Electrode and chemical reactions during electrodeposition of tantalum products in CsCl melt

This work was accomplished in the context of systematic examination of a role played by electrolyte cation composition in electroreduction processes. The electrochemical behaviour of molten salts systems where CsCl was used as solvent for potassium and caesium oxyfluorotantalates was investigated. In particular, the influence of the electrolysis parameters, such as concentration of tantalum species in electrolyte, temperature and current density on the cathodic products phase composition was determined by X-ray diffraction and scanning electron microscopy. Several phases generally crystallized at the cathode simultaneously. Among identified phases were metallic tantalum in cubic ($\alpha$) and tetragonal (β) crystal modifications and TaO. But the most characteristic phases for the melt under study were two isostructural compounds with pyrochlor type crystal lattice CsTa$_{2+z}^5$O$_{5+y}$F$_{1-y}$ and CsTa$_{2+z}^{5- x}$O$_{5+y}$F$_{1-y}$. The former deposited in the form of transparent dielectric crystals and the later – in the form of metal-like conductive ones. This latter compound seems to be synthesized for the first time. The peculiarities of its structure were described. Electrochemical redox processes in melts containing potassium oxyfluorotantalates dissolved in CsCl were studied by cyclic voltammetry. Three discharge peaks were detected on voltammograms in the temperature range 700-850 $^\circ$C. They were associated with the discharge of TaOF$_6^{3-}$ and TaO$_2$F$_4^{3-}$ complexes and alkali metal cations

Ionic liquids at electrified interfaces

Until recently, “room-temperature” (<100–150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)–(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of “first-generation” room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the “later generation” RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in “cocktails” of one’s choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost “universal” solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) “sister-systems”.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules

Etude calorimétrique et analyse thermodynamique du mélange liquide AgCI—LiCI—KCI

Les seules données thermodynamiques expérimentales relatives au système ternaire de sels fondus AgCI—LiCI—KCI sont les enthalpies libres partielles du chlorure d’argent. Des données plus complètes existent pour les trois systèmes binaires AgCI—LiCI, AgCI—KCI et LiCI—KCI qui limitent ce mélange ternaire :

Study of binary systems NdF3- MF (M = Li, Na, K): experimental, modeling and thermodynamic computation

The excess molar enthalpies HEm of the binary systems MF-NdF3 (M = Li, Na, K) were measured in the present work by high temperature calorimetry on a wide temperature (1220 K < T < 1400 K) and composition range. Some points of the equilibrium phase diagram have been also obtained by differential thermal analysis. Using the Hoch-Arpshofen model we represent the excess quantities of different systems. This will allow us thereafter to calculate the phase diagrams of binary systems NdF3-MF (M = Li, Na)

Estimation de I' enthalpie de fusion de mélanges eutectiques de sels fondus utilisables pour le stockage thermique de l'énergie

The use of the enthalpy of fusion of eutectic molten salt mixtures has been considered for thermal energy storage. A simple thermodynamic calculation has been stated : it enables to evaluate the enthalpy of fusion from the known enthalpy variations of pure substances. The enthalpies of fusion has been so determined for about fourty eutectic binary and ternary molten salt mixtures.Nous avons envisagé l'utilisation de l'enthalpie de fusion de mélanges eutectiques de sels fondus pour le stockage thermique de l'énergie. Un calcul thermodynamique simple a été établi : il permet d'évaluer l'enthalpie de fusion à partir de la connaissance des variations d'enthalpie des corps purs. Nous avons ainsi déterminé les enthalpies de fusion d'une quarantaine de mélanges eutectiques binaires et ternaires de sels fondus