KCl Melt Research Articles

Fabrication of an Ni–Pr Coating by the Application of EMF in an Equimolar NaCl–KCl Melt

Fabrication of an Ni–Pr Coating by the Application of EMF in an Equimolar NaCl–KCl Melt

Pb cathode assisted electrochemical extraction of Pr(III) by formation of Pb3Pr in LiCl–KCl melts

Pb cathode assisted electrochemical extraction of Pr(III) by formation of Pb3Pr in LiCl–KCl melts

A Holistic Approach for Elucidating Local Structure, Dynamics, and Speciation in Molten Salts with High Structural Disorder.

To examine ion solvation, exchange, and speciation for minority components in molten salts (MS) typically found as corrosion products, we propose a multimodal approach combining extended X-ray absorption fine structure (EXAFS) spectroscopy, optical spectroscopy, ab initio molecular dynamics (AIMD) simulations, and rate theory of ion exchange. Going beyond conventional EXAFS analysis, our method can accurately quantify populations of different coordination states of ions with highly disordered coordination environments via linear combination fitting of the EXAFS spectra of these coordination states computed from AIMD to the experimental EXAFS spectrum. In a case study of dilute Ni(II) dissolved in the ZnCl2+KCl melts, our method reveals heterogeneous distributions of coordination states of Ni(II) that are sensitive to variations in temperature and melt composition. These results are fully explained by the difference in the chloride exchange dynamics at varied temperatures and melt compositions. This insight will enable a better understanding and control of ion solubility and transport in MS.

Anode processes on Pt and ceramic anodes in chloride and oxide-chloride melts

Platinum anodes are widely used for metal oxides reduction in LiCl–Li2O, however high-cost and low-corrosion resistance hinder their implementation. NiO–Li2O ceramics is an alternative corrosion resistant anode material. Anode processes on platinum and NiO–Li2O ceramics were studied in (80 mol.%)LiCl-(20mol.%)KCl and (80 mol.%)LiCl-(20 mol.%)KCl–Li2O melts by cyclic voltammetry, potentiostatic and galvanostatic electrolysis. Experiments performed in the LiCl–KCl melt without Li2O illustrate that a Pt anode dissolution causes the Pt2+ ions formation at 3.14 V and 550°С and at 3.04 V and 650оС. A two-stage Pt oxidation was observed in the melts with the Li2O at 2.40 ÷ 2.43 V, which resulted in the Li2PtO3 formation. Oxygen current efficiency of the Pt anode at 2.8 V and 650°С reached about 96%. The anode process on the NiO–Li2O electrode in the LiCl–KCl melt without Li2O proceeds at the potentials more positive than 3.1 V and results in the electrochemical decomposition of ceramic electrode to NiO and O2. Oxygen current efficiency on NiO–Li2O is close to 100%. The NiO–Li2O ceramic anode demonstrated good electrochemical characteristics during the galvanostatic electrolysis at 0.25 A/cm2 for 35 h and may be successfully used for pyrochemical treating of spent nuclear fuel.

Electrochemical Behavior of SmF3 in Alkali Chloride Melts

Electrochemical studies of the Sm(III)/Sm(II) redox couple were carried out in NaCl-KCl, KCl and CsCl melts in a temperature range of 973–1173 K by cyclic voltammetry. Diffusion coefficients (D) of Sm(III) in these melts were determined using the Randles–Sevchik equation. Diffusion coefficients decrease with a change in the composition of the second coordination sphere from sodium to cesium. It is associated with a decrease in the counter-polarizing effect during the transition from Na to Cs, which in turn causes a decrease the metal—ligand bond length in the complexes. The standard rate constants of charge transfer (k s) of the Sm(III)/Sm(II) redox couple were determined by cyclic voltammetry in all studied melts using the Nicholson’s equation, which is valid for quasi-reversible processes. The following series of the standard rate constants of charge transfer was found k s(CsCl) < k s(KCl) < k s(NaCl–KCl).

Kinetic and Thermodynamic Properties of Samarium Chlorides Dissolved in Alkali Chloride Melts Obtained by Electrochemical Transient Techniques

The electrochemical behavour of samarium in NaCl-KCl, KCl and CsCl melts have been studied in the temperature range 973–1173 K by different electrochemical methods. The diffusion coefficients (D) of Sm(III) and Sm(II) have been determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Sm(III)/Sm(II) redox couple have been calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The nature of working electrode on the standard rate constants of charge transfer for the Sm(III)/Sm(II) redox couple has been studied. The formal redox potentials E * Sm(III)/Sm(II) have been obtained in alkali chloride melts from the cyclic voltammetry data.

Kinetic Properties and Electrochemical Separation of Uranium on Liquid Bismuth Electrode in LiCl–KCl Melt

Electrochemical studies of UCl3 and LnCl3 (Ln: La, Ce, Pr, Nd) in LiCl–KCl melt were performed on inert tungsten and reactive bismuth electrodes. Galvanostatic pulse (GP) and electrochemical impedance spectroscopy (EIS) were carried out to investigate the exchange current density j0 of UCl3/U on liquid Bi electrode at the temperature range of 723–873 K. The impedance data were well fitted with the equivalent circuit. The relationship between j0 and the temperature was determined to model the electrowinning by using liquid Bi electrode. In addition, the electrochemical separation in low concentration uranium from multi-component lanthanide chlorides was demonstrated on liquid Bi electrode. Three electrochemical techniques, including coulometric titration, galvanostatic electrolysis and potentiostatic electrolysis, were applied for the separation of uranium. In which, the coulometric titration showed good separation results. The separation of uranium from lanthanides in terms of mole ratio (U/Ln) was determined, and the different values were discussed in detail. In general, the data from this work can provide theoretical reference for the separation process of various metals by electrochemistry.

Synthesis of Niobium Diboride Nanoparticles by the Reaction of Amorphous Boron with Niobium in KCl and Na2B4O7 Ionic Melts

Close to spherical nanosized niobium diboride particles with an average diameter of 65 nm were synthesized by the reaction of amorphous boron with niobium powder at 1073 K in an argon atmosphere in KCl and Na2B4O7 ionic melts (autoclave, argon pressure of 4 MPa, 32 h).

Degradation of the Ceramics Based on MgO, Al2O3, or Si3N4 in the LiCl–KCl Melt with (Ce,Nd,U)Cl3 Additives

Degradation of the Ceramics Based on MgO, Al2O3, or Si3N4 in the LiCl–KCl Melt with (Ce,Nd,U)Cl3 Additives

Silicon Electrodeposition From the KCl-K &lt;sub&gt;2&lt;/sub&gt;SiF &lt;sub&gt;6&lt;/sub&gt; Melt

In this work, possible use of the KCl-K2SiF6 system for silicon electrodeposition has been studied. Kinetics of silicon electroreduction on glassy carbon in the KCl melt with the addition of 1 and 5 wt% K2SiF6 at 790°C was studied by electroanalytical methods (cyclic chronovoltammetry, square-wave voltammetry, chronoamperometry). Voltammetry was also used to determine equilibrium concentration of silicon containing-ions in the melt, and to estimate its decomposition rate to SiF4. It was shown that appearance of fluoride ions provides the required amount of silicon ions for the electrolytic refining of silicon due to the decomposition of K2SiF6.

Electrochemical preparation and properties of a Mg-Li-Y alloy via co-reduction of Mg(ii) and Y(iii) in chloride melts.

Mg–Li based alloys have been widely used in various fields. However, the widespread use of Mg–Li based alloys were restricted by their poor properties. The addition of rare earth element in Mg–Li can significantly improve the properties of alloys. In the present work, different electrochemical methods were used to investigate the electrochemical behavior of Y(iii) on the W electrode in LiCl–KCl melts and LiCl–KCl–MgCl2 melts. In LiCl–KCl melts, typical cyclic voltammetry was used to study the electrochemical mechanism and thermodynamic parameters for the reduction of Y(iii) to metallic Y. In LiCl–KCl–MgCl2 melts, the formation mechanism of Mg–Y intermetallic compounds was investigated, and the results showed that only one kind of Mg–Y intermetallic compound was formed under our experimental conditions. Mg–Li–Y alloys were prepared via galvanostatic electrolysis, and XRD and SEM equipped with EDS analysis were used to analyze the samples. Because of the restrictions of EDS analysis, ICP-AES was used to analyze the Li content in Mg–Li–Y alloys. The microhardness and Young's modulus of the Mg–Li–Y alloys were then evaluated.

Electrochemical Reduction Behavior of Boron in Molten LiCl–KCl–KBF4

1. Introduction The consumption and demand of Nd-Fe-B magnets, so-called neodymium magnets, is increasing year by year. Since the rare earth elements such as Nd can be obtained from sparse mineral resources, the technology for the recycling system of Ne-Fe-B magnets are highly required. The authors have been developing a technique to separately recover Nd and Dy from used Ne-Fe-B magnets using alloy diaphragm and molten salt [1].Although the electrochemical behavior of Nd and Dy was intensively investigated, the Ne-Fe-B magnet contains B as well as Fe, and the behavior of B in molten salt has not been clarified yet. Therefore, in this study, we investigated the behavior of B in LiCl–KCl eutectic melts at 723 K. The LiCl–KCl eutectic melt was chosen because a high separation ratio of Nd and Dy was obtained in our past experiments [2]. 2. Experimental The experiments were conducted in LiCl–KCl (44:56 wt%) eutectic melt in a dry Ar atmosphere at 723 K inside a glove box with an electronic furnace. 300 g of LiCl–KCl was vacuum dried at 473 K for more than 24 hours before elevating the temperature. As working electrodes, Ni, and Ag wire (φ1 mm) electrodes were used for cyclic voltammetry. Ni and Ag plate electrodes (5 mm×15 mm×0.1 mm(t)) were used for electrodeposition. A glassy carbon rod was used as a counter electrode. A reference electrode was an Ag+/Ag electrode, which was prepared by immersing an Ag wire in a LiCl−KCl melt containing 1 mol% of AgCl set in a Pyrex glass tube. The potential of the reference electrode was calibrated by the Li+/Li potential obtained by open circuit potential measurement on a Mo wire (φ1 mm) electrode just after electrodepositing Li metal. All the potential hereafter is described in reference to this Li+/Li potential.Cyclic voltammetry was conducted at KBF4 concentrations of 0, 0.5 and 2.0 mol%. Potentiostatic and galvanostatic electrolysis was conducted at KBF4 concentrations of 2.0 mol%. After the electrolysis, the plate electrodes were rinsed by distilled water, and then characterized by SEM and XRD. 3. Results and Discussion 3-1. Cyclic Voltammetr y Cyclic voltammograms (CV) obtained by Ni and Ag electrodes are shown in Fig.1(a) and (b), respectively. In the case of Ni electrode, cathodic current was observed at around 1.2 V shown “a” in the figure. The couple of peaks “b” and “c” at around 0.0 V correspond to Li metal deposition and dissolution, respectively. In addition to current peak “a”, a small current peak “e” appeared at 1.8 V, which seems to correspond to a formation of Ni-B compounds. Except for the peak “e”, essentially the same results were obtained in the case of Ag electrode. In both cases, the peak current at around 1.2 V increased with the concentration of KBF4 (shown as “a” in the figures). This peak can correspond to the reduction of B(III) to B(0), although further investigation is needed to confirm it. 3-2. Characterization of Products Prepared by Potentiostatic and Galvanostatic Electrolysis Fig. 2 shows a microscope image and a surface SEM image of the deposit on the Ni plate electrode obtained by potentiostatic electrolysis at 1.2 V, Q= −50 C. The granules with a diameter of c.a. 1-2 μm were observed. From XRD measurement, the diffraction peaks coincided to Ni, Ni2B, and NiCl2 was confirmed. Weak peaks that might correspond to B were partially observed.Next, the galvanostatic electrolysis was conducted at −9.8 mA cm−2, Q= −15 C for a Ni and an Ag plate electrode, respectively. In the case of Ni electrode, Ni, Ni2B, NiCl2 and KCl were detected by XRD analysis. This is almost the same result as the potentiostatic electrolysis at 1.2 V. Ag was selected as the substrate because no alloys of Ag and B exist in phase diagram. From the XRD results, only clear diffraction peaks coincided to Ag was confirmed. Other peaks were also detected, but they did not correspond to elemental B or other expected compounds. From the observation by sight, some deposits were actually formed. Therefore, the deposit can be amorphous B. In the future, further analysis and experiments are needed to clarify the behavior of B on Ag electrode. Acknowledgement This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Electrochemical Behavior of the SmF3 in Alkali Chloride Melts

Today, existing methods of recycling spent nuclear fuel do not solve the problem of separation of transuranium elements and lanthanides. Electrolysis of molten salts is promising for separation of lanthanides and actinides. To solve this problem, it is necessary to have experimental data on the electrochemical behavior of various lanthanides in molten salts.The aim of this study is the electrochemical investigation by cyclic voltammetry of the Sm(III)/Sm(II) redox couple in NaCl-KCl, KCl and CsCl melts containing SmF3.Electrochemical studies were carried out in a temperature range of 973-1173 K by cyclic voltammetry using an AUTOLAB PGSTAT 20 potentiostat with a package of application programs GPES (version 4.4.). The sweep rate (v) varied between 0.1 up to 3.0 V s-1. The melt container was a glassy carbon crucible of SU-2000 brand, which also served as an auxiliary electrode. Tungsten wire was used as a working electrode and platinum wire was utilized as a quasi-reference electrode.It was found in NaCl-KCl-SmF3, KCl-SmF3 and CsCl-SmF3 melts that the recharge process was reversible up to the scan rate 1.0 V s-1. In this range of sweep rate the diffusion coefficients (D) of Sm(III) were calculated using the Randles–Shevchik equation. The diffusion coefficients decrease with a change of the composition of the second coordination sphere from sodium to cesium. Similar dependencies for D values are well known. It is associated with a decrease of the counter-polarizing effect during the transition from Na to Cs, which in turn causes a decrease of the metal – ligand bond length and increase the strength of samarium complexes.A transition from reversible to quasi-reversible process was found at v > 1.0 V s-1 in NaCl-KCl-SmF3, KCl-SmF3 and CsCl-SmF3 melts.The standard rate constants of charge transfer (k s) of the redox couple Sm(III)/Sm(II) were determined by cyclic voltammetry in all studied melts by using the Nicholson’s equation, which is valid for quasi-reversible processes.The following series of the standard charge transfer constants was found k s(CsCl)<k s(KCl)<k s(NaCl–KCl). According to the theory of elementary charge transfer, the smaller and stronger bond complexes require a higher rearrangement energy, and in consequence, the charge transfer proceeds at a slower rate. Therefore, a decrease of the standard rate constants for the redox reaction would have been expected, which is in an agreement with obtained experimental results.

Electrodeposition of Tungsten from Molten KF–KCl–WO3 and CsF–CsCl–WO3

Introduction Tungsten metal is known for its robustness, especially high melting and boiling points and hardness. However, its hardness and brittleness make it difficult to work. Thus, electrodeposition of flat and dense tungsten films is worth investigating. There are a number of reports on the electrodepositon of tungsten from high temperature molten salts such as fluorides [1], chlorides [2], oxides [3], etc. It is known that dense and coherent tungsten deposits are more easily obtained from molten fluorides compared to molten chlorides. One drawback of typical fluoride melts like LiF–NaF–KF is difficulty in removing the adhered molten salts by water washing because LiF and NaF have limited solubility to water [4]. Although good tungsten deposits can be electrodeposited from molten oxides [3], the operation temperature tends to be very high, typically over 1123 K.From this background, we proposed new electrolyte baths, molten KF–KCl [5,6] and CsF–CsCl. Since all the components salts of KF, KCl, CsF and CsCl have large solubility to water [4], solidified salts on deposited films can be easily removed by water washing. Results & Discussion First, electrodeposition of tungsten was investigated in eutectic KF–KCl melt to which WO3 was added at 923 K. Cyclic voltammograms at copper and gold electrodes indicated the deposition of tungsten metal at more negative potential than 1.55 V vs. K+/K. The effects of electrolysis conditions on the morphology of deposits were studied by changing the cathodic current density from 12.5 to100 mA cm−2. As shown in Fig.1(a), a dense tungsten film with a thickness of approximately 20 µm was obtained on a copper substrate electrode at 12.5 mA cm−2 for 120 min. From the Raman spectra of molten KF–KCl and molten KF–KCl–WO3 at 923 K, the coordination structure of W(VI) complex ion was indicated to be fac-[WO3F3]3−.Secondly, eutectic CsF–CsCl melt was used to lower the operation temperature. After adding 2.0 mol% of WO3, the electrodeposition was investigated using copper and gold electrodes at 823–923K. As shown in Fig.1(b), a flat and dense tungsten film was obtained by galvanostatic electrolysis at 12.5 mA cm−2 for 120 min at 873 K. Acknowledgement This study is supported by Sumitomo Electric Industries, Ltd. The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University.

Electrochemical Behavior of the SmF3 in Alkali Chloride Melts

Electrochemical studies of the redox couple Sm(III)/Sm(II) were carried out in NaCl-KCl, KCl, and CsCl melts in a temperature range of 973-1173 K by cyclic voltammetry. Diffusion coefficients (D) of Sm(III) in these melts were determined using Randels–Shevchik equation. The diffusion coefficients decrease with a change in the composition of the second coordination sphere from sodium to cesium. It is associated with a decrease in the counter-polarizing effect during the transition from Na to Cs, which in turn causes a decrease the metal–ligand bond length in the complexes. The standard rate constants of charge transfer (k s) of the redox couple Sm(III)/Sm(II) were determined by cyclic voltammetry in the all studied melts using the Nicholson’s equation, which is valid for quasi-reversible processes. The following series of the standard charge transfer constants was found k s(CsCl)<k s(KCl)<k s(NaCl–KCl).

Kinetic and Thermodynamic Properties of Samarium Chlorides Dissolved in Alkali Chloride Melts Obtained by Electrochemical Transient Techniques

The electrochemical behavior of samarium in NaCl-KCl, KCl, and CsCl melts was studied in the temperature range 973-1173 K by different electrochemical methods. The diffusion coefficients (D) of Sm(III) and Sm(II) were determined by linear sweep voltammetry, chronopotentiometry, and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Sm(III)/Sm(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The nature of working electrode on the standard rate constants of charge transfer for the Sm(III)/Sm(II) redox couple was studied. The formal redox potentials E* Sm(III)/Sm(II) were obtained in alkali chlorides melts from the cyclic voltammetry data.

Electrochemical behavior and electrolytic preparation of lead in eutectic NaCl−KCl melts

Abstract A novel molten salt extraction process consisting of chlorination roasting and molten salt electrolysis was proposed to develop a more efficient and environmental friendly technology for recovering lead from spent lead acid batteries (LABs). The feasibility of this process was firstly assessed based on thermodynamics fundamentals. The electrochemical behavior of Pb(II) on a tungsten electrode in the eutectic NaCl−KCl melts at 700 °C was then investigated in detail by transient electrochemical techniques. The results indicated that the reduction reaction of Pb(II) in NaCl−KCl melts was a one-step process exchanging two electrons, and it was determined to be a quasi-reversible diffusion-controlled process. Finally, potentiostatic electrolysis was carried out at −0.6 V (vs Ag/AgCl) in the NaCl−KCl−PbCl2 melts, and the obtained cathodic product was identified as pure Pb by X-ray diffraction analysis. This investigation demonstrated that it is practically feasible to produce pure Pb metal by electrochemical reduction of PbCl2 in eutectic NaCl−KCl melts, and has provided important fundamental for the further study on lead recovery from spent LABs via molten salt extraction process.

Liquid Al assisted electrochemical extraction of lanthanum by formation of Al11La3 in chloride melts

In this work, different electrochemical measurements were employed to investigate the electrochemical behavior of La(III) on W and liquid aluminum electrodes, respectively. In LiCl–KCl melts, the diffusion coefficients of La(III) on W electrode at different experimental temperatures were determined by chronopotentiometry. The cyclic voltammetry results obtained on liquid aluminum electrode revealed only one pair of redox signal corresponding to the formation of Al–La intermetallic compound in LiCl–KCl–LaCl3 melts. The diffusion coefficient of La atom on the liquid Al–La alloy electrode was evaluated by anodic chronopotentiometry at 973 K. The electrochemical extraction of La was realized by galvanostatic electrolysis on a liquid aluminum electrode in LiCl–KCl–LaCl3 melts at 973 K, and the phases of Al11La3 and Al were identified by XRD. The SEM images disclosed needlelike precipitates in alloy, and the element La mainly distribute in the needlelike precipitates. After electrolysis, the extraction efficiency of element La was evaluated to be 99.4%, indicates that the electrochemical extraction of lanthanum with the help of liquid aluminum cathode is feasible in practice.

Density of KF–KCl–KI Melts

The densities of the KF–KCl–KI melts with KF/KCl molar ratios of 0.8 and 2 are measured as a function of the KI content by hydrostatic weighing. The measurements were performed in an inert atmosphere using structural materials resistant against the melts. The densities of the 45 mol % KF–55 mol % KCl–KI and 66.6 mol % KF–33.4 mol % KCl–KI melts with KI contents of from 0 to 100% were measured in a temperature range of 973–1073 K. KI additions to the KF–KCl melt were found to increase the density. The temperature dependences of the densities of the melts are described by linear functions. KI is found to increase the coefficient of temperature dependence of the density. Data on the densities of the KF–KCl–KI melts are used to calculate the molar volumes. Dependences of variations in the molar volume on the temperature and the melt composition are given. The molar volumes of the melts are shown to be close to those calculated by the additivity rule, which indicates that the initial salts are mixed without marked chemical interaction.

Corrosion Electrochemical Behavior of Molybdenum in the LiCl–KCl Melt Containing Additives of Cerium and Neodymium Trichlorides

The corrosion electrochemical behavior of molybdenum depending on the melt composition (imitators of spent nuclear fuel (SNF) components) in an oxidizing atmosphere is studied. Thermodynamic analysis of possible corrosion processes is performed using the HSC Chemistry 9.0 software in the Equilibrium calculations module. The rate of metal corrosion is estimated using gravimetry. The real products of the corrosion process and those expected from the thermodynamic calculations are compared using electron probe microanalysis (EPMA) and X-ray diffraction (XRD) analysis. The molybdenum concentration in frozen melt samples is studied by an atomic absorption method. The rate of molybdenum corrosion depends on the testing time. The decrease in the corrosion rate in time can be explained by the accumulation of Nd3+ and Ce3+ ions in the near-electrode layer, and corrosion occurs in the diffusion mode. The corrosive activity of the salt melt increases with the temperature and the ionic strength of the melt.