Structure and dynamics in yttrium-based molten rare earth alkali fluorides.
The transport properties of molten LiF-YF3 mixtures have been studied by pulsed field gradient nuclear magnetic resonance spectroscopy, potentiometric experiments, and molecular dynamics simulations. The calculated diffusion coefficients and electric conductivities compare very well with the measurements across a wide composition range. We then extract static (radial distribution functions, coordination numbers distributions) and dynamic (cage correlation functions) quantities from the simulations. Then, we discuss the interplay between the microscopic structure of the molten salts and their dynamic properties. It is often considered that variations in the diffusion coefficient of the anions are mainly driven by the evolution of its coordination with the metallic ion (Y(3+) here). We compare this system with fluorozirconate melts and demonstrate that the coordination number is a poor indicator of the evolution of the diffusion coefficient. Instead, we propose to use the ionic bonds lifetime. We show that the weak Y-F ionic bonds in LiF-YF3 do not induce the expected tendency of the fluoride diffusion coefficient to converge toward one of the yttrium cation when the content in YF3 increases. Implications on the validity of the Nernst-Einstein relation for estimating the electrical conductivity are discussed.
Electrochemical extraction of europium from molten fluoride media
Abstract This work concerns the extraction of europium from molten fluoride media. Two electrochemical ways have been examined: (i) the use of a reactive cathode made of copper and (ii) the co-deposition with aluminium on inert electrode, leading to the formation of europium–copper and europium–aluminium alloys, respectively, as identified by SEM-EDS analysis. Cyclic voltammetry and square wave voltammetry were used to identify the reduction pathway and to characterise the step of Cu–Eu and Al–Eu alloys formation. Then, electrochemical extractions using the two methodologies have been performed with extraction efficiency around 92% for copper electrode and 99.7% for co-reduction with aluminium ions.
Formation d'alliages tantale-nickel par voie électrochimique
Resume L'obtention d'alliages TaNi a ete realisee par reduction electrochimique d'ions TaF 7 2− dans les fluorures fondus, sur une cathode en nickel, dans des conditions galvanostatiques, potentiostatiques ou galvaniques, le domaine de temperatures etant de 850 a 1050 °C. Dans ce procede, l'alliage est forme par suite d'une diffusion du tantale depose dans le substrat en nickel. Bien que des composes metastables aient ete identifies pendant le processus, la composition finale de la couche formee correspond au compose stable TaNi 3 ; la croissance de la couche suit une loi parabolique. L'utilisation des techniques electrochimiques d'analyse conduit a l'evaluation de grandeurs thermodynamiques concernant la formation de composes intermetalliques TaNi et egalement de parametres cinetiques de la diffusion intermetallique.