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International audience; The charge and electron transport properties of molten ionic systems are among the most relevant properties to consider in the control of several electrochemical processes. First-principles-based equilibrium molecular dynamics (EMD) can provide reliable predictions of both the total and partial charge transport properties. In this work we calculate the charge transport properties of the electrolytic bath (Na 3 AlF 6-AlF 3-Al 2 O 3) of the Hall-Héroult electrolysis cells. We predict both the individual and collective charge transport properties (total, partial conductivity and self diffusion coefficients) for 11 different compositions typical of industrial conditions via a series of EMD simulations. The predicted total and partial ionic conductivities and their composition dependence are compared to available experimental data. A good agreement is obtained for all studied compositions. From a more fundamental point of view, the microscopic aspect of the charge transport properties of cryolitic melts is discussed through its correlation to the local structure of different melts. Deviations between the calculated partial conductivities and those derived via the Nernst-Einstein approximation can be explained by the presence of strong short-range ordering within the melts.

International audience; In situ high temperature NMR spectroscopy was used to characterize the NaF-ScF3 melt over a wide range of compositions. 19 F, 23 Na, and 45 Sc NMR spectra were acquired in NaF-ScF3 melts of up to 70 mol% of ScF3. The interpretation of all experimental results obtained in situ in the melt is significantly enhanced by the contribution of Molecular Dynamics (MD) calculations. A new interatomic potential for the molten NaF-ScF3 system was developed by using a Polarizable Ion Model (PIM). The potential parameters were obtained by force-fitting to density functional theory (DFT) reference data. MD simulations were combined with further DFT calculations to determine NMR chemical shifts for 19 F, 23 Na, and 45 Sc. The agreement between the experimental NMR data and the corresponding calculated data from our applied computational protocol indicated the polymerization and network formation in the melt. Additionally, the density and the electrical conductivity in the molten state were calculated from the statistical analysis of ionic trajectories obtained through MD simulations.

Knowing the charge-transport properties of molten oxides is essential for industrial applications, particularly when attempting to control the energy required to separate a metal from its ore concentrate. Nowadays, in the context of a drastic increase of computational resources, research in industrial process simulation and their optimization is gaining popularity. Such simulations require accurate data as input for properties in a wide range of compositions, temperatures, and mechanical stresses. Unfortunately, due to their high melting points, we observe a severe lack of (reproducible) experimental data for many of the molten oxides. An alternative consists in using molecular dynamic simulations employing nonempirical force fields to predict the charge-transport properties of molten oxides and thus alleviate the lack of experimental data. Here, we study molten alumina using two polarizable force fields, with different levels of sophistication, parameterized on electronic structure calculations only. After validating the models against the experimental sets of density and electrical conductivity, we are able to determine the various ionic contributions to the overall charge transport in a wide range of temperatures.

International audience; Molten cryolite (NaF-AlF 3) plays a key role for aluminum production since it is used as a solvent. Among the various leads to improve the electrochemical processes, adding other fluoride salts is one of the most promising. However there is very few data on the impact of these additional species on the physico-chemical properties of the melt. In order to fill this gap we investigate the properties of high temperature KF-AlF 3 liquids by combining NMR spectroscopy, molecular dynamics and DFT calculations. Our results show that the speciation, and consequently the transport properties differ from that of cryolite. This work will allow to assess the interest of adding KF in aluminium production processes.

For aluminum production, the alumina (Al2O3) dissolution in the electrolyte is one of the important step in the industrial process. The electrolyte is a cryolitic bath containing mainly NaF and AlF3 at around 1000 °C. In this liquid, the main anionic species are fluoroaluminates ions such as [AlF6]3–, [AlF5]2–, [AlF4]−, and F–. During the Al2O3 dissolution, different kinds of oxyfluoroaluminates species are formed. However, due to the difficult experimental conditions and the large number of potential ions, no quantitative speciation could be made up to now. Here, we propose a speciation of alumina–cryolite melts combining in situ NMR experiments, classical molecular dynamics simulations, and electronic structure calculations. This allows us to establish the nature and quantities of each species, depending on the Al2O3 concentration, for two different initial cryolitic compositions. In particular, we show that the O atoms are always linked to at least two Al atoms, leading to the formation of polymeric ox...

Individual transport numbers provide a measure of the charge ratio which is carried by each ionic species of an electrolyte. However, unlike the electrical conductivity or diffusion coefficients, this quantity lacks a clear definition from the statistical mechanics point of view. In practice, it is measured via complex experimental setups, and most of the interpretation of the available data is made by using the Nernst–Einstein approximation. Here we show that this approach is not suitable in molten salts due to the large contributions of the cross-terms due to the ionic interactions in the total ionic conductivity. We propose a partition scheme that allows to attribute these cross-terms to the various ions, allowing for an estimate of the transport numbers in a series of molten salt formed by mixing NaF and AlF3 at various compositions. The results are interpreted using the speciation of the melt, which is characterized by the formation of various AlFx clusters. At large AlF3, the Na+ ions are shown to contribute almost totally to the ionic conductivity.

A thermodynamic evaluation and optimization of the CALPHAD type of the Cu-O-F system, together with phase diagram measurements, are considered in the present work as the first step towards a complete evaluation of Cu in the multicomponent system Cu-Fe-Ni-Na-Al-Ca-O-F. Differential Scanning Calorimetry experiments were conducted using a closed crucible to identify the phase transitions in the CuF2-Cu and CuF2-Pt pseudo-binary systems in the presence of oxide impurities. The thermograms and the diffractograms, as measured by X-Ray Diffraction, showed that reactions occurred in both systems, where the CuO impurity from the CuF2 reactant led to the formation of Cu2O after three or four runs. All new model parameters of the fluoride-rich region of the Cu-O-F system were optimized based on this study’s experimental results. Measured and calculated results are in good agreement and provide a new interpretation of the phase transitions reported in the literature.

N,N,N-Tri(1-pyrazolyl)methane europium complexes, [Eu{HC(pz)3}(H2O)6]Cl3, encapsulated with polymethyl methacrylate (PMMA) gel, polyvinyl acetate (PVA) gel or hexagonal mesoporous silica–PVA (HMS–PVA), have been synthesized, by using a sol–gel technique, as hybrid materials. The geometric structure of the new Eu complex has been confirmed by single crystal X-ray analysis. The hybrid Eu–PVA sample has performed the most effective unit mass luminescence emission with a longer lifetime 444 μs, higher quantum efficiency, greater thermal stability and better exposure durability in comparison to the other Eu–PMMA (379 μs) and Eu–HMS–PVA (55 μs) samples. The characterization results support that these hybrid polymers have made a proper network structure with the Eu3+ complex and act as antennae for the transfer of energy to the central Eu3+ ions, and could be use for enhanced OLED light.

Single-walled carbon nanotubes (SWNTs) with Ni/Co have been prepared using an arc discharge technique and Ni/Co-carbon composite rods in an inert atmosphere and were surface modified using 3-aminophenyl trimethoxysilane. These NH2-functionalized magnetic carbon nanotubes have been used as a novel support for Pd((II)) and Pt((II)) pincer complexes immobilized as magnetic nano-catalysts. The morphology of the support and the catalysts have been characterized by IR, EPR, SEM, TGA, TEM, XRD, AAS and EDS analysis. These magnetic nano-catalysts have been tested on the industrially important cyclohexane (Cy-hx) oxidation with O2 and significantly high TONs of 1678 to 1946 were achieved under solvent free and relatively mild conditions. The SWNTs/Pd catalyst provided the best conversion, 22.7%, but the SWNTs/Pt system also provided a good conversion of 20.7%.