Processes

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12 pages, 2342 KiB

Open AccessFeature PaperArticle

Melting Behavior and Densities of K₂B₂OF₆ Melts Containing KReO₄

by Aleksandr A. Chernyshev, Alexey P. Apisarov, Andrey V. Isakov, Anastasia O. Khudorozhkova and Michael V. Laptev

Processes 2023, 11(11), 3148; https://doi.org/10.3390/pr11113148 - 3 Nov 2023

Viewed by 527

Abstract

Methods of simultaneous thermal analysis (differential scanning calorimetry, thermogravimetry) and an analysis of cooling curves were used to study the melting of K₂B₂OF₆–(0–15 wt. %) KReO₄ melts. The synthesis of K₂B₂OF₆ [...] Read more.

Methods of simultaneous thermal analysis (differential scanning calorimetry, thermogravimetry) and an analysis of cooling curves were used to study the melting of K₂B₂OF₆–(0–15 wt. %) KReO₄ melts. The synthesis of K₂B₂OF₆ was performed by alloying KF, KBF₄, and B₂O₃ components. The liquidus temperature dependence on the content of potassium perrhenate in the K₂B₂OF₆–(0–15 wt. %) KReO₄ melts was determined. It was found that the addition of up to 6 wt. % KReO₄ caused an increase in the melt liquidus temperature to 733 K. Further increases in potassium perrhenate did not change the temperature of the primary crystallization (733 ± 5 K) of the K₂B₂OF₆–KReO₄ melt. This fact testifies to the presence of the monotectic reaction. It was found that the relative loss of mass of the K₂B₂OF₆–(0–15 wt. %) KReO₄ melts did not exceed 2.1%. The delamination of the K₂B₂OF₆–KReO₄ melt was revealed according to the values of the primary crystallization temperatures (liquidus temperatures) in different layers of the melt. The density of the K₂B₂OF₆–KReO₄ melts as a function of potassium perrhenate content (0–15 wt. %) was investigated at 628–933 K. The temperature dependence of the K₂B₂OF₆–KReO₄ melts’ densities was recorded. They are presented as linear functions. The curves of the density temperature dependence of the K₂B₂OF₆–KReO₄ melts were used to determine the critical temperatures, i.e., the boundaries of the miscibility gap. The miscibility gap of the K₂B₂OF₆–KReO₄ melts is limited to 1 wt. % and 15 wt. % KReO₄ content. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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18 pages, 4526 KiB

Open AccessArticle

Effect of Cation Nonstoichiometry on Hydration and Charge Transport Processes in Yb-Doped SrZrO₃ Perovskite-Type Proton Conductor for Ceramic Electrochemical Cells

by Adelya Khaliullina, Anastasia Meshcherskikh and Liliya Dunyushkina

Processes 2023, 11(10), 2939; https://doi.org/10.3390/pr11102939 - 10 Oct 2023

Viewed by 697

Abstract

The effect of Sr deficiency on the hydration process and ionic and electronic conductivity of Yb-doped SrZrO₃ proton conductors with a perovskite-type structure was investigated. Dense Sr_xZr_0.95Yb_0.05O_3-δ (x = 0.94–1.00) ceramics were prepared using solution [...] Read more.

The effect of Sr deficiency on the hydration process and ionic and electronic conductivity of Yb-doped SrZrO₃ proton conductors with a perovskite-type structure was investigated. Dense Sr_xZr_0.95Yb_0.05O_3-δ (x = 0.94–1.00) ceramics were prepared using solution combustion synthesis. Thermogravimetry and Raman spectroscopy methods were used to determine the concentration of bulk protonic species. Sr deficiency was found to enhance the hydration ability of the zirconate; however, lowering of Sr content to x = 0.94 deteriorated the proton uptake. The conductivity of the Sr_xZr_0.95Yb_0.05O_3-δ series depending on the oxygen partial pressure at different humidities was studied by the four-probe direct current technique. Sr-deficient ceramics with x = 0.96 and 0.98 were shown to become purely protonic conductors in humid atmospheres at a temperature close to 500 °C. The ionic conductivity reaches its highest value at a Sr content of x = 0.98 (2 × 10⁻⁴ S cm⁻¹ at 500 °C and pH₂O = 3.17 kPa). The hydration behavior and transport properties of Sr_xZr_0.95Yb_0.05O_3-δ are discussed in terms of the defect chemistry model that assumes the distribution of Yb ions over Sr and Zr sites at a large Sr deficiency. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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20 pages, 7379 KiB

Open AccessArticle

Electrochemical Behavior of Dysprosium Ion and Its Co-Electroreduction with Nickel Ions in the Molten KCl-NaCl-CsCl Eutectic

by Khasbi B. Khushkhov, Anna S. Kholkina, Astemir A. Khotov, Zhubagi Z. Ali, Zalina A. Zhanikayeva, Vadim A. Kvashin, Vadim A. Kovrov, Anastasia A. Mushnikova and Daria P. Mirzayants

Processes 2023, 11(10), 2818; https://doi.org/10.3390/pr11102818 - 22 Sep 2023

Viewed by 714

Abstract

The electrochemical behavior of dysprosium ions, as well as dysprosium and nickel ion co-reduction, on inert tungsten electrodes and active nickel electrodes were studied in the eutectic KCl-NaCl-CsCl melt at a temperature of 823 K using the methods of cyclic and square-wave voltammetry [...] Read more.

The electrochemical behavior of dysprosium ions, as well as dysprosium and nickel ion co-reduction, on inert tungsten electrodes and active nickel electrodes were studied in the eutectic KCl-NaCl-CsCl melt at a temperature of 823 K using the methods of cyclic and square-wave voltammetry and open circuit chronopotentiometry. The process of Dy³⁺ ions electroreduction was found to be reversible and to proceed within a single three-electron stage up to the polarization rate of 0.1 V/s. The increase in the polarization rate indicates a slower rate of the charge transfer, which causes the quasi-reversible character of the charge transfer. It is shown that when the KCl-NaCl-CsCl eutectic melt contains both nickel and dysprosium ions, the voltammetry curves at 823 K have a wave of nickel ion reduction at the potentials of −(0.22–0.28) V and a dysprosium ion reduction at the potentials of −(2.175–2.250) V relative to a chlorine-silver reference electrode. Apart from these waves, the voltammograms have two reduction waves at the potentials of −(1.9–1.95) V and −(2.05–2.1) V. These waves are associated with the reduction of dysprosium ions and their depolarization on metallic nickel, which was preliminary deposited on the tungsten electrode, as well as the formation of the intermetallic phases of dysprosium and nickel of various Dy_xNi_y compositions. The (E-t) dependencies of the open circuit chronopotentiometry elucidate plateaus of the potential delay, which correspond to the dissolution of separate dysprosium and nickel intermetallic phases. Based on the results of the voltammetry changes and the chronopotentiometry of the open circuit, a series of electrochemical syntheses were performed in the potentiostatic regime at the potentials of −(1.7–2.1) V. The intermetallic phases of DyNi₅, DyNi₃ and DyNi₂ were obtained at a definite ratio of the dysprosium and nickel chloride concentrations in the KCl-NaCl-CsCl eutectic melt and at a temperature of 823 K. The synthesized intermetallic samples were characterized by X-ray diffraction and scanning electron microscopy. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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13 pages, 3868 KiB

Open AccessFeature PaperArticle

Efficiency of Electrochemical Methods of Purification and Control over the Oxide Concentration in Halide Melts: PbCl₂

by Andrey Nikolaev, Albert Mullabaev, Andrey Suzdaltsev and Yuriy P. Zaikov

Processes 2023, 11(2), 636; https://doi.org/10.3390/pr11020636 - 19 Feb 2023

Cited by 2 | Viewed by 1703

Abstract

The purification of molten salts from admixtures as well as the effective control of admixture concentration has attracted researchers’ interests. In the present paper, the possibility of the electrochemical purification of PbCl₂ from PbO and the effective control over the oxide ions [...] Read more.

The purification of molten salts from admixtures as well as the effective control of admixture concentration has attracted researchers’ interests. In the present paper, the possibility of the electrochemical purification of PbCl₂ from PbO and the effective control over the oxide ions concentration in molten PbCl₂ is studied at the temperature of 520 °C. The PbCl₂ melt with the initial addition of 0.5 wt% of PbO was used as a molten salt sample. The method of potentiostatic electrolysis was used to remove the oxide additions from the melt; the linear and square-wave voltammetry dependencies were recorded, and the melt samples were taken for analysis. Based both on the results of the electrochemical measurements and the analysis of oxygen concentration in the electrolyte, we built linear empirical dependencies of the anode peak current of the oxidation of oxygen-containing electroactive anions on the PbO concentration in the studied melt. We demonstrated that the obtained dependencies may be used for direct electrochemical nondestructive in-situ control over the concentration of PbO dissolved in the PbCl₂ melt containing up to 0.5 wt% of PbO. The deep electrochemical purification of the chloride PbCl₂ melt from molten oxide (up to 0.044 wt% PbO or to 0.007 wt% of oxygen) was achieved by the potentiostatic electrolysis. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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12 pages, 2244 KiB

Open AccessFeature PaperArticle

Interaction between Iron Fluoride and Molten FLiBe

by Stepan P. Arkhipov, Yury P. Zaikov, Pavel A. Arkhipov and Albert R. Mullabaev

Processes 2022, 10(12), 2742; https://doi.org/10.3390/pr10122742 - 19 Dec 2022

Cited by 2 | Viewed by 1543

Abstract

The equilibrium potentials of iron in a LiF-BeF₂-FeF₂ melt were measured using the EMF method and were dependent upon the temperature and iron fluoride concentrations. The empirical equations for the isotherms and equilibrium polytherms of the iron fluoride concentration were [...] Read more.

The equilibrium potentials of iron in a LiF-BeF₂-FeF₂ melt were measured using the EMF method and were dependent upon the temperature and iron fluoride concentrations. The empirical equations for the isotherms and equilibrium polytherms of the iron fluoride concentration were obtained. The cathode polarization of iron fluoride in the molten mixture of lithium and beryllium fluoride was measured using the current switch off method from the stationary state. It was found that in the studied temperature and concentration ranges of iron fluoride in the LiF-BeF₂ electrolyte, the valence state of iron in the melt is mainly +2. According to the experimental values of the equilibrium potentials of the iron electrode in the LiF-BeF₂-FeF₂ melt, the conditional standard potentials of iron were calculated relative to the fluoride reference electrode in the molten mixture of lithium and beryllium fluoride. The conditional standard values of the Gibbs energy change were calculated at the formation of iron difluoride from the element in the form of dilute solutions, as were the thermodynamic values (enthalpy and entropy) when iron difluoride was mixed with LiF-BeF₂. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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15 pages, 2350 KiB

Open AccessArticle

Ionic Equilibria in Polytungstate Melts

by Alexander V. Kosov, Olga L. Semerikova, Sergey V. Vakarin, Olga V. Grishenkova, Alexey S. Vorob’ev, Anastasia O. Khudorozhkova and Yury P. Zaikov

Processes 2022, 10(12), 2658; https://doi.org/10.3390/pr10122658 - 9 Dec 2022

Cited by 2 | Viewed by 1140

Abstract

Polytungstate melts are used for the electrodeposition of oxide tungsten bronzes (OTBs). The scarce information on the ionic composition and properties of these electrolytes hinders effective control of the electrochemical synthesis of OTBs with desired electrical and optical properties. In this work, a [...] Read more.

Polytungstate melts are used for the electrodeposition of oxide tungsten bronzes (OTBs). The scarce information on the ionic composition and properties of these electrolytes hinders effective control of the electrochemical synthesis of OTBs with desired electrical and optical properties. In this work, a comprehensive study of Na₂WO₄–WO₃ melts that contained up to 55 mol% of tungsten trioxide was performed in the temperature range from 983 to 1073 K. Melt densities were measured using the Archimedes method. DFT calculations were carried out for various tungsten-containing compounds, including

W_{x} O_{3 x - 1}^{2 +}

,

W_{x} O_{3 x + 1}^{2 -}

,

{NaW}_{x} O_{3 x + 1}^{-}

, and

{Na}_{2} W_{x} O_{3 x + 1}

. The calculated values of the W–O bond energy indicate that the tested compounds are stable in the specified temperature range, and the

{WO}_{2}^{2 +}

cation is the most stable. The experimental dependences of the redox potential on the mole fraction of tungsten trioxide in the Na₂WO₄–WO₃ melt were obtained using the EMF method. A model that considers the processes of interaction between tungsten-containing ions and O²⁻ ions was proposed for the quantitative interpretation of these dependences. The equilibrium constants were found through fitting according to the Levenberg–Marquardt algorithm. The effect of the WO₃ mole fraction and temperature on the concentrations of

{WO}_{4}^{2 -}

,

W_{2} O_{7}^{2 -}

,

W_{3} O_{10}^{2 -}

,

W_{4} O_{13}^{2 -}

,

{WO}_{2}^{2 +}

, and O²⁻ ions was analyzed. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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8 pages, 2009 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Synthesis, Hydration Processes and Ionic Conductivity of Novel Gadolinium-Doped Ceramic Materials Based on Layered Perovskite BaLa₂In₂O₇ for Electrochemical Purposes

by Nataliia Tarasova, Anzhelika Bedarkova, Irina Animitsa and Evgeniya Verinkina

Processes 2022, 10(12), 2536; https://doi.org/10.3390/pr10122536 - 29 Nov 2022

Cited by 6 | Viewed by 1422

Abstract

The search for novel highly effective materials with target properties for different electrochemical purposes is active for now. Ceramic materials with high levels of ionic conductivity can be applied as electrolytic materials in solid oxide fuel cells and in electrolyzers. Layered perovskites are [...] Read more.

The search for novel highly effective materials with target properties for different electrochemical purposes is active for now. Ceramic materials with high levels of ionic conductivity can be applied as electrolytic materials in solid oxide fuel cells and in electrolyzers. Layered perovskites are a novel class of ionic conductors demonstrating almost-pure proton transportation at mid-temperatures. Gadolinium-doped ceramic materials based on layered perovskite BaLa₂In₂O₇ were obtained and investigated for the first time in this study. The effect of the dopant concentrations on the hydration processes and on ionic conductivity was revealed. It was shown that compositions 0 ≤ x ≤ 0.15 of BaLa_2–xGd_xIn₂O₇ exhibited proton conductivity when under wet air and at mid-temperatures (lower than ~450 °C). Gadolinium doping led to an increase in the conductivity values up to an order of magnitude of ~0.5. The protonic conductivity of the most conductive composition BaLa_1.85Gd_0.15In₂O₇ was 2.7∙10⁻⁶ S/cm at 400 °C under wet air. The rare earth doping of layered perovskites is a prospective approach for the design of ceramics for electrochemical devices for energy applications. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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17 pages, 5057 KiB

Open AccessArticle

Peculiarities of Holmium and Iron Triad Ions Co-Reduction: Formation of Ho_xNi_y (Ho_xCo_y, Ho_xFe_y) Intermetallic Compounds in Chloride Melts

by Khasbi Kushkhov, Ranetta Kardanova and Anna Kholkina

Processes 2022, 10(9), 1723; https://doi.org/10.3390/pr10091723 - 30 Aug 2022

Cited by 1 | Viewed by 1276

Abstract

The present paper is focused on the analysis of Ni²⁺, Co²⁺, Fe³⁺, and Ho³⁺ ion co-reduction in the background equimolar NaCl-KCl melt at 973 K using the method of cyclic voltammetry. It was found that the [...] Read more.

The present paper is focused on the analysis of Ni²⁺, Co²⁺, Fe³⁺, and Ho³⁺ ion co-reduction in the background equimolar NaCl-KCl melt at 973 K using the method of cyclic voltammetry. It was found that the co-reduction potentials of Ho³⁺ and iron triad ions differ greatly. The depolarization of metallic holmium electrodeposition on one of the iron triad metals preliminary deposited on the tungsten electrode was determined. This process resulted in the formation of the Ho_xNi_y, Ho_xCo_y, and Ho_xFe_y intermetallic compounds. It was observed that the Ho_xNi_y, Ho_xCo_y, and Ho_xFe_y intermetallic compounds may be synthesized in a kinetic regime. The influence of the current density, electrolytic bath composition, and electrolysis time on the composition of the obtained intermetallic compounds was studied. The possibility of synthesizing cathode deposits composed solely of intermetallic compounds is verified. It is demonstrated that the intermetallic compounds may be formed by the addition of the iron triad metals (in particular, metallic iron) via anode dissolution. Synthesized Ho_xNi_y, Ho_xCo_y, and Ho_xFe_y samples were characterized by X-ray diffraction analysis, scanning electron microscopy, and photon correlation spectroscopy. Full article

(This article belongs to the Special Issue Electrochemical Technology for New Materials Synthesis and Reprocessing)

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