Eutectic KCl Research Articles

Corrosion Behavior of High-Chromium Alloys in Molten LiCl–KCl Eutectic

Corrosion Behavior of High-Chromium Alloys in Molten LiCl–KCl Eutectic

Permeation Tendency of Rare-earth Elements through a Ni-based Alloy Diaphragm in LiCl–KCl Eutectic Melts

Permeation Tendency of Rare-earth Elements through a Ni-based Alloy Diaphragm in LiCl–KCl Eutectic Melts

Electrochemical and thermodynamic properties of Pu(III) ions at the Mo electrode in LiCl–KCl eutectics

Electrochemical and thermodynamic properties of Pu(III) ions at the Mo electrode in LiCl–KCl eutectics

Thermodynamic Simulation of UCl3 Oxidation with Lead Chloride and UCl4 Reduction with Metallic Uranium in the Molten LiCl–KCl Eutectic

Thermodynamic Simulation of UCl3 Oxidation with Lead Chloride and UCl4 Reduction with Metallic Uranium in the Molten LiCl–KCl Eutectic

CORROSION PERFORMANCE OF PLASMA SPRAYED ALUMINA–40 wt.% TITANIA COATED HIGH-DENSITY GRAPHITE IN MOLTEN LiCl–KCl EUTECTIC SALT

The corrosion performance of plasma sprayed alumina–40[Formula: see text]wt.% titania (A40T) coated high-density graphite was investigated in molten LiCl–KCl eutectic salt at [Formula: see text]C for periods of 500, 1000, and 2000[Formula: see text]h under argon atmosphere. The microstructural and compositional investigations of corrosion-tested A40T coatings by scanning electron microscopy and energy dispersive X-ray spectroscopy showed that the samples exhibited better corrosion resistance up to 500[Formula: see text]h. The poor corrosion behavior and failure of A40T coating from graphite substrate in the long-term (1000 and 2000[Formula: see text]h) immersion was discussed in detail based on the microstructure and composition analysis. The phases existing in the as-sprayed coating ([Formula: see text]-Al2TiO5, [Formula: see text]-Al2O3, R-TiO2, and [Formula: see text]-Al2O3) remained in the detached coating after 1000[Formula: see text]h exposure to the molten salt. The reaction between molten salt and A40T coating was not evident from XRD analysis. A40T coatings with chromium carbide–nichrome (Cr3C2–NiCr) bond coat showed complete spallation of the top coating and oxidation of the bond coat as evident from the X-ray diffraction analysis. Detachment of the A40T coating occurred due to the penetration of the molten salt into the coating through the voids and pores present on the surface, which weakened the adhesion strength between the substrate and the A40T coating or top coat-bond coat interfaces.

Investigation of the Redox Potential of Lithium and Its Dissolution in the LiCl–KCl Eutectic

This present paper reports two fundamental thermodynamic data, including redox potential of Li+ and dissolution rate of metallic lithium in the LiCl–KCl eutectic for promoting the development of metallic lithium. Firstly, data from the first-principles molecular dynamics (FPMD) simulation was used for deep potential (DP) model training. The model’s reliability was then evaluated by the consistency of the energy, force, and radial distribution functions by comparing with FPMD simulation. After that, machine learning-driven molecular dynamics was performed by deep potential molecular dynamics (DPMD) to predict the redox potential of Li+/Li vs Cl2/Cl− in the LiCl–KCl eutectic. Compared with electromotive force measurements results, the maximum relative error is 6.86%. Finally, we investigated the effects of current density and temperature on lithium metal dissolution rate in the LiCl–KCl eutectic by the strategy of current reversal chronopotentiometry, respectively. In the current density range (0.041–0.245 A cm−2), the effect of current density on the dissolution rate of metallic lithium is negligible. As expected, lithium metal prefers to dissolve at high temperatures, and the activation energy of dissolution of lithium in LiCl–KCl eutectic is Ea = 27.78 kJ·mol−1.

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl-KCl Eutectics.

Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3- with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl-KCl-Li3 N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3- to NH3 is grossly over-simplified. We find that Li3 N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H- (H oxidation state -1) and H+ in the form of NH2- /NH2 - /NH3 (H oxidation state +1) in the absence of applied current, resulting in non-Faradaic release of NH3 . It is further observed that NH2- and NH2 - possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3 N, N2 can be reduced to N3- while stoichiometric amounts of H- are oxidised to H2 . The H2 can then react spontaneously with N3- to form NH3 , regenerating H- and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10-8 mol cm-2 s-1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15 N2 confirms the resulting NH3 is from catalytic N2 reduction.

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

AbstractMolten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3− with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3− to NH3 is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H− (H oxidation state −1) and H+ in the form of NH2−/NH2−/NH3 (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2− and NH2− possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2 can be reduced to N3− while stoichiometric amounts of H− are oxidised to H2. The H2 can then react spontaneously with N3− to form NH3, regenerating H− and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10−8 mol cm−2 s−1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15N2 confirms the resulting NH3 is from catalytic N2 reduction.

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.

Template-Directed Directionally Solidified 3D Mesostructured AgCl-KCl Eutectic Photonic Crystals.

3D mesostructured AgCl-KCl photonic crystals emerge from colloidal templating of eutectic solidification. Solvent removal of the KCl phase results in a mesostructured AgCl inverse opal. The 3D-template-induced confinement leads to the emergence of a complex microstructure. The 3D mesostructured eutectic photonic crystals have a large stop band ranging from the near-infrared to the visible tuned by the processing.

Electrochemical preparation of Al–Sm intermetallic compound whisker in LiCl–KCl Eutectic Melts

This work presents the electrochemical study of Sm(III) on an aluminum electrode in LiCl–KCl melts at 773K by different electrochemical methods. Three electrochemical signals in cyclic voltammetry, square wave voltammetry, open circuit chronopotentiometry, and cathode polarization curve are attributed to different kinds of Al–Sm intermetallic compounds, Al2Sm, Al3Sm, and Al4Sm, respectively. Al–Sm alloy with different phase structure (Al2Sm and Al3Sm) could be obtained by the potentiostatic electrolysis with the change of electrolytic potentials and time. Al–Sm alloy containing whiskers (Al4Sm) was obtained by potentiostatic electrolysis (−2.10V) on an aluminum electrode for 7hours with the change of electrolytic temperature and cooling rate in LiCl–KCl–SmCl3 (16.5wt. %) melts. The XRD and SEM&EDS were employed to investigate the phase composition and microstructure of Al–Sm alloy. SEM analysis shows that lots of needle−like precipitates formed in Al–Sm alloy, and their ratios of length to diameter are found to be greater than 10 to 1. The TEM and electron diffraction pattern were performed to investigate the crystal structure of the needle–like precipitates. The results show that the needle−like precipitates are intermetallic compound whiskers. The micro–hardness test and potentiodynamic polarization test illustrate that the micro–hardness and corrosion property of Al–Sm alloy containing whiskers are remarkably improved in comparison with the Al–Sm alloy without whiskers, respectively.

Understanding size effects on the strength of single crystals through high-temperature micropillar compression

Compression tests of 〈111〉-oriented LiF single-crystal micropillars 1–5μm in diameter were carried out from 25°C to 250°C. While the flow stress at ambient temperature was independent of the micropillar diameter, a strong size effect developed with elevated temperature. This behavior was explained by rigorously accounting for the different contributions to the flow stress of the micropillars as a function of temperature and pillar diameter: the lattice resistance, the forest hardening; and the size-dependent contribution as a result of the operation of single-arm dislocation sources. This was possible because the micropillars were obtained by chemically etching away the surrounding matrix in directionally solidified LiF–NaCl and LiF–KCl eutectics, avoiding any use of focused ion beam methods, yielding micropillars with a controlled dislocation density, independent of the sample preparation technique. In particular, the role of the lattice resistance on the size effect of micrometer-size single crystals was demonstrated unambiguously for the first time. This result rationalizes the different values of power-law exponent for the size effect found in the literature for face-centered cubic and body-centered cubic metals as well as for covalent and ionic solids.

Novel fluidised cathode approach for the electrochemical reduction of tungsten oxide in molten LiCl–KCl eutectic

The electrochemical reduction of metal oxides is an important step in refractory metal production and in the pyroprocessing of spent nuclear materials. The FFC Cambridge process has revolutionised molten salt electrolysis; however, it has quite a low efficiency and has diffusion and oxide build-up issues. The fluidised cathode approach eliminates some of these issues. To illustrate the process, the electroreduction of tungsten oxide particles from a LiCl–KCl eutectic is demonstrated. Cyclic voltammetric measurements were taken and show the main reduction peak for WO3 to W to be at −2.135V (vs. Ag/Ag+) at an operating temperature of 450°C. Chronoamperometry shows an increase in current associated with an increasing current collector size and the spalling of deposited W from the surface. SEM and EDS analyses of the product reveal the deposit to be pure W.

Electrochemical and thermodynamic properties of lanthanides (Nd, Sm, Eu, Tm, Yb) in Alkali metal chloride melts

Electrochemical and thermodynamic properties of Nd, Sm, Eu, Tm, and Yb chlorides in melts of individual LiCl, NaCl, KCl, and CsCl, of 3LiCl-2KCl, LiCl-KCl-CsCl, NaCl-KCl-CsCl, and NaCl-2CsCl eutectics, and of the equimolar NaCl-KCl mixture in the temperature interval 573–1173 K were studied by stationary and nonstationary methods. The mechanism of reduction of lanthanide(III) ions to metal was elucidated, and the main kinetic and thermodynamic characteristics of the process in alkali metal chloride melts were calculated. The influence of the ionic potential and polarizing power on the behavior of lanthanides in molten salts of various cationic compositions was determined.

Reduction behavior of [formula omitted] in molten LiCl–RbCl and LiCl–KCl eutectics by using tungsten

The reduction of uranium from UO22+ to UO2+ or U4+ in molten LiCl–RbCl and LiCl–KCl eutectics was examined by using tungsten and chlorine gas. Spectrophotometric technique was adopted to determine the concentration of uranium species. When tungsten was immersed into the LiCl–RbCl eutectic melt at 400°C without supplying chlorine gas, 36% of the total weight of the hexavalent of UO22+ was reduced to the pentavalent of UO2+. Under purging chlorine gas into the melt, 96% of UO22+ was reduced to the tetravalent of U4+. Tungsten oxy-chloride of WOCl4 was produced via the reductions of UO22+, which was volatized from the melt and adsorbed on the upper part of experimental cell. On the other hand, 84% of UO22+ in the LiCl–KCl eutectic melt at 500°C was reduced to U4+ by using tungsten and chlorine gas.

Electrochemical Behavior of Zr on a Liquid Cd Electrode in LiCl–KCl Eutectic Melts

The electrochemical behavior of zirconium on a liquid cadmium electrode was studied in LiCl–KCl melts containing at 773 K. In a cyclic voltammogram of the liquid cadmium electrode, a cathodic peak was observed at around (vs ) as well as at attributed to zirconium metal deposition. Because the deposit obtained by potentiostatic electrolysis at was confirmed to be from X-ray diffraction analysis, the cathodic peak at corresponded to formation. The open-circut-potential of the liquid cadmium electrode with was measured to calculate thermodynamic properties such as relative partial molar Gibbs energies of zirconium in . The quantity of zirconium recovered in the liquid cadmium electrode by the potentiostatic electrolysis at was measured by inductively coupled plasma-atomic emission spectroscopy. The result indicated of the zirconium recovery efficiency, which was defined as the quantity of electricity corresponding to the recovered zirconium divided by the total quantity of passed electricity.

Fundamental aspects of chlorine induced corrosion in power plants

Chlorine induced corrosion is the most important corrosion process in power plants, firing waste, coal and/or biomass. Depending on the process, chlorine is present as HCl gas, as solid KCl and NaCl in ashes or as eutectic melts i.e. KCl–ZnCl2 in deposits of waste fired boilers. In the presence of HCl gas and solid chlorides, ‘active oxidation’ is generally accepted as the major corrosion mechanism. Metal chlorides are formed by inward diffusion of chlorine to the metal/oxide interface, evaporating and subsequently oxidized to non-protective oxides and additional chlorine. In this mechanism, the role of alloying elements has not been fully understood until now. Hence, experiments were conducted on the influence of the alloying elements Mo, Ti, Si, Al on Fe–15Cr model alloys in an N2–5 vol.% O2 gas mixture with addition of 500 and 1500 vppm HCl with the use of thermogravimetric experiments at 600°C. The corrosive attack by ‘active oxidation’ strongly depends on the alloying elements. Fe–(15–25) wt% Cr alloys without any further addition of alloying elements show catastrophic ‘active oxidation’, characterized by the formation of metal chlorides at the metal–oxide interface. The addition of molybdenum, silicon and aluminium generally decreases the corrosive attack, whereas Ti has no beneficial effect and the corrosion is enhanced compared to Fe–15Cr.The presence of molten chlorides on heat exchanger tubes leads to catastrophic corrosion rates, even at relatively low temperatures of 250°C. Thick oxides scales of Fe2O3 are formed in contact with the gas phase. At the metal–oxide interface, a mixture of KCl–FeCl2 chloride phases are detected, probably molten at a reaction temperature of 400°C. Short term experiments on 2.25Cr–1Mo steel at 400°C in N2–5 vol.% O2–HCl gas mixtures covered with a eutectic KCl–ZnCl2 melt have shown that the metal is dissolved in the chloride melt at the melt/scale interface and precipitated as a thin layer of oxide at the melt/gas phase boundary. The kinetics of the corrosion strongly depends on gas phase composition i.e. p(HCl) and p(O2).

Electrode Processes in a Eutectic KCl–KF Melt Containing Gadolinium Oxide

The electroreduction of gadolinium from a eutectic KCl–KF melt containing 0.210–1.233 wt % Gd2O3 on molybdenum and glassy carbon electrodes is studied at 1008 K. The solubility of gadolinium oxide is determined. It is shown that the reduction of a gadolinium oxyfluoride complex proceeds reversibly, with a subsequent reversible chemical reaction. The gadolinium reduction on an iron electrode in a eutectic KCl–KF melt purified of unwanted oxide ion impurities yields an iron-gadolinium alloy.

Precipitation of Rare Earth Compounds in LiCl ‐ KCl Eutectic

The 3:1 compounds of and , precipitate from the eutectic melt containing trivalent rare earth species, RE(III), at 723 K. In the presence of O2−, and/or precipitate from the melt. In the case of Gd, the formation of and strongly depends on O2− ion concentration in the melt. Only precipitates selectively from the melt while precipitates selectively when . The relative stability of against , thermodynamically evaluated for the same melt condition, shows is preferentially formed for light earths while the formation of is dominant for heavy earths.

Electrochemistry of Molybdenum Solutions in Molten LiCl ‐ KCl Eutectic at 500°C

The chemical and electrochemical properties of solutions of molybdenum chlorides in the fused eutectic were studied at 500°C. The chemical stability of solutions is an important parameter which must be controlled to ensure reproducible electrochemical measurements. Polarization curves at vitreous carbon electrodes revealed the existence of an electronic exchange between the stable species Mo(III) and Mo(IV) with a standard potential equal to 880 mV vs. the reference electrode. The reduction process appeared as a simple irreversible three‐electron exchange coupled with significant crystallization problems.