical binary systems. The calculations are compared with experimentally measured integral enthalpies of mixing in the ternary system MnCl2–NaCl–CsCl, and shown to give accurate predictions of the behaviour of the system.

Emf measruements in additive ternary molten salt systems lead chloride-potassium chloride-sodium chloride and lead chloride-cesium chloride-sodium chloride

Emf measruements in additive ternary molten salt systems lead chloride-potassium chloride-sodium chloride and lead chloride-cesium chloride-sodium chloride

Thermodynamic treatment and electromotive force measurements of the ternary molten salt systems silver chloride-sodium chloride-potassium chloride and silver chloride-sodium chloride-cesium chloride

Thermodynamic treatment and electromotive force measurements of the ternary molten salt systems silver chloride-sodium chloride-potassium chloride and silver chloride-sodium chloride-cesium chloride

The topology of phase diagrams of ternary molten salt systems

Phase diagrams of simple ternary reciprocal salt systems are compared with calculations from recent statistical mechanical theories. The major topological features are predicted from the theory. The comparison of theory with experimental phase diagrams gives an insight into the fundamental ionic interactions which lead to particular topological features. A theoretical expression for predicting miscibility gaps in these systems is shown to provide a fundamental explanation of the empirical rules deduced by previous workers. Certain regions of composition in additive (ordinary) ternary systems are analogous to reciprocal systems and the analogy helps in understanding some of the topological properties of these additive ternary systems including miscibility gaps within the ternary composition triangle.