Molten NaCl-KCl Research Articles

Corrosion behaviour of FeCoNiCrAl high-entropy alloy in molten NaCl–KCl–MgCl2 chloride salt

Molten NaCl–KCl–MgCl2 is becoming a potential heat transfer fluid (HTF) and thermal energy storage (TES) material in the third generation of concentrated solar energy power (CSP) stations due to its excellent heat storage-capacity and thermal stability. However, the strong corrosion of the molten chloride salt at high temperature limits its industrial application. In this study, the corrosion behaviour of FeCoNiCrAl HEA with BCC + FCC phase structure in molten NaCl–KCl–MgCl2 (24.5–20.55–54.95 wt-%) at 650 °C under argon was investigated by a combination of weight loss and electrochemical methods. The results show that, the corrosion of FeCoNiCrAl HEA in molten chloride salt mainly manifests as the selective dissolution of Fe and Cr. With the further increase of immersion time, oxides gradually crack and slightly flake, resulting in large weight loss of FeCoNiCrAl HEA.

Hot corrosion behavior of Co-W coated ferritic stainless steel in molten chloride salt

The hot corrosion behavior of CoW multilayered oxide-coated FSS430 in molten NaCl-KCl (44.53–55.47 wt%) at 700 °C in an air atmosphere was investigated. The effects of CoW multi-layer oxide coating on the oxidation resistance and hot corrosion resistance of the substrate were studied by analyzing the mass change, corrosion products, surface morphology, and cross-sectional structure. The results showed that the CoW multi-layer oxide coating suppressed the interdiffusion of elements, and thus, effectively reduced the corrosion rate under the experimental conditions from 4.98 × 10−8 to 2.42 × 10−9 (g2·cm−4·s−1). Also, the coating was proved to inhibit the outward diffusion of Cr in the substrate and reduced the hot corrosion caused by the loss of Cr into the molten chloride salts.

Study on the corrosion behavior of 316H stainless steel in molten NaCl–KCl–MgCl2 salts with and without purification

Study on the corrosion behavior of 316H stainless steel in molten NaCl–KCl–MgCl2 salts with and without purification

A fundamental study on indium electrochemistry in molten NaCl-KCl eutectic: toward new technology development for indium secondary resources recycling

A fundamental study on indium electrochemistry in molten NaCl-KCl eutectic: toward new technology development for indium secondary resources recycling

Corrosion characteristics of Inconel 625 cladding layer and NiCrMoAl cladding layer in molten NaCl-KCl and NaCl-KCl-Na2SO4

The high-temperature corrosion characteristics of Inconel 625 and NiCrMoAl cladding layers were investigated in molten NaCl-KCl and NaCl-KCl-K2SO4. In NaCl-KCl, the corrosion was dominated by “electrochemical” mechanism, subsequently triggering “chlorine-active corrosion” mechanism. NiCrMoAl cladding layer provided significantly higher corrosion resistance than Inconel 625 cladding layer, due to the generated greatly Al2O3 enhanced the difficulty of inward diffusion of Cl-. In NaCl-KCl-K2SO4, protective Al2O3 and Cr2O3 faced “basic fluxing” mechanism, considerably aggravating the corrosion. Additionally, Al easily reacted with SO42-, which further consumed Al and generated free S, causing NiCrMoAl cladding layer to suffer serious corrosion than Inconel 625 cladding layer.

Recycling of waste indium tin oxide target for In-Sn alloy production based on molten salt electrochemistry

In the present study, an efficient method for waste ITO target recycling producing In-Sn alloy has been proposed based on molten salt electrochemistry. The thermodynamic analysis delivers a wide potential window of 2.26 V for the co-reduction of In2O3 and SnO2 at 750 °C in the molten NaCl-KCl system, indicating the theoretical feasibility of In-Sn alloy production through direct electro-deoxidation of waste ITO target. The electrochemical behaviors of indium and tin ions, as well as waste ITO target in NaCl-KCl were systematically investigated through the transient electrochemical techniques such as cyclic voltammetry, square wave voltammetry, open circuit chronopotentiometry, and potentiodynamic linear sweep, and the results generally accord well with each other. The electro-deoxidation experiments were conducted using waste ITO target as the cathode at a constant cell voltage of 3.0 V for varied time intervals. The reaction mechanism was clarified based on the analysis of the phase composition and microstructure changes of the cathodic products during electrolysis. The results indicate that the reactions such as In2O3/SnO2 electro-deoxidation, InO2- formation between In2O3 and O2-, as well as electro-reduction of InO2- generating metallic In, could proceed simultaneously during the electrolytic process.

The role of zinc sulfide in the electrochemical extraction of molybdenum

The main form of molybdenum in nature is molybdenum sulfide. It also exists in iron ore magnetic separation tailings together with zinc sulfide. Considering separating and extracting molybdenum and zinc, a large amount of SO2 is released and environmental pollution is caused by high energy consumption for the traditional pyrometallurgy process. This research proposes a novel process to achieve efficient extraction and separation of molybdenum and zinc through co-desulfurization of MoS2-ZnS in molten salt. It was found that the sulfur in MoS2 and ZnS could be effectively removed and collected as solid sulfur by constant potential electrolysis in molten NaCl-KCl at 750 °C. Furthermore, electrochemical testing showed that the decomposition of MoS2 was carried out in two steps, ZnS was reduced in one step, and the decomposition voltage of ZnS was smaller than that of MoS2. Zinc was obtained at the first stage, and the MoS2 or its intermediate compounds were wrapped around by liquid zinc. The substitution reaction, 2Zn + MoS2 = Mo + 2ZnS, was able to promote the decomposition of MoS2 in the electrolysis process. Zinc sulfide was then formed in the second stage, and it can be electrolyzed to metallic zinc again for reduction of MoS2. Zn/ZnS played the role of a reducing agent in the process of MoS2-ZnS co-desulfurization, which facilitated the process of desulfurization, and enabled the reduction of MoS2 at a smaller voltage while zinc could be reused. In this work, molybdenum metal containing zinc was extracted at a cell voltage of 2.7 V. Metallic zinc and molybdenum were separated and purified in the final stage by vacuum distillation.

Effect of fluoride ions on coordination structure of titanium in molten NaCl-KCl

Effect of fluoride ions on coordination structure of titanium in molten NaCl-KCl

Optimized Process for Melt Pyrolysis of Methane to Produce Hydrogen and Carbon Black over Ni Foam/NaCl-KCl Catalyst

Methane pyrolysis transforming CH4 into hydrogen without a CO2 byproduct is a potential hydrogen production process under the net-zero emission target. The melt pyrolysis of methane is a technology that could simultaneously obtain hydrogen and carbon products. However, its catalytic activity and stability are still far from satisfactory. In this work, a new strategy for the melt pyrolysis of methane to hydrogen production was proposed using Ni foam and molten NaCl-KCl. The increase in the amount of Ni foam was found to enhance the methane conversion rate from 12.6% to 18%. The process was optimized by the different amounts of catalysts, the height of the Ni foam layer, and the filling method of Ni foam, indicating that the methane conversion rate of the string method could reach 19.2% at 900 °C with the designed aeration device. Furthermore, we observed that the addition of molten salt significantly alleviated the carbon deposition deactivation of the Ni foam and maintained its macrostructure during the reaction. The analysis of the carbon products revealed that carbon black could be obtained.

Synthesis of a (Ti, Mo)B2 coating by electro‐codeposition in NaCl–KCl–AlCl3–MoO3 melt containing TiB2 nanoparticles

AbstractThis paper demonstrates the availability of electro‐codeposition (i.e., the simultaneous occurrence of electrophoretic deposition of nanoparticles and electrochemical deposition of metal ions) in molten salts without the assistance of stirring of the bath. In molten NaCl–KCl–AlCl3–MoO3 system containing TiB2 nanoparticles at 710°C, the electro‐codeposition of TiB2 nanoparticles and Mo(VI) ions has been achieved, and a (Ti, Mo)B2 coating has been prepared.

Electrochemical behavior and separation of dysprosium from molten NaCl-KCl eutectic by co-reduction with aluminum

To electrolytically separate dysprosium from spent fuel, the electrochemical behavior of Dy3+ and its co-reduction process with Al3+ on inert Mo electrode in molten NaCl-KCl eutectic was systematically investigated employing a series of electrochemical methods. Dy3+ ions were directly reduced to dysprosium metal on inert Mo electrode through one step with three electrons exchanged. The reduction of Dy3+ was considered to be a quasi-reversible process, and the deposition of dysprosium on Mo follows the progressive nucleation mode. However, the co-reduction of Dy3+ with Al3+ on the Mo electrode allows the reduction of Dy3+ at more positive potentials because of the formation of Dy-Al intermetallics. The electromotive force method was then adopted to determine the thermodynamic properties of the Dy-Al intermetallics, such as the relative partial molar Gibbs free energy and the activity of dysprosium, and the standard formation Gibbs energy for Dy-Al intermetallics. Finally, potentiostatic electrolysis was conducted to extract Dy-Al alloys from the NaCl-KCl-0.40mol%DyCl3-0.56mol%AlCl3 melts. The XRD and FE-SEM/EDS analyses indicated that DyAl3, DyAl2 and DyAl intermetallics and metallic Al were generated in the products by electrolysis at −1.8 V, while the dysprosium-rich phases of DyAl2 and DyAl were produced as electrolysis at −2.0 V. The electrochemical separation of dysprosium from molten NaCl-KCl eutectic on inert Mo electrode was proved to be practically feasible by co-reduction with aluminum.

Impact of the additive manufacturing process on the high-temperature corrosion of 316L steel in the presence of NaCl–KCl–ZnCl2 molten solar salt

A comparative study of the high-temperature oxidation and corrosion resistance of wrought and additive manufacturing selective laser melting (SLM) 316L stainless steel was performed in presence of molten NaCl–KCl–ZnCl2 salt used for thermal energy storage in the new generation of concentrated solar plants. Isothermal tests at 650 and 700 °C in a dry air atmosphere were conducted to evaluate (i) the effect of the manufacturing process and (ii) the effect of molten salts on the corrosion behavior of the steel by dimensional metrology analysis, scanning electron microscopy and X-ray diffraction characterization. The manufacturing process had a significant influence on the oxidation resistance. The wrought samples had a mass gain after 48 h that was four times greater than that of SLM samples at 650 °C, and 50% greater at 700 °C. The presence of the salt primarily increased the corrosion rate of all the samples and, again, the wrought pieces suffered 13% and 6% more corrosion in terms of metal loss than the SLM ones at 650 and 700 °C, respectively. The presence of more pathways for Cr diffusion associated with a higher number of defects in the microstructure of the SLM sample, as dislocations and grain boundaries, facilitated the formation of Cr2O3 scales in the SLM sample, avoiding the intergranular attack shown in the wrought one.

Corrosion behavior of pressureless-sintered SiC in molten NaCl–KCl–MgCl2 salt at 700 °C

The corrosion behavior of pressureless-sintered SiC in a molten NaCl–KCl–MgCl2 salt at 700 °C was investigated. Results indicate that it is prior for SiC and sintering aid B around grain boundaries to be corroded. MgCl2⋅xH2O(x=4,6) in the salt plays an important role in the corrosion of SiC. MgCl2⋅xH2O is hydrolyzed to HCl, H2O, and MgO, which react with SiC and B to form C, SiO2, SiCl4, B2O3, and Mg2SiO4. The corrosion depth of SiC and the concentrations of elements Si and B in the salt increase with the corrosion time, which are fitted well with Fick's law of diffusion.

Hot corrosion behavior of NiCr-Cr3C2-CaF2/BaF2 composite coating with NiAl bond coating in molten NaCl-KCl and NaCl-Na2SO4 at 800 ℃

The NiCr-Cr3C2-CaF2/BaF2 coating with the NiAl bond coating was sprayed on a Ni16Cr13Co4Mo(wt%) alloy by detonation-gun spray, and hot corrosion behaviors were studied by electrochemical measurements. In molten NaCl-KCl, the corrosion products were mainly Cr2O3. Gas phases such as Cl2 led to spallations and cracks on the coating surface. In molten NaCl-Na2SO4, Na2SO4 decomposed and reacted with the coating. Mixed oxides formed a continuous corrosion layer, and Al diffused outward from bond coating to be oxidized. Some liquid phases existed in the corrosion layer and promoted hot corrosion. The detailed hot corrosion mechanisms in two molten salts were discussed.

Fabrication of TiB2 coatings by electrophoretic deposition of synthesized TiB2 nanoparticles in molten salts

This paper presents a novel process for preparation of TiB2 coatings, which is a combination of synthesis of TiB2 nanoparticles by borothermal reduction of TiO2 in molten NaCl–KCl–AlF3 system and subsequent electrophoretic deposition of the as-synthesized TiB2 nanoparticles in the same molten salts system. The electrophoretic deposition under various cell voltages was carried out, which resulted in preparation of dense and relatively flat TiB2 coatings. The effect of applied cell voltages on the electrophoretic deposition rate and mechanical properties of produced TiB2 coatings has been presented. The thickness of the coatings increased with the rise of cell voltages due to elevated migration and deposition rate of TiB2 nanoparticles. The hardness of the fabricated TiB2 coatings was assessed by nanoindentation, indicating that the values of hardness and elastic modulus increased with elevated electrophoretic voltages, which probably has an influence on the structure of the TiB2 coatings. Under the cell voltage of 1.2 V, the values of hardness and elastic modulus could reach 32.4 ± 1.2 GPa and 420.2 ± 23.9 GPa, respectively. This proposed process should also be applied for preparation of additional types of transition metal diboride coatings.

Electrochemical study on the hot corrosion behavior of Ni16Cr13Co4Mo alloy in molten NaCl-KCl and NaCl-KCl-Na2SO4

The hot corrosion behaviors of a novel Ni16Cr13Co4Mo alloy were investigated in molten NaCl-KCl and NaCl-KCl-Na2SO4 through electrochemical measurements, GIXRD and EPMA. The results showed that the overall corrosion was controlled by the diffusion process. Hot corrosion process was promoted by the increases in temperature and presence of Na2SO4. In molten NaCl-KCl, the corrosion layer was mainly composed of Cr2O3, and exhibited p-type semiconductive properties. In molten NaCl-KCl-Na2SO4, intergranular corrosion was observed and the corrosion layer consisted of a Cr2O3 outer layer (p-type) and a TiO2-Al2O3 inner layer (n-type). The relationship between the electrochemical mechanism and hot corrosion was discussed.

Molten Salt Assisted Synthesis of Boron Carbon Nitride Nanosheets for Enhanced Photocatalytic Activity of Silver Phosphate

Thin 2D boron carbon nitride nanosheets (BCNNS) possess high thermal and chemical stability as well as tunable electronic properties, but the lack of effective synthesis methods hinders their practical application. Herein, a facile and efficient approach for the synthesis of large-area boron carbon nitride nanosheets in molten KCl–NaCl salt media has been proposed. A Single precursor compound, ethylenediamine bisborane, was first heated to 1000 °C in KCl–NaCl salt melts and then held for only two minutes to produce BCNNS. Benefiting from the effective solvation of precursors and reduced surface energy in liquid salt melt, the lateral size of resultant BCNNS can reach up to 12 microns. The as-prepared products are subsequently used as a co-catalyst with silver phosphate (Ag3PO4) for degradation methyl orange under simulated sunlight. Due to the improved electronic property and interfacial effect of BCNNS, the photocatalytic performance of Ag3PO4 was significantly improved. The photodegradation rate increased from 0.369 min−1 of Ag3PO4 to 1.006 min−1 of BCN/Ag3PO4 composite with only 0.6 wt% BCNNS loading, a 2.73-fold higher value than that of pure Ag3PO4.

ELECTROREDUCTION OF DITUNGSTATE AND CARBONATE ANIONS IN CHLORIDE MELT

Electrocatalysis is one of the actively developing fields of application of tungsten carbides. For the synthesis of catalytically active carbides (materials with a large specific surface area, small particle size and structural defects) a large number of different technologies are being developed in the world. The method of high-temperature electrochemical synthesis is promising one. For its successful realization, it is necessary to study in detail the electrochemical behavior of each carbide component (tungsten and carbon) and the features of their partial and joint discharge. The aim of this paper is a voltammetric study of the partial and joint electroreduction of Na2W2O7 and Li2CO3 in molten NaCl–KCl electrolyte under CO2 pressure at a temperature of 750 °C.
 As a result of research, it was found that in the system Na,K|Cl–Na2W2O7–Li2CO3–CO2 joint reduction of tungsten carbide synthesis components occurs from lithium complexes of tungstate (LixWO4)2-x and carbonate- (LixCO3)2-x anions at potentials -1.65 – -1.8 V. Introduction of СО2 into the system (creation of its excess pressure in the cell) is necessary for the binding of oxide anions O2-, released during the discharge of anionic complexes, into a carbonate complex. The released oxide anion in the near-electrode layer inhibits the cathodic process. Also, a necessary condition for the sustainability production of tungsten monocarbide WC is the presence of free carbon, which is formed during the decomposition of CO2.
 Nanosized composites of tungsten carbides with free carbon WC/C (5 wt%) were obtained by potentiostatic electrolysis at a potential of -1.8 V as a cathode product. The properties of the obtained compounds were analyzed by XRD, SEM, BET, and Raman spectroscopy. Tungsten carbide has a particle size of ~ 10 nm and consists of hollow spherical structures. The synthesized composite is mesoporous material with a specific surface area of ~ 140 m2/g.
 The properties of the synthesized compo­site, namely: structural defects, the presence of free carbon, spherical morphology, nanometer size and high specific surface area, make it possible to use it as an effective electrocatalyst, for example, in the reaction of hydrogen evolution in acidic aqueous solutions.

Electrochemical Reduction of Cobalt Sulfide in Molten NaCl–KCl

Electrochemical Reduction of Cobalt Sulfide in Molten NaCl–KCl

Electrochemical Behavior and Separation of Dysprosium from Molten Nacl-Kcl Eutectic by Co-Reduction with Aluminum

Electrochemical Behavior and Separation of Dysprosium from Molten Nacl-Kcl Eutectic by Co-Reduction with Aluminum