INTERNATIONAL SYMPOSIUM ON MOLTEN SALTS AND IONIC LIQUIDS 2011

Bronsted acids are formed in ionic liquids by the introduction of a protic molecule to a liquid salt or by reaction of it with an appropriate neutral base (e. G. HCl + pyridinium chloride, H2SO4 + 1-methylimidazole). The mixture of the pure protic acid HA, with pure base B, is often gauged for its ability to react to completion, thus forming the pure liquid salt [BH]+[A]-, from the behaviour of HA and B in water. While aqueous acid-base solutions are often the starting point of any discourse regarding acidity in general, we must realise that water is an atypical solvent. In this way, water is unsuitable as the universal acid-base reference system, since the varieties of acidities possible in non-aqueous media, either cannot form, or, are unstable, in water, due to the levelling effects of [H3O]+ or [HO]-. Indeed, acid speciation outside the realm of aqueous solution chemistry is rather varied and much more complex than that available in water, where homo- and hetero-conjugate ion speciation (e. G. [HCl2]-, [H2F3]+ and [HCl (AlCl4)]- ) can occur. Furthermopre, these species can form on either side of full 1:1 (or 1:2 etc) equivalence, where quantities of unreacted HA can be consumed by [A]- formed post proton-transfer, prior to consumption by unreacted base B. The current situation for acid/base chemistry in ionic liquids needs much more attention, with actual acidities determined on a per system basis: This can be done using available spectrophotometric and electrochemical methods. We present the wide world of acidity beyond that available in water, from the gas phase to the solvated proton under various constraints, and emphasize the differences in solvent levelling, ionisation, dissociation, ion speciation and the stabilisation of proton transfer products, for various acids in various media ( proton affinities and pK values are included for protic molecules in various solvents).

Pyrochemical separations technology using high-temperature molten salt and metal media shows potential as a component of an overall separation and transmutation strategy for long-lived radionuclides. It could also be used for advanced fuel cycles associated with new types of reactors (Gas Cooled Reactor, Molten Salt Reactor, Fast reactor with metallic fuels, Accelerator Driven Systems). A pyrochemical process has been developed at the laboratory scale. The separation between the actinides and the fission products is operated by liquid-liquid extraction between a molten fluoride salt and a liquid metallic aluminum phase. Actinides are then back-extracted from the aluminum phase in a molten LiCl-CaCl2 salt at 700°C. Among the different steps of the process that still need to be studied is the head-end step with the recovery of the actinides from the molten chloride salt under an oxide form. The use of carbonate salts that deliver O2- ions and induce the actinides precipitation under oxide and oxychloride forms is known. However this method is increasing the solvent volume and therefore the waste production. Another method consists in precipitating the actinides with a carrier gas that brings O2- ions. This paper presents the results of our back-extraction and precipitation studies from the molten LiCl-CaCl2 salt at 700°C with lanthanides and actinides. We first describe our methodology used to monitor both reactions and to determine the reaction yield. The characterization of the different phases obtained after the precipitation and the calcination is then presented. As a conclusion, the viability of this process is discussed.

High temperature alkali metal chloride-based melts are prospective media for non-aqueous pyrochemical processing of fresh and reprocessing of spent nuclear fuels. Knowing and understanding the behaviour and properties of the spent fuel constituent elements is important for developing feasible technological process. Of all the elements of interest radioactive ones, for obvious reasons, are the least studied. Spectroscopic techniques, especially applied in situ, offer a valuable tool for determining speciation and studying the reactions taking place in molten salt media. Combining spectroscopy with electrochemistry provides even deeper inside into the properties of studied systems. In the present work electronic absorption spectroscopy was applied for studying the behaviour of uranium species containing the metal in the oxidation states +3, +4, +5 and +6 that were formed in a variety of reactions including anodic dissolution of uranium, chlorination of the metal and its oxides, chemical and electrochemical oxidation and reduction of uranium ions. Experimental conditions, such as temperature or even cationic composition of the solvent melt, often influence the outcome of the reactions taking place. An example of this is the reaction of uranium dioxide with hydrogen chloride that depending on temperature and chosen solvent can lead to the formation of U(IV) or U(V) species. Technetium is one of the least studied d-metals. The reactions of technetium metal and its dioxide were studied in fused alkali chlorides by spectroscopic and spectroelectrochemical techniques. The behaviour of technetium is compared with that of rhenium, the element often employed in experimental studies as a stable substitute for technetium. For uranium and technetium the information obtained from the EAS measurements is compared with the results of X-ray absorption spectroscopy experiments performed with molten and quenched chloride salts.

Among industrial processes, extraction and separation of actinides and lanthanides from nuclear waste is one of the most challenging fields. For this purpose, liquid–liquid extraction procedures using neutral organophosphorus compounds, such as carbamoylmethylphosphine oxides (CMPO), are used in current practice in the TRUEX process. Ionic-liquid phases are suitable extraction solvents for metallic radioactive species in liquid/liquid extraction processes as they show high stability under a and γ irradiations and enhanced safety towards criticality. Several groups reported that replacing dodecane in the TRUEX process by a ‘‘hydrophobic’’ IL significantly enhances the extraction of the metal cation by CMPO. Another very promising approach for metal extraction (and many others applications) lies in the concept of task-specific ionic liquids (TSILs). These compounds, consisting of extracting entities grafted onto the cation of the IL, combine the properties of ILs (e. G., nonvolatility, nonflammability) with those of conventional extracting compounds. Upon grafting complexing substructures onto the organic cation of RTILs, the resulting TSILs behave both as the organic phase and the extracting agent, suppressing the problems encountered through extractant/solvent miscibility and facilitating species extraction and solvent recovery. We report the synthesis of a functionalized ionic liquid based on quaternary ammonium cations bearing a CMPO substructure (N, N-dibutylcarbamoylmethyldiphenylphosphine oxide). TSIL In order to evaluate the extracting properties of the newly synthesized TSIL, the extraction of a number of radioactive elements was investigated. Experimental tests with Am(III), Eu(III) and U(VI) were performed at different acid conditions and different TSIL concentrations. Preliminary studies show that high extraction values can be obtained for U(VI) and Am(III) with the new TSIL. The americium loaded in the RTIL phase could be back extracted by contacting the organic phase with a 6M nitric acid solution.

Mould powders with a C/S-ratio between 0.61 and 1.34 were investigated with respect to their melting and crystallisation behaviour. Therefore the Hot Stage Microscope (HSM), Simultaneous Thermal Analysis (STA) and Single Hot Thermocouple Technique (SHTT) were used. With the STA differences in enthalpy according to the reactions taking place during heating and cooling are detected. Contrary the HSM enables the in-situ observation of a polished sample during heating. Crystallisation of transparent slags can be investigated with the HSM and the SHTT. For the SHTT the slag is stretched to a thin layer. Therefore the evaporation of alkalis and fluorine has to be taken into account. Some differences between the results of the methods applied are caused by the following circumstances: Thermocouple measures rather the furnace temperature in case of STA and the specimen temperature in case of HSM and SHTT. Furthermore for detection of effects in the DTA-curve more intense reactions have to take place. Also the higher magnification factor of the HSM compared to the SHTT for continuous cooling measurements has impact on the deviation of especially the crystallisation temperature. Using the HSM for some mould powders the formation of intermediate liquid with following crystallisation is observed during heating. This leads to the assumption of disequilibrium due to a too high heating rate. In contrast to this detection of intermediate phases by STA is hindered by overlap of peaks. Using the HSM during cooling diverse crystal shapes are observed. On the contrary the results of the SHTT show the crystallisation of denrites for continuous cooling and isothermal measurements at high temperatures. But for lower temperatures small crystals precipitate in the whole sample. Comparing results of these methods with mineralogical investigations of samples taken from service analogies are observed.

The phase diagrams of trivalent lanthanide–alkali metal halide systems range from simple eutectic systems to systems with one (several) congruently or incongruenly melting compounds. Using both literature information and our extensive experimental results, the LnX3-MX binary mixtures phase diagrams were screened in terms of the IPM+/IPLn3+ ratio (IPi= zi/ri ; Zi: Ionic charge; Ri: Ionic radius; Ln: Lanthanide, X: Halide and M: Alkali metal). A similar approach was conducted on the divalent LnX2-MX lanthanide-alkali halides phase diagrams ranging from simple eutectic to one or more congruently melting compounds. Lanthanides being widely used as simulants of actinides, this classification can constitute a useful predictive tool for those still unexplored systems.

Specimens of Ni were conditioned in the test piece with a work area of 0.07917 cm2, each one of them was polished. The electrochemical information was obtain by mean of anodic potentiodinamic polarization and polarization resistance. The anodic polarization indicates that the critical current has a linear relationship with the NaOH concentration. The diffusion coefficient was determinated by the Randles- Sevcik.

The world faces some considerable challenges over the next 50 years and these include the use of renewable energy, its generation and storage, green processing of materials (including recycling), feeding an ever growing population and, finally, care of an ageing population. The skills of the Chemical Metallurgy community include thermodynamics, phase diagrams, kinetics and mass transfer and electrochemistry of aqueous solutions, solid electrolytes and molten salts. However, it is not just sufficient to have these skills – it is equally important to be aware of the problems that need solving. The combination of these two factors can lead to innovation but this can only be successful when the ideas are put into practice and this requires a partner with the financial and technical resources to make the projects a successful reality. Several examples will be given and these may include: (1) novel anodes for lithium ion batteries deriving insight from phase diagrams and intercalation to produce tin filled carbon nanotubes, (energy generation and storage), (2) production of metal and oxygen directly from metal oxides (green processing), (3) treatment of waste electronic scrap(recycling), (4) widening the supply of fertiliser (feeding a growing population), (5) healing of long term wounds (caring for an ageing population)This paper will illustrate how knowledge of a problem coupled with an understanding of the requisite science can lead to innovative solutions that can attract venture capital leading to their successful industrial development.

Partial or full solidification of metallurgical slags occurs in many industrial pyrometallurgical processes. To enhance the fundamental knowledge of this phenomon, this research focuses on the simulation and in-situ observation of crystallizing minerals in oxide melts. The isothermal crystallization of Wollastonite (CaO. SiO2) in a ternary CaO-Al2O3-SiO2 melt is investigated. We used a confocal laser microscope (CLSM) to observe the dendritic crystallization and measured the dendrite tip radius and its velocity as a function of undercooling. The phase field method is chosen to model and simulate the crystallization, because it has proven its power for phase transformations in metals. The phase field model uses a vast number of physical input data, such as Gibbs energies of the phases, diffusion coefficients of the components and the interfacial energy of the solid-liquid interface. The thermodynamic data is retrieved from the FACTSage database for oxide systems. Diffusion coefficients are taken from literature, while surface energies are estimated from both Molecular Dynamics data and wetting experiments. By comparing experimental values for the dendrite tip velocity with values obtained with simulations, the influence of surface energy and diffusion coefficients on the crystallization behavior can be assessed.

Electrorefining process for dendrite-free aluminum deposition on copper cathodes was investigated by using low temperature AlCl3-1-Ethyl-3-methyl-imidazolium chloride (EMIC) ionic liquid electrolyte. The bulk electrodeposition of aluminum was carried out using aluminum Al scrap as an anode. Experiments were conducted at fixed voltage of 1.5 V, electrolyte concentration (molar ratio AlCl3: EMIC = 1.65) and electrode surface modification (modified/unmodified). The effect of electrode surface modification and deposition time on deposit morphology, cathode current density and their role in production of dendrite-free aluminum deposit was investigated. The deposits were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the modified cathode electrodes showed lower over potentials compared to unmodified. The maximum over potentials obtained with unmodified and modified electrode is -0.339 V and -0.653 V, respectively. The average current densities for unmodified and modified copper cathode are 195 A/m2 and 204 A/m2, respectively. The results suggest that electrode surface modification and cathode overpotential play an important role in producing dendrite-free deposit. The critical over potential ( ) for dendrite free deposit for the experimental conditions was calculated. The cathode overpotential of -0.53 V or lower is recommended for dendrite-free deposit of aluminum using copper cathodes in electrorefining of aluminum from aluminum scrap.

Production of metals from metal compounds has been a major activity of human kind from time immemorial and metals played a vital role in shaping the modern world as it is today. With the discovery of electricity in the nineteenth century, electrochemical processes for metal production were developed which enabled the production of many metals that were difficult to be produced by the conventional chemical reduction processes. Electrochemical processes were also suitable for scaling up and hence economical. Extraction of reactive metals from stable metal compounds necessitated the use of molten salt as the solvent medium and the elevated temperature of operation of the molten salt processes helped to increase the product yield significantly. Transition metals and actinides mostly exist as stable oxides in nature and are reduced by using strong reductants. Direct extraction of these reactive metals from the metal oxides is avoided due to the chemical affinity of oxygen with the metal and hence the possible contamination. Often such metals were converted to the halides and the metal halides were chemically reduced to high purity metals. However, Chen et al discovered recently that a metal oxide could be converted directly to the metal by molten salt electrolysis and this triggered worldwide research activities in the new process called ‘FFC Cambridge process’ for extraction of a host of metals from their respective oxides. The unique configuration of the oxide as a solid electrode in the electrochemical process and the oxide to metal conversion taking place in the solid state give considerable advantages to the process but with equal challenges. Removal of oxygen from a solid oxide matrix can be kinetically limiting and this could pose challenges in the large-scale production of metals by the process. The process efficiency will depend a great deal on the design of the metal oxide electrode for faster removal of oxygen. The electro-deoxidation process has potential applications in the nuclear technology and significant efforts are now underway to develop the process for conversion of actinide oxides to metal. Sodium-cooled fast reactor with metal fuel is proposed as one of the future reactor systems in the Generation IV concept and electro-deoxidation process can be used to prepare the fuel metals from spent oxide fuels. The spent oxide fuel is converted to a metallic alloy by the electro-deoxidation process and the alloy is separated from fission products by the molten salt electro-refining technique. In the Advanced Conditioning Process (ACP) being developed by Republic of Korea, electro-deoxidation is also used as a step in the pyroprocessing of spent oxide fuel for reduction of its volume, radiotoxicity and heat load. The paper presents an overview of the electro-deoxidation process and the developments that are taking place in this area in the nuclear and non-nuclear domains. Some of the critical issues of the molten salt process, identified from a technological perspective, will be discussed with inputs from the open literature and author’s work.

Tungsten carbide (WC) was produced via the electrochemical reduction of calcium tungstate (CaWO4) and carbon preforms in molten calcium chloride at 1173K. The products were characterised by X-ray diffraction analysis, scanning electron microscopy and energy dispersive X-ray analysis. It was observed that after 2-3h of polarisation, CaWO4 was fully reduced to form metallic tungsten, which subsequently reacted with carbon to form WC via the formation of W2C. The pure WC products obtained had nodular structure and hexagonal phase, and were typically 300–50nm in size.

Specimens steel 1060 were pack aluminized at 760, 830 and 900°C in order to provide a rich aluminium coating and were used as work electrodes, tungsten wire was used as reference electrode and counter electrode also. The dissolution rate was determinate at 884°C in melt salt Na2SO4 using the polarization resistance technique. The aluminium film offers an excellent resistance to the oxidation reaction, although it corresponds to the accelerate dissolution, which was compared to the steel without aluminized. The experimental determination for four prepared series (steel pack aluminized at 760,830,900°C and without aluminized) showed a reasonable anodic dissolution decrease to the specimen pack aluminized at 900°C, due the relationship that exist between the temperature of aluminizing process and thickness film formed on metallic surface.

Public concerns over the foreseeable exhaustion of fossil fuels and CO2 emission related climate change have grown rapidly in the past decade. This period is in coincidence with the invention and research history of the FFC Cambridge Process which is in principle lower in energy consumption and CO2 emission than many existing industrial metallurgical processes. Thus, when developed commercially, the FFC Cambridge Process can contribute to mitigating the environmental strains on the energy and material industries. For example, in all known methods for harvesting solar energy, the highest conversion efficiency achieved over 40%, although the achievable efficiency using affordable materials and techniques is about 10% (1-3). This sounds not very high, but even at this

Pyrometallurgical processing using LiCl-KCl molten salt system is considered for safe recovery of proliferation resistant nuclear fuel elements from the spent fuel. Pyrometallurgical process is preferred because of the stability of the molten salts to high radiation and shorter cooling times. The major constituents of the fission products are lanthanide series elements, which have electrochemical behavior close to that of actinides. Therefore, very careful control over the process parameters is required for an efficient separation process. Most of the available thermodynamic data on the molten salt systems pertain to binary or ternary systems. When multiple fission product elements are present in the electrolyte, the reduction behavior of the actinides could be significantly altered because of possible under potential reduction of lanthanides and slower diffusion kinetics of actinides. This presentation reports the variations in melting point and electrochemical behavior of LiCl + KCl eutectic mixture containing multi-components of RECl3 additions. Cyclic voltammetry results of binary, ternary, and quaternary LnCl3-(LiCl-KCl)Eutectic systems at 500°C indicated that the incipient potentials of cathodic reduction waves shifted to less negative values with increased additions of lanthanide components. The shift in the reduction potentials could be attributed to the free energy change associated with formation of mischmetal solid solutions and decreased stability of the solvated clusters of lanthanides in the molten salt. The positive shift of the reduction potentials of multi-component lanthanide system indicates that enrichment of fission products in the re-processing cell could detrimentally affect the separation of actinides from the lanthanides. No significant change in the melting temperature was observed with the addition of multiple lanthanide chlorides o the LiCl-KCl eutectic.

Specimens of Ni were conditioned in the test piece with a work area of 0.2 cm2, each one of them was polished and using as work electrode , graphite electrode and platinum electrode were used as reference electrode and counter electrode respectively. The work electrode was changing each test. The concentration ratios were 1N NaCl, 1N NaCl : 0.8N H2SO4 and 1N NaCl : 1N H2SO4 with the volume ratio 1:1 in all cases. The presence of H2SO4 increase the corrosion rate. The corrosion current intensity was determinated by polarization resistance method. The scanning rate was 2 mV per second. Due to the acid medium provides favorable conditions to the oxide film formed on the niquel surface become in a no resistance film, which is broke out, and consequently exist a pitting surface. The calculation showed a considerable increasing corrosion rate with the acid enviroment; However the pH plays an important role since it has a strong relation with the H2SO4 concentration.

It is known that coatings of refractory metals and their carbides on metal and nonmetallic surfaces sharply increase firmness of materials and products to deterioration and corrosion. In the present work are presented results of investigation by electrochemical synthesis of double carbides of tungsten and molybdenum coatings on metal and nonmetallic surfaces in ionic melts at 1173 K. We investigated the influence of concentration of sodium tungstenate, sodium molybdate, lithium molybdate and lithium carbonate, the electrolysis temperature, the cathodic current density on process of joint electrosynthesis of double tungsten and molybdenum carbides on copper, nickel plates, and also natural diamonds crystals. Solid double carbide molybdenum (tungsten) deposits are obtained at 1173 K. At temperature more low 900°C powder deposits drop out. The investigation of influence current density on products of electrolysis was carried out in molten system Na2WO4 - Na2MoO4 - Li2MoO4 - Li2CO3 at temperature 1173 K. It was established that optimal values of current density is in an interval 0.05-0.1 А/cm2. At a current density more than 0.1 А/cm2 covering roughness decreases that is caused by considerable deterioration of its cohesion with surface. At a current density less than 0.05 А/cm2 speed of corrosion of a substrate exceeds speed of carbide deposition, therefore and the covering with good cohesion is impossible. Thus, the possibility of electrochemical synthesis of double tungsten (molybdenum) carbides is established. The thickness of double tungsten (molybdenum) carbides was in range 5-50 microns. The influence of temperature and electrolyte structure on double tungsten (molybdenum) carbides coatings on metal and nonmetallic (diamond) substrates were determinate for tungstenate-molybdate-carbonate melts. This work is carried out with support by the program FPP "Scientific and scientific-pedagogical personnel of innovative Russia" for 2009-2013 years.

In this paper, studies were carried out to determine the conditions and parameters of the electrochemical synthesis of pure nanosized hexaborides neodymium and praseodymium. Electrosynthesis borides we performed in potentiostatic (because voltage determines the course of the reactions and control the nature of the deposition reaction) and galvanostatic (to establish the limiting current density) mode. The appearance of boride phases in the cathode deposit starts at a molar ratio NdCl3: KBF4 = 1: 1. With a further increase in the content fluoroborates potassium in the melt increases the content of boride phases in the cathode deposit, at a molar ratio NdCl3: KBF4 = 1 : 2 are formed as tetraborides and hexaboride. X-ray analysis of the products potentiostatic electrolysis of molten NaCl-KCl-NdCl3-KBF4 with four-, six-fold excess of potassium fluoroborates compared to neodymium trichloride showed only the presence of neodymium hexaboride. Product of the potentiostatic electrolysis of the melt NaCl-KCl-NdCl3-KBF4 at potential recovery of neodymium ions and more negative, until the potential release of alkali metal is neodymium hexaboride. The phase composition identified by XRD on a DRON-6, he showed the presence of only phase NdB6. The size of the powder particles were determined using a scanning probe microscope Solver PRO P47.The addition of fluoride ion to chloride melt should contribute to the stabilization of chloride complexes of rare earth and fluoroborates ions. We have studied the system with the addition of sodium fluoride as a stabilizer - the system NaCl-KCl-NdCl3-KBF4 with the addition of 10 wt. % NaF. However, due to a sharp increase in corrosion materials the crucible and the electrochemical cell was preferred chloride composition of the background (without the addition of sodium fluoride). Authors obtained the optimal concentration ratio NdCl3: KBF4, range of current density and voltage for nano-sized powder of neodymium hexaboride. The results of galvanostatic electrolysis showed that the synthesis hexaborides performed in the range of current densities from 0.1 to 4.0 A/cm2. The product yield galvanostatic electrolysis of molten NaCl-KCl-NdCl3-KBF4 was 95%, current efficiency 53%.

The quinone’s redox chemistry is important in a variety of applications such as enzyme electrochemistry, redox catalysis and bulk industrial processes. It is very well known that the electrochemistry of quinones is pH-sensitive where, under protic conditions, quinone reduction leads to hydroquinone form via a 2-electron/2-proton reduction; Whereas, under aprotic conditions, reduction occurs via two consecutive one-electron process leading to the radical anion and di-anion, respectively [1]. Since certain room temperature ionic liquids (RTILs) are effectively aprotic [2], these have become popular media for fundamental and applied electrochemical investigations [3, 4] where reactive intermediates are electrogenerated. Since the redox chemistry of quinones is of both fundamental and applied importance, the introduction of quinone functionality into RTILs’ structure and their use as catalytic reaction media requires investigation. This communication reports the electrochemistry of a variety of RTILs possessing quinone functionality (benzo-, naphtha- and anthra-) using the cavity microelectrode arrays. The advantages and difficulties of using this type of cavity microelectrode over conventional electrodes will be presented. It will also be shown that creation of task-specific ionic liquid possessing the quinone functionality within their molecular structure facilitates dissolution in RTILs of otherwise insoluble quinones moieties.

Electrochemical behaviour of rare-earth metal trichlorides (RECl3), where RE-Nd, Sm, Eu, Yb was studied by different electrochemical methods in NaCl-KCl, KCl and CsCl melts. The diffusion coefficients (D) for the oxidation states RE3+ and RE2+ were determined by linear sweep voltammetry, chronoamperometry and chronopotentiometry methods showing that D decreases with increase in the oxidation state of RE, while the activation energy for diffusion increases. On the basis of the data obtained in the temperature range 973-1123 K it is possible to conclude that DNd(III, II)>DSm(III, II)>DEu(III, II)>DYb(III, II) in chloride melts. The standard rate constants of charge transfer (ks) for the redox couples Nd(III)/Nd(II), Sm(III)/Sm(II), Eu(III)/Eu(II) and Yb(III)/Yb(II) were calculated on the basis of cyclic voltammetry. The values of constants testify that the redox processes proceed quasi-reversibly, mostly under diffusion control. It was found that ksNd >ksSm>ksEu >ksYb and the standard rate constants increase when going from NaCl-KCl to CsCl melt. According to the theory of elementary charge transfer, the smaller and stronger bond complexes require higher rearrangement energy, and in consequence the electroreduction proceeds with slower rate. The complex size and metal-ligand bond length decreases from NaCl-KCl to KCl and CsCl. Therefore a decrease of the charge transfer constants would have been expected that contradicts data for the redox reactions RE(III) + e- = RE(II) (1) However, the previous approach is not valid for all electrochemical systems. Our experimental results allow to suggest that for the redox reaction (1) the limiting stage is not rearrangement of complexes, but electron transfer over outer sphere cations. In this case the explanation of the larger values observed for the standard rate constants in CsCl melt is the larger polarizability of caesium. The formal redox potentials of E*Nd(III)/Nd(II), E*Sm(III)/Sm(II), E*Eu(III)/Eu(II), E*Yb(III)/Yb(II) were determined from cyclic voltammetry, chronopotentiometry and steady-state voltammetry data. Some thermodynamic properties for dilute solutions of rare-earth metal chlorides such as relative partial molar enthalpy of mixing and activity coefficients were calculated. In present work the study of mechanism and kinetics of boron and RE joint electrodischarge in chloro-fluoride molten systems is reported too. The optimum regime of neodymium, europium and gadolinium boride manufacture has been worked out on the base of voltammetric experiments. It is necessary to note that europium and gadolinium compounds were synthesized as monophase products (EuB6 or GdB6), while co-deposition NdB4 and NdB6 was found for neodymium.

In this presentation results of studies of electrodeposition of refractory metals from molten salts and manufacturing of near-net shape components performed at Plasma Processes, Inc will be outlined. High melting point and strength are driving the increased utilization of refractory metals for high temperature applications. Molten salts electrolysis offer unique opportunities to deposit dense, coherent layers of refractory metals with desired shape and very low impurities level. Because of high temperature and high reactivity of melts, containing refractory metals salts, special equipment for high temperature electrolysis has been designed and built. Utilization of oxidation and corrosion resistance materials for melt containers and electrolyzers, electrolysis under inert atmosphere and tight process control provide stable and reproducible properties of electrodeposited metals. Influence of parameters of electrolysis and annealing on structure and properties of refractory metals was investigated. Electroforming techniques have been developed to produce near-net shape components from iridium, rhenium, niobium, hafnium and tungsten. The electrodeposition from molten salts has been demonstrated as a viable fabrication tool for commercial application. Various examples of the electroformed product and coating will be presented.

Chloride-oxide melts are the possible electrolytes for electrochemical refining of crude lead. The physical-chemical properties are very important for technological process optimization. The specific conductivity of KCl-PbCl2-LiCl and KCl-PbCl2-PbO molten mixtures have been evaluated via molar volume and electrical field strength. The mixtures under investigation contained from 0 to 10 wt. % of PbO and LiCl. At the moment the approaches describing properties of halide melts from one hand and oxide melts from the other hand are very different. There is a need to find some common points for modeling physical properties of halide-oxide melts. The initial point can periodical table of elements. Bockris with co-workers found that influence of different component of molten glasses depends on the valence of cation[1]. They placed all cations into 3 groups. Group 1 contains alkali cations : Li, Na+, K+ . The second one is formed from divalent cations: Mg, 2+Ca2+, Sr2+, Ba2+, M2+n and Fe2+. The third group consists of A3+l and Ti4+ . The most conductive are cations of the first group and the less conductive are cations of third group. The same influence of valence on electrical conductivity of molten chlorides was found by Biltz and Klemm[2]. They divided all molten chlorides on good conductors and bad ones depending on the place of an element at periodic table. The best conductors are alkali and alkaline-earth chlorides. It was found recently that this classification can explained using ionic potential (charge/radius) of cations[3]. It allows dividing all individual molten chlorides into some groups according their ionic potential. Inside every group electrical conductivity can be described as a function of molar volume. For example, electrical conductivity of molten alkali chlorides is lnx = 4,9* exp[-(2747-33724/V)/T] *exp(53,7/V) [1]Where V-molar volume, cubic cm/mol, x -specific conductivity, Sm/cm, T - temperature, K This expression is valid as for pure salts and for some mixtures such as NaCl-KCl, LiCl-NaCl, KCl-CsCl. It is possible to use eq. 1 for alkali chloride mixtures with other salts such as PbCl2 with some additional coefficient. Electrical conductivity can be also evaluated via electrical field strength [4]

Ionic liquids (ILs), particularly those based on imidazolium, can be thought of as “supramolecular fluids”, since in the liquid state they display a high degree of self-organisation. In these media, ionic channels, formed by extended hydrogen-bond networks between the anions and cation head-groups, coexist with non-polar “pockets”, created by the grouping of lipophilic alkyl side chains. This 3D structuring induces specific IL solvation properties which have been used to generate in situ metallic nanoparticles (MNPs), with a predictable and controlled size. Indeed, the size control is a highly important factor in potential applications (e. G. Catalysis, microelectronics). In particular, the goal of controlling the size of MNPs in ILs may be achieved by simply varying the nature of the ionic liquid or the reaction conditions. Although the in situ synthesis of MNPs in ionic liquids (ILs) has been largely reported in the literature, the mechanism of formation and stabilisation remains elusive. This will be discussed in this communication, taking into account the nature of the metal precursor the IL, the experimental conditions, and the presence or absence of additional stabilisers.

Combustion of fossil fuels during energy production generates pollutants in the fluegases which have to be effectively removed to avoid emission. In this work, we demonstrate how ionic liquids (ILs) can be tuned by design to perform as selective, high-capacity absorbents of environmentally problematic gases like, e. G. SO2 and in a pioneering project also for NO. Reversible absorption performance has been tested for several different ILs at different temperatures, pressures and flue gas compositions. Furthermore, different porous, high surface area carriers have been applied as supports for the ILs to obtain Supported Ionic Liquid-Phase (SILP) absorber materials. The use of solid SILP absorbers with selected ILs were found to significantly improve the absorption capacity and sorption dynamics at low flue gas concentration, thus making the applicability of ILs viable in temperature or pressure swing processes eventually turning the pollutants to useful mineral acids byseparate catalytic conversion.

Electro-deoxidation of metal oxides in molten chloride medium to produce metals and alloys is an area of great interest in pyroelectrometallurgy today. Several metal oxides have been reduced by the process and efforts are now underway to develop the process for commercial exploitation. In the FFC Cambridge process, the solid oxide is electro-deoxidised in molten calcium chloride medium at 850-950 oC with graphite as the counter electrode. Generally the process is carried out under a constant applied voltage in the range of 2.8-3.1V between the solid oxide cathode and graphite anode. Several metal oxides have been reduced by this process and TiO2 assumes a special place in these investigations owing to the commercial interests of titanium metal in the modern world. We have been studying the electro-deoxidation process with different metal oxides like UO2, Nb2O5, CeO2, ZrO2 in both constant current (CC) and constant voltage (CV) modes. We report in this paper the results of the investigations carried out on the electro-deoxidation of powder compacted and sintered TiO2 pellets by galvanostatic electrolysis, for the first time. These investigations are also unique because we have measured the half-cell potentials of the electro-deoxidation cell during the entire course of electro-deoxidation of the metal oxide to metal using an in-house developed graphite psuedo-reference electrode. The results of the investigations are very encouraging and they could provide the answers to some of the very fundamental questions on the FFC Cambridge process, which cannot be otherwise sorted out by the conventional method of CV electrolysis. Some of these questions are : (i) Is FFC Cambridge process a calciothermic reduction process or an oxygen ionization process? (ii) What are the cathodic and anodic potentials of the process? (iii) What is the magnitude of polarization possible for an electrode under a given electrolysis condition? (iv) How does the electrical resistance of the cathode and the cell change during electro-deoxidation and what are its implications? .

Extreme conditions of articles exploitation cause utilization of expensive refractory metals and alloys ensuring their adequate performance. The problem can be approached by depositing coatings on the surface of units and mechanisms, i. E. Creating composite materials. In this case, the substrate material provides the strength and electric characteristics while the coatings realize the necessary surface properties. Nowadays coatings are mostly produced by CVD, PVD methods, plasma and detonation spraying. Electrochemical synthesis from molten salts offers considerable advantages over other methods. For example, electrochemical methods such as pulse plating and reversed plating provide a unique means of controlling the structure and phase composition, the thickness of the coatings, the grain size (down to the nano scale), the porosity, the smoothness, and the texture of the layer. Other advantages are: (i) a relatively low synthesis temperature (700-850°С); (ii) the parameters of electrochemical deposition can be easily adapted in scaling-up synthesis; (iii) the method can be applied to all kinds of substrates with a complicated geometry for obtaining of uniform coatings with respect to thickness, grain size and composition of the layer; (iv) high purity of resulting coatings even with low-grade initial reactants; (v) the production costs are much lower comparing to other methods. This study presents our findings in the area resulting in the production of functional materials of different application:1. Heat-resistant material: From hafnium and niobium-hafnium alloy on borosiliconizing graphite with the temperature of exploitation up to 1700-2000°С.2. Composite material MoSi2-MoB4 for protection of molybdenum from oxidation in an air-water mixture at temperature 500-700°С.3. A new generation of highly active and stable catalysts based on nanostructured Mo2C coatings for the water-gas shift reaction.4. Material for hydrogen storage on the base of V-Ti alloys.5. Glass-ceramic shells for hot isostatic pressing with titanium and niobium barrier coatings.

In the FFC Cambridge process, a solid metal oxide cathode is directly reduced to the metal by molten salt electrolysis in calcium chloride medium containing small quantities of calcium oxide at ~ 900 oC. The cathodic and anodic process can be represented as MOx+ 2ne- → MOx-n+ nO2- at cathode nO2- + nC → nCO + 2ne- at anode or nO2- + n/2C → n/2CO2 + 2ne- at anodeThe cathodic process of the FFC Cambridge process, i. E the electro-generation of oxygen ions and its release to the electrolyte melt are very unique features of the process, which determine the efficiency of the ‘cathode-centric’ electrochemical process. The cathodic ionization of a solid metal oxide can take place only at those points where the three phases viz. Electron (conductor), the oxide and the electrolyte meet. Also the cathodically produced oxygen ions in the bulk of the solid specimen should diffuse towards the surface of the pellet. These conditions require that the electrode be good conducting and also sufficiently porous. For the process to be efficient, the three-phase contact points must be spread across the entire volume of the solid oxide preform. When the oxide preform is poor conducting, this condition cannot be satisfied and hence it may end up with a better-reduced outer layer and a partially reduced inner bulk. Both the chemical and physical characteristics of a solid oxide preform are very important in determining the efficiency of its electro-deoxidation. We have studied some of these aspects of the FFC process with powder compacted and sintered electrodes and powder electrodes of TiO2, ZrO2 and SiO2, three metal oxide cathodes with different chemical and physical characteristics, in molten calcium chloride at 900 oC. In-house developed novel electrochemical techniques were used as part of these studies to gain insight into the electrode behaviour (electrode potentials and resistance) of the oxide cathode during the entire course of the electro-deoxidation. The studies have shown that the electro-deoxidation of a solid oxide pellet depends on many factors such as the sintering temperature-dependent morphology of the starting pellet, the intermediate compounds and the metal phase; The cathodic reactions, electrical nature of the starting pellet and the intermediate products, the IR drop of the cell, the method of application of electric potential to the electrode, the configuration of the electrodes etc. These factors influenced more prominently the electro-deoxidation of poor conducting ZrO2 than good conducting TiO2 electrode. The details of the study are presented in this paper.

Room-temperature molten salts, or ionic liquids, are complex fluids. In order to be fluid around room temperature, the ions composing them must be bulky, asymmetric, flexible, with delocalized electrostatic charge, or contain non-polar moieties. Combinations of some or all of these factors are usual. This variety of features leads to diverse physical-chemical properties, the understanding of which requires a description of the molecular interactions taking place in bulk ionic liquids, when solutes are solvated in them, or when they are in presence of mesoscopic objects such as colloidal particles and macroscopic surfaces. Molecular interaction models can be used to provide structural and energetic information about ionic liquid systems, and help design new compounds for applications in chemical processes, devices and materials. An important effort has been put into accurately describing molecular interactions of ionic liquids, starting from ion-ion interactions, ion-solute interactions (where the solute is a molecular compound) and leading to ion-surface interactions including glass or metallic surfaces. The methodologies used are quantum chemical calculations and molecular simulation. These methods provide insight into the local order of the ionic liquid phases and into the dominant energetic terms, allowing us to investigate how an ionic liquid is organized at the molecular scale, to elucidate important questions regarding the dominant contributions within the interactions, and to put in evidence the mechanisms of solvation of different compounds. Illustrative applications include ionic liquids tailored for the capture of CO2, biodegradable ionic liquids, new media for hydrogenation catalysis using metallic nanoparticles, and the friction properties of ionic liquids at metal surfaces in the context of the development of novel ionic lubricants.

In this work, we explore the relations between the acid–base reactions implicit in the definition of protic ionic liquids and their solutions, the existence of reactive azeotropy, and the continuity between the aprotic and protic classes of ionic liquids. The profound impact caused by this type of homogenous azeotropy on the fluid phase behaviour (liquid–gas equilibria) of this class of compounds is also discussed. The differences and similarities between ionic liquids and traditional molten salts will also be highlighted, namely their liquid-gas equilibria, the nature of the gas phase and the use of the former class of compounds in solutions with molecular solvents.

The vaporisation behaviour of lanthanide halides with unstable Ln valence state is a challenging topic in high temperature materials science. Complex vapor composition is due to the decomposition (2LnX3,s => 2LnX2,s + X2,g) and disproportionation (3LnX2,s => Ln, s + 2LnX3,s) reactions, which in addition enter into competition at elevated temperatures. Our purpose was to identify the molecular and ionic species in the saturated vapour over Yb-Br systems by an upgraded technique of the Knudsen Effusion Mass Spectrometry and, being supplemented by the DSC measurements and quantum chemical calculations, to study their thermodynamic properties. In the temperature range 850 – 1300 K the following ions were registered in the mass spectra: Yb+, YbBr+, YbBr2+, YbBr3+, Br2+, Br+, Yb2Br+, Yb2Br2+, Yb2Br3+, Yb2Br4+, Yb2Br5+ (electron-impact-ionization mode) and YbBr3−, YbBr4− (thermionic emission mode). Analysis of the temperature and time dependences of ion currents, ionisation efficiency curves and ion appearance energies along with the special mathematic procedures of mass spectrum interpretation led us to establish the molecular vapour composition at different stages of vaporisation. It was found out that initial incongruent stage of vaporisation of pure YbBr2 or YbBr3 samples passed gradually to the stationary congruent stage with nearly the same vapor composition. A novel approach based on (i) measurements of equilibrium constants of the molecule/molecule and ion/molecule reactions in the Ln-Br systems of different compositions and (ii) solution of a system of thermochemical equations is proposed to derive the formation enthalpies of YbBrn (n = 1 - 3) molecules and YbBr3−, YbBr4− ions.

Molten Salt Electrochemical Preparation of Multi-walled Carbon NanotubesC. Schwandt, A. R. Kamali, A. T. Dimitrov, D. J. FrayDepartment of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB2 3QZ, United KingdomGraphite may be converted directly into nano-structured carbonaceous material by way of electrolysis of molten alkali metal chlorides in the presence of graphite electrodes. However, because of the heterogeneous nature of the product and the low yields achieved to date, the method is generally regarded inappropriate for the production of carbon nanotubes. This presentation summarises recent research work that has the potential to change this view. By rigorously optimising the process parameters and implementing a novel type of process control, it has now become possible to prepare nano-structured carbonaceous material with nanotube contents as high as 70 to 80% in gramme quantities. The nanotubes are curved and multi-walled and occur in large agglomerates. The process is straightforward and uses conventional laboratory equipment, and thus has the potential to become a viable option for nanotube production.

The next generation of modified phase change material (PCM) composite is elaborated for utilizing both, a high thermal capacity of the molten salts NaNO3/KNO3 eutectics and a good thermal conductivity of the graphite matrix. The form of containment to prevent leakage of the liquid phase change material is another function of a graphite matrix. Particle porosity and larger specific surface are intended to avoid a salt clusters formation during solidification alongside the heat flow exchange improved. An extensive study on structural and thermal behavior of the modified PCM was carried out for molten salts NaNO3/KNO3/graphite composite samples, structured through different manufacturing routes with variety graphite content (10–30 wt%). Thermophysical data, collected by DSC and thermal cycling methods, include the composite phase transition temperatures from 215 to 2600C and thermal storage capacity of 75-88 [kJ/kg]. The molten salts NaNO3/KNO3/graphite crystallization process, responsible for heat released, was studied by LINKAM thermal microscopy, scanning electron microscopy (SEM). The precise imaging allowed identification of the adhesive bonding development among surfaces of the molten salts and graphite matrix. The spectral FTIR study performed before and after the composite re-crystallization, did not register additional functional groups due to chemical destruction of molten salts. The elemental characterization of the composite surface by the use of X-ray microanalysis (EDS) method specified a few areas of Na-rich spherical masses and the K-rich layered structure on the graphite plane. As the areas of inhomogeneous elemental distribution influence thermal stability of the salt/graphite composite structure, the research focus on solidification/nucleation process is obvious and planned for controlling the composite structural stability during repeatable thermal cycling process. The correlation between morphology and thermal storage capacity allowed selection of the molten salts NaNO3/KNO3/graphite composite samples with optimal thermal storage behavior. Applicability of the new generation modified PCM composite to the high temperature thermal storage process would increase energy efficiency of saturated and superheated steam commercial plants through accumulating and use the waste heat.

Molten salts and liquid metals are compatible phases, i. E. They can co-exist at high temperatures. Traditionally, molten salts (fluxes) are used to keep the surface of liquid aluminium clean from oxidation. In this paper more advanced possibilities to create advanced materials will be presented, using molten salts and controlling interfacial phenomena in the system. This will include the production of Al-alloys, Al-matrix micro-nano-composites and Al-micro-nano powder (emulsion). Additionally, the separation of Al-matrix composites into its original phases using a molten salt flux will be presented.

Computer models of T-x-y-z diagrams permits to obtain not only three-dimensional images of diagram hyper-surfaces and phase regions as the different projections sets (XYZ, TXY, TXZ, TYZ), but to perform the investigation of one-, two- and three-dimensional sections as well . At that, the section view can be suggested from the section arrangement. This permits to avoid the errors in representation of surfaces intersections associated with an incorrect understanding of phase diagram structure. Knowledge of ruled hyper-surfaces geometrical structure of T-x-y-z diagrams with quaternary eutectic makes possible to modify a tie-lines method based on the vertical sections set construction for the determination of quaternary eutectic point coordinates. For this case, such arrangement of two two-dimensional vertical sections of four-dimensional hyper-prism is considered, when these two firs sections common base does not belong to a general plane parallel to the one of tetrahedron faces. In the first stage it is sets the section indicating the point belonging to general forming two-dimensional simplex of two ruled hyper-surfaces at the quaternary eutectic temperature. In the second stage one more section passing through the obtained point and the arbitrary point of tetrahedron edge disposed nearby of the section is constructed. This section will intersect one-dimensional forming segment of the ruled hyper-surface at the quaternary eutectic temperature. In the third stage the section passing through the obtained point and neighboring tetrahedral vertex intersects the opposite tetrahedral side. This section will contain the required quaternary eutectic point. A matrix transformation needs to use for calculation of points coordinates defining the vertical sections arrangement . First section can be made through two ternary eutectics points as the optimal scheme of tie-lines method.

Electrochemical measurements are powerful tools for investigating electrowinning processes in molten salts. Recently, we have developed several innovative methods to obtain in-situ information on molten salt behaviour and phenonoma: • Dynamic measurements of resistance and capacitance obtained simultaneously during electrolysis; • A Fast Fourier Transform Current Pulse technique to investigate anode bubble resistance. However, non-electrochemical techniques are often required in order to more fully understand the complex processes that occur. To this end, the electrolysis group at CSIRO has collaborated with a number of other groups within CSIRO to develop additional tools. This paper will describe a number of these techniques, including: • High–precision, gas chromatographic–mass spectrometric detection (GC-MS) of perfluorocarbon and other off-gases in both laboratory- and plant-scale Hall-Héroult cells. • Synchrotron X-ray diffraction phase-mapping of an inert anode in an operating FFC-type laboratory cell;

The electrochemical nucleation of Mo2C and W2C crystals for tungstate-molybdate-carbonate melts of specific compositions on Ag, Au, Cu, Pt and Ni substrates has been studied by the electrodeposition method. The influence of the electrocrystallization conditions - temperature, depo¬sition time, initial current pulse and current density was characterized. Experimental measurements indicate that crystallization overvoltage is associated with three-dimensional nucleation. Carbide deposition onto the substrates prepared from the same solid materials was not associated with crystallization overvoltage. The maximum value of the initial overvoltage max which includes crystallization and electrolysis overvoltages is propor¬tional to the electrode surface area. Under these conditions, the stage of surface diffusion does limit the rate of the process at the electrode. Increase in the rate of carbide deposition leads to the number of crystallization centres increase which reduces deceleration related to surface diffusion. At high overvoltages, change the limiting stage is observed so that the process rate is determined either by the rate of electron transfer or by the rate of diffusion from the melt volume. An increase in melt temperature leads to complication of the crystallization process by alloy-formation phenomena. The height of the overvoltage maximum for metals which do not form alloys is proportional to the reciprocal time of their formation. An increase in the melt temperature promotes the interdiffusion rate of the refractory metal, carbon and the substrate, and also intensifies their chemical interaction. Structural mismatch is observed during molybdenum and tungsten carbide electrodeposition onto different single-crystal substrates.

In recent years, TiAl-based intermetallic alloys are being increasingly considered for application in areas such as (i) automobile/transport sector (passenger cars, trucks and ships) (ii) aerospace industry (jet engines and High Speed Civil Transport propulsion system) and (iii) industrial gas turbines. These materials offer excellent (i) high temperature properties (at higher than 600C) (ii) mechanical strength and (iii) resistance to corrosion and as a result have raised renewed interest. The combination of these properties make them possible replacement materials for traditional nickel-based super-alloys, which are nearly as twice as dense (than TiAl based alloys). Since the microstructures of these intermetallic alloys affect, to a significant extent, their ultimate performance, further improvements (by way of alteration/modification of these microstructures), have been the subject matter of intense research investigations. It has now been established that the presence of alloy additives, such as niobium, tantalum, manganese, boron, chromium, silicon, nickel and yttrium etc, in specific quantities, impart marked improvement to the properties, viz. Fatigue strength, fracture toughness, oxidation resistance and room temperature ductility, of these alloys. From a number of possible alloy compositions, γ-TiAl and Ti-Al-Nb-Cr have, of late, emerged as two promising engineering alloys/materials. . The conventional fabrication process of these alloys include steps such as melting, forging and heat treatment/annealing of the alloy compositions. However, an electrochemical process offers an attractive proposition to prepare these alloys, directly from the mixture of the respective oxides, in just one step. The experimental approach, in this new process, was, therefore, to try to electrochemically reduce the (mixed) oxide pellet to an alloy phase. The removal of oxygen, from the (mixed) oxide pellet, was effected by polarizing the oxide pellet against a graphite electrode in a pool of molten calcium chloride at a temperature of 900C. The dominant mechanism of the oxygen removal was the ionization of oxygen followed by its subsequent discharge, as CO2/CO, at the anode surface. The removal of oxygen from the oxide mixture helped form the alloy in situ. The presentation shall cover the detailed experimental results pertaining to the preparation, evaluation and characterization of Ti-47Al-2Nb-2Cr (atom%) alloy.

Ni and Ni-Fe alloy Specimens were risked to acid environment H2SO4 solutions at different concentration by anodic polarization the passive zone was investigated which appear from potential corrosion to potential transpassive process that correspond to electrochemical inactivity due the characteristics of Ni(OH)2 film that is formed in the beginning corrosion process.

Green fluorescence protein (GFP) consists of 238 peptides, which is shaped into a barrel structure with a fluorophore inside the barrel. The fluorophore is a tripeptide of Ser-Tyr-Gly, which is rearranged into 4-(p-hydroxybenzylidene)-5-imidazolinone (p-HBI) after folding and autocatalytic reaction. The wild-type GFP has excited-state proton transfer, which causes fluorescence emission a bathchromic shift. This natural phenomenon inspired me to calculate properties of ground-state GFP ionic liquid and excited-states GFP ionic liquid. We used density function theory (DFT) to optimize geometric and electronic structures of ground-state and excited-state GFP, respectively. Mullican charge distribution was used to analyze charge/electron distribution of ground-state and excited-state GFP. The charge/electron distribution make a significant contribution to the solvation properties of the ground-state and excited-state GFP.

We have been investigating molten salts formulated with mixed cations and anions for over 20 years which has led to the discovery of low melting salts with liquidus temperatures below 80 C. The composition of these mixtures is reported to contain lithium, sodium, potassium and/or calcium cations with nitrate/nitrite anions. Physical and chemical properties like viscosity, heat capacity and density are critical parameters to optimize for concentrated solar power generation. As new power generation concepts emerge, the demands on molten salts are increased. We are now investigating the thermal stability of molten salts up to 700 C and optimizing other properties such as heat capacity.

This paper is concerned with physical characterization of carbon nanotubes produced by an original procedure for reduction of lithium molten salts onto graphite cathode. Several techniques were employed for characterization, i. E. Electron microscopy (SEM and TEM), Raman spectroscopy, thermogravimetric and differential thermal analysis (TGA and DTA). SEM and TEM images show that nanotubes are mostly of curved shape with length of 1÷20 µm and diameter of 20÷40 nm. Raman peaks indicate that the crystallinity of produced nanotubes is rather low. The obtained results suggest that formed product contains of up to 80% multiwalled carbon nanotubes (MWCNTs), the rest being non-reacted graphite and fullerenes. DTA curves show that combustion process of the nanotubes takes place in two stages, i. E. At 450oC and 720oC. At the lower temperature combustion of MWCNTs occurs, while at higher one fullerenes and non-reacted graphite particles burn.

Fine Nb-Sn and Nb-Ta intermetallic powders were produced by hydrogen reduction from their chloride vapors which were mixed uniformly, while Nb-Al intermetallic powders were synthesized by sodium reduction of chlorides in a LiCl-KCl-NaCl-CaCl2 molten medium. The obtained Nb-Sn and Nb-Ta powders were fine and uniform with a certain agglomeration of 20-40nm. The particle size of Nb-Al powders synthesized by sodium reduction was appropriately in the range of 50-300nm.

Hydrogen is assumed to be very important energy source to improve the energy efficiency although it is a secondary energy. However, the problem is in the storage and transport of hydrogen. LiH is the most promising candidate because LiH is stable chemically at ambient pressure and temperature by separating from air and moisture. Furthermore, LiH has smaller volume than liquid hydrogen per unit amount of hydrogen and it is easy to obtain the hydrogen by reacting water. Therefore, it is necessary that LiOH as a by-product of the reaction must be reduced to metallic lithium to establish the storage, transport and usage cycle of hydrogen. In this work, the electrolysis of LiOH was successfully carried out by separating the anode and cathode compartments to prevent the contact of LiOH with metallic lithium electrolyzed.

Building chemical functionality into the molecular framework of ionic liquids provides an approach to generating new fluid materials which exhibit the many advantages of ionic liquids along with the chemo-selective properties of the functionalising unit. Many applications for such materials are easy to envisage including homogeneous catalysis, chemical sensors and energy storage devices. In this presentation, the synthesis and characterization of quinone-functionalised ionic liquids along with a detailed description of the electrochemical properties will be presented. Their application as redox catalysts in chemical transformations and as electrical energy storage materials will also be presented.

Reactions between polycrystalline Ti3SixAl(1-x)C2 solid solutions (x = 0 - 1) and a Na3AlF6-AlF3-CaF2-Al2O3 electrolyte melt were studied using the immersion test method in argon at 960 and 1010 °C, respectively. Analyses of the tested samples by XRD and SEM-EDS showed that the Si was stable whereas the Al was leached out of crystal structure of the Ti3SixAl(1-x)C2 sample into the melt x = 0.2. Both Si and Al were leached out of the Ti3SixAl(1-x)C2 solid solutions at x ≠ 0.2 into the melt. A further XRD analysis of the tested Ti3SixAl(1-x)C2 samples at x ≠ 0.2 revealed that the leaching of both Si and Al of the solid solutions resulted in phase transformations of the hexagonal matrix phase to a phase similar to TiCσ (0 < σ < 1) due to the leaching of Si and Al atoms out of the basal plans of the crystalline phases into the melt. An inspection by SEM-EDX further revealed that the TiC-like phase exhibited finely grained textures and was chemically stable towards the melt. The mechanism of Ti3SixAl(1-x)C2/melt reactions and subsequent dissolution of the leached atoms into the melt is discussed in detail.

Reactions between polycrystalline Ti3SixAl(1-x)C2 solid solutions (x = 0 - 1) and a Na3AlF6-AlF3-CaF2-Al2O3 electrolyte melt were studied using the immersion test method in argon at 960 and 1010 °C, respectively. Analyses of the tested samples by XRD and SEM-EDS showed that the Si was stable whereas the Al was leached out of crystal structure of the Ti3SixAl(1-x)C2 sample into the melt x = 0.2. Both Si and Al were leached out of the Ti3SixAl(1-x)C2 solid solutions at x ≠ 0.2 into the melt. A further XRD analysis of the tested Ti3SixAl(1-x)C2 samples at x ≠ 0.2 revealed that the leaching of both Si and Al of the solid solutions resulted in phase transformations of the hexagonal matrix phase to a phase similar to TiCσ (0 < σ < 1) due to the leaching of Si and Al atoms out of the basal plans of the crystalline phases into the melt. An inspection by SEM-EDX further revealed that the TiC-like phase exhibited finely grained textures and was chemically stable towards the melt. The mechanism of Ti3SixAl(1-x)C2/melt reactions and subsequent dissolution of the leached atoms into the melt is discussed in detail.

Often the errors in graphics of T-x-y-z diagrams for the quaternary salt systems and their sections are associated with the incorrect understanding of phase diagram structure. For example, at the consideration of eutectic type system LiF-LiCl-LiVO3-Li2CrO4 we have revealed that the intersection lines of two ruled hyper-surfaces on one of the two-dimensional section are missed. Such diagrams have two types of ruled hyper-surfaces sets: 1) with one-dimensional forming simplex and two directing surfaces; 2) with two-dimensional forming simplex and three directing lines. One directing line of first type ruled hyper-surface is degenerated on the hyperprism edge in the case of system without solid-phase solubility. In the same case, a ruled hyper-surface of the second type has two degenerated directing lines, which are projecting into tetrahedron tops. So the section view can be suggested from the section arrangement relative to the diagram elements in the tetrahedron. The errors in graphics of diagrams with the anomalous structure of solid-phase solubility are met too. For example, two-phase region RbJ+NaF was depicted as the homogeneous region of solid solution a on the base of RbJ on the vertical section NaJ-(0,5RbJ+0,5NaF) in the eutectic subsystem NaJ-RbJ-NaF of ternary reciprocal system Na, Rb//J, F. Analogous mistake takes place nearby the component NaJ: Two-phase region NaJ+NaF was indentified as the homogeneous region of solid solution b on the base of NaJ. Furthermore the boundary of regions L+a and L+a+NaF has incorrect view as horizontal line. As the solid-phase solutions a and b have anomalous form on the horizontal sections of T-x- diagrams, they can be described as the triangular ones, in accordance with the point-type, linear and planar phases.

The nuclear energy industry is facing the challenges of new build and the need for reducing the amounts and volume of radioactive waste, amongst many other technical challenges. The general public particularly support the reduction of Low and Intermediate Level Wastes (LLW and ILW) and the number of such. The industry generally prefers to develop existing technologies with which they are familiar and have experience. This contribution describes a well researched novel technique that can reduce the volume of LLW and ILW currently being idly held in large warehouses on nuclear sites, specifically contaminated paper, cotton wipes and lab coats. Molten Salt Oxidation, MSO, is a technique for the flameless oxidation of waste and originally employed oxygen (from air) and molten sodium carbonate at 900-1100°C. Oxidation was slow and often incomplete, particularly for paper, cotton and plastics, and abandoned twenty years ago. However, its efficiency for other wastes was particularly high. We have now established that the early workers had misunderstood the mechanism of the oxidation process. Consequently, upon reassessment, we have improved the speed and efficiency of the process. Using a ternary carbonate melt at 550°C our process, Catalyst Enhanced Molten Salt Oxidation, completely oxidised paper, cotton and plastics. Thus CEMSO is a particularly useful technique for reducing the quantities of both slightly and heavily contaminated radioactive waste. CEMSO oxidises the organic component of waste into CO2 and steam while retaining all the inorganic and radioactive constituents in the molten carbonate, from which they can be readily removed, including as insoluble phosphates, now suitable for vitrification (and the carbonate recycled). Previously molten carbonate was considered to act as a catalyst but our studies found that oxidation proceeds because oxygen dissolves chemically, not physically, in molten carbonate, yielding peroxide and superoxide ions, the active species. Their concentration is further increased when nitrate is added as catalyst, since nitrate reacts with peroxide to form superoxide and nitrite and the nitrite is now regenerated into nitrate by reaction with oxygen. This has been confirmed by Density Functional Theory: The formation constants of the adduct intermediates all show negative entropy. Molten Salt Oxidation destroys completely ion exchange resins and hence is a suitable treatment for exhausted radioactive resins. We have shown that tributyl phosphate and kerosene are completely oxidised, with phosphorus remaining in the melt as phosphate, thus revealing that the quantities of exhausted TBP and kerosene on nuclear sites can be very considerably reduced in volume to phosphates plus phosphates of the radionuclides, again suitable for vitrification. We have also shown that UO2, including ceramic UO2, and uranium compounds are converted into diuranates, the solubilities of which are < 500 ppm. Plutonium contaminated waste yielded >99.9% plutonium in the melt and the element was only detected in the first pre-filter of the off-gas. Sr, Eu and Cs compounds, to simulate fission products, have been added to molten carbonate sparged with oxygen, and all remained completely in the melt. Since aqueous cyanide has been reported as >99.99% destroyed we consider that the volume of raffinate might be lowered by CEMSO. Finally, other hazardous wastes have been oxidised by>99.9999% efficiency, including sarin and other chemical warfare agents, PCBs, and both liquid and solid chlorinated hydrocarbons. We shall describe how CEMSO can be implemented to reduce and render radioactive waste into smaller volumes and suitable for immobilisation.

The U. S. Department of Energy’s Global Threat Reduction Initiative – Convert Fuel Development program (formerly known as Reduced Enrichment for Research and Test Reactors – RERTR) has developed a next generation fuel to enable conversion of research reactors from high enriched uranium (HEU) fuel to low enriched uranium (LEU) fuel. The novel fuel design consists of a monolithic fuel meat (U-Mo alloy), a zirconium foil interface, and an aluminum clad. To complement the implementation of this new fuel, a study was performed to assess the separation and recovery of uranium after irradiation of the fuel in a research reactor. Specifically, an approach involving the dissolution of the aluminum cladding in caustic solution followed by electrorefining of the fuel meat was developed and characterized at bench scale with both unirradiated and irradiated material. The product was refined uranium metal devoid of aluminum, zirconium, and molybdenum. The results of the bench-scale demonstration will be presented along with projected process scale up requirements for applying the prescribed treatment to this new research reactor fuel.

A new process for the production of cheaper and pure zirconium has been recently developed. In the new process, molten salt electrolysis is used to prepare the crude zirconium metal for the zirconium – hafnium separation and zirconium refining. It is thus essential to understand the behavior of ZrO2 in the electrolyte, including the solubility of ZrO2 in various molten salt system (CaO – CaCl2 – NaCl –KCl – LiCl). The solubility results will lead to an optimum control of the added amount of ZrO2 as raw material into the electrolyte, and to have a better performance and operation of the molten salt electrolysis process. According to the information in the public literature, no solubility data of zirconium oxide in the molten salt systems was found. To provide the basic knowledge for zirconium electrolysis, the solubility of ZrO2 in NaCl-KCl and NaCl-CaCl2 based equi-molar molten salt system was experimentally determined in the present work. According to the experimental results, ZrO2 has generally limited solubility in the chloride system even at 850°C. It was found that addition of NaF and CaO has positive effect on the solubility. At 750°C, NaCl-CaCl2 system with addition of CaO and NaF gives highest solubility of 2.8 wt%. This provides the fundamental information of the electrolytes systems for the molten salt electrolysis of zirconium.

The aim of our work is to understand, on experimental and theoretical bases, why Room-Temperature Ionic Liquids (RTILs) that are immiscible with water can be so specific in terms of solvation, complexation and extraction of both cations and anions. RTILs, being by definition composed exclusively of ions, display unique and unusual (as compared to molecular solvents, either polar -water- or non polar -hexane-) features as far as complexation and extraction processes are concerned. In particular, they have a great potential for liquid/liquid extraction of metallic moieties, often displaying much higher extraction efficiencies compared to conventional organic media. So far, the best choice (“solvent design”) of the cation / anion components of the RTIL for a given process (liquid/liquid extraction, catalysis, organic synthesis) remains empirical and hampered by the very limited knowledge of the microscopic state and solvation of solutes in RTILs, thus requiring more fundamental studies. We thus have carried out investigations on the solvation, complexation and extraction abilities of hydrophobic RTILs towards the cation UO22+, and the anion ReO4- (the non-radioactive homologue of TcO4-) that are both of industrial relevance to the nuclear fuel cycle. Investigations are led by coupling experimental techniques (UV-visible spectroscopy, TRLFS, EXAFS) to molecular dynamics calculations. In this presentation, we will focus on the results obtained on the complexation phenomena evidenced between UO22+ and ReO4- in hydrophobic ionic liquids (C4mimTf2N, Me3BuTf2N, Bu3MeTf2N), and compare it with results obtained in more conventional solvents, i. E. Water and acetonitrile. The stoechiometry of the limit complexes formed was shown to depend on the solvent, and in particular, is different between an imidazolium- and a tetra-alkyl-based RTILs. Those experimental results are compared and supplemented with molecular dynamics calculation which allowed to gain insights on the solvation of cationic and anionic species in RTILs.

Electrochemical deoxidation of a solid metal oxide cathode in molten calcium chloride medium at 900 oC was reported about a decade ago and there has been a spurt of research activities world over to develop the process for production of metals and alloys. The process, with some modifications, was adapted to nuclear technology for consolidation of spent-oxide nuclear fuels. The electro-deoxidation process is also being developed as a head-end step in the pyrochemical reprocessing of spent oxide fuels by atomic energy programmes of USA, South Korea and Japan. In the FFC Cambridge process, molten calcium chloride is used as the electrolyte and graphite serves as the anode. However, due to issues of handling of materials with radioactivity, a lower temperature is preferred for the nuclear applications of the process and hence most of the work in this area was carried out in molten lithium chloride containing 1-3 wt. % lithium oxide at 650 oC. Platinum is used as the anode for purity concerns of the nuclear materials. We have initiated a programme on the electro-deoxidation of actinide oxides with the above stated objectives. In order to gain insight into the electro-deoxidation phenomenon at the elevated temperatures, we have carried out electro-deoxidation studies with solid UO2 in the typical FFC method, i. E with actinide oxide as the cathode, graphite as the anode and molten calcium chloride as the electrolyte. Platinum anode is also used in few experiments. Prior to the electrodeoxidation of the oxide, Cyclic voltammetry of different electrodes were carried out in the calcium chloride melt to characterise the melt and also to relate the redox potentials to the electro-reduction of the oxide. Powder compacted and sinterered UO2 pellets (sintering temperature 1550 oC) were used in the electrodeoxidation studies. The experimental results showed that the surface of thick UO2 pellets (4 mm thick)pellets was transformed to an impervious uranium metal layer, but the bulk remained as unreduced UO2. A thin UO2 disc (1 mm thick) could be completely reduced under similar experimental conditions. The experimental results indicated that it is difficult to achieve bulk reduction of thick UO2 preforms in the calcium chloride melt as the uranium metal preferentially forming on the surface of the preform sinteres as an impervious metal layer at the elevated temperature of operation (900oC) of the cell. The non-porous surface metal layer prevents the electrolyte contact to the bulk of the pellet and hence the bulk reduction. The results also indicated that it may be possible to achieve complete reduction of UO2 in molten calcium chloride provided the metal oxide is made as thin discs. The electro-reduction experiments with platinum anode showed significant mass loss of the platinum metal from the electrode. The details of the studies are presented in the paper.

The electrodeoxidation of Dy2O3 for preparing Dy metal in CaCl2 melt was studied by cyclic voltammetry, constant potential electrolysis techniques and thermodynamics analysis. Two electrodes system was employed during measuring cyclic voltammograms. Only one cathodic current peak(at about -1.75V ) was discovered before the decomposition of CaCl2 which corresponded to the electrodeoxidation of Dy2O3 in the cyclic voltammograms in molten CaCl2 at 850℃. The validity of the cyclic voltammograms was further confirmed by thermodynamics analysis and the CO2、CO anodic gas detected. In constant potential electrolysis products there were no other intermediates except Dy2O3 and Dy by XRD. And the above results confirmed the following electrodeoxidation sequence: Dy2O3→Dy.

The capture of carbon dioxide from combustion of fossil fuels, treatment of natural gas or from chemical process in general represents a critical component of efforts aimed to reduce the greenhouse gases in the atmosphere. In this way, significant effort has been put in order to design new and more efficient process for capturing carbon dioxide and with lower losses. The state-of-the art technology based on absorption to capture carbon dioxide normally uses solutions of alkanolamines, commercial diluted solutions of monoethanolamine or diethanolamine (MEA and DEA respectively), absorbents with high absorption capacity and reasonably stability, or physical solvents such as Selexol (polyethylene glycol) or Rectisol (MeOH), effective and attractive for carbon dioxide removal for treatment of sour gases. Nevertheless, a new approach can be considered to design more efficient and specialized absorbents. To this end, ionic liquids (ILs) have been proposed as solvent reagents for gas separation, mainly due to its low vapor pressure, selectivity, tunable solubility properties and thermal stability. The purpose of the present work is to utilize the ILs 1-butyl-3-methylimidazolium bromide ([bmim] Br) and 1-n-propylamin-3-methylimidazolium bromide ([pamin] Br), as carbon dioxide capture absorbing media for biogas upgrading. Both ILs (being the latter not previously reported in literature) were synthesized from commercially available starting compounds, using ultrasonic techniques, and characterized by NMR and IR analysis. In despite of both to be imidazolium based ILs with good characteristic as absorbers, the latter is a task-specific (TSIL), with a specialized amine (-NH2) group which should improve the carbon dioxide solubility. As a potential application of intensive carbon dioxide absorption system a model biogas (CO2/CH4 equivalent to 40/60), the ILs [bmim] Br and [pamin] Br were tested as absorbents for enrichment of methane of a biogas stream, evaluating the impact of the amine group in the fixation of CO2 and making a systematic comparison with the conventional organic solvents MEA/DEA under similar operating conditions. The effects of temperature and moderated changes of pressures are analyzed and discussed as well.

During the treatment of used metallic fuel with pyrometallurgical processes, sodium, fission products, and actinides are oxidized from their metallic states to chlorides in an electrorefiner. Uranium trichloride is present in the electrorefiner salt, a eutectic mixture of LiCl-KCl, as an oxidant for the metallic species. In the course of fuel processing, uranium trichloride is depleted from the salt and must be replenished to allow continued operations. For used driver fuel, cadmium chloride is added to the Mk-IV electrorefiner for the oxidation of uranium into the salt. The resultant cadmium metal reports to the cadmium pool of the Mk-IV electrorefiner. Processing of the used blanket fuel is also performed in an electrorefiner, the Mk-V, except sans the cadmium pool. Thus, the use of cadmium chloride in the Mk-V electrorefiner is not acceptable and a source of uranium trichloride for blanket processing must be generated. A limited inventory of uranium trichloride was produced for the demonstration operations of the Mk-V electrorefiner. This uranium trichloride was produced in small batches via the reaction of uranium metal and cadmium chloride since no viable commercial source could be determined [1]. Since this source of uranium trichloride has been exhausted, uranium trichloride production has been performed in order to continue operations at the Mk-V electrorefiner. Approximately 44 kg of uranium trichloride is required per metric ton (MT) of blanket fuel processed. Thus, with an inventory near 20 MT of blanket fuel to be processed, approximately 900 kg of uranium trichloride will be consumed during the processing of the blanket fuel. A total of nine experiments have been performed up to the kilogram scale for the production of uranium trichloride. The experiments have been performed in three different furnaces capable of high-temperature distillation operations. The distillation of chloride salts away from metallic species results in a purified uranium trichloride product. All three induction-heated furnaces are capable of temperatures to 1400oC and vacuums to less than 1 Torr. Several metal chlorides have been utilized for the reaction with uranium metal to produce uranium trichloride. The test conditions, observations, and results for these experiments will be presented along with a recommended path forward for the continued production of uranium trichloride.

The mixed molten salts NaCl-CaCl2, KCl-NaCl and KCl-NaCl-CaCl2 were introduced into the direct electrolysis reduction of solid TiO2 to the solid metal Ti (FCC process). Related physical properties of thephysical property physical property physical property three mixed molten salts were studied in this paper. The mixed molten salts have significant advantage over original molten salt CaCl2 (low melting point, high conductivity). The low electrolysis reduction temperature could decrease the energy consumption of heating equipments and the high conductivity could decrease the energy consumption of the molten salts’ resistance. Mixed molten salts with different ratios should be an effective way to reduce the secondary reactions caused by intermediate Ca because the rate of intermediate Ca producing was determined by the Ca2+ ion concentration in the molten salts. The results showed that the current efficiency (CE) increased and the total energy consumption (TEC) decreased due to the change of molten salts as expected. Current efficiency of 52.2% in CaCl2-NaCl (mole ratio=52:48, 873K), 65.9% in KCl-NaCl (mole ratio=50:50, 973K) and 59.5% in KCl-NaCl- CaCl2 (mole ratio= 42.5:42.5:15, 973K) were obtained in this work.

The potential ranges of the deposition of tungsten, carbon, and tungsten carbide dissolved in a NaCI-LiCl (3:1 mass ratio) melt were determined. The reduction of tungstate ions to tungsten proceeds at potentials by 100-150 mV more negative than the reduction of carbon to carbonate ions. At the concentrations corresponding to the composition of the melt used in the synthesis, the electroreduction of tungstate and carbonate ions is accomplished simultaneously in a sufficiently narrow potential range. Experiments at 1173 K have shown that tungsten carbide coatings can be deposited from a melt containing 5 wt % Na2WO4. When the Na2CO3 content does not exceed 0.2 wt %, continuous deposits of W-W2C alloys (the composition of which also depends on the carbonate concentration) are deposited on the cathode. Continuous W2C deposits appear at a concentration of 0.2-0.5 wt %; Continuous W2C-WC deposits appear at 0.5-1.0 wt %; Poorly adhered deposits W2C-WC are formed at still higher concentrations. To study the effect of the other electrolysis parameters on the properties and structure of W2C coatings, we have chosen the optimal melt NaCl-LiC1: 0.5 wt %, Na2WO4-0.4 wt % Na2CO3. Continuous deposits were obtained at 1073-1173 K. At lower temperatures, tungsten oxides are deposited together with metal and carbide. Well adhered, uniform, and nonporous coatings were obtained at a cathodic current density of 2-15 A/dm2 and a deposition rate from 2 to 20 μm/h. Chronovoltammetric studies have shown that stable discharge of combined complexes of zirconium and boron can be achieved by maintaining the molar ratio at a level [Zr(IV) + B(III)] : [F-] > 1 : 4 (at a ratio [Zr(IV) : [B(III)] = 1 : 2) in the KC1-NaC1 melt. Under these conditions, the voltammograms demonstrate a wave of electroreduction of chloride-fluoride heterocenter complexes of zirconium and boron in place of the waves of partial electroreduction of zirconium and boron. In this case, the uniform phase of zirconium diboride is formed in a wide current density range. The absolute magnitude of the overall concentration of Zr(IV) and B(III) in the electrolyte (in a range of 0.6-30 wt %) has no significant effect on the product composition, as well as technological and economic parameters of the process. The temperature threshold of synthesis in the melt studied lies in the interval of 923-943 K. The temperature interval of 1073-1173 K is optimum at a cathodic current density of 5-20 A/dm2.

Alkali halide based molten electrolytes have a wide range of potential applications for electrowinning and electrorefining of metals and also for pyrochemical reprocessing of spent nuclear fuels. However, the industrial scale use of fused salts is limited by the problem of finding suitable corrosion resistant materials stable in contact with molten media. Corrosion of metals in molten salts was studied for a number of years, but there is no single point of view concerning mechanism of stainless steal corrosion in halide melts. In the current work we used a variety of methods for studying the phenomenon of stainless steel corrosion including gravimetric and chemical analysis, surface examination, electrochemical measurements and in situ high temperature electronic spectroscopy. Corrosion behavior of stainless steel types AISI 316L, 316Ti and 321 were studied here at 750 0C in melts based on NaCl-KCl equimolar mixture. Time of the corrosion tests was varied from 1 to 30 h and several cylindrical samples of each type of steel were used in each experiment. After conducting the experiments the weight decrease of the samples was determined and averaged. Quenched melt samples taken after each experiment were analyzed to determine the content of the elements of interest using ICP MS method (Elan 9000, Perkin Elmer) and X-ray fluorescence spectroscopy (ARL QUANT’X). The surface of steel samples after corrosion tests was examined using metallographic analysis (Olympus GX-71F) and Х-ray microanalysis (JSM 6490). All the electrochemical measurements were performed using high-temperature three-electrode cell and Autolab 302N potentiostat/galvanostat with Booster 20A amplifier. The electronic absorption spectra (EAS) were recorded between 200 and 1500 nm using an original set-up based on Avantes AvaSpec-2048-2 and NIR256-1.7 fiber optic spectrometers. In a separate series of experiments anodic dissolution of a number of individual elements representing the major components of stainless steels was first studied and the EAS of iron, chromium, nickel, molybdenum, manganese and titanium chloro-species were recorded. It was found, that the major corrosion products of steels are iron, manganese and chromium species. Prolongation of anodic dissolution leads to increasing chromium-to-iron ratio in the melt. Titanium in steels forms very stable carbonitride species that aren’t dissolved during anodic oxidation. We conclude that under applied anodic potential the corrosion of stainless steels in molten chlorides is electrochemical in nature. At the initial period the exchange reaction between steel components and alkali metal cations takes place in parallel with the electrochemical process. In case of absence of anodic polarization the following mechanism of stainless steel corrosion in molten chlorides under inert atmosphere was proposed: 1) chemical interaction between the alloy and the salt intensified by the formation of microgalvanic pairs; 2) sensitization, i. E. Formation of chromium and molybdenum carbide-containing phases in steel as a result of heating to 750 0C; 3) additional formation of galvanic pairs between the grains of austenitic alloys and the carbide phases at the grain boundaries resulting in enhanced intergranular corrosion.

The perspectives of widening rare metals application in modern technologies are determined by the metals purity and availability and thus depend on the improvements in refining techniques. The majority of less-common metal refining technologies, such as vacuum melting, distillation, electrotransport, zone recrystallization are based on the metals physical properties. The effectiveness of such processes is determined by achievement of very clean industrial conditions and prevention of metal contamination by corrosion products of constructive materials. Moreover, it is necessary to take into account the high costs of such type equipment and its maintenance. Electrolytic refining in molten salts presents a substantial alternative to the physical methods of metal purification. This approach can be realised at considerably lower temperatures using simpler equipment, and in this case a highly automatic continuous technological process can be organized. The most effective way of producing high purity metals with total impurities content of less than 0.01 wt. %, is the combination of physical and electrochemical methods. Elaboration of an electrorefining technology involves several stages. The first is the selection of working electrolyte. The basis for selecting a suitable salt mixture is the information on physico-chemical properties of electrolytes. The data concerning melting points, electrical conductivity, density and other properties of the melts should be integrated in a united universal database for convenient and fast access. Using database control options one can automatically chose salt compositions that satisfy necessary requirements. The information about speciation of refined metal is also important for organization of electrorefining process. These data can be obtained during analysis of physico-chemical and thermodynamic properties of molten salts using different models of liquid structure or spectroscopic data. The combination of spectroscopic and electrochemichal methods of analysis is a very prospective direction of research. The optimal organization of electrolytic production of metals from molten salts should be based on understanding mechanisms of processes taking place when the electric current is passed through the system. The electrorefining consists of two phases: Anodic dissolution and cathodic deposition of the metal. If the electrorefining process can be performed under equilibrium conditions we’ll purify the refined metal from electropositive impurities during the anodic stage and retain the electronegative metals in the electrolyte in the course of the cathodic cycle. However, in real life we encounter the phenomenon of electrode polarization, i. E. The shift of electrode potential from the equilibrium value. The subject of the electrode process kinetics is determination of reasons of polarization and its characteristics. Galvanostatic methods are the most fully corresponding to the conditions of electrolytic refining. At the same time the useful information about electrode reactions and kinetic parameters can be obtained from other voltammetric methods. The main task of electrorefining process is production of maximum quantity of highly purified metal. The quantitative parameters characterizing solving this task are the degree of extraction and purity of the obtained product. A number of factors influence the result of the refining process including the electrolyte composition, temperature, cathodic and anodic current densities, specific quantity of electricity, etc. The goal of the process optimization can be effectively achieved using the theory of mathematical planning of experiments. The latter allows building an adequate model of the experiment. Subsequently it becomes possible by applying this model to predict the result of any experiment performed in the field of the model validity and to found conditions for obtaining required result. After fulfilling the described stages one can start applying electrorefining technology to a semi-industrial scale including elaboration of electrolyser design, choice of technology of cathodic deposit reprocessing and other associated procedures.

In high temperature processes are molten salts/slag often used as solvent or reaction medium due to their specific properties or simply as reaction product. Both exhibit partial ionic character which enhances the dissociation of foreign species. This specificity is widely employed when used as solvent for purification. Molten salts/slags are encountered is a wide range of domains such aluminium, sodium electrolysis, metallurgy, thermal batteries, glass industry, gasification, earth science (magma) …The modelling of such industrial or natural processes requires the knowledge of a number of thermochemical and thermophysical properties of these media. Their properties are closely related to their local microstructure and environmental conditions. The latter can be determined by Ab-Initio calculations combined with Molecular Dynamics simulation whereas experimental data can be gained from X-ray or neutrons scattering using containerless techniques or by high temperature spectroscopy (Raman, NMR..). This provides valuable information on the solvatation of cations which depends on the environmental conditions, e. G. Oxygen partial pressure for slags. This data can be further used as input for phase diagram modelling using the Calphad approach. In addition number of experimental information may be required for the optimisation of complex multicomponent systems: Chemical activity (emf…), vapour pressure (KEMS), Cp(T), Δ Hf° (calorimetry), phase composition (XRD). Finally, the challenging step for this research field is the modelling of thermophysical properties such as viscosity, surface tension, thermal and electrical conductivity as a function of the Gibbs’ energy. This approach combining experimental and theoretical considerations from the atomistic to the macroscopic scale will be illustrated through examples for different applications. Finally, the discussion will be extended to the case of Room-Temperature-ionic-Liquids: Can we use this approach and the experience gained with molten salts/slags to this new class of materials and where the key factor of success are.

Phase equilibrium in the DyBr3-KBr binary system (Fig. 1) was established by Differential Scanning Calorimetry (DSC). The phase diagram exhibits two eutectics and two stoichiometric compounds. The first compound, K3DyBr6, undergoes a solid-solid phase transition at 694 K and melts congruently at 991 K. The second one, K2DyBr5, melts incongruently at 733 K. The compositions of KBr-K3DyBr6 and K2DyBr5-DyBr3 eutectic mixtures were determined by the Tamman method as x(DyBr3) = 0.159 (886 K) and 0.454 (689 K), respectively. The electrical conductivity of the DyBr3-KBr liquid mixtures, together with that of pure components was measured down to temperatures below solidification. Results obtained are discussed in terms of possible complex formation.

Vapour pressure is a sensitive method for thermodynamic characterization of molten salts due to proportionality between activity and pressure. The method has also validity over a large temperature range as Log P is proportional with 1/T. Pressure can be measured in the range 1 to 60 Pa by use of the following methods: Knudsen effusion, transition flow, static, transpiration or boiling point. Determination of vapour pressure of Cloroaluminates melts and NaF-Al2O3-SiO2 slags are given as examples. Solubility of gas in molten salt is also discussed.

Chemical characteristics of trivalent lanthanides (Ln) and actinides (An) in molten chlorides were studied by UV/Vis/NIR spectrophotometry and electrochemical methods. Various mixtures of alkali chlorides and alkaline earth chlorides were chosen as solvent media. We focused on the structural property of LnCl63- and AnCl63- in chloride melts. Spectroscopic and electrochemical properties were strongly correlated with each other. The highly symmetric octahedral coordination was confirmed in the NaCl-2CsCl eutectic. The symmetry was found to be distorted by adding solvent cations with strong polarizing power like Li+.

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