Molten Salt Composition Research Articles

Morphology and magnetic properties of barium hexaferrite ceramics synthesized in xwt% NaCl-(100−x) wt% KCL molten salts

Micron size barium hexaferrite (BaFe12O19) platelets were prepared by the molten-salt synthesis method in various weight proportions of NaCl–KCl salt mixtures as a liquid medium. The effect of molten salt composition—x wt% NaCl and (100−x) wt% KCl—on the amount of barium hexaferrite phase formation, as well as, on the morphology and magnetic properties of the final products are discussed. Inductively coupled plasma-mass spectroscopy (ICP-MS) was used to determine the solubility of the starting materials in the salts in order to understand the formation mechanism of barium hexaferrite. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) were used to identify the characteristics of the synthesized barium hexaferrite platelets. ICP-MS analysis showed that the Fe2O3 solubility is negligible, however, BaCO3 has very high solubility in both molten KCl and NaCl. Quantitative XRD and SEM results showed that molten salt containing 100 wt% NaCl at 900 °C (for 2 h) resulted in the highest production of barium hexaferrite. Further, SEM results showed that KCl-rich molten salt led to the formation of sharper faceted platelet morphology, whereas NaCl-rich ones resulted in more round platelets. Data from magnetic measurements showed that as the content of NaCl in the molten salt increases, hysteresis losses became higher. This is a characteristic of the achievement of a harder magnetite behavior in the synthesized barium hexaferrite ceramics. The composition of the KCl/NaCl molten salts was shown to play an important role on the extent of barium hexaferrite formation, resulting platelet morphology and the magnetic properties.

Study of extraction of indium by molten salts from metal waste

A study of the extraction kinetics of indium-zinc chloride with molten salt from lead-tin alloys and the effect of the molten salt compositions have been performed. The dependence of the positive effect of ammonium chloride and lead chloride on the kinetics of the extraction of indium from molten metal to salt has been revealed. The results of this research can be used in the development of the industrial extraction method and the extraction apparatus of indium from tin-lead alloys and secondary waste.

Synthesis in molten salts and formation reaction kinetics of tantalum carbide coatings on various carbon fibers

Tantalum carbide (TaC) coatings were prepared on polyacrylonitrile (PAN)-based, graphitized PAN-based and pitch-based carbon fibers by synthesis in molten salts. The characteristics of the TaC coating were studied in relation to the structure of the carbon fiber, the molten salt composition, reaction temperature and reaction time. Thicker TaC coatings with larger grain sizes tended to form on carbon fibers with a lower degree of crystallinity. Molten salt mixtures with a relatively low melting point are appropriate for use as the reaction medium for synthesis of TaC coatings on carbon fibers. However, with increasing reaction temperature and reaction time, the thickness and grain size of the TaC coating increase obviously. Internal diffusion control and external diffusion control models of TaC coating growth were established on the basis of mass transfer and reaction dynamics theory. The result indicates that the TaC coating growth is controlled by the internal diffusion of tantalum in the TaC coating.

Preparation of needlelike Sr0.5Ba0.5Nb2O6 particles using molten SrCl2-BaCl2 salt

Needlelike Sr0.5Ba0.5Nb2O6 powder particles were prepared from SrCO3, BaCO3, and Nb2O5 in the presence of a mixture of molten SrCl2 and BaCl2. When the composition of the mixture of oxide and carbonate was fixed to be SrCO3:BaCO3:Nb2O5 = 1:1:2, the phase and morphology of the product particles were dependent on the composition of molten salt. The exchange reaction, BaO + SrCl2 = BaCl2 + SrO, enriched Sr in the oxide phase. The relation between the compositions of the salt mixture and the reaction product was determined, and needlelike Sr0.5Ba0.5Nb2O6 particles were obtained by using the molten salt containing 18 mol % SrCl2.

Electrical Conductivity of Molten Electrolytes with a Common Cation

The electrical conductivity of molten electrolytes with a common cation has been considered as a function of molar volume and temperature. The empirical coefficients for all alkali halides have been obtained. The validity of equations has been verified on some molten salt compositions.

High Temperature Corrosion of 625 Supperalloy under Iron-Zinc-Lead Oxide/Sulfate/Chloride Salt Mixtures

The corrosion resistance and degradation mechanisms of 625 supperalloy at 800 oC under three molten salt compositions containing PbSO4, PbO, PbCl, ZnO, Fe2O3 and CdO in air atmosphere were studied. The concentrations of Fe2O3 and CdO were varied to evaluate the effect of these compounds on the corrosion reaction. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization technique were applied to evaluate the degradation mechanisms and corrosion properties of the alloy. Corrosion products and surface layer of the corroded specimens were studied by SEM/EDX and X-ray map analyses. Electrochemical evaluation confirmed that increasing the concentration of CdO in the molten phase could increase the corrosion rate of the alloy and in this condition the corrosion phenomena occurred under the control of charge transfer effect. The presence of a Cr-depleted layer on the surface of the alloy was the reason for the formation of an internally attacked area at the alloy/oxide interface.

SnO2–NiO–C nanocomposite as a high capacity anode material for lithium-ion batteries

Carbon-coated SnO2–NiO nanocomposite was successfully synthesized via the molten salt route, using SnCl2·H2O and NiCl2·6H2O as the starting materials, with a molten salt composition of H2O2 : LiOH·H2O : LiNO3 as a solvent at 300 °C. The synthesis was followed by a carbon layering process. The phases and morphology of the as-prepared samples were examined by X-ray diffraction and transmission electron microscopy. Electrochemical investigation was carried out by using a series of complementary techniques, including galvanostatic charge–discharge, cyclic voltammetry, and impedance spectroscopy. The results confirmed that the carbon-coated SnO2–NiO nanocomposite has higher discharge capacity, better rate capability, and excellent cycling performance in comparison to the uncoated SnO2–NiO nanocomposite. The carbon-coated SnO2–NiO nanocomposite electrode exhibited a reversible capacity of about 529 mA h g−1 at 800 mA g−1, and 265 mA h g−1 at 1600 mA g−1, even after 500 cycles. The excellent electrochemical performance of the SnO2–NiO–C nanocomposite can be mainly attributed to the combined effects of the nanostructure, the carbon layering on the SnO2 and NiO nanoparticles, and the ultra-fine carbon matrix, because the three factors would contribute to high electronic conductivity, reduce the traverse time of electrons and lithium ions, and also prevent high volume expansion during cycling. Due to its excellent electrochemical performance, the SnO2–NiO–C nanocomposite could be considered as a promising anode material for future lithium-ion batteries to be used in electric vehicles and hybrid electric vehicles.

Molten Salt Fuel Version of Laser Inertial Fusion Fission Energy (LIFE)

Molten salt with dissolved uranium is being considered for the Laser Inertial Confinement Fusion Fission Energy (LIFE) fission blanket as a backup in case a solid-fuel version cannot meet the performance objectives, for example because of radiation damage of the solid materials. Molten salt is not damaged by radiation and therefore could likely achieve the desired high burnup (>99%) of heavy atoms of 238U. A perceived disadvantage is the possibility that the circulating molten salt could lend itself to misuse (proliferation) by making separation of fissile material easier than for the solid-fuel case. The molten salt composition being considered is the eutectic mixture of 73 mol% LiF and 27 mol% UF4, whose melting point is 490°C. The use of 232Th as a fuel is also being studied. (232Th does not produce Pu under neutron irradiation.) The temperature of the molten salt would be ∼550°C at the inlet (60°C above the solidus temperature) and ∼650°C at the outlet. Mixtures of U and Th are being considered. To minimize corrosion of structural materials, the molten salt would also contain a small amount (∼1mol%) of UF3. The same beryllium neutron multiplier could be used as in the solid fuel case; alternatively, a liquid lithium or liquid lead multiplier could be used. Insuring that the solubility of Pu3+ in the melt is not exceeded is a design criterion. To mitigate corrosion of the steel, are fractory coating such as tungsten similar to the first wall facing the fusion source is suggested in the high-neutron-flux regions; and in low-neutron-flux regions, including the piping and heat exchangers, a nickel alloy, Hastelloy, would be used. These material choices parallel those made for the Molten Salt Reactor Experiment (MSRE) at ORNL. The nuclear performance is better than the solid fuel case. At the beginning of life, the tritium breeding ratio is unity and the plutonium plus 233U production rate is ∼0.6 atoms per 14.1 MeV neutron.

Sequential Electrolysis of U-Pu Alloy Containing a Small Amount of Am to Recover U- and U-Pu-Am Products

Sequential electrolysis testing was performed in a LiCl-KCl eutectic molten salt bath, in which variation in current efficiency, composition of product or molten salt, etc. were measured successively. Porous or dense U-Pu alloys containing a small amount of Am were dissolved one after another from the anode and, simultaneously, U dendrites or U-Pu-Am alloys were recovered on the iron rod or in the liquid cadmium cathode, respectively. The current efficiencies were mostly maintained to be 100% except for the anodic dissolution of the porous alloy and the cathodic recovery of U-Pu-Am in the liquid cadmium. The Pu and Am concentrations in the U dendrites varied in the ranges of 120–350 and 4–15 ppm, respectively. The separation factors for U/Pu and Am/Pu in the liquid cadmium varied in ranges of 1.69–1.74 and 0.66–0.78, respectively. The sum of U, Pu, and Am concentrations in the molten salt bath was maintained in the entire sequence, although the U concentration decreased or increased when using the iron rod or liquid cadmium cathode, respectively. The variation in the Pu concentration compensated for the U concentration variation. Material balance of Pu was mostly maintained at 100% with respect to the initial amount at each step of the sequence. These results indicate that the sequence used in the present study can be recycled.

Compatibility of Selected Ni-Based Alloys in Molten Li,Na,Be/F Salts with PuF3 and Tellurium Additions

In the last years, there has been a real growth of interest in the use of high-temperature molten salt fluorides as coolants and fuel salts in nuclear power systems. For all molten salt reactor (MSR) concepts, material selection is a very important issue. This paper summarizes results of recent work done within the ISTC#1606 project and the present state of knowledge about container materials for MSRs. The central focus is the compatibility of Ni-based alloys with the molten Li,Na,Be/F salt system as applied to the primary circuit of the MOlten Salt Actinide Recycler & Transmuter (MOSART) fueled with different compositions of actinide trifluorides from light water reactor spent fuel without U-Th support. Results from recent studies with a Li,Na,Be/F thermal convection loop at temperatures up to 700°C are presented. Material specimens of three modified Hastelloy N alloys, particularly HN80M-VI with 1% of Nb, HN80MTY with 1% of Al, and MONICR with 2% of Fe, were used for our study in corrosion facilities. Methods to purify the molten salt composition and to improve Ni-based container alloy compatibility by maintaining the salt at a low redox potential are discussed. The effect on materials compatibility of adding plutonium trifluoride and tellurium to the Li,Na,Be/F solvent system is also considered. Last, testing of advanced Ni-based alloys with various compositions to enhance first of all its resistance to tellurium intergranular cracking should be continued in thermal convection loops with a long exposure time for the MOSART fuel salts as well as the novel nonmoderated thorium sustainable MSR concept in the framework of the new ISTC#3749 project.

Synthesis of Ba<sub>1-x</sub>Sr<sub>x</sub>TiO<sub>3</sub> Powders by KOH-KNO<sub>3</sub> Molten Salt Method

The synthesis of Ba0.5Sr0.5TiO3 (BST) powders was attempted using KOH-KNO3 molten salt. Single-phase BST powders could not be obtained when stoichiometric powders were regardless of the molten salt composition. Only when powders with excessive TiO2 were used, single-phase BST powders were obtained. The shape and aggregation state of the single-phase BST powder changed according to the heating temperature and the molten salt composition.

Evaluating physical properties of molten salt reactor fluoride mixtures

In the last years, interest in the use of high-temperature molten fluoride salts as fluid fuels and coolants in nuclear power systems has been increasing. The comprehensive information on the properties of molten fuel and coolant salts is necessary for development of new designs. Experimental data on physical properties of some prospective molten salt mixtures of Li, Na, Be, Zr fluorides containing fertile and fissile materials as well as soluble fission products are unknown. At the first stage of the conceptual development estimation of the required properties from the known experimental data can be useful for selection of suitable molten salt compositions. In this paper the approaches for estimation of the physicochemical properties such as density ( ρ), dynamic viscosity ( η), isobaric heat capacity ( c p ), and thermal conductivity ( λ) for molten salt fluoride mixtures are proposed. The calculation algorithm was based on the additivity principle for the properties ( P x ) of multi-component molten salt mixtures, which can be found from the relationship P x = Σ N i P i. Here N i and P i denote mole fraction and corresponding property of individual molten salts or their binary mixtures as constituents of the more complex systems. The empirical expressions connecting the property with molar volume and molecular mass of selected fluoride compositions are also derived and tested. Estimated values are compared with each other and available experimental data.

Experiences with Inconel 625 in Biomass and Waste Incineration Plants

Inconel 625 is utilised in both biomass and waste incineration plants in Denmark. In both cases, the performance is good however the morphology of corrosion attack is different which indicates different corrosion mechanisms. In waste incineration plants there is general attack and shallow pitting, and in some cases dendritic attack especially on the fins of waterwalls. The dendritic attack is in the dendritic core. The presence of pits or dendritic attack is linked to the temperature of the metallic surface and the molten salt composition. In a woodchip biomass plant, chromium depletion was observed on the surface of the weld overlay leaving behind a nickel and molybdenum rich porous structure. The corrosion attack was not related to the dendritic microstructure of the weld. In two straw-fired biomass plants, co-extruded Sanicro 63 (alloy 625 type) as well as Inconel 625 weld overlay revealed the same type of attack, again chromium depletion. This indicates that the corrosion mechanism in woodchip and straw power plants are similar. Another interesting result in straw-fired boilers was that Nibas welds (alloy 625 composition) could provoke excessive corrosion in adjacent 18-8 stainless steels indicating a galvanic reaction. The corrosion mechanisms observed in each case are discussed in relation to temperature and corrosive environment.

Titanium powder production by TiCl4 gas injection into magnesium through molten salts

A process to produce titanium powder continuously is proposed and its applicability is examined experimentally. The method is based on the chemical reaction in the conventional Kroll reduction process; however, TiCl4 gas is injected into molten salt on which a molten magnesium layer is floated as the reductant. Bubbles of gaseous TiCl4 can be reacted at the lower surface of the liquid Mg layer, while TiCl4 gas reacts on the upper surface in the Kroll process. The fine Ti particles produced in this study were well separated from magnesium and could be recovered from the bottom of the molten salts. The particles were small and fine enough for use in powder metallurgy, while congregated lumps of about 20 µm in size are obtained by the Kroll process. The composition of molten salts and an operation temperature above 1073 K did not affect the morphology of the Ti particles, if suitable material for the reaction vessel was chosen.

四塩化チタンのマグネシウム熱還元における金属導電体を介した反応(LR-EMR)によるチタンの析出部位の制御

The Long Range Electronically Mediated Reaction (LR-EMR) has been tested for controlling the location of titanium deposit during magnesiothermic reduction of TiCl4. An iron cathode tube immersed in molten salt was electrochemically connected with Mg-18 mol%Ag liquid alloy placed at the bottom of an anode crucible through an external circuit. When TiCl4 was fed into the cathode tube at 1073 K, electrochemical reduction of TiCl4 was confirmed by detecting current in the external circuit. This titanium reduction is attributed to LR-EMR because the concentration of silver is less than 50 mass ppm in the resultant titanium deposit, despite Mg-Ag alloy was used as the reductant. In this work, 70% of titanium deposit could be localized at the vicinity of cathode by adjusting the experimental conditions such as configuration of electrodes and molten salt compositions. Such localized deposition on the cathode tube was found to increase up to 80% by decreasing TiCl4 feed rate. The conventional Kroll process is known to be difficult to control the location of titanium deposit during metallothermic reduction. However, the LR-EMR concept can bring about a significant breakthrough in this difficulty, as it has been demonstrated in this work. The present results also stimulate the development of semi-continuous titanium reduction process possible when applying LR-EMR.

The effect of different surface treatments on the molten salt hot corrosion of IN-657 superalloy

The influence of different surface treatments (laser surface treatment, silicon nitride, and 25 wt.% Al 2(OH) 4Si 2O 5—75 wt.% Na 2SiO 3), on the hot corrosion behaviour of IN-657 superalloy has been studied. The corrosion tests were performed in an oxidizing atmosphere in contact with a molten mixture of 82% K 2S 2O 7—18% V 2O 5. The effects of operation temperature and carbon residues as component of the molten mixture were also analyzed. The best results were obtained for the kaolin and methasilicate mixture coating. Laser surface treatment and the CVD-silicon nitride are not recommended for surface modification of the IN-657 superalloy. Taking into account the results obtained, the authors suggest the average temperature and molten salt compositions where the above coating can work satisfactorily.

Formation of Lead Niobates in Molten Salt Systems

The formation mechanisms, phase stability, impurity incorporation, and morphological characteristics of lead niobates obtained by molten salt synthesis were studied by X‐ray diffraction analysis, scanning electron microscopy, and energy dispersive analysis. Results indicate that PbO is the fastdissolving component of the constituent oxides and that the formation of lead niobates initiates at the surface of Nb2O5 powders. Reaction rates were faster in molten salts when compared to those of solid‐state synthesis. Significant morphological differences were observed between the powders prepared by both solid‐state and molten salt synthesis. At low PbO/Nb2O5 molar ratios, reaction between starting powders and molten salts resulted in the formation of NaNbO3, along with potassium incorporation into lead niobates. Orthorhombic PbNb2O6, monoclinic Pb2Nb2O7, and fcc Pb3Nb3O8 phases were stabilized using molten salt synthesis, while only rhombohedral PbNb2O6 and Pb2Nb2O7, and tetragonal Pb3Nb2O8, were obtained by solid‐state synthesis. Molten salt compositions containing PbO/Nb2O5 ratios of 2 and 3 resulted in the stabilization of phases different from those obtained using solid‐state synthesis. For a PbO/Nb2O5 ratio equal to 3, Pb5Nb4O13 observed in solidstate synthesis was not found in the products of molten salt synthesis.

Chemical strengthening of Na 2OAl 2O 3SiO 2 system glasses by surface controlled crystallization

Appropriate glass compositions of the Na 2OAl 2O 3SiO 2 system and glass melting technology were investigated. The dependence of some factors, such as composition of molten salts, time and temperature of ion exchange treatment on the modulus of rupture was studied. As expected, the coefficient of interdiffusion is a function of concentration and has the mixed-alkali effect. The order of the interdiffusion coefficient is 10 −6 cm 2/s. The effect of binary and ternary salt baths on the surface controlled crystallization was reported. The experimental data showed that there is a series of technological advantages from applying molten salts of the ternary system Li 2SO 4Na 2SO 4K 2SO 4 in comparison with the binary system Li 2SO 4Na 2SO 4.

Electrode Potentials in Fused Systems X. Measurement of Cation Concentration in Molten Salts Using Glass Membrane Electrodes.

A potentiometric method utilizing glass membrane reference electrodes in a concentration cell for the continuous measurement in situ of molten salt composition is presented. Relevant data for the AgCl-NaCl, AgBr-NaBr, and Ag2SO4-Na2SO4 systems are given. Using cells of the type where the a's are activities, the unknown mole fraction X 2 can be calculated from the equation where t' is a concentration-independent constant of the system and X R is the concentration of M 1 A in the reference electrode. The method is capable of measuring X 2 in molten salt with an accuracy of better than 5 percent over a concentration range of 104. Application of the method to cations other than silver is discussed.