Fluoride Melts Research Articles

Extraction of plutonium by fluoride melts

Extraction of plutonium by fluoride melts

Growth of Complex Oxide Single Crystals from Fluoride Melts

Single crystals of a barium magnesium tantalate, a lead tantalate, calcium niobate, and potassium germanate were synthesized by the reactions of oxides and fluorides at high temperatures. The technique is very much like the flux method, except that some of the fluoride cations combine chemically with the oxide nutrients. Starting compositions and conditions for growth are given. The most probable reactions were calculated using free energies of formation with known thermo‐chemical data for an analogous system. Complex fluoride‐forming reactions, hydrolysis reactions, and reactions which form fluorides and oxyfluorides are possible. The reaction products were also studied by X‐ray analysis of the single crystal and polycrystalline products. Lattice parameters, space groups, and X‐ray powder patterns are presented for the single crystal materials.

E.M.F. measurements on the nickel—nickel(II) couple in molten fluorides,

E.m.f. measurements on the concentration cells Ni/Ni(II) (a1=constant) ‖ BN sheath ‖ Ni(II) (a2)|Ni in molten LiF−NaF−KF (42.0−11.5−46.5 mole%) and LiF−BeF2−ZrF4 (65.6−29.4−5.0 mole%) at ∼500° result in linear plots of e.m.f. vs. log X2 (the mole fraction of Ni(II) in the bulk of the melt), and the slopes predicted from the Nernst equation. The measured e.m.f. values are stable. The Ni/Ni(II) couple, contained in a boron nitride sheath, is a useful reference electrode for fluoride melts.

E.M.F. measurements on the nickel-nickel(II) couple in molten fluorides

Summary E.m.f. measurements on the concentration cells Ni/Ni(II) ( a 1 =constant) ‖ BN sheath ‖ Ni(II) ( a 2 )|Ni in molten LiF−NaF−KF (42.0−11.5−46.5 mole%) and LiF−BeF 2 −ZrF 4 (65.6−29.4−5.0 mole%) at ∼500° result in linear plots of e.m.f. vs . log X 2 (the mole fraction of Ni(II) in the bulk of the melt), and the slopes predicted from the Nernst equation. The measured e.m.f. values are stable. The Ni/Ni(II) couple, contained in a boron nitride sheath, is a useful reference electrode for fluoride melts.

Electrodeposition of Coherent Deposits of Refractory Metals: VI . Mechanism of Deposition of Molybdenum and Tungsten from Fluoride Melts

not Available.

Growth striations in vertically pulled oxide and fluoride single crystals

Temperature oscillations have been detected in oxide and fluoride melts which can be directly correlated to the movement of convection patterns visible on the melt surface. It is shown that such oscillations cause growth striations in single crystals grown from these melts. Additional experiments are reported in which the effect of changes in growth parameters upon the oscillations and melt temperatures have been investigated.

Electrode Overvoltages in Molten Fluorides: The Anodic Behavior of Nickel Electrodes in Fluoride Melts

Anodic overvoltage measurements on nickel electrodes in , , , and melts of eutectic composition have been carried out by the galvanostatic, potentiostatic, and potential‐sweep methods at temperatures ranging from 450° and 800°C. In oxide‐free melts no activation overvoltage for the anodic and cathodic reactions has been observed. It was, however, observed that nickel behaves as a “ covering‐layer electrode ” in the presence of traces of oxides, added to the melts as , or resulting from the hydrolysis of the residual water in the melt after a high vacuum drying process. The semiconducting behavior of nonstoichiometric surface layers has been considered and the results of the present work have been compared with the literature data on the electrode in molten salts.

Electrowinning rare-earth and uranium metals from their oxides

A discussion of the technique developed by the Federal Bureau of Mines: the electrolysis of a fluoride melt containing the oxide of the metal in question, depositing the molten metal at the cathode, and evolving carbon monoxide at the anode.

Analysis of Surface Features on Single Crystals of Synthetic Garnets

Surface features observed on the faces of synthetic garnets grown from lead oxide-lead fluoride melts are described and interpreted in terms of growth processes. The growth processes involve (1) nucleation of new growth layers at corners and edges between crystal faces and (2) propagation of layers associated with growth systems located on the crystal faces. Growth systems on the faces of crystals that terminated growth at about 1000°C appear as growth hillocks. Continuing growth to lower temperatures produces large vicinal faces, which result from the propagation of polygonized growth steps associated with a single, dominant growth system. Growth steps on the vicinal faces in turn possess faces that are parallel to the nearest adjacent crystal faces. Growth spirals have been observed on the faces of crystals that were grown slowly by evaporation of flux. Several observations, including the presence of growth spirals, the nature and location of line imperfections and hollow tubes, and the etching behavior of crystal faces and polished sections, are interpreted as evidence in favor of a latter-stage growth mechanism that involves the propagation of steps associated with screw dislocations.

Growth of Single Crystals of Yttrium Aluminum Garnet from Lead Oxide—Lead Fluoride Melts

Growth of Single Crystals of Yttrium Aluminum Garnet from Lead Oxide—Lead Fluoride Melts

Growth Spirals on Synthetic Magnetoplumbite Crystals

IN connexion with a study of crystal growth from lead oxide and lead oxide–lead fluoride melts, we have recently observed growth spirals on (0001) faces of tabular magnetoplumbite (PbFe12O19) crystals. The spirals on crystals obtained from lead oxide–lead fluoride melts are polygonal, relatively open, and show concave growth fronts as well as reversed curvatures near the outer edges of the crystals. The step heights appear to be small multiples of the unit cell dimension in the c direction. The spirals on crystals grown from lead oxide melts are polygonized to various degrees, are more tightly wound, and exhibit greater step heights.

Electrolytic Reduction of Thorium Oxide

Thorium metal was prepared by electrolytic reduction of thorium oxide in two systems, a fused mixture and a fused mixture. The average decomposition potential measured in both systems was 1.92 v. Electrolysis in the fluoride melt proved to be a superior process, the metal product having higher purity and larger average particle size than the product from the chloride melt. In addition, the recovery of thorium from recycle streams proved to be much simpler in the fluoride process than in the chloride process. The feasibility was demonstrated for all the essential steps of a complete process for production of the metal in the fluoride system.