Valence Bond Study of Dissociation Behavior and Spectroscopic Constants for the Ground States of LiF and NaF

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Complete basis set extrapolated potential energy, dipole, and polarizability surfaces of alkali halide ion-neutral weakly avoided crossings with and without applied electric fields

Complete basis set extrapolations of alkali halide (LiF, LiCl, NaF, NaCl) energy, dipole, and polarizability surfaces are performed with and without applied fields along the internuclear axis using state-averaged multireference configuration interaction. Comparison between properties (equilibrium separation, dissociation energy, crossing distance, diabatic coupling constant, dipole, and polarizability) derived from the extrapolated potential energy (or dipole) surfaces are made with those obtained from direct extrapolation from the basis set trends. The two extrapolation procedures are generally found to agree well for these systems. Crossing distances from this work are compared to those of previous work and values obtained from the Rittner potential. Complete basis set extrapolated crossing distances agree well with those derived from the Rittner potential for LiF, but were significantly larger for LiCl, NaF, and NaCl. The results presented here serve as an important set of benchmark data for the development of new-generation many-body force fields that are able to model charge transfer.     

Key Experimental Results of the PYROSMANI Project

The presented key results were obtained in the course of experiments carried out within the PYROSMANI (PYROchemical processes Study for Minor ActiNIdes recycling in molten salt chlorides and fluorides) Project supported by Rosatom. The individual and joint solubility of UF₄, PuF₃ and CeF₃ in ternary LiF–NaF–KF and LiF- ThF₄-UF₄ melts was measured by method of isothermal saturation for the temperature range 550-800°C. The solubility measurement technique based on isothermal saturation was verified in LiF–NaF–KF eutectics for praseodymium trifluoride by the reflectance spectroscopy. The process under investigation was the extraction of lanthanum, neodymium, europium and samarium trifluorides from 73LiF-27BeF₂ melt (mole %) into liquid bismuth at 600-610°C. There were defined temperature dependences of kinematic viscosity and melting temperatures for molten 46.5LiF–11.5NaF–42KF; 73LiF-27BeF₂; 85LiF-15AlF₃ and 43.5LiF–24.3NaF–32.2UF₄ salt mixtures from liquidus temperature to 840°C.     

AB Initio study of the ground state anions of LiF,NaF, BeO and MgO

We report the results of ab initio calculations on LiF, NaF, BeO, MgO and their anions. Our vertical electron affinities of BeO and LiF are 2.10 and 0.31 eV, respectively. Our BeO electron affinity is 0.33 eV larger and our LiF electron affinity 0.11 eV smaller than the corresponding values of Jordan et al. We also predict stable anions of NaF and MgO, the calculated vertical electron affinities being 0.42 and 2.64 eV, respectively. The variation with bond length of the dipole moments and the Koopmans' theorem and Hartree-Fock estimates of the electron affinities is studied.     

Les systemes binaires fluorure de lithium-fluorure d'hydrogene et fluorure de sodium-fluorure d'hydrogene

Liquid-solid equilibria in the binary systems LiF-HF and NaF-HF were studied up to 400° by thermal analysis. On account of the properties of hydrogen fluoride, a special apparatus was built. Several compounds were observed: LiF · HF-NaF · HF; NaF · 2HF; NaF · 3HF and NaF · 4HF. The characteristic temperatures of the systems, and especially the peritectic decompositions of LiF · HF and NaF · HF were determined, and the bibliographic data were corrected.     

Phase equilibria in the NaF-LiF-LaF3 system

The NaF-LiF-LaF₃ system was studied by differential thermal and X-ray powder diffraction analyses. In the system, there are two ternary invariant points, a eutectic (580 ± 2°C, 44.0 mol % NaF, 42.0 mol % LiF, 14.0 mol % LaF₃), and a peritectic (595 ± 2°C, 45.0 mol % NaF, 39.0 mol % LiF, 16.0 mol % LaF₃). The ternary peritectic point results from the intersection of the crystallization fields of LiF, LaF₃, and NaLaF₄.     

Interaction of metallic zirconium and its alloys Zry-2 and E110 with molten eutectic salt of LiF—NaF—KF containing zirconium fluoride components

The interactions of selected zirconium alloys used as special construction materials (Zr-pure, Zry-2, E-110) with the molten system of (LiF—NaF—KF)_(eut.) with additions of K₂ZrF₆ or Na₇Zr₆F₃₁ were studied. Corrosion losses of pure zirconium decrease sharply with 5 mole% addition of K₂ZrF₆ to (LiF—NaF—KF)_(eut.). The presence of alloying additives (Sn, Nb) has a positive influence on corrosion resistance in the eutectic mixture — up to 60% increase in corrosion resistance in comparison with pure zirconium. The mass losses of pure zirconium indicate an increasing corrosion attack with increasing Na₇Zr₆F₃₁ content in (LiF—NaF—KF)_(eut.) mixtures.     

Phase analysis of the solidified KF–(LiF–NaF–UF4)–ZrF4 molten electrolytes for the electrowinning of uranium

The X-ray diffraction (XRD) phase analysis of different solidified uranium-based fluoride systems ((LiF–NaF)_eut–UF₄; (KF–LiF–NaF)_eut–UF₄; (LiF–NaF)_eut–UF₄–ZrF₄ and (KF–LiF–NaF)_eut–UF₄–ZrF₄) were examined in order to provide the basis for pyro-electrochemical extraction of uranium in molten fluorides. Several uranium-based species (Na₂UF₆, Na₃UF₇, K₂UF₆, K₃UF₇, UO₂, K₃UO₂F₅) were identified in the solidified melts. The role of oxygen in argon atmosphere was found to be critical in the formation of uranium species during the melting and solidification. In order to reduce the accumulated level of free oxygen traces in our experiments, zirconium (in the form of ZrF₄) was used inside the melt as an oxygen buffer. It was found that ZrF₄ can really stabilize the uranium species by complexation and protects them against the oxygenation. The results of this work highlight the importance of oxygen removal for obtaining pure deposit in the electrorefinning of uranium.     

Trace Determination and Pressure Estimation of Fluorine F2 Caused by Irradiation Damage in Minerals and Synthetic Fluorides

Irradiated alkali and earth alkali halides can form metal colloids and halogen molecules, which stay trapped inside the crystal. In this paper we provide ¹⁹F NMR spectroscopic evidence of trapped F₂ fluids in heavy ion‐bombarded synthesized LiF crystals as well as in a variety of the mineral Villiaumite (NaF). This is the 2nd mineral in which F₂ is unambiguously detected in nature. The trace quantification of the latter is in the order of magnitude of 10^?6 mol g^?1. Pressures and densities of the F₂ fluids are estimated based on the theory of nuclear spin relaxation in dilute gases.     

Calculation of one-electron properties of diatomic molecules using the SCF-Xα scattered-wave method

Some one-electron properties of LiH, BH, CO. LiF, NaF, KF and RbF are calculated within the framework of the overlapping atomic sphere model, using wavefunctions of the SCF-Xα scattered-wave method. The influence of the functional form of the wavefunction in the intersphere region on the values of the calculated properties is investigated and the dependence of these values on various approximations of the method is demonstrated. It is shown that the virial theorem must be the criterion for optimizing the degree of overlap of the spheres in calculations of one-electron properties of molecules by the SCF-Xα scattered-wave method.     

On the solubility of lanthanum oxide in molten alkali fluorides

The solubilities of lanthanum oxide in LiF, NaF, KF and eutectic melt LiF-NaF-KF (46.5 mole% LiF; 11.5 mole% NaF and 42.0 mole% KF) were measured in order to find the suitable electrolyte for electrodeposition of lanthanum. Solidus-liquidus lines were obtained by the method of thermal analysis. The solubility of lanthanum oxide in alkali fluorides is rather low and decreases in the order LiF>NaF>KF. It was found that lanthanum oxide reacts with the components of the melt. LaOF and alkali metal oxide are formed during dissolution of La₂O₃ in the melt.     

Modelling of diffusion-controlled solid-solid reactions

A model describing the initial step of diffusion-controlled solid-solid reactions is presented. The kinetic equation obtained was used to evaluate the activation energy of the reaction LiCl(s)+NaF(s)=LiF(s)+NaCl(s) from DTA data.

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Zusammenfassung Es wird ein Modell zur Beschreibung des einleitenden Schrittes von diffusionskontrollierten Feststoffreaktionen beschrieben. Die erhaltene kinetische Gleichung wurde zur Bestimmung der Aktivierungsenergie der Reaktion LiCl(s) + NaF(s)=LiF(s) + NaCl(s) aus DTA-Daten angewendet.

     

Structure and physical properties of ternary NaF–LiF–LnF3 (Ln = La,Nd) systems of eutectic compositions

Ternary NaF–LiF–LnF₃ (Ln = La, Nd) systems of eutectic compositions were studied by means of X-ray diffraction method in the solid and liquid states. It was found that the crystalline phases LiF, NaF and NaLnF₄ coexist in the solid state up to the melting temperatures. Above the melting point, a decrease in the nearest interatomic distances with a pronounced minimum has been observed, which correlates with the extreme behaviour of the temperature-dependent structure-sensitive physical properties of the investigated alloys.     

Density of lithium fluoride—lithium carbonate-based molten salts

The density of the LiF-Li₂CO₃ melts system was measured using the Archimedean method. Using the quadratic regression orthogonal design with two factors, a regression equation for the density of LiF-Li₂CO₃ melts was obtained in which the concentration of LiF and temperature were considered. The results indicated that the density of the LiF-Li₂CO₃ melts decreased with either increasing the concentration of LiF or increasing temperature; a linear relation was observed between density and temperature. In addition, the influences of NaF, KF, NaCl, and KCl additives on the densities of the given systems were studied. The addition of NaF and KF increased the density of the melts, whereas NaCl and KCl resulted in an initial increase and subsequent decrease with an increasing additive concentration. The density attained a maximum at NaCl and KCl mass fraction of approximately 15%.     

Refinement of electron momentum densities of ionic solids using an experimental energy constraint

It is demonstrated how one can refine a given approximate momentum density distribution using a constraint of the experimental electronic energy. The technique developed is based on the calculus of variations. This technique has been applied to ionic solids such as LiF, LiCIl NaF, NACl, MgO, KF and KCl.     

Structure of solvates of Y3+ ion in yttrium trifluoride-alkali metal fluoride melts at 1300 K according to molecular dynamic modeling

Structural features of the solvation of Y(III) ion in LiF, NaF, KF, and CsF model melts at 1300 K were studied by means of molecular dynamics modeling.     

Determination of refractory elements in U(3)O(8) by carrier distillation emission spectrography

An emission spectrographic method using carrier distillation for the determination of the refractory impurities Ta, Hf, Nb, Th, and W in uranium is described. Different carriers, such as Ga₂O₃, AgCl, AgCl + LiF, and AgCl + NaF in various proportions, were investigated: a 1% NaF + 9% AgCl mixture as carrier at 10% of total charge arced was found to be the most suitable. Spectra were excited in a d.c. arc at 12 A and were photographed with 35-sec exposures. Palladium was used as an internal standard. The lowest limits of determination lie in the range 1–10 ppm for a 100-mg charge. The precision of the method is about 16% or better.     

Phase relations and thermodynamic properties in the ternary reciprocal system LiFNaFNa3AlF6Li3AlF6

The ternary reciprocal sytem LiFNaFNa₃AlF₆Li₃AlF₆ has been investigated by thermal analysis, differential thermal analysis, quenching, X-ray diffraction, microscopy, and calorimetry. The phase diagrams of the following systems are given: LiFNaF (revised), LiFAlF₃, Na₃AlF₆LiF, and LiFNaFNa₃AlF₆Li₃AlF₆. Some values of heat of mixing and heat content in the system have been measured.It is shown that molten mixtures in this system can be treated as consisting of the following species: Li⁺, Na⁺, AlF^3-₆, AlF₃ and F^-. At high contents of alkali fluoride the dissociation of the AlF^3-₆ ion to AlF₃ and F^- will, however, be negligible.On the basis of the calorimetric data, heats of mixing and dissociation, together with the degree of dissociation of AlF^3-₆, in the systems LiFAlF₃ and LiFNa₃AlF₆ have been calculated. The partial Gibbs free energy, enthalpy and entropy of Na₃AlF₆ in the system LiFNa₃AlF₆ have also been calculated. Finally the activity of Na₃AlF₆ in the latter system has been calculated by treating it as a part of the ternary reciprocal system 3LiF+Na₃AlF₆→Li₃AlF₆+3NaFA satisfactory agreement between the Flood, Førland and Grjotheim theory and the experimental values is obtained at small Na₃AlF₆ concentrations.     

Electrochemical behavior and electrowinning of uranium(IV) from FLiNaK molten salt

Journal of Radioanalytical and Nuclear Chemistry - The electrochemical behaviors and electrowinning of uranium from LiF–NaF–KF (46.5–11.5–42.0 mol%, FLiNaK) molten...     

The oxidation of UF4 in FLiNaK melt and its electrolysis

Journal of Radioanalytical and Nuclear Chemistry - The oxidation of UF4 in LiF–NaF–KF (FLiNaK) melt with oxygen sparging was conducted at 823 K and analyzed by in situ infrared...