Fluoride, rare-earth

Re OPe . The final step in the chemical processing of rare earths depends on the intended use of the product. Rare-earth chlorides, usually electrolytically reduced to the metallic form for use in metallurgy, are obtained by crystallisation of aqueous chloride solutions. Rare-earth fluorides, used for electrolytic or metaHothermic reduction, are obtained by precipitation with hydrofluoric acid. Rare-earth oxides are obtained by firing hydroxides, carbonates or oxalates, first precipitated from the aqueous solution, at 900°C. 

We solved the first problem by bombarding large amounts of uranyl nitrate with neutrons at the cyclotrons at the University of California and Washington University plutonium concentrates were derived from these sources through the efforts of teams of chemists who used ether extractions to separate the bulk of the uranium and an oxidation-reduction cycle with rare earth fluoride carrier to concentrate the product. I managed to convince chemists trained in the techniques of ultramicrochemistry to join us to solve the second problem—Burris B. Cunningham and Louis B. Werner of the University of California and Michael Cefola from New York University. 

This precipitate of 94, which was viewed under the microscope and which was also visible to the naked eye, did not differ visibly from the rare-earth fluorides. 

The reason for the ultramicrochemical test was to establish whether the bismuth phosphate would carry the plutonium at the concentrations that would exist at the Hanford extraction plant. This test was necessary because it did not seem logical that tripositive bismuth should be so efficient in carrying tetrapositive plutonium. In subsequent months there was much skepticism on this point and the ultramicrochemists were forced to make repeated tests to prove this point. Thompson soon showed that Pu(Vl) was not carried by bismuth phosphate, thus establishing that an oxidation-reduction cycle would be feasible. All the various parts of the bismuth-phosphate oxidation-reduction procedure, bulk reduction via cross-over to a rare earth fluoride oxidation-reduction step and final isolation by precipitation of plutonium (IV) peroxide were tested at the Hanford concentrations of... 

Starting from rare earth oxides, rare earth fluorides can be prepared by the hydro-fluorination of the oxides with anhydrous hydrogen fluoride. For example,... 

The double fluoride, ammonium hexafluorovanadate ((NH4)3VF6), forms from the oxide at 210 to 250 °C, but decomposes at 600 to 700 °C to yield pure vanadium fluoride. Examples of metal fluorides obtainable through the double fluoride route include uranium tetrafluoride, beryllium difluoride and the rare earth fluorides ... 

Fluorides are nonhygroscopic, and their melting points are higher than those of the corresponding chlorides. Besides, the fluoride reduction reactions are considerably more exothermic. The prime examples of the use of fluorides as intermediates are the reduction of uranium tetrafluoride by calcium or magnesium the reduction of rare earth fluorides by calcium, reduction of beryllium fluoride by magnesium and the reduction of potassium tantalum double fluoride by sodium. 

All the rare earth metals except samarium, europium, and ytterbium can be prepared in a pure form by reducing their trifluorides with calcium. Magnesium fluoride is less stable than the rare earth fluorides and so magnesium does not figure as a reductant. Lithium forms a fluoride which is stabler than some of the rare earth fluorides and thus finds some use as a reductant. 

The difference in the heats of formation of calcium fluoride and of the rare earth fluorides, on an equivalent basis, is not very large and the exothermicity of the reaction... 

Some rare-earth fluoride samples had been wet-ashed incompletely with the three mixed acids and some gave low results. These samples, now containing pyridine, were reprocessed by addition of more acids and slow evaporation on a hot-plate. One of the samples frothed up and then exploded violently. Pyridinium perchlorate seems likely to have been involved. 

The third major invention for the use of the rare earth elements was the addition of rare earth fluoride as a wick in arc light carbons which, at that time, were used for a wide range of lighting purposes and later also for cinema production and for search lights. This use of rare earth compounds is based on the intensive arc light developed by Beck in Germany in 1910. 

All the early work on plutonium was done with unweighable amounts on a tracer scale. When it became apparent that large amounts would be needed for the atomic bomb, it was necessary to have a more detailed knowledge of the chemical properties of this element. Intensive bombardment of hundreds of pounds of uranium was therefore begun in the cyclotrons at Berkeley and at Washington University in St. Louis. Sepa-ration of plutonium from neptunium was based on the fact that neptunium is oxidized by bromate while plutonium is not, and that reduced fluorides of the two metals are carried down by precipitation of rare earth fluorides, while the fluorides of the oxidized states of the two elements are not. Therefore a separation results by repeated bromate oxidations and precipitations with rare earth fluorides. 

Nitric Acid, Pyridine, and Sulfuric Acid. Formation of pyridinium perchlorate presents an explosion hazard during wet-ashing of rare earth fluorides.21... 

The bombarded oxides are dissolved In HHO3 from which the rare earth fluoride Is ppted. This Is dissolved and the hydroxide ppted. and dissolved In cone. HC1, which is sucked through a column of anion exchange resin (Dowex A-l). The rare earth hydroxide Is then prepared for counting sample. 

Kirschenbaum, A. D., and J. A. Cahill Liquid Density of Yttrium and Some Rare-Earth Fluorides from the Melting Point to 2500° K. J. Chem. Eng. Data 7, 98 (1962),... 

Solid-state reaction between rare-earth oxide and rare-earth fluoride,... 

Fig. 2. TG curves for pyro-hydrolysis of rare-earth fluorides in an ordinary atmosphere. TG measurement was performed under the water vapour pressure of 1.8 x 103 Pa at the heating rate of 5 C min-1.

Rare-earth fluoride stabilized zirconia, LnFSZ... 

Reaction conditions, compositions and lattice constants of cubic rare-earth fluoride stabilized zirconia... 

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