Chloride Melts Research Articles

Electrochemical Obtaining and Studying Structural Characteristics of Nanopowders of Intermetallides of Golmium and Nickel

This research is devoted to an electrochemical way of synthesis holmium and nickel compounds nanopowders from chloride melts and also identification of samples by methods of the X-ray phase analysis and the scanning electronic microscopy. The conducted researches have shown a possibility of synthesis of intermetallic compounds of holmium and nickel by electrolysis from the halide melts; Results of the high-temperature electrochemical synthesis carried out in the galvanostatic mode at a temperature of 973K are presented. As a result of researches optimum conditions of holmium and nickel compounds synthesis i.e. optimum composition of an electrolysis bath KCl-NaCl-HoCl3-NiCl2, a cathodic current density, a duration of electrolysis and temperature of process are found. The received results on the X-ray phase analysis and the laser diffraction analysis of the size of particles of the synthesized powders show existence of various phases of alloy of holmium with nickel (HoNi, HoNi5, HoNi3) and confirm a possibility of synyhesis their nanodimensional powders (more than 51% of particles up to 100 nanometers).

Electrochemistry of SmCl3 and SmF3 in Molten NaCl-KCl

Electrochemical studies of the redox couple Sm(III)/Sm(II) were carried out in NaCl-KCl-SmCl3 and NaCl-KCl-SmCl3 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. It was found that D in the NaCl-KCl-SmF3 melt are less than D in the NaCl-KCl-SmCl3 melt. At the same time activation energies for diffusion (ΔU) of Sm(III) in the NaCl-KCl-SmF3 melt are higher than ΔU in the NaCl-KCl-SmCl3 melt that is related to the increased strength of the complexes in transition from SmCl3 to SmF3 molten system. The standard rate constants of charge transfer (k s) for the Sm(III)/Sm(II) redox couple were determined by cyclic voltammetry both in NaCl-KCl-SmCl3 and NaCl-KCl-SmF3 molten salts using the Nicholson’s equation. The higher values of k s were obtained in chloride melt than in chloride-fluoride molten system.

An Electrochemical Study of Divalent Ytterbium Species in NaCl–KCl and NaCl–KCl–CsCl Based Melts

Reduction of Yb(III) to Yb(II) species was investigated in NaCl–KCl and 6NaCl–9KCl–5CsCl melts at 700–850 and 550–850 oC, respectively. Reduction was performed using hydrogen as a reducing agent or employing potentiostatic electrolysis under hydrogen atmosphere. Stability of Yb(II) ions in chloride melts was assessed and Yb(II)/Yb(III) red-ox potentials were determined.

Corrosive Resistance of Nickel Hastelloy G-35 Superalloy in Various Aggressive Media

The corrosion resistance of nickel-based Hastelloy G-35 alloy was investigated in molten chloride salts and aggressive aqueous solutions. The corrosion rates of the alloy in NaCl–KCl, 3LiCl–2KCl, AlCl3–KCl melts at 750 °C and in boiling sulfuric acid solution in the presence of iron(III) sulphate were determined. Mechanism of the corrosion depended on the oxidizing ability of the chloride melts. Intergranular corrosion dominated in the weakly oxidizing melts and general corrosion prevailed in the highly corrosive molten salts. The presence of oxygen in the system led to a significant increase in the rate of corrosion and a change in the mechanism of corrosion.

Cadmium Refining in Chloride Melts Using a Bipolar-Electrode Electrolyzer

The kinetics and mechanism of the formation of complex Cd (I) ions via the reaction of metallic cadmium with Cd2+ ions in the Cdo-CdCl2-ZnCl2-NH4Cl system are studied spectroscopically. The formation of Cd2 2+ and Cd2 3+ is evidenced by absorption bands around 270 and 335 nm, respectively, in the electronic spectrum of the melt. The anode current efficiency is determined for cadmium electrorefining in a chloride melt. A method is proposed for electrolytic cadmium refining in molten cadmium chloride with the use of bipolar Cd electrodes. The effect of electrolysis conditions on the refining process is analyzed, and the distribution ratios of typical metallic impurities in Cd are evaluated. The results demonstrate that high-purity Cd can be obtained in a single electrolysis cycle.

DFT study on Raman frequencies of molten lead (II) chloride

ABSTRACTThe study concerns ab inito calculations of the essential Raman frequencies of molten lead (II) chloride near the melting point. Modelling of topologically disordered lead (II) chloride was carried out within the framework of the density functional theory using the Perdew–Burke-Ernzerhof (PBE) functional and optimised basis sets. Calculations were performed for a cluster containing 24 formula units. The optimum geometry of the cluster was determined and the local structure parameters were found. Nano-size effect leads to the picture of damped oscillations on radial atomic density distributions typical of molten salts. Distorted octahedra of PbCl6 were detected inside the cluster. Ab initio calculation of the Raman spectrum of the octahedral complexes inside the cluster structure was implemented. It was shown that the spectrum has a peak at 192 cm−1, which agrees well with the experimental Raman spectra of lead (II) chloride melt near the melting point.

Electrochemical Formation of Dy Alloys in a Molten CaCl2-LiCl System

The molten salt electrochemical process has been studied by Ito and co-workers including the present authors and many other researchers. The authors reported a unique phenomenon during the electrochemical formation of Dy-Ni alloys in molten LiCl-KCl-DyCl3: DyNi2 film with thickness of 60 µm was formed in 2 h at 700 K. The growth rate of DyNi2 was extremely high, compared with the conventional solid phase diffusion at temperatures lower than half of the melting temperature of DyNi2, i.e., 1531 K. In addition, the growth rate was found to be strongly affected by electrochemical parameters such as potential and current density. This phenomenon was termed “electrochemical implantation”, because it was different from the ordinary concepts of electrodeposition followed by solid phase diffusion. The authors also reported that anodic polarization of the formed DyNi2 resulted in the rapid dissolution of Dy to form other Dy-Ni phases. The obtained phase and morphologies were dependent on the applied potential. This phenomenon was named “electrochemical displantation”. The use of rare earth (RE) - iron group alloys has increased significantly in a number of industrial fields over the past few decades. In particular, the demand for Dy-added Nd-Fe-B magnets is rapidly increasing because these magnets are indispensable for high-performance motors in electric vehicles and hybrid electric vehicles. These magnets need to possess sufficient thermal stability for use in such motors in high-temperature environments. The addition of Dy is necessary to improve the thermal stability of Nd-Fe-B magnets. However, there is the concern about a shortage of RE metals because of the uneven distribution of RE resources. Against this background, it is necessary to develop an inexpensive and environmentally friendly recovery/separation process for RE metals, especially the recovery of Dy and Nd from magnet scraps. We proposed a new separation and recovery process for RE metals from scraps using molten salt and an alloy diaphragm. The new process is based on our previously discovered phenomena, i.e., “electrochemical implantation” and “electrochemical displantation”. RE containing scrap is used as the anode. A RE-transition metal (TM) alloy is used as the diaphragm, which functions as a bipolar electrode. During electrolysis, all the RE metals in the anode are dissolved in the molten salt as RE ions. One or several specific RE ions are selectively reduced to form RE-TM alloys on the alloy diaphragm according to their formation potentials and/or alloying rates. Subsequently, the RE atoms chemically diffuse through the alloy diaphragm and are dissolved into the molten salt as RE ions in the cathode room. The permeated RE ions are finally deposited on the Mo or Fe cathode as RE metals. The RE ions remaining in the anode room can be collected by electrolysis using another cathode in the anode room. Almost all impurities remain in the anode room as residue or anode slime. This new process was first applied to chloride melts, and the separation of Dy from Nd and Pr were investigated using Cu, Ni and Zn cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3 and LiCl-KCl-DyCl3-NdCl3-PrCl3 systems. The highest mass ratio of Dy/Nd+Pr in Dy-Nd-Pr-Ni alloy sample was found to be 50 at 0.65 V (vs. Li+/Li) for 1 h by ICP-AES. The present study focused on the electrochemical formation of Dy alloys in a molten CaCl2-LiCl system at 873 K. Furthermore, the separation of Dy and Nd was investigated with Fe electrodes.

Electroreduction of manganese chloride on the backgrounds of chloride: KCl-NaCl and chloride – fluoride melts

By polarographic method the electroreduction of manganese chloride from chloride and fluoride-chloride melts has been studied in air atmosphere. Optimal parameters of the process were established. In both melts the metallic manganese was obtained. The mechanism of the reduction of manganese – ions is presented.

Electrodeposition and characterization of silicon films obtained through electrochemical reduction of SiO2 nanoparticles

We have reported electrodeposition of silicon films on metal substrates obtained through electrochemical reduction of silicon dioxide nanoparticles (SiO2-NP) at high temperature of 855 °C in the calcium chloride (CaCl2) melt. Electrodeposition was conducted using a three-electrode based electrochemical cell. Reduction of the SiO2 was found possible with applying a negative potential of 0.9 V or more negative on the metal substrate with respect to the graphite reference electrode. Mechanism of the reduction and electrodeposition process was discussed using cyclic voltammetry (CV), and chronoamperograms (CA) techniques in relation to the applied reduction potentials during experiments. Raman spectroscopy, and X-ray diffraction method confirmed formation of the Si-film on the silver (Ag) substrate using the electrodeposition technique. Effect of the various reduction potentials on the properties of the formed Si layer was studied using Raman spectroscopy, photoluminescence (PL), and Scanning electron microscopy (SEM). Crystallinity of the electrodeposited Si-films were found to be correlated with the reduction potential. Nanocrystalline Si (nc-Si) film was obtained through electrodeposition with lower reduction potentials, while higher reduction potential was found to be effective to get Si-films with uniform crystalline quality, and better morphology. Effect of the substrate materials on the electrochemical reduction of SiO2 was also investigated.

Ion-Exchange Interaction of Glass-Forming Silicate Melts with Mixed Chloride Melts

The ion-exchange interaction of the sodium aluminosilicate and sodium galliumsilicate melts with a mixture of molten Li, Na, K, Rb, Cs, and Ba chlorides is studied. It is established that two alkaline silicate melts are characterized by negative deviations from the ideal behavior, and silicate melts containing alkaline and alkaline-earth cations are characterized by noticeable positive deviations from the ideal behavior.

Electrical Conductivity and Raman Spectra of Disperse Systems α-Al2O3–Li2CO3–Na2CO3–K2CO3–NaCl Melt

The conductivities of the disperse system α-Al2O3–molten carbonate chloride mixture Li2CO3–Na2CO3–K2CO3–NaCl are dtermined in the temperature range 455–550°C. As follows from Raman spectroscopy data, α-Al2O3 does not interact chemically with the carbonate–chloride melt in this temperature range. The force and energy characteristics of the CO32- anion in the systems are revealed.

Voltammetric Response of Water in Deep Eutectic Solvent Based on Choline Chloride and Urea

This work investigates the electrochemical role of water in the research of deep eutectic solvent (DES) based on urea and choline chloride. The motivation comes from the growing use of this DES, and on reports where a characteristic voltammetric cathodic pre-wave is observed. However, there has been no direct study to verify if such interpretation of the pre-wave is appropriate. In this regard, cyclic voltammetry has been used in this paper to interrogate the reactions inducing the appearance of the pre-wave. These experiments have been carried out using reline (the eutectic mixture of urea and choline chloride) melts containing different amounts of water, compounds which can be incorporated as impurities from air, or as decomposition products of reline. The analyses showed that a pre-wave in voltammograms in reline originates from water electroreduction accompanied with a subsequent choline hydroxide formation. In this sense, reline behaves like a typical mixture of organic solvent + alkali cation salt + water. The voltammetric signal depends on water content in reline. Importantly, this offers a possibility for in-situ electrochemical determination of water content in reline, provided that a calibration curve is constructed.

Facile Electrochemical Preparation of Al-Sm Alloys in Molten Calcium Chloride

The direct preparation of metallic Sm or alloys from raw oxide Sm2O3 is an attracting but challenging process. The stable electrochemical behavior and low solubility of Sm2O3 limit the extraction of Sm element in molten salts. Here, it is found that metallic Sm is hardly obtained by electro-deoxidation and aluminothermic reduction of solid Sm2O3 pellet according to experiment and calculation. Through the novel electrochemical reduction of solid Sm2O3-Al pellet, Al3Sm alloy with ∼0.4 Sm/Al molar ratio is successfully prepared in calcium chloride melt at 1173 K. The reduction potential of Sm2O3-Al pellet to Al-Sm alloy is more positive than that of calcium. Al plays an indispensable role in the reduction of Sm2O3. The preparation process of alloy can be well identified as two steps: Sm(III) → Sm(II) and Sm(II) → Sm(0). Sm2O3 is firstly converted to Sm(II) based on the combination of electrochemical and aluminothermic reduction. Then, Al3Sm is formed by electrochemical reduction and alloying with Al.

Fluorescence, Biological Activity and Spectroscopic Studies of Azo-linked Schiff Base Ligand Type (ONO) and Its Complexes with CrIII, CoII NiII and CdII Ions

The precursor [W] [2-(2-(naphthalen-5-yl) diazenyl)-4-amino-3-hydroxynaphthalene-1sulfonic acid] was synthesized from reaction of diazonium salt with 1-amino-2-naphtol-4sulfonic acid. Then the tridentate Schiff base ligand type ONO was synthesized from the reaction of the precursor with salicyaldehyde in 1:1 mole ratio to produce the ligand H2L [2-(2-(naphthalen5-yl) diazenyl)-4-(2-hydroxynaphthalen-3-yl)methyleneamino)-3-hydroxy salicyalene-1-sulfonic acid],the reaction achieved in methanol as a solvent under reflux. Spectroscopic methods IR, U.V, 1H,13C-NMR was used to characterize the ligand. Complexes of [CrIII, CoII, NiII and CdII] ions were also prepared through reaction of ligand with metal salts in 2:1 mole ratio at reflux, using KOH as a base, ethanol as a solvent. Chloride content, molar conductivity and melting point measurements along with I.R and U.V-Vis, atomic absorption (A.A) spectroscopy were used to characterize the complexes.1H-NMR spectroscopy was used to characterize Cd complex. Thermal analysis was used to insure the presence of crystallized H2O molecule in the complexes structure. The following formula was proposed for Cr complex: K[Cr(L)2]. H2O, while CoII, NiII and CdII complexes have the K2[M(L)2].H2O formula. The biological activity of the prepared compounds was studied. Fluorescence properties of the prepared compounds were studied (at room temperature) which indicate that the ligand may behave as strong fluorescent emitter. The complexes also showed fluorescence characteristic with the ligand. The ligand revealed high relative intensity and its fluorescence peak were also shifted to the lower or higher wavelength when compared with the complexes.

Electrical Conductivity of Molten DyCl3-NaCl and DyCl3-KCl Systems: An Approach to Structural Interpretations of Rare Earth Chloride Melts

Abstract Electrical conductivities (κs) of molten DyCl3-NaCl and DyCl3-KCl systems were estimated by measuring the impedances of each mixture melt at any temperature and/or frequency. The molar volumes (V ms) were measured by dilatometry and represented as a polynomial empirical equation of temperature and composition. Due to both the properties, the molar conductivities (Λms) were calculated and their temperature and/or composition dependences were discussed from the standpoint of structural features as well. The κs increased curvilinearly with increasing temperature across the whole composition ranges. This trend was also applied to the Λms which was fitted by an Arrhenius-type equation. The relationship of Λms with melt composition was studied and the Λms were found to decrease with increasing composition of DyCl3. These findings were interpreted based on the results of structural science so far reported, and finally, the relationship between Λms and the structures of pure rare earth chloride melts was discussed.

Electrochemical behaviors of Ti(III) in molten NaCl-KCl under various contents of fluoride

In order to investigate an optimal concentration of fluoride in alkali chloride melt which the Ti(III) can be reduced into metallic titanium in one step, a systematic study of the electrochemical properties of Ti(III) was carried out in molten NaCl-KCl. KF was used as a source of fluoride ions, and the molar ratio of fluoride ions and titanium ([F−]/[Tin+] ratio) was employed as a parameter to illustrate the influence of fluoride anions on the electrochemical behaviors of Ti(III). The experiments were carried out with various concentrations of fluoride ions using a glassy carbon electrode at a temperature of 1023K. Transient electrochemical techniques, such as cyclic voltammetry and square wave voltammetry, were performed to reveal the reduction steps and reduction potentials of the electroactive species. Results suggest that there are two steps for Ti(III) ion reduction in molten NaCl-KCl: Ti(III)→Ti(II) and Ti(II)→Ti. Ti(III) can be reduced directly to Ti in one step when KF was added in the melt in increasing amount.

Electrochemical Formation of Dy and Nd Alloys Using Liquid Metal Electrodes in Molten LiCl-KCl Systems

We proposed new separation and recovery process for RE metals from Nd magnet scraps using molten salt electrolysis and an alloy diaphragm. This new process was first applied to chloride melts, and the separation of Dy and Nd were investigated using Ni cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3 systems. The highest mass ratio of Dy/Nd in Dy-Nd-Ni alloy samples was found to be 72. We focused on the liquid metals as the alloy diaphragms. Liquid metals have higher diffusion rates of elements than those of solid metals during the electrolysis. In this work, Bi, Sn and Zn electrodes were used as liquid metal electrodes. The alloy samples were prepared by potentiostatic electrolysis using liquid Bi, Sn and Zn electrodes in molten LiCl-KCl added DyCl3(0.50 mol%) and NdCl3(0.50 mol%) at 723 K.

Corrosion of Austenitic Steels and Their Components in Uranium-Containing Chloride Melts

The corrosion resistance of AISI 316L, 12Kh18N10T (analogue of AISI 321) austenitic stainless steels and their basic components (metallic iron, nickel, chromium, molybdenum) was investigated in the melts based on the NaCl–KCl equimolar mixture at 750 ºC. Austenitic stainless steels underwent high temperature sensitization, and it was shown that this phenomenon determined the intergranular type of the steel corrosion. It was demonstrated that the presence of uranium ions in the electrolyte intensified corrosion processes. Metallic molybdenum demonstrated the highest corrosion resistance among the construction materials studied.

Fabrication of high-alloy powders consisting of spherical particles from ultradispersed components

It is shown that powders of a model high alloy consisting of spherical particles 25–50 μm in size can be synthesized from a starting ultradispersed powder, which is made of a mixture of the alloy components and is fabricated by the magnesiothermal reduction of metal chlorides in the potassium chloride melt. The synthesis includes the stages of microgranulation of an ultradispersed powder, heat treatment of microgranules, classification of the microgranules with the separation of microgranule fraction of 25–50 μm, spheroidization of the separated fraction in a thermal plasma flow, and classification with the separation of a fraction of micro- and submicrometer-sized particles.

On some regularities of magnesium oxide solubility in melts with different content of alkaline earth metal chlorides

Experimental data on solubility of magnesium oxide in melts based on mixed chlorides of alkali and alkaline earth metal are complemented by investigation in SrCl2-rich melt of KSr2Cl5 composition. The changes of MgO solubility in the chloride melts based on CaCl2 and SrCl2 at melt temperature variation obeys to predictions of the Shreder-Le Chatelier equation. This brings MgO solubility in the different melts to the same conditions (T=973K). The oxoacidic properties of the melt strengthen with increase of the concentration of alkaline earth cations and different complexes are formed due to the solvation of oxide ion in the melts based on these cations: BaO in Ba2+-based chloride melts and 2SrCl2·SrO in Sr2+-based ones. In CaCl2-based melts simultaneous formation of complexes of 4CaCl2·CaO and 2CaCl2·CaO compositions is possible.