Molten Medium Research Articles

Solubilization of platinum in KOH-B2O3 molten medium

Platinum (Pt) was converted into water-soluble compounds in a KOH-B2O3 molten medium. By controlling the heating temperature and shape of the alumina reaction container, the Pt compounds were synthesized efficiently. The reaction with the alumina container generates Al–O–Al linkages in the compound, resulting in the formation of an insoluble Pt compound. Fluoride addition to the medium prevented insolubilization of the compounds.

Technoeconomic assessment of hydrogen production from natural gas pyrolysis in molten bubble column reactors

Natural gas pyrolysis to produce carbon and hydrogen, known as “turquoise hydrogen, using molten metals and salts is a promising route to clean hydrogen production. Methane pyrolysis produces significantly less or near-zero CO2. Additionally, the solid carbon can be separated and sold as a valuable co-product, making industrial-scale production of hydrogen via pyrolysis economically attractive. To better understand the potential of turquoise hydrogen, this study presents a comparative techno-economic assessment of molten media pyrolysis processes in bubble column reactors using Ni0.27Bi0.73, Ga, and KCl–MnCl2 (33:67). The study evaluates techno-economic assessment with a clear understanding of kinetics of natural gas pyrolysis and reactor process modeling. According to the modeling results, Ga had the lowest reactor cost and total bare erected cost. Nevertheless, the pyrolysis process that used inexpensive KCl–MnCl2 molten salt was more economically advantageous. Due to uncertainties in the density separation of solid carbon in the molten salt at temperatures above 1000 °C, Ni0.27Bi0.73 was selected as the promising molten medium for the long term. Sensitivity analyses were carried out to assess the impact of the costs of natural gas, hydrogen, and electricity on the industrial concept. In regions where gas is produced, such as Saudi Arabia, mature molten pyrolysis plants that use grid electricity at a rate of $48/MWh and solar photovoltaic systems with storage at a rate of $24/MWh can be economically feasible at natural gas prices of $132/ton and $198/ton, respectively, even if carbon is not sold. The cost of producing turquoise H2 is comparable to the global average for grey H2 and selling carbon can generate additional revenue or improve the profitability of the plant. The net energy demand of the molten pyrolysis plant is found to be approximately 21% of the energy requirement for current methods of green hydrogen production through PEM (proton exchange membrane) electrolysis.

How to efficiently intercalate alkaline-earth metals into graphite using LiCl-KCl molten salts: An overview on the case of barium

In this paper, we present the three first stages currently known Ba-based Graphite Intercalation Compounds (GIC). They are synthesized using the LiCl-KCl molten salts method, which is especially efficient in order to help the intercalation of barium into the 2D graphitic galleries. According to the chosen reaction conditions, it is possible to obtain either the BaC6 binary compound or one of the two quaternary phases whose intercalated sheets contain simultaneously lithium, potassium and barium. By combining X-ray diffraction measurements and ion beam analyses for these compounds, their chemical formula is well established: Li0.2K0.6Ba0.35C6 for the α-phase, Li0.2K0.75Ba0.6C6 for the β one and BaC6 for the binary.The intercalated sheets of this last compound are single-layered. Its repeat distance reaches 529 pm and its 2D unit cell is hexagonal and commensurate with the graphene one with a parameter of 430.6 pm However, α- and β-phases are much more complex. For α- compound, the intercalated sheets are three-layered with an interplanar distance of 650 pm, while for β-phase, they are six-layered and the interplanar distance reaches 950 pm Both 2D unit cells are hexagonal, with a planar lattice parameter a of 1074 pm and 1280 pm respectively.Finally, a model of reaction mechanism is proposed, which breaks down the intercalation process into several steps: intercalation of lithium (LiC6), then replacement by barium (BaC6), next, formation of the β-phase, and ultimately its elimination to the benefit of the α one. Thus, this latter appears as the most stable GIC in this LiCl-KCl molten medium.

Molten Metals and Molten Carbonates in Solid Oxide Direct Carbon Fuel Cell Anode Chamber: Liquid Metal Anode and Hybrid Direct Carbon Fuel Cells

To enhance the contact between the electrolyte (source of O2−) and the carbon fuel in solid oxide–direct carbon fuel cells (SO-DCFCs), molten metals and molten salts were used in the anode chamber. Oxygen ions can dissolve and be transported in the molten medium to the anode three-phase boundary to reach and oxidize the carbon particles. To improve the sluggish kinetics of the electrochemical oxidation of carbon, the same molten media can act as redox mediators. Moreover, using a liquid metal/salt anode, tolerant to fuel impurities, the negative effect of carbon contaminants on cell performance is mitigated. In this work, an overview of SO-DCFCs with liquid metals, liquid carbonates, and mixed liquid metals/liquid carbonates in the anode chamber is presented and their performance was compared to that of conventional SO-DCFCs.

A dual-electrode oxide ion sensor for molten carbonates

• A simple sensor for detecting O 2– concentration in molten carbonate was proposed. • The sensor is applicable over both wide temperature and O 2– concentration ranges. • A fast response corresponding to varying O 2– activity can be achieved within a few seconds. • The electrochemical sensor is reliable and reusable with an excellent long-term stability. • The sensor can serve as an indicator for O 2– -involved (electro)chemical reactions. The concentration of oxide ions (O 2– ) determines the physicochemical properties of molten carbonates and modulates (electro)chemical reactions. However, it still lacks an efficient and reliable method to measure O 2– concentration in molten carbonates. Herein, we design a dual-electrode sensor to monitor the O 2– content in real time. For sensing O 2– in the target molten medium, we deliberately selected a Ni/NiO redox couple to serve as an O 2– -responding internal reference membrane electrode (RE in ) assembled in an yttrium-stabilized zirconia tube, which is accessible to achieve a stable and excellent response of O 2– from the bulk melt. To measure the membrane potential of RE in that is associated with the O 2– concentration in the bulk melt, we paired a Ag/Ag 2 SO 4 external reference electrode (RE ex ), which can indicate the potential difference between RE in and RE ex by measuring the open circuit potential (OCP), therefore figuring out the O 2– concentration based on Nernst equation. Taking molten Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 for example, the homemade dual-electrode sensor is well-responsive with a reliable linear correlation coefficient of R 2 = 0.9992 even the O 2– content is as low as 1.27 × 10 −4 mol kg −1 . The proposed dual-electrode gives clues to the rational design of anion sensor for relatively high-temperature systems.

Direct carboxylation of thiophene with CO2 in the solvent-free carboxylate-carbonate molten medium: Experimental and mechanistic insights

A feasible synthesis route is devised for realizing direct carboxylation of thiophene and CO 2 in a relatively mild solvent-free carboxylate-assisted carbonate (semi) molten medium. The effects of reaction factors on product yield are investigated, and the phase behavior analysis of the reaction medium is detected through the thermal characterization techniques. Product yield varies with the alternative carboxylate co-salts, which is attributed to the difference in deprotonation capacity caused by the base effect within the system. Besides, the detailed mechanism of this carbonate-promoted carboxylation reaction is studied, including two consecutive steps of the formation of carbanion through breaking the C—H bond(s) via the carbonate and the nucleophile attacking the weak electrophile CO 2 to form C—C bond(s). The activation energy barrier in C—H activation step is higher than the following CO 2 insertion step whether for the formation of the mono- and/or di-carboxylate, which is in good agreement with that of kinetic isotope effect (KIE) experiments, indicating that the C—H deprotonation is slow and the forming presumed carbanion reacts rapidly with CO 2 . Both the activation energy barriers in deprotonation steps are the minimal for the cesium cluster system since there have the weak the cesium Cs-heteroatom S (thiophene) and Cs-the broken proton interactions compared to the K 2 CO 3 system, which is likely to enhance the acidity of C—H bond, lowering the C—H activation barrier. Besides, these mechanistic insights are further assessed by investigating base and C–H substrate effects via replacing Cs 2 CO 3 with K 2 CO 3 and furoate ( 1a ) with thiophene monocarboxylate ( 1b ) or benzoate ( 1c ).

NaNO3 -Promoted Mesoporous MgO for High-Capacity CO2 Capture from Simulated Flue Gas with Isothermal Regeneration.

NaNO3 -promoted MgO composite materials have been prepared and their ability to sorb CO2 at a concentration relevant to CO2 capture from flue gas is explored. The uptake kinetics and capacities of sorbents of different NaNO3 /MgO ratios are measured at intermediate temperatures of 230-300 °C. The sorbent with a NaNO3 /MgO ratio of 0.10 has the highest 12 h sorption capacity among sorbents with different NaNO3 loadings, and the highest sorption capacity of 11.2 mmol g-1 is observed at 260 °C. Intriguingly, an induction period is observed in the initial stage of CO2 sorption. In situ XRD analysis, in situ FTIR spectroscopy, and a comparison of the CO2 sorption behavior under simulated flue gas conditions in comparison to prior studies employing pure CO2 indicated that the sorption of CO2 occurred through nucleation of MgCO3 crystallites in the material. The data indicate that the concentration of CO2 within the molten medium of NaNO3 , which is affected by both the solubility of CO2 in molten NaNO3 and the partial pressure of CO2 in the surrounding atmosphere, has a critical impact on the length of the induction period. A partially desorbed sample after sorption of CO2 displays much-improved sorption kinetics in the next cycle and was able to sorb and desorb CO2 over multiple cycles at isothermal conditions by simply switching the feed gas from CO2 to inert gas.

Reactivity of metallic palladium in a K2CO3-K2O-B2O3-Al2O3 melt

The reactivity of metallic palladium in a K2CO3-K2O-B2O3 melt is investigated as a function of heating temperature and time. The aqueous solubility of heat-treated palladium is enhanced by controlling the heating conditions leading to an optimum palladium extraction of 53% from the heat-treated product. The alumina crucible used as a reactor partially dissolves during the heating of metallic Pd, which requires the analysis of palladium solubilization to be discussed in terms of K2CO3-K2O-B2O3-Al2O3 system. Oxidized palladium combines with boron and aluminum oxyanions as ligands in the molten medium to form water-soluble palladium compounds. Information regarding water-soluble palladium compounds was obtained by analyzing the precipitate collected from the palladium-containing solution produced by water-leaching of the heat-treated product. The precipitate contained Pd (0.19 wt%), Al (0.74 wt%), B (2.6 wt%), and K (45 wt%). Raman spectroscopy confirmed the presence of oxidized palladium in the precipitate. Aluminum oxyanions with AlO4 and AlO6 structures and boron oxyanions as diborate groups also were detected in the precipitate.

Structure-Sensitive Properties of Liquid Steel: Efficacy Evaluation of Its Treatment with Modifiers and Refining Slag

It is proposed to consider the oxidation potential of the ladle slag coating as the factor affecting the modification efficiency. Conditions of modifiers effective influence on steel are determined. Samples of industrial steels smelted with the determined conditions accordance are obtained. The impact of new rapidly quenched modifiers with rare-earth metals on the molten medium carbon steels 40Kh and 38KhM was studied by method of viscometry. Such steels have no hysteresis of viscosity. According to the alloys influence on the liquid steel supercooling during solidification, limits of the rational using of new alloys are established.

Electrochemical Behavior of Plutonium in Molten Fluoride Medium

A pyrochemical process for slag recycling containing trapped actinide particles into a CaF2-CaO matrix is currently in progress. Since the process requires to melt the slag (melting point above 1300°C), an additional amount of CaCl2 must be used to decrease the operating temperature below 1000°C. Then, a reducing agent (calcium) is added into the molten medium to remove the actinides in a stable metallic form after decantation. The clean salt product meets the radiological requirements to be discarded to the dedicated way (ANDRA). However, the extraction process is operated in a molten chloro-fluoride salt which is complex and quite unknown. Pu investigation in simplified media, chloride and fluoride, must lead to understand the mechanism of Pu reduction in chloro-fluoride media. Pu behavior has already been investigated in molten chloride media via electrochemical techniques by J. Serp et al. [1], O. Shirai et al. [2] and Lambertin et al. [3]. Nevertheless, data regarding this actinide behavior in molten fluoride media are incomplete [4]. Consequently, a detailed electrochemical study was carried out on plutonium in fluoride salt. The selected solvent is a mixture of two well-known salts, LiF and CaF2, melted in a crucible made of vitreous carbon in an oxygen free atmosphere (argon). Plutonium ions were introduced into the melt in the form of PuF4 powder. The setup consisted of a three electrodes assembly: tungsten as working electrode, vitreous carbon as auxiliary electrode and the potentials were referred to a platinum electrode. Cyclic voltammetry, square wave voltammetry and chronopotentiometry were coupled with thermodynamic calculations (potential-oxoacidity diagram) to investigate the electrochemical system. The acquired data will be used for a better understanding of Pu extraction from the melt. [1] J. Serp, R.J.M. Konings, R. Malmbeck, J. Rebizant, C. Scheppler, J.-P. Glatz, Electrochemical behaviour of plutonium ion in LiCl-KCl eutectic melts, J. Electroanal. Chem., 561 (2004) 143. [2] O. Shirai, T. Iwai, Y. Suzuki, Y. Sakamura, H. Tanaka, Electrochemical behavior of actinide ions in LiCl-KCl eutectic melts, J. Alloys Compd., 271-273 (1998) 685. [3] D. Lambertin, S. Ched’homme, G. Bourgès, S. Sanchez, G. Picard, Plutonium chemical properties in NaCl-KCl and CaCl2 at 1073 K, J. Nucl. Mater., 341 (2005) 124. [4] C. Hamel, Séparation actinides-lanthanides (neodyme) par extraction électrolytique en milieux fluorures fondus, vol. 3, 2005. Thesis, Toulouse.

Factors Governing MgO(111) Faceting in the Thermal Decomposition of Oxide Precursors

The preparation of metal oxide particles, such as MgO, NiO, and ZnO, exposing polar facets via the decomposition of suitable precursors in air, molten salts, ionic liquids, or other media has been reported; however, the main driving force(s) and factors that determine their morphology have largely remained elusive. For instance, the adsorption of ions within a molten medium on a growing oxide surface has been proposed to stabilize MgO{111} facets by the so-called molten salt route (MSR). In this article, we examine the thermal decomposition of MgO precursors to assess the influence of precursor decomposition pathways, including the physical state of the reaction intermediates and the possibility of dissolution–recrystallization processes in the formation of octahedral MgO particles. We found that solid-to-solid conversions and recrystallizations in molten nitrates or chlorides are usually incapable of producing well-defined MgO{111} facets, indicating that ion adsorption on MgO may not be the main morphol...

Investigation of the structure of CaO-Al2O3-SiO2 melts as a basis for the development of new agglomerated welding fluxes and industrial refractories

A significant number of welding fluxes and industrial ceramics are produced in the Ukraine. The production of these materials is sufficient for both domestic needs and significant export. It is assumed that the ternary CaO-Al2O3-SiO2 system may become the basis for the development of agglomerated welding fluxes and technical ceramics. Three samples of ternary CaO-Al2O3-SiO2 system were studied by means of high-temperature X-ray diffraction above the melting point: 23.3CaO- 14.7Al2O3-62.0SiO2 wt. % (sample 1, eutectic), 9.8CaO-19.8Al2O3-70.4SiO2 wt. % (sample 2, eutectic), 15.6 CaO- 36.5Al2O3-47.9SiO2 wt. % (sample 3). Experimental scattering intensity curves, structure factors and the radial distribution function of atoms were obtained. The structural parameters of short-range order were calculated using melt structure models obtained by Reverse Monte Carlo method. The existence of microparticle associates of the mullite or sillimanite type immersed in the slag matrix is assumed. It is assumed that the calcium ions coordinated aroundthese associates are surrounded by oxygen melt anions. Such a structure can be considered as a colloidal solution. The microparticle of mullite is the core of the aggregate that is surrounded by calcium and oxygen ions from the molten medium.

Solution behavior of ZnS and ZnO in eutectic Na2CO3−NaCl molten salt used for Sb smelting

The solution behavior, including solubility, reactivity and sedimentation, of ZnO and ZnS in a Na2CO3−NaCl molten salt used for Sb smelting was investigated in the temperature range of 700-1000 oC. The saturated amount of dissolved ZnO in the molten salt remained constant at 0.02% and was unaffected by temperature; additionally, ZnO did not react with the molten salt. In contrast, the saturated amount of dissolved ZnS in the eutectic molten salt increased with increasing temperature, and the content of ZnS was 0.53% at 1000 oC. In addition, ZnS reacted with Na2CO3 above 900 oC to give ZnO. The sedimentation rates of these three species in the molten salt followed the order of Sb>ZnS>ZnO. It was thus concluded that ZnO is an appropriate sulfur-fixing agent for low-temperature Sb smelting in a Na2CO3−NaCl molten medium, and that the optimal smelting temperature is below 900 oC.

Neutron adsorption performance of Dy2TiO5 materials obtained from powders synthesized by the molten salt method

Dy2TiO5 powders were synthesized by molten salt and solid-state methods. The influences of molten medium on phase compositions and microstructures were analyzed. The addition of molten salt lowered significantly the synthesis temperature and resulted in uniform powders. Green bodies compacted from the prepared powders were pressureless sintered at 1600°C. Sinterability, mechanical properties and neutron absorption performance of the sintered pellets were studied. Results showed that molten salt synthesis resulted in materials with higher fracture toughness and bending strength, excellent hardness and neutron adsorption performance compared to the solid-state process. The neutron absorption rate reached 86.6% for 8cm thick pellets.

Comparative Corrosion Behavior of Austenitic Stainless Steels in Carbonate Melt at 650 °C Under Controlled CO2-O2 Environment

Concentrated solar power (CSP) has recently attracted much attention as clean energy mainly for base load applications. High temperature CSP technology has high efficiency and it can attract wide commercial applications. Corrosion of metallic materials is a key problem for high temperature CSP systems. Careful selection of molten medium and metallic material can slow down the corrosion processes and hence extend the overall life span of CSP plants. High temperature oils and nitrate-based salts are commonly used for commercial CSP plants. These materials are not stable at temperature higher than 600 °C. However, alkali metal carbonates are stable beyond 800 °C and have working temperature of ~ 400-800 °C. These carbonates are less expensive and more environment friendly than the state-of-art high temperature oils [1]. Employing high corrosion resistance of cheaper alloys, like stainless steels, could significantly promote the popularity of CSP plants. In this study, corrosion behavior of austenitic stainless steels (SS) is observed in ternary alkali carbonate melt at 650 °C under defined CO2-O2 gas environment. Weight loss, electrochemical characterization and morphological and microstructural examination were carried out to understand the corrosion behavior of Type 304 SS, Type 316L SS and Type 310S SS in 43Li2CO3-31.5Na2CO3-25K2CO3 (mol%) melt at 650 °C under flowing 0.98 atm CO2-0.02 atm O2 mixed gas. Weight loss observed due to 24 hours corrosion is 7.7 mg cm-2 for Type 304 SS, 6.5 mg cm-2 for Type 316L SS and 1 mg cm-2 for Type 310S SS. Potentiodynamic polarization showed that corrosion of SS is a cathodic-controlled process. Corrosion potential of Type 310S SS is nobler than that of Type 316L and Type 304 SS. Reduced weight loss of Type 310S SS due to corrosion should be due to high potential of anode reaction. Cathodic limiting current is not significantly different for all the SS; however, it is slightly higher for Type 304 SS than that of Type 316L and should be responsible for slightly higher weight loss of Type 304 SS. Anodic polarization behavior well agrees with the weight loss observed for all the examined SS. SEM and EDS analysis showed that a very thin Cr-rich uniform corrosion layer is formed on Type 310S; however, thicker corrosion layer formed on Type 304 is composed of a heterogeneous mixture of Cr- and Fe-rich phases. Corrosion layer formed on Type 316L is Cr-rich but locally contains Fe-rich phases. Corrosion resistance of SS in carbonate melt in decreasing order is as: Type 310S>Type 316L>Type 304. This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (Funding agency: JST). Reference K. Vignarooban, X. Xu, A. Arvay, K. Hsu, A. M. Kannan, Applied Energy, 146 (2015) 383-396

High-quality spinel LiCoTiO4single crystals with co-exposed {111} and {110} facets: flux growth, formation mechanism, magnetic behavior and their application in photocatalysis

Novel spinel LiCoTiO4 single crystals with co-exposed {111} and {110} facets were grown for the first time using a facile LiCl flux method. The obtained cubic-phase LiCoTiO4 crystals exhibit high crystallinity and regular octahedron-like geometric morphology. In this method, LiCl was used not only as an effective lithium source without any additives but also as the optimum molten medium compared with LiCl–NaCl and LiCl–KCl eutectic mixtures. The formation mechanism responsible for the flux-grown spinel LiCoTiO4 crystals with co-exposed {111} and {110} facets was also proposed. Moreover, the spinel LiCoTiO4 crystals showed a weak ferrimagnetic behavior with some antiferromagnetic effects. Photocatalytic tests revealed that the pure LiCoTiO4 sample had a relatively low photocatalytic activity although it had a relatively narrow band-gap energy (1.58 eV) corresponding well to the broad visible spectrum. However, the spinel LiCoTiO4 crystal could serve as an efficient visible-light sensitizer, and when coupled with graphitic carbon nitride (g-C3N4) nanosheets, the novel LiCoTiO4/g-C3N4 composites exhibited higher activity than pure g-C3N4 for the photocatalytic degradation of organic pollutants under simulated sunlight. A possible mechanism for the improved photocatalytic performance was also proposed. Overall, our present work opens a new approach to fabricating other lithiated transition-metal oxide spinel crystals for broad industrial applications.

Technoeconomic study of hightemperature acid sludge processing in molten medium

Throughout theterritoryofUkraine2 million tons of hazardous wastes are accumulated in outdoor areas. Recently, the determination to solve the problem of waste management is increased. Acid sludges are wastes of hazard class 2, containing free sulfuric acid (up to 70%) and organic part (mostly high-molecular aromatic compounds), which complicate the effective disposal. The problem state of acid sludges is considered and the main directions in their processing are defined. The combination of systems with a high-temperature coolant and aerosol nanocatalysis on an autonomous mobile unit, allowing to dispose acid sludges not less than 99.99 % is first considered. A basic energotechnological scheme including stages of preparation, high-temperature oxidation in sodium chloride melt and catalytic flue gas final purification in the aerosol reactor with obtaining electricity and sulphates, is proposed. The technicoeconomic analysis showed that the pay-back period of capital investment could reach 2 years. The obtained results will resolve the problem of half a million tons of acid sludges inUkraine.

Production of intermetallic compound powders through hydrogen and sodium reduction of chlorides

Fine Nb–Sn and Nb–Ta intermetallic powders were produced by hydrogen reduction from their uniformly mixed chloride vapours, while Nb–Al intermetallic powders were synthesised by sodium reduction of their chlorides in a LiCl–KCl–NaCl–CaCl2 molten medium. The obtained Nb–Sn and Nb–Ta powders were fine and agglomerated, with a uniform particle size distribution and a typical particle size of 20–40 nm. The particle size of Nb–Al powders synthesised by sodium reduction was approximately in the range of 50–300 nm.

Evaluation of Centrifugal Casting Process Parameters for In Situ Fabricated Functionally Gradient Fe-TiC Composite

A gradient Fe-TiC composite was successfully produced via combination of in situ reaction with centrifugal casting techniques. Additionally, some of the effective parameters of the centrifugal casting process have been studied. Cast iron and ferrotitanium, which were used as raw materials, were melted using a high-frequency induction furnace coupled with centrifugal equipment. The microstructure and phase characterization of the fabricated composite was studied by scanning electron microscopy, optical microscopy, and X-ray diffraction. The results show that the production of a pearlite matrix composite reinforced by TiC particles is feasible. The distribution of TiC in the pearlitic matrix is completely uneven as a result of density difference between molten medium and TiC in the centrifugal casting process.

Low temperature synthesis of nano-crystalline gadolinium titanate by molten salt route

Nano-crystalline Gadolinium Titanate (Gd 2 Ti 2 O 7 ) powder was successfully synthesized by “ Single Step Molten Salt Technique ”. LiCl–KCl eutectic mixture was used as a molten medium for the reaction. The duration of the synthesis was 10 h. Stoichiometric proportion of the reactants were mixed in an (LiCl–KCl) eutectic medium and treated at 750 °C in an electrical resistance furnace. Single phase Gadolinium Titanate compound was obtained by the thermal process. The synthesized powders were characterized using XRD, FT-IR, UV, EDAX and XPS analyses. The morphology of the powder was examined using SEM and TEM techniques. From the above studies, it has been concluded that pure crystalline Gadolinium Titanate powders can be synthesized via low temperature molten salt process.