The lead sulfide films obtained by the chemical bath deposition from the solutions contained KMnO4, NH4I or their combination are studied. The kinetic studies of the transformation of lead salt into sulfide under conditions of spontaneous nucleation of the solid phase show the inhibitory effect of the additives the rate of the process and resulting in a decrease of the thickness of PbS films from 640 to 370 nm. A comprehensive analysis of the composition, morphology and structure of the synthesized layers was carried out using scanning electron and atomic force microscopy, energy dispersive analysis, Auger spectroscopy and X-ray diffraction. The average content of the main elements Pb, S, I, O in the films and their distribution over the thickness were established. From the features of changes in the lattice parameter, crystallographic orientation, the magnitude of microdeformations, internal microstresses, and coherent scattering regions, the "critical" character of concentration of KMnO4 equal to 1 mM was revealed. From measurements of the Raman and infrared transmission spectra, the formation of I2O5 or I2O4 on the surface of the films is found. A synergistic effect of the combination of KMnO4 and NH4I in reaction bathes caused by the formation of photoactive phases of iodine oxides and resulting in increasing the voltage sensitivity of PbS films synthesized has been revealed.

Abstract—The eutectic LiF–NaF–KF mixture is considered as a fuel salt for molten salt reactors for the transmutation of minor actinides; therefore, information on the solubility of fluorides and oxides in it as both fissile materials and fission products is necessary to substantiate reactor operating conditions and to develop methods for fuel salt refabrication. From this point of view, cerium and neodymium can be considered as both representatives of fission products and imitators of actinides. Cooling curves and isothermal holding are analyzed to determine the temperature dependence of the solubility of a mixture of cerium and neodymium fluorides and cerium and neodymium oxides in the LiF–NaF–KF melt. The total solubility of rare earth trifluorides is found to reach 51 wt

The thermophysical properties of molten salts promising for the nuclear industry are crucial, but the available data are limited and contradictory. The thermal diffusivity of the molten mixtures (NaF-KF)eut–UF4 containing 30, 40, and 50 mol

This work presents the electrochemical study of LiCl-KCl-UCl3 solutions at the temperature range 673–823 K on inert and reactive electrodes, i.e. W and Cd, respectively. On inert electrode, U(III) ions were reduced to metallic uranium through one step and the mechanism of the cathode reaction was irreversible. The diffusion coefficients of U(III) ions in molten chloride eutectic and liquid cadmium were calculated. On reactive electrode, U(III) ions were reduced with depolarization and were accompanied by the formation of intermetallic compound UCd11. The reactions of the cathodic deposition and anodic dissolution of the U-Cd alloy were studied and the conditions of the alloy formation via galvanostatic electrolysis were found. The solubility and the activity of uranium in liquid cadmium were determined.

The paper considers the reduction of rare earth metal (REM) oxides and uranium dioxide with lithium produced during the electrolysis of LiCl–Li2O melt with the formation of intermetallics and palladium. At a cathode potential of 0.6–0.8 V relative to E_Li^+/Li^0 , intermetallic compounds of CePd3, NdPd3, and UPd4 compositions are formed. The formation current for REM intermetallic compounds is significantly greater than that for uranium. Therefore, when they are co-present in samples, REM intermetallics are formed first, followed by intermetallic compounds of uranium in the presence of palladium unbound by REM alloys. This is due to the significantly greater solubility of neodymium and cerium oxides in the salt melt compared to uranium dioxide. At a cathode potential close to or equal to the potential of liquid lithium, intermetallics with palladium, lanthanides, and uranium Ln3Pd4, LnPd, UPd3 are formed. In this case, an important role is played by the ability of lithium and palladium to form alloys that are liquid at 650 °C.

The paper presents experimental data on the thermal conductivity of molten salt mixtures of the following compositions: 0.66LiF–0.34BeF2, 0.73LiF–0.27BeF2, (0.73LiF–0.27BeF2) + 1 mol

The electrochemical reduction of pelleted heterophase powder Pd-Nd2O3-CeO2 mixtures was studied in molten LiCl-Li2O (1–1.5 wt%) at 650 °C. The influence of the composition of the mixture, as well as electrochemical factors—i.e., the amount of electricity passed and the cathode potential during electrolysis—were considered. It was found that in the presence of metallic palladium, neodymium and cerium oxides are reduced by lithium released at the cathode and form intermetallic compounds of different compositions. At potentials more positive than the formation of a phase based on liquid lithium at 0.5–0.8 V, CePd3 and NdPd3 intermetallic compounds are present in the reduced product. At potentials close to the formation of liquid lithium, a whole spectrum of intermetallic compounds is synthesized: CePd, NdPd, Ce3Pd4, and Nd3Pd4. The mechanisms of formation of palladium alloys with neodymium and cerium are proposed and considered. The degree of the reduction of lanthanide oxides was calculated from the data on the concentration of residual oxygen in the reduced product.

The present paper is dedicated to the quantitative determination of oxygen-containing impurities in the LiF–NaF–KF eutectic using electrochemical (cyclic and square-wave voltammetry) and reduction melting methods. The LiF–NaF–KF melt was analyzed before and after purifying electrolysis. The amount of oxygen-containing impurities removed from the salt during purification was determined. It was found that after electrolysis, the concentration of oxygen-containing impurities decreased by 7 times. The results obtained via electrochemical techniques and reduction melting were well-correlated, which made it possible to evaluate the quality of the LiF–NaF–KF F melt. To verify the analysis conditions, mechanical mixtures of LiF–NaF–KF containing Li2O were analyzed using the reduction melting method. The oxygen concentration in the mixtures varied from 0.672 to 2.554 wt. %. Based on the analysis results, the dependence approximated by the straight line was obtained. These data may be used to draw calibration curves and to further develop the procedure of oxygen analysis of fluoride melts.

When reprocessing spent nuclear fuel, it is supposed to use LiCl–KCl melt (0.49:0.51) in an inert atmosphere, all metal materials in this salt melt are extremely susceptible to corrosion, besides, during the processing of spent fuel, both the liquid (melt) and the gas phase are saturated with decay products that can act as additional oxidizing agents, increasing the aggressiveness of the environment. The pyrochemical technology of SNF includes operations such as soft chlorination, electrofining and metallization, implying the presence in the melt of compounds of chlorides of rare earth metals lanthanum, cerium and neodymium, as well as uranium(III, IV) chlorides. In this work, the corrosion behavior of 12CR18NI10TI steel in LiCl–KCl melt containing NdCl3, CeCl3, LaCl3, UCl3 and UCl4 additives up to 2 wt % was investigated. Corrosion tests lasting 100 hours were performed at a temperature of 500°C in an inert argon atmosphere. It was found that the presence of REM chlorides significantly reduces the degradation of the steel under study. The addition of (REM)Cl3 leads to the formation of a compound (REM) on the surface of the samples OCl, the thickness and continuity of which increases in the following row: LaCl3 NdCl3 CeCl3. The formation of such a compound leads to the inhibition of the corrosion process of steel 12CR18NI10TI due to salt passivation of the surface. The addition of UF4 to the melt causes significant corrosion of 12CR18NI10TI intercrystalline steel. The introduction of UF3 into the melt leads to a decrease in the corrosion rate, which is associated with the predominant interaction of trivalent uranium chloride with dissolved molecular oxygen contained in the melt, and the formation of a non-stoichiometric compound with the crystal chemical formula U3O7 on the surface of samples according to microrentgenospectral analysis.

Although the thermal conductivity of molten salt mixtures is of interest for many potential technological applications, precise values are often hard to obtain. In this study, the thermal diffusivity of FliNaK was studied in a molten state using the laser flash method and found to be very slightly dependent on temperature. The heat capacity of FliNaK was measured using the DSC method. There was a minor difference between our results and data from the literature. From calculations based on thermal diffusivity, density and heat capacity values, thermal conductivity was shown to decrease with temperature.

Rotational viscometry with the FRS 1600 (Anton Paar, Austria) high-temperature rheometer was used to obtain temperature dependences of the dynamic viscosity of molten lithium and beryllium fluoride salts considered as candidate fuel and coolant compositions for the molten salt reactor (MSR) for burning long-lived actinides from the spent nuclear fuel of the PWR 1000/1200 pressurized water reactor. 0.66LiF–0.34BeF2 and (0.73LiF–0.27BeF2)+UF4 molten salt mixtures containing 1 and 2 mol.% UF4 were investigated with regard to the MSR intermediate and fuel circuits. Salt mixtures were prepared by the direct melting of components and certified using X-ray phase and elemental analysis. The «shear rate» parameter was selected according to the viscosity curves obtained in the studied melts at 700 °C. It was found that the viscosity does not depend on the shear rate in the range of γ = 6÷20 s–1. When measuring the temperature dependence of viscosity, the shear rate was 11 s–1. Viscosity values of LiF–BeF2–UF4 melts obtained from experiments in the temperature range from liquidus to 800 °C are described by the linear equation logη = a + b/t, but their temperature coefficients differ evidently, which indicates a significant dependence of the viscosity of these melts on composition and temperature. Viscosity values obtained for the 0.66LiF–0.34BeF2 melt agree with the available literature data within 7–10 % in the temperature range of 650–750 °C. With an increase in the LiF content, melt viscosity decreases: it is lower by 20 % in the 0.73LiF–0.27BeF2 melt at t = 650 °C. However, when 2 mol.% UF4 is added, the 0.73LiF–0.27BeF2+UF4 fuel salt viscosity increases by 10 % at the same temperature.

Molten fluorides of alkali metals are considered a technological medium for molten salt reactors (MSRs). However, these media are known to be extremely corrosive. The successful implementation of high-temperature technological devices using molten alkali metal fluorides requires the selection of such structural materials that have high corrosion resistance in melts with compositional characteristic of MSRs. In this research, the corrosion behavior of 12Cr18Ni10Ti steel, the alloy Ni60Cr20Mo15, and the alloy Monel 404 (Ni50Cu50) was investigated in the LiF–NaF–KF eutectic melt, containing additions of CeF3 and NdF3 from 0 to 5 wt.% as imitator fluorides of actinides in an inert argon atmosphere at 550 °C for 100 h. Gravimetry, energy-dispersive X-ray (EDX) microanalysis of surfaces and cross-section of samples, and ICP-MS were used to establish the corrosion behavior of the investigated alloys. Corrosion resistance of the studied materials was found to decrease in a row from Monel 404 > Hastelloy C2000 > 12Cr18Ni10Ti. The addition of cerium fluoride into the melt resulted in the additional etching of the alloy surface. The addition of neodymium fluoride resulted in the formation of the point/inter-crystalline corrosion damages in the sample bulk. The samples of steel 12Cr18Ni10Ti were subjected to local cracking corrosion. The austenitic nickel-based alloys suffered specific local corrosion with formation of subsurface voids. Excellent corrosion resistance of the Monel alloy under the test conditions was found.

The LiF–BeF2 system is used as a heat transfer medium in molten salt reactors (MSRs). The thermal diffusivity of Li2BeF4 was studied using the laser flash analysis (LFA) method in solid and transition states. While the thermal diffusivity is shown to decrease slightly in solid-state Li2BeF4, it drops significantly at temperatures close to phase transition. The heat capacity of Li2BeF4 was measured by differential scanning calorimetry (DSC). Some differences were observed between the results obtained in cooling and heating modes. Thermal conductivity was calculated using thermal diffusivity-, density-, and heat-capacity data. The good thermal conductivity of the Li2BeF4 compound in solid and liquid states justifies its use as a heat transfer medium for molten salt reactors.

A eutectic mixture of lithium, sodium, and potassium fluorides is considered as a fuel salt for molten-salt reactors. For this reason, information about the solubility in it of fluorides of fissile materials and fission products is the most important when choosing a salt composition for a molten-salt reactor. In this work, the liquidus and solidus temperatures of the LiF–NaF–KF–CeF3 quasi-binary system are determined by thermal analysis and differential scanning calorimetry. The system has one eutectic point at CeF3 content 3 mol.% and temperature 445°C and three peritectic points – 7.5, 15, and 20.5 mol.% at 472, 512, and 600°C, respectively. The solubility of CeF3 in LiF–NaF–KF is 10 mol.% at 500°C and reaches 25 mol.% at 665°С.

The thermal properties of 2LiF-BeF2 and LiF-BeF2-UF4 systems currently under active development for use in molten salt reactor designs, in various countries are studied. In order to establish liquidus and solidus temperatures of these systems, the Differential Scanning Calorimetry (DSC) method at a constant heating (cooling) rate was used. A distinction between results obtained in heating and cooling mode is identified on the basis of the much lower solidus peaks observed on cooling curves than on heating ones. This can be explained in terms of peculiarities of LiF-BeF2 peritectic compositions. The rate of cooling is much higher than the peritectic reaction rate.

The NdF3 solubility in molten eutectic FLiNaK, which is a conceivable medium for a molten salt reactor (MSR), was determined by the quasi-binary phase diagram FLiNaK-NdF3. The eutectic mixture FLiNaK was prepared by direct melting of components LiF, NaF and KF·HF. The acidic anhydrous salt (KF·HF) was used instead of the hygroscopic KF. The NdF3 was sintered by hydrofluorination of Nd2O3. The oxygen impurity in the prepared eutectic FLiNaK, determined by an oxygen analyzer LECO OH836, was 0.036 wt.%, whereas the NdF3 contained 0.04 wt.% of oxygen. A part of the FLiNaK-NdF3 quasi-binary phase diagram was obtained using two thermal analysis techniques: differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The FLiNaK-NdF3 phase diagram in the region of 0–30 mol.% NdF3 contains one eutectic at 2 mol.% NdF3 and 450 °C and two peritectic points: 8 mol.% NdF3 at 500 °C and 22 mol.% NdF3 at 575 °C. The region of the FLiNaK-NdF3 phase diagram below the liquidus line is rather complicated due to the complex structure of the multicomponent system in its molten state, as in its solid state. The NdF3 solubility in FLiNaK is about 5 mol.% at 490 °C and 29 mol.% at 700 °C; this means that the process of the MA transmutation in the MSR can be carried out in molten FLiNaK with a content of actinides as high as 15–20 mol.% in the temperature range of 550–650 °C.

The density of molten mixtures of lithium, beryllium and uranium fluorides was studied by Archimedean method. The densities of mixtures without UF4 are of close values, uranium fluoride increases density. Heat capacity was measured by DSC method. There is some difference between results obtained in cooling and heating modes due to presence of peritectic compound Li2BeF4 which manifests overcooling behavior. The dependence of specific and molar heat capacity on composition was drawn for LiF-BeF2 system. The thermal expansion values were calculated from density results. Correlation was found between heat capacity and thermal expansion of melts studied. (C) 2021 Elsevier B.V. All rights reserved.

The separation of lanthanides and actinides can be successfully used in the liquid metal–molten salt system. The separation factors of lanthanum, praseodymium, and neodymium from uranium have been calculated at various temperatures in the molten Me(Ga–In)/3LiCl–2KCl system. The effect of the nature of lanthanide on the separation factor of the Ln/U couple is established.

The uranium (III) ions behaviour in fused 3LiCl–2KCl eutectic versus the Cl−/Cl2 reference electrode in the temperature range of 723–823 K on the liquid cadmium electrode by transient electrochemical techniques on the tungsten or molybdenum electrodes was studied. The mechanism of electrochemical reduction on cadmium cathode and the influence of temperature, cathode current density and the duration of electrolysis were studied. The activity coefficients and the base thermodynamic properties of uranium in fused U–Cd/3LiCl–2KCl system were calculated.