KCl Eutectic Mixture Research Articles

CsCl enrichment during solidification of molten LiCl–KCl–CsCl salt mixture

Metallic alloy fuels from fast reactors will be reprocessed by a non-aqueous electrochemical technique known as electrorefining. Electrorefining of spent metal fuel results in the accumulation of heat generating fission products especially 137Cs in the electrolyte, which is a eutectic salt mixture of 44 wt% LiCl and 56 wt% KCl. The fission products need to be removed from the salt so as to reduce the decay heat load and contamination thereby facilitating reuse of the salt and minimizing waste generation. Melt crystallization technique is a simple separation process being pursued for separation of fission products. This is a single step process which utilizes the difference in solubility of fission products in the solid and liquid phase. Crystallization involves purification of a substance from a liquid mixture by solidification of the desired component. Numerical modeling of separation of CsCl from a LiCl–KCl eutectic mixture by solidification was carried out using ANSYS Fluent (19.2). The enrichment of CsCl during solidification, its distribution in molten salt and segregation time were evaluated. Further, solidification experiments were conducted using the molten salt mixture and the predicted numerical results were validated.

Molten salt synthesized La- substituted CaTiO3 thermoelectric ceramics

Benefiting from molten salts as reaction media, molten salt synthesis (MSS) offers advantages such as control of local reaction conditions to tailor material characteristics, the production of uniform and homogeneous crystallites, as well as reduced energy consumption and emissions. In this study, we successfully synthesized regular polyhedral La-substituted CaTiO3 with an orthorhombic perovskite structure under molten salt conditions, utilizing a NaCl–KCl eutectic mixture at 1073 K for 6 h. The phase compositions of the prepared samples were determined through powder X-ray diffraction (XRD), and their morphologies were characterized via scanning electron microscopy (SEM). Our investigation of the thermoelectric properties reveals that the substitution of La3+ ions significantly enhances electrical conductivity and simultaneously introducing defects that substantially reduce lattice thermal conductivity. We achieved a maximum thermoelectric figure of merit (ZT) of approximately 0.27 at about 1200 K for the sample with a nominal composition of Ca0.8La0.2TiO3. This study is intended as a reference to experimentalists working in MSS for synthesizing CaTiO3-based ceramics and discloses the transport properties of La-doped CaTiO3-based ceramics.

Effect of excess Mg to control corrosion in molten MgCl2 and KCl eutectic salt mixture

Structural alloys may experience corrosion when exposed to molten chloride salts due to selective dissolution of active alloying elements. One way to prevent this is to make the molten salt reducing. For the KCl + MgCl2 eutectic salt mixture, pure Mg can be added to achieve this. However, Mg can form intermetallic compounds with nickel at high temperatures, which may cause alloy embrittlement. This study shows that an optimum level of excess Mg could be added to the molten salt which will prevent corrosion of alloys like 316 H, while not forming any detectable Ni-Mg intermetallic phases on Ni-rich alloy surfaces.

Molten salt synthesis of nano structured pyrochlore lanthanum zirconate: a potential material for high temperature applications

Molten salt synthesis of nanocrystalline pyrochlore lanthanum zirconate (La2Zr2O7) powders with NaCl–KCl alone as reaction aid was prepared in the present investigation with low synthesis temperature for the first time. The structural and morphological data of the synthesized lanthanum zirconate powder was characterized using XRD, FESEM—EDS and TEM. Functional group identification was carried out using FT-Ir and simultaneous themal analysis on the starting material was also carried out characterized by thermogravimetric analysis and differential thermal analysis. Simultaneous thermal analysis of the starting materials was carried out and the results show the suitability of the molten salt synthesis below 900 °C. The XRD pattern reveal the existence of pyrochlore structure La2Zr2O7 matches with the standard ICDD pattern. The average crystallite size was measured to be 34.66 nm by Debye Scherer formula and 35.53 nm using WH plot. The particle size measured using the particle size analyser, scanning electron microscope and transmission electron microscope shows in the order of 40–50 nm and the powders are seen clearly without agglomerations. Energy dispersive spectrum results show the clear presence of La–Zr–O without any other inclusions and confirms the results obtained through x-ray photo emission spectroscopy. SAED pattern obtained through TEM shows the polycrystalline nature of the synthesised nano La2Zr2O7. The structural functional group evolution was examined using FT-Ir confirms the formation of La–Zr–O chemical bonds. The results confirms that nano crystalline pyrocholore La2Zr2O7 can be successfully synthesised using relatively low temperature molten salt route at 850 °C with the aid of anhydrous NaCl–KCl eutectic salt mixture alone as reaction aid and anhydrous La2O3 and ZrO2 as precursors.

Preparation and Thermal Performance Enhancement of Low Temperature Eutectic Composite Phase Change Materials Based on Na₂SO₄·10H₂O.

In this paper, a series of Na2SO4·10H2O–KCl eutectic mixtures were prepared by adding different mass fractions of KCl (1 wt.%, 3 wt.%, 5 wt.%, or 7 wt.%) to Na2SO4·10H2O. Polyacrylamide (PAM) was proposed as the thickener, sodium tetraborate decahydrate (STD) was proposed as the nucleating agent, and expanded graphite (EG) was proposed as the high thermal conductivity medium for Na2SO4·10H2O–5 wt.% KCl eutectics. The results showed that in Na2SO4·10H2O–5 wt.% KCl eutectics with 5 wt.% PAM and 5 wt.% STD, almost no phase separation occurred, and the degree of supercooling was reduced to 0.4 °C. The thermal performance of Na2SO4·10H2O–5 wt.% KCl composite phase change materials (CPCMs) with varying contents of EG was explored. The results showed that EG could improve the thermal conductivity effectively and that the mass fraction of EG should be no more than 3%, otherwise the crystallization value and supercooling would deteriorate. The thermal reliability of the Na2SO4·10H2O–5 wt.% KCl eutectic CPCMs containing 5 wt.% PAM, 5 wt.% STD, and 3 wt.% EG was investigated, mainly through the ambient temperature, thermal cycling test, and TGA analysis. The results demonstrated that these CPCMs showed perfect thermal reliability.

Molten salt synthesis of LaCoO3 perovskite

LaCoO3 perovskite was successfully synthesized in molten NaCl–KCl eutectic mixture. Heating the La-nitrate, Co-nitrate and NaCl–KCl mixture to 800 °C yielded large (up to 5 microns) LaCoO3 cubic particles. Conversely, when La- and Co-nitrates were fed into the NaCl–KCl mixture, molten and stabilized at 800 °C, much smaller (sub-micron) particles were obtained. These results expound the mechanistic aspects of the perovskites formation in molten salts involving nucleation and crystal growth phenomena.

Deep Oxidation of Fluorinated Hydrocarbons in Molten Catalysts

<p>The oxidation of fluorine-containing organic substances: fluorocarbon liquid M-1, fluorinated alcohol H(CF<sub>2</sub>)<sub>8</sub>CH<sub>2</sub>OH, and powder polytetrafluoroethylene with air has been studied in melts: NaOH; 43 mol.% LiCl - 33 mol.% NaCl - 24 mol.% KCl (eutectic mixture); (LiCl-NaCl-KCl)eutec. + 10 mass.% V<sub>2</sub>O<sub>5</sub>; (LiCl-NaCl-KCl) eutec. + 15 mass.% V<sub>2</sub>O<sub>5</sub>; 56 mol.% Na<sub>2</sub>CO<sub>3</sub> - 44 mol.% K<sub>2</sub>CO<sub>3</sub> (eutectic), (Na<sub>2</sub>CO<sub>3 </sub>K<sub>2</sub>CO<sub>3</sub>)eutect. + 15 mass.% V<sub>2</sub>O<sub>5</sub>, and K<sub>3</sub>V<sub>5</sub>O<sub>14</sub>. The compositions of the melts have been examined by GC, DTA, chemical analysis and XRD, and they have been shown to change during the reaction, depending on the composition and partial pressure of the gaseous products over the melt surface. The alkali metal chloride melt containing 15 mass.% V<sub>2</sub>O<sub>5</sub> has been found to be most stable to the action of fluorine compounds. Possibility of deep oxidation of fluorine-containing organic substances in melts based on hydroxides, carbonates and chlorides of alkali metals doped with oxides of vanadium has been proved. The process of deep oxidation of fluorinated hydrocarbons is accompanied by formation of an equilibrium mixture containing hydroxides, carbonates, chlorides and fluorides of alkali metals, as well as their vanadates, if V<sub>2</sub>O<sub>5</sub> additive is used. The relative amounts of these substances in molten systems are determined by the partial pressure of oxygen, CO<sub>2 </sub>and water vapor.</p>

High-quality spinel LiCoTiO4single crystals with co-exposed {111} and {110} facets: flux growth, formation mechanism, magnetic behavior and their application in photocatalysis

Novel spinel LiCoTiO4 single crystals with co-exposed {111} and {110} facets were grown for the first time using a facile LiCl flux method. The obtained cubic-phase LiCoTiO4 crystals exhibit high crystallinity and regular octahedron-like geometric morphology. In this method, LiCl was used not only as an effective lithium source without any additives but also as the optimum molten medium compared with LiCl–NaCl and LiCl–KCl eutectic mixtures. The formation mechanism responsible for the flux-grown spinel LiCoTiO4 crystals with co-exposed {111} and {110} facets was also proposed. Moreover, the spinel LiCoTiO4 crystals showed a weak ferrimagnetic behavior with some antiferromagnetic effects. Photocatalytic tests revealed that the pure LiCoTiO4 sample had a relatively low photocatalytic activity although it had a relatively narrow band-gap energy (1.58 eV) corresponding well to the broad visible spectrum. However, the spinel LiCoTiO4 crystal could serve as an efficient visible-light sensitizer, and when coupled with graphitic carbon nitride (g-C3N4) nanosheets, the novel LiCoTiO4/g-C3N4 composites exhibited higher activity than pure g-C3N4 for the photocatalytic degradation of organic pollutants under simulated sunlight. A possible mechanism for the improved photocatalytic performance was also proposed. Overall, our present work opens a new approach to fabricating other lithiated transition-metal oxide spinel crystals for broad industrial applications.

Electrochemical Formation and Phase Control of Mg–Cu Alloys

AbstractMg–Cu alloys with different phases were electrodeposited in a molten LiCl–KCl eutectic mixture containing a small amount (0.5 mol %) of MgCl2 at 673 K. The electrochemical behavior of the MgII ion and alloy formation processes were studied at inert molybdenum (Mo) and active copper (Cu) electrodes in the molten salts, respectively. Different electrochemical techniques, such as cyclic voltammetry, square‐wave voltammetry, chronoamperometry, and open‐circuit potentiometry were carried out to investigate the electrochemical formation mechanism of Mg–Cu alloys. Three signals, corresponding to the formation of metal Mg and two different Mg–Cu alloy phases, are observed when using cyclic voltammetry, square‐wave voltammetry, and open‐circuit potentiometry. Chronoamperometry studies indicate the different interfacial properties of the magnesium metal versus the Mg–Cu alloys. The results of X‐ray diffraction and scanning electron microscopy show that the MgCu2 and Mg2Cu phases could be obtained at −2.30 and −2.38 V (vs. Pt), respectively.

High dispersibility and enhanced luminescence properties of BaMgAl10O17:Eu2+ phosphors derived from molten salt synthesis

BaMgAl10O17:Eu2+ (BAM) phosphors were prepared via the molten salt synthesis (MSS) method. The NaCl–KCl eutectic mixture and LiF were used as the molten salt and flux, respectively. X-ray powder diffraction (XRD) patterns indicate that the BAM phase is formed above 1200°C and that the addition of LiF leads to an obvious improvement in crystallinity. The emission intensity of the BAM phosphor with 10wt% LiF is about 85% higher than that of the phosphor without LiF and about 200% higher than that of the phosphor without molten salt and LiF. Scanning electron microscopy (SEM) reveal that the as-prepared phosphors have good crystallinity and regular morphology, and most importantly, they are not aggregated. Li+ doping is benefit for the thermal stability and results in a slightly longer decay times of 1.17μs.

Low temperature synthesis of nano-crystalline gadolinium titanate by molten salt route

Nano-crystalline Gadolinium Titanate (Gd 2 Ti 2 O 7 ) powder was successfully synthesized by “ Single Step Molten Salt Technique ”. LiCl–KCl eutectic mixture was used as a molten medium for the reaction. The duration of the synthesis was 10 h. Stoichiometric proportion of the reactants were mixed in an (LiCl–KCl) eutectic medium and treated at 750 °C in an electrical resistance furnace. Single phase Gadolinium Titanate compound was obtained by the thermal process. The synthesized powders were characterized using XRD, FT-IR, UV, EDAX and XPS analyses. The morphology of the powder was examined using SEM and TEM techniques. From the above studies, it has been concluded that pure crystalline Gadolinium Titanate powders can be synthesized via low temperature molten salt process.

Synthesis of LaMnO3 in molten chlorides: effect of preparation conditions

LaMnO3 perovskite was successfully synthesized in molten chlorides. In order to explore the effect of the molten salt type, NaCl-KCl and LiCl-KCl eutectic mixtures were employed as a liquid medium for the perovskite formation process. The synthesis included heating the La-nitrate, Mn-nitrate and chlorides mixture to above the melting point of the corresponding chlorides. This procedure yielded a LaMnO3 phase integrated in the fused chloride matrix. Washing with water removed the salts completely, yielding pure LaMnO3 perovskite crystals. The synthesis without molten salt at 800 °C yielded several by-products in addition to the LaMnO3 phase, while with LiCl-KCl the pure perovskite phase was obtained at temperatures as low as 600 °C. Variation of temperature in the range 600-800 °C for LiCl-KCl and 700-800 °C for NaCl-KCl had no significant effect either on the morphology or on the particle size of the product. On the other hand, the effect of the molten salt type on the morphology and size of perovskite particles was remarkable. The synthesis in NaCl-KCl resulted in sub-micron LaMnO3 particles with shapes that range from truncated hexahedrons to spheres, while in LiCl-KCl mostly cubic particles of up to 2-microns were obtained. The effect of the molten salt type on LaMnO3 perovskite formation is explained based on the nucleation and crystal growth model and difference in the melting point of eutectic mixtures.

Photovoltaic performance of dye sensitized solar cell based on rutile TiO 2 scaffold electrode prepared by a 2 step bi-layer process using molten salt matrices

Dye sensitized solar cells were made on TiO 2 scaffold anodes of rutile particles. These TiO 2 scaffold anodes were grown from rutile seeds by using a molten salt synthesis technique. Different thickness coatings of mixed amorphous titanium hydroxide and NaCl–KCl eutectic salt mixture on the rutile seeds were heat treated at different temperatures. The rutile whiskers of different aspect ratios were grown depending on the growth temperature. The best photovoltaic performances were obtained for the device made from the scaffold of 20–50 nm diameter and 0.5–1 μm length nanowhiskers obtained at 700 °C for 5 h of treatment.

Synthesis of TiO 2 scaffold by a 2 step bi-layer process using a molten salt synthesis technique

TiO 2 scaffolds of anisotropic rutile particles were grown from rutile seeds by using molten salt synthesis techniques. The rutile seeds were either in the form of a separate layer applied on a substrate or a sintered bulk pellet. Mixtures of amorphous titanium hydroxide and salt applied as coatings on the rutile seeds were heat treated. Depending on the morphology of the seed layer, heat treatment temperature, time and salt medium, rutile was grown with different morphologies and microstructures. For NaCl–KCl eutectic salt mixture and heat treatment at 700 °C for 5 h, nano-whiskers of 20–50 nm diameter and 0.5–1 μm length were obtained. For the NaCl salt sample treated at 850 ºC for 20 h, rutile platelets of 2–5 μm thick, 2–10 μm wide and 5–25 μm in length were produced. X-ray diffraction and Raman scattering were used to identify and characterize the rutile phase of the nanowhiskers.

Effect of Addition of Multi-Component Lanthanides to LiCl-KCl Eutectic on Thermal and Electrochemical Properties

Pyrochemical or pyrometallurgical processing using LiCl-KCl molten salt systems is considered one of the alternatives to the PUREX process for safe and proliferation resistant recovery of nuclear fuel elements from the spent fuels. Most of the available thermodynamic data on the molten salt systems pertain to binary or ternary systems. When multiple fission product elements are present in the electrolyte, the reduction behavior of the actinides could be significantly altered because of possible under potential reduction of lanthanides and slower diffusion kinetics of actinides. This presentation reports the variations in melting point and electrochemical behavior of LiCl + KCl eutectic mixture containing multi-components of RECl3 additions. No significant change in the melting temperature was observed with the addition of multiple lanthanide chlorides o the LiCl-KCl eutectic. However, the reduction potential was shifted in the positive direction with the addition of multiple lanthanides, especially when CeCl3 was one of the constituent.

Molten Salt Synthesis of Bi4(V0.85Co0.15)2O11−δ (BICOVOX) Ceramic Powders

Cobalt (15 at.%)‐doped bismuth vanadate, Bi4(V0.85Co0.15)2O11−δ (BICOVOX) is known to have high oxygen ion conduction. However, the conductivity is highly anisotropic due to its layered structure. In this paper, we report the synthesis of BICOVOX powders with platelet habit by molten salt synthesis using a NaCl–KCl eutectic mixture as the reaction medium. The effects of treatment temperature and time on the morphology and phase content of the BICOVOX powders were investigated. By this method, it is possible to synthesize powders with platelets of major face dimension ∼50 μm and aspect ratio (major face dimension to thickness) as high as 15.

Molten salt synthesis of lead lanthanum zirconate titanate ceramic powders

Lead lanthanum zirconate titanate (Pb 0.95La 0.03)(Zr 0.52Ti 0.48)O 3 (PLZT) was synthesized by one step molten salt method with the starting materials of PbC 2O 4, La 2O 3, ZrO(NO 3) 2·2H 2O and TiO 2 in the NaCl–KCl eutectic mixtures in the temperature range of 700–1000 °C. The single phase of (Pb 0.95La 0.03)(Zr 0.52Ti 0.48)O 3 powders was prepared at a temperature as low as 850 °C for 5 h. The effects of process parameters, such as soaking temperature and time, salt species, and the amount of flux with respect to the starting materials were investigated. The growth process of the PLZT particles in the molten salt undergoes a transition from a diffusion controlled mechanism to an interfacial reaction controlled mechanism at 900 °C.

Electrochemical studies on plutonium in molten salts

Electrochemical studies on plutonium have been supporting the development of pyrochemical processes involving plutonium at CEA. The electrochemical properties of plutonium have been studied in molten salts – ternary eutectic mixture NaCl–KCl–BaCl 2, equimolar mixture NaCl–KCl and pure CaCl 2 – and in liquid gallium at 1073 K. The formal, or apparent, standard potential of Pu(III)/Pu redox couple in eutectic mixture of NaCl–KCl–BaCl 2 at 1073 K determined by potentiometry is equal to −2.56 V (versus Cl 2, 1 atm/Cl − reference electrode). In NaCl–KCl eutectic mixture and in pure CaCl 2 the formal standard potentials deduced from cyclic voltammetry are respectively −2.54 V and −2.51 V. These potentials led to the calculation of the activity coefficients of Pu(III) in the molten salts. Chronoamperometry on plutonium in liquid gallium using molten chlorides – CaCl 2 and equimolar NaCl/KCl – led to the determination of the activity coefficient of Pu in liquid Ga, log γ = −7.3. This new data is a key parameter to assess the thermodynamic feasibility of a process using gallium as solvent metal. By comparing gallium with other solvent metals – cadmium, bismuth, aluminum – gallium appears to be, with aluminum, more favorable for the selectivity of the separation at 1073 K of plutonium from cerium. In fact, compared with a solid tungsten electrode, none of these solvent liquid metals is a real asset for the selectivity of the separation. The role of a solvent liquid metal is mainly to trap the elements.

Molten salt synthesis of lead lanthanum zirconate titanate stannate powders and ceramics

Powders and ceramics with a composition (Pb 0.97La 0.02) (Zr 0.66Sn 0.27Ti 0.07)O 3 were prepared by the molten salt synthesis (MSS) method, using Li 2SO 4–Na 2SO 4 and NaCl–KCl eutectic mixtures as the flux. The influences of processing parameters, such as temperature, time, and type of molten salts, on the formation and sinterability of PLZST were investigated. XRD and SEM were used for characterization of the as-prepared powders and ceramics. It was found that the PLZST powders and ceramics obtained by the MSS method have a relatively uniform particle size and microstructure. With other conditions being kept the same, chloride flux is preferential to the formation of tetragonal perovskite structure PLZST. The compact PLZST ceramics can be obtained at 1150 °C by MSS method, and then their dielectric properties are excellent.

Determination of a stability potential-pO2- diagram of samarium in the eutectic LiCl-KCl

Abstract:Reaction between samarium trichloride and oxide ions was studied in the fused LiCl – KCl eutectic mixture at 723 K, by potentiometry with an yttria-stabilised zirconia membrane electrode. Titration curve demonstrated the existence of a precipitated samarium oxychloride (SmOCl), under this experimental conditions, with a solubility product value of 7.59 ţ 0.3 (molality scale). The combination of this value with the standard potentials allowed setting up the potential–pO2- stability diagram which summarises the properties of Sm species in the eutectic LiCl – KCl melt.