Electromotive Force Measurements Research Articles

Electrochemical Deposition of Alkaline-Earth Elements (Sr and Ba) into Liquid Metals in Molten LiCl-KCl-SrCl2-BaCl2 salt

Electrochemical deposition of Sr and Ba into liquid metals (Bi and Sb) was investigated in LiCl-KCl-SrCl2-BaCl2 electrolytes at 500–650 °C as a means to separate stable alkaline-earth ions from the molten salts (eutectic LiCl-KCl) utilized for recycling used nuclear fuel. Considering the higher stability of Sr and Ba ions relative to the Li and K ions in the chloride system, it would seem impractical to deposit Sr and Ba from the molten chloride solutions by electrochemical means; however, this work will present that the deposition of Sr and Ba into liquid metal electrodes becomes thermodynamically feasible by leveraging the strong chemical interactions between alkali/alkaline-earth metals and liquid metals. The thermodynamic properties of four binary alkaline earth-liquid metal alloys, (Sr, Ba)-(Bi, Sb), were determined by electromotive force (emf) measurements using solid-state electrolytes to examine the degree of chemical interactions (activity) between alkaline-earth metals and liquid metals. Using a pure alkaline-earth metal A (A = Sr or Ba) as the reference electrode and binary A-B alloys (B = Bi or Sb) as working electrodes in solid-state binary CaF2-AF2 electrolyte, emf measurements were conducted over a temperature range of 450–850 °C in 25 °C increments. Reproducible emf values were obtained within ±5 mV accuracy during cooling-heating cycle at alloy mole fractions up to x A(in B) = 0.40. Based on the experimentally determined emf values of alkaline-earths in liquid Bi and Sb electrodes, the electrode reactions involving Sr and Ba elements were found to be thermodynamically feasible due to substantially larger emf values of Sr and Ba in Bi, compared to those of Li and K in Bi. Namely, the chemical interactions of liquid metals (Bi and Sb) were stronger for alkaline-earths (Sr and Ba) than for alkali (Li and K) metals. Based on thermodynamic measurements, the liquid metal electrodes were subjected to cathodic discharge at a constant current density of 50 mA cm–2 in eutectic LiCl-KCl with the addition of 5–10 mol% of SrCl2 and/or BaCl2. As shown in Figure 1, the use of liquid metals (Bi and Sb) resulted in the deposition of Ba in LiCl-KCl-10mol%BaCl2 electrolyte. Further study in LiCl-KCl-SrCl2-BaCl2 electrolytes also indicated that the use of strongly interacting liquid metal electrodes could result in the co-deposition of Sr and Ba in addition to Li. The results of this work show that alkaline-earth fission products (Sr2+ and Ba2+) accumulated in molten salts can be recovered into liquid metals by electrochemical separation, which could be employed as a critical step for recycling the process salt (LiCl-KCl) in order to minimize the generation of additional nuclear wastes. Figure 1. Cross-section analyses of Bi (discharged at 510 °C) and Sb (discharged at 650 °C) electrodes under constant current density at 50 mA cm– 2 in LiCl-KCl-10mol%BaCl2 electrolyte, using SEM and elemental X-ray mapping. Figure 1

Thermodynamic Study of (KCl + N,N-Dimethylformamide + Water) System Based on Potentiometric Measurements

In this research, the thermodynamic properties of (KCl + N,N-dimethylformamide + water) system were determined based on potentiometric technique. The electromotive force measurements were carried out by using self-made electrodes on the galvanic cell of type Ag|AgCl|KCl (m), N,N-dimethylformamide (w), and H2O (1 – w)|K-ISE in various mass fractions of N,N-dimethylformamide in water (0, 0.10, 0.20, and 0.30) in the molality ranging from 0.0094 to 2.5200 mol·kg–1 at T = (298.2 and 308.2) K and P = 0.1 MPa. Thermodynamic properties modeling was implemented using the Debye–Huckel extended equation, Pitzer ion interaction, and Pitzer–Simonson–Clegg models. Subsequently, unknown parameters for each model were determined and utilized to calculate the thermodynamic properties such as the mean activity coefficients, the osmotic coefficients, the excess Gibbs free energy, and the solvent activity for the system under investigation.

Electromotive force study of lanthanum in liquid bismuth

The thermodynamics of lanthanum (La) dissolved in liquid bismuth (Bi) were determined by means of the electromotive force (EMF) measurement using a galvanic cell consisting of molten chloride and liquid bismuth at the temperature ranging from 723 K to 975 K. A considerable increase of the activity coefficient with temperature was observed for the La-Bi alloy. In addition, the activity coefficient increased slightly with the concentration of La. The values of the molar excess free energy of formation, the excess enthalpy, and the excess entropy of La dissolved in Bi were determined. The heat of formation of liquid La-Bi alloys (ΔHLa–BiM) was deduced from the measured activity coefficient. There is a linear dependence of experimental ΔHLa–BiM on the La concentration.

Phase Equilibria and Thermodynamics of Selected Compounds in the Ag–Fe–Sn–S System

Polythermal sections in the vicinity of the quaternary compounds Ag2FeSnS4 and Ag2FeSn3S8 have been modeled. The mechanism of formation of these quaternary compounds and their thermal stability have been investigated. Measurements of electromotive force allowed calculations of the standard thermodynamic functions ΔG°, ΔH°, and S° of the Ag2FeSnS4 and Ag2FeSn3S8 compounds. Based on calorimetric measurements, the enthalpies of phase transitions of the selected compounds were determined. Furthermore, the heat capacities of both quaternary compounds were estimated by applying different calculation methods. Thermodynamic properties of the quaternary compounds, which are regarded as functional magnetic materials, were analyzed and are discussed in detail.

Fabrication of highly dense isotropic Nd-Fe-B nylon bonded magnets via extrusion-based additive manufacturing

Magnetically isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts. The density of the printed magnet is ∼ 5.2 g/cm3. The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 T), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m3). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability as revealed by flux aging loss measurements. Tensile tests performed at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Finally, we demonstrate the performance of the 3D printed magnets in a DC motor configuration via back electromotive force measurements.

Negative Deviations from the Debye-Hückel Limiting Law for High-Charge Polyvalent Electrolytes: Are They Real?

In the past few decades, electromotive force (emf, E) measurements using improved electrochemical cells have afforded the derivation of mean ionic activity coefficients (γ±'s) of very dilute solutions of binary electrolytes, within the 10-6-10-3 molar range (Malatesta et al., J. Solution Chem. 1994, 23, 11 ). Such measurements are especially important for highly charged electrolytes whose behavior at very low concentration is not yet fully understood, and whose γ± values, derived from E data, have been claimed by Malatesta and co-workers to exhibit "negative deviations" from the Debye-Hückel (DH) limiting law. Here I examine electrolytes studied by the Malatesta group, which belong to the 3-1, 1-3, 2-3, and 3-3 valence families, and analyze their E and γ± data using the Smaller-ion Shell (SiS) theoretical treatment ("DH-SiS") of strong electrolyte solutions (Fraenkel, J. Chem. Theory Comput. 2015, 11, 178 and 193 ). The DH-SiS physical model incorporates all three ion-size parameters of a binary ionic solution as the "true" ion-ion collision distances, and leads to an improved DH-like electrostatic theory of ionic activity. Correcting Malatesta's data by better extrapolation of E to zero concentration results in a more accurate "standard potential", E°; this affords improved γ± values that (1) fit well with the DH-SiS equations and (2) agree with the DH limiting law.

The Ideal Ionic Liquid Salt Bridge for Direct Determination of Gibbs Energies of Transfer of Single Ions, Part II: Evaluation of the Role of Ion Solvation and Ion Mobilities.

An important intermediate goal to evaluate our concept for the assumption-free determination of single-ion Gibbs transfer energies Δtr G°(i, S1 →S2 ) is presented. We executed the crucial steps a) and b) of the methodology, described in Part I of this treatise, exemplarily for Ag+ and Cl- with S1 being water and S2 being acetonitrile. The experiments showed that virtually all parts of the liquid junction potentials (LJPs) at both ends of a salt bridge cancel, if the bridge electrolyte is an "ideal" ionic liquid, that is, one with nearly identical diffusion of anion and cation. This ideality holds for [N2225 ]+ [NTf2 ]- in the pure IL, but also in water and acetonitrile solution. Electromotive force measurements of solvation cells between S1 and S2 demonstrated Nernstian behavior for Ag+ concentration cells and constant like cell potentials for solutions with five tested Ag+ counterions.

The Ideal Ionic Liquid Salt Bridge for Direct Determination of Gibbs Energies of Transfer of Single Ions, Part II: Evaluation of the Role of Ion Solvation and Ion Mobilities

AbstractAn important intermediate goal to evaluate our concept for the assumption‐free determination of single‐ion Gibbs transfer energies ΔtrG°(i, S1→S2) is presented. We executed the crucial steps a) and b) of the methodology, described in Part I of this treatise, exemplarily for Ag+ and Cl‐ with S1 being water and S2 being acetonitrile. The experiments showed that virtually all parts of the liquid junction potentials (LJPs) at both ends of a salt bridge cancel, if the bridge electrolyte is an “ideal” ionic liquid, that is, one with nearly identical diffusion of anion and cation. This ideality holds for [N2225]+[NTf2]‐ in the pure IL, but also in water and acetonitrile solution. Electromotive force measurements of solvation cells between S1 and S2 demonstrated Nernstian behavior for Ag+ concentration cells and constant like cell potentials for solutions with five tested Ag+ counterions.

The Ideal Ionic Liquid Salt Bridge for the Direct Determination of Gibbs Energies of Transfer of Single Ions, Part I: The Concept.

Described is a procedure for the thermodynamically rigorous, experimental determination of the Gibbs energy of transfer of single ions between solvents. The method is based on potential difference measurements between two electrochemical half cells with different solvents connected by an ideal ionic liquid salt bridge (ILSB). Discussed are the specific requirements for the IL with regard to the procedure, thus ensuring that the liquid junction potentials (LJP) at both ends of the ILSB are mostly canceled. The remaining parts of the LJPs can be determined by separate electromotive force measurements. No extra-thermodynamic assumptions are necessary for this procedure. The accuracy of the measurements depends, amongst others, on the ideality of the IL used, as shown in our companion paper Part II.

The Ideal Ionic Liquid Salt Bridge for the Direct Determination of Gibbs Energies of Transfer of Single Ions, Part I: The Concept

AbstractDescribed is a procedure for the thermodynamically rigorous, experimental determination of the Gibbs energy of transfer of single ions between solvents. The method is based on potential difference measurements between two electrochemical half cells with different solvents connected by an ideal ionic liquid salt bridge (ILSB). Discussed are the specific requirements for the IL with regard to the procedure, thus ensuring that the liquid junction potentials (LJP) at both ends of the ILSB are mostly canceled. The remaining parts of the LJPs can be determined by separate electromotive force measurements. No extra‐thermodynamic assumptions are necessary for this procedure. The accuracy of the measurements depends, amongst others, on the ideality of the IL used, as shown in our companion paper Part II.

Thermodynamic Properties of Strontium-Lead Alloys Determined by Electromotive Force Measurements

The thermodynamic properties of Sr-Pb alloys were determined by electromotive force (emf) measurements. A Sr(s)|CaF2-SrF2|Sr(in Pb) electrochemical cell was used to measure emf values at 773–1073 K for Sr-Pb alloys at mole fractions xSr = 0.07–0.59. These emf measurements were used to determine thermodynamic properties of Sr-Pb alloys, including activity, partial molar entropy, and partial molar enthalpy. At 873 K, activity values of Sr in Pb were as low as aSr = 1.72 × 10–9 at mole fraction xSr = 0.07, implying strong atomic interactions between Sr and Pb. Phase transition temperatures of Sr-Pb alloys, observed during emf measurements, were corroborated by thermal analysis (0.07 ≤ xSr ≤ 0.34) by differential scanning calorimetry (DSC), and the phase constituents of Sr-Pb alloys (0.07 ≤ xSr ≤ 0.75) were characterized using X-ray diffraction (XRD). Experimentally-determined thermodynamic properties were compared to the assessed thermodynamic properties of the Sr-Pb system, confirming the phase transition temperatures and highlighting discrepancies in solution properties (activity and excess Gibbs energy).

Electrochemical and Thermodynamic Properties of Uranium on the Liquid Bismuth Electrode in LiCl-KCl Eutectic

This work presents the electrochemical behaviors of U on a liquid Bi electrode and the formation of Bi-U intermetallic compounds in LiCl-KCl eutectic. It was found that the deposition of U on the liquid Bi electrode was a two-step process. The activity coefficient of U in the liquid Bi was determined by coulometric titration and in-situ open circuit chronpotentiometry versus two different reference electrodes at the temperature range of 723 to 813K. The solubility of U in liquid Bi was evaluated by pulse electrolysis. Furthermore, thermodynamic properties of Bi-U intermetallic compounds were measured by open circuit chronopotentiometry. The linear dependence of the Gibbs free energy of formation as a function of temperature was obtained, from which the enthalpy and entropy of formation were also determined. The activities and partial molar Gibbs free energies of U in two phase coexisting states were calculated through the measurement of electromotive force. Galvanostatic electrolysis was then conducted to prepare Bi-U intermetallic compound in the LiCl-KCl-UCl3 melt on a liquid Bi electrode. The phase composition and microstructure of the alloy was characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS).

Magnetic Circuit Modeling and Analysis of Unilateral Axle-Counting Sensor

The unilateral axle-counting sensor, as a new type of axle-counting device, is gradually substituting other axle counters owing to its simple structure and great performance, which lead to an excellent application prospect. In this paper, we analyze the working principle of this sensor and establish an equivalent magnetic circuit model based on the sensor structure characteristics and its spatial relation with the track and wheel. In addition, we propose a rapid calculation method for magnetic circuits based on the division of the magnetic flux area according to the magnetic flux distribution characteristics of the sensor and provide the calculation expressions of reluctance for each area; furthermore, we calculate the induction electromotive force generated in the induction coils. Using 3-D finite-element method and the actual measurement of the induction electromotive force, the correctness and rapidity of the magnetic circuit model and the method of calculating the induction electromotive force are proved.

Bi/Bi2O3 sensor for quantitation of dissolved oxygen in molten salts

To quantify the oxygen content in molten salts, we examined the performance of an yttria-stabilized zirconia solid electrolyte oxygen sensor with a Bi/Bi2O3 reference electrode, focusing on its output accuracy. When the above sensor was tested in a flow of gas with known oxygen partial pressure, p_{O_2}, a linear relationship between lgp_{O_2} and the electromotive force (EMF) was observed, and the correlation slope exhibited a positive deviation from Nernstian behavior. EMF measurements performed in molten NaCl–KCl indicated that the oxygen content of this salt mixture increased with increasing oxygen partial pressure in the covering gas, in agreement with Henry’s law. Moreover, the EMF exhibited a linear decrease with increasing melt temperature of molten NaCl–KCl, in agreement with the theoretical model. Finally, a relationship between the structure of molten NaCl–KCl and its oxygen diffusion behavior was established. As a result, the developed sensor was demonstrated to be well suited for determining the oxygen content of molten salts.

Thermodynamic study of the Ag-Tl-Se system using the EMF method with AG4RbI5 as a solid electrolyte

The Ag-Tl-Se ternary system in the composition region Ag2Se-Tl2Se-Se was studied in the temperature range 300–450 K by measuring the electromotive force (EMF) in a concentration cell containing a silver electrode and Ag4RbI5 as a solid electrolyte. A previously constructed solid-phase equilibria diagram of this system that included the ternary compounds AgTlSe, Ag3TlSe2, and Ag7TlSe4 was confirmed. The EMF measurements allowed the partial molar functions $$ \left(\Delta \overline{G},\Delta \overline{H},\Delta \overline{S}\right) $$ of silver in some phase regions of the Ag2Se-Tl2Se-Se subsystem to be calculated. Using the solid-phase equilibria diagram, the potential-forming reactions were defined and the standard thermodynamic functions of formation and the standard entropy values of the ternary compounds mentioned above were calculated. Besides experimental results, data reported in the literature for thermodynamic functions of TlSe as well as the standard entropy values of silver and selenium were used in the calculations. The results of the calculations were compared with relevant data in the literature. The results confirmed that it is possible to study the thermodynamics of silver-containing complex systems using this modified EMF method, even if the system contains a more electropositive component than silver.

Mean Activity Coefficients Measurements and Thermodynamic Modeling of the Ternary Mixed Electrolyte KCl + Lactose + Water System at T = 298.15 K

In this work, the mean activity coefficients of KCl in the KCl+lactose +water system were determined using the potentiometric method. The electromotive force measurements were carried out on the galvanic cell without liquid junction of the type: Ag|AgCl|KCl (m), lactose (wt.%), H2O (1−wt.) %|K-ISE, in various mixed solvent systems containing 0, 5,7.5, 10 and 12.5 % mass fractions of lactose. The ionic strengths range was from 0.0003 to 2.000 kg.mol−1. The modeling of this ternary system was made based on the Pitzer ion-interaction model. The mean activity coefficients were correlated with Pitzer model and the adjustable Pitzer parameters (βo, β1 and Co) were determined for the series under investigated system. Then, these parameters were used to calculate the amounts of thermodynamic properties such as osmotic coefficients and excess Gibbs free energies for under investigated systems. The results clearly indicated that a good correlation was obtained with the Pitzer model to describe this system.

Thermodynamic study of antimony chalcoiodides by EMF method with an ionic liquid

Thermodynamic properties of antimony chalcoiodides have been determined experimentally by means of electromotive force (EMF) method measurements of the $$(- )\;{\text{Sb}}\;({\text{solid}}) / {\text{ionic}}\;{\text{liquid}},{\text{ Sb}}^{3 + } /\left( {{\text{SbXI}} - {\text{SbI}}_{3} - {\text{X}}} \right)\;({\text{solid}})\;( + )$$ concentration chains within temperature range 300–430 K (X–S, Se, Te). A mixture of morpholine and formic acid with adding 0.5 mol% anhydrous SbCl3 was used as an electrolyte, whereas equilibrium alloys from the SbXI–SbI3–X three-phase regions of the corresponding systems were exploited as right electrodes. From the EMF measurements, the partial molar functions of antimony in the SbXI–SbI3–I three-phase regions are calculated. The potential formation reactions were determined based on the solid-phase equilibria diagrams of the Sb–X–I systems, and the standard thermodynamic functions of formation and standard entropies of the ternary compounds SbSI, SbSeI, and SbTeI were calculated. For the calculations, the standard thermodynamic functions of SbI3, as well as standard entropies of chalcogens, were used.

ТЕРМОДИНАМИЧЕСКИЕ СВОЙСТВА ТВЕРДЫХ РАСТВОРОВ В СИСТЕМЕ Cu8GeS6 - Ag8GeS6

Измерением ЭДС концентрационных цепей с твердым электролитом Cu4RbCl3I2 в интервале температур 300÷380 К изучена система Cu8GeS6-Ag8GeS6. Показано образование широких областей твердых растворов на основе исходных соединений. Из данных измерений ЭДС вычислены парциальные молярные функции меди в сплавах.

Thermodynamic Properties of Superionic Phase Ag4HgSe2I2 Determined by the EMF Method

Triangulation of the Ag-Hg-Se-I system in the vicinity of quaternary phase Ag4HgSe2I2 was performed by differential thermal analysis, X-ray diffraction and electromotive force (EMF) methods. The spatial position of the phase region Ag4HgSe2I2-Se-HgI2 regarding the figurative point of silver was used to write the chemical reaction of formation of Ag4HgSe2I2. The EMF measurements were carried out by applying an electrochemical cell: (–) C|Ag|Ag2GeS3 glass|Ag4HgSe2I2, HgI2, Se|C (+), where C is graphite and Ag2GeS3 glass is the fast purely Ag+ ions conducting electrolyte. The linear dependence of the EMF of the electrochemical cell on temperature was used to determine the standard thermodynamic values of Ag4HgSe2I2 for the first time.

The Phase Relationships in the Sb-S-I System and Thermodynamic Properties of the SbSI

The phase relationships in the Sb-S-I ternary system were determined experimentally over entire concentration range by means of differential thermal analysis (DTA) and x-ray diffraction (XRD) techniques. Two quasi-binary, three isopleth sections, 300 K isothermal section and liquidus surface projection of the system were revised. The primary crystallization fields of all existing phases, the types and coordinates of all invariant and monovariant equilibria were determined. The electromotive force measurements (EMF) method was used to calculate the partial molar functions of antimony in alloys and the standard integral thermodynamic functions of SbSI.