Authors:D. Schumann, R. Dressler, St. Taut, H. Nitsche, Z. Szeglowski, B. Kubica, L. Guseva, G. Tikhomirova, A. Yakushev, O. Constantinescu, V. Domanov, M. Constantinescu, Dinh Lien, Yu. Oganessian, V. Brudanin, I. Zvara, and H. Bruchertseifer
The title goal was achieved using a DOWEX 50Wx8 cation exchange column saturated with La(OH)3 and ammonia solution as eluent. Hf, Ta and Lu were adsorbed on this column, whereas W remained in the solution. This chemical system may be used for fast on-line separations of element 106.
Authors:Donivan Porterfield, Lav Tandon, Alexander Plionis, David Mercer, Dominic Peterson, and John Auxier
The development of two generations of a one-dimensional gamma mapping system is described. These systems use high-Z shielding,
linear stage, and a high-purity germanium detector. Application to items of forensic interest is described and results for
such items are presented. The presented results show the fission product (137Cs) and activation product (60Co) distributions along one-dimension of an archival item.
Authors:Martin Tjahjono, Martin Karl Schreyer, Liangfeng Guo, and Marc Garland
consisting of calcium fluoride (CaF 2 ), titanium nitride (TiN), and tungsten carbide (WC); and (iii) polymorphic mixtures of α- and γ-glycine. All systems are investigated at 298.15 K and at atmospheric pressure. Combined experimental measurements using
Carrier-free radionuclides of tungsten and tantalum, 176,177W and 176,177Ta have been produced by heavy ion activation of holmium target with 97 MeV 16O5+ beam. Radiochemical separation scheme has been developed to isolate tungsten and tantalum radionuclides from the holmium target matrix.
A method is described for the carrier-free separation of rheniumisotopes from deuteron-irradiated tungsten. After being irradiated,
metallic tungsten is first treated with a mixture of hydrofluoric acid and nitric acid, and the residue is then dissolved
in ammonia and hydrogen peroxide. Ammonium nitrate is added to the solution, and thepH is adjusted to 4.5–5. The separation is performed on a column of hydrous zirconium dioxide using 2% ammonium nitrate solution;
≥99.9 of the tungsten is retained on the ion exchanger. The solution containing the rheniumisotopes is evaporated to dryness,
and the ammonium nitrate removed by heating to about 160°C.
A method is described for the simultaneous determination of tin and tungsten in cassiterite ores by photon activation analysis
using both elements and zirconium and zinc as internal standards. By using a 15-MeV photon beam, some interfering reactions
with higher threshold energies can be eliminated. Thus the data processing becomes simpler and more accurate. The proposed
procedure can be used for the routine analysis of tin and tungsten in cassiterite samples.
Authors:Li Zongwei, Zhao Zhizheng, Yang Weifan, Mo Wantong, Yang Yongfeng, and Cai Xicheng
A rapid radiochemical separation procedure has been finished by using of radiochemical separation and -spectrum measurement methods. In this isolation procedure, tantalum nuclides produced by the irradiation of natural tungsten targets with 14 MeV neutrons were extracted by methyl isobutyl ketone (MIBK) in the system of HF-HNO3 mixed solutions. It has been found that tantalum was rapidly and efficiently separated in the isolation procedure and the decontamination factors of tungsten were more than 104. The procedure is simultaneously used to separate tantalum from tungsten bombarded with intermediate energy (47 MeV/u)18O beams. The measured -spectra showed that tantalum can be separated from most elements produced in the nuclear reactions except for a few elements.
Authors:I. Szilágyi, J. Madarász, F. Hange, and G. Pokol
Thermal decomposition of ammonium paratungstate
tetrahydrate, (NH4)10[H2W12O42]4H2O has been followed by simultaneous TG/DTA and online evolved
gas analysis (TG/DTA-MS) in flowing 10% H2/Ar directly
up to 900C. Solid intermediate products have been structurally evaluated
by FTIR spectroscopy and powder X-ray diffraction (XRD). A previously unexplained
exothermic heat effect has been detected at 700–750C. On the basis
of TG/DTA as well as H2O and NH3
evolution curves and XRD patterns, it has been assigned to the formation and
crystallization heat of γ-tungsten-oxide (WO2.72/W18O49)
from β-tungsten-oxide (WO2.9/W20O58)
and residual ammonium tungsten bronze.
Scheelite (calcium tungstate)is the product of one of the processing methods of wolframite by its roasting with calcium oxide
or limestone or its fusion with calcium chloride, followed by acid processing of calcium tungstate with the formation of tungstic
acid. Scheelite occurs in contact metamorphic deposits, hydrothermal veins and pegmatites.
The present work illustrates a thermal analysis study of synthesis of scheelite by sintering of wolframite with calcite and
sintering of tungsten oxide with calcite or calcium oxide using a derivatograph. The reaction products were identified microscopically
and by using a Siemens Crystalloflex diffractometer.
The DTA curve of sintering of wolframite with calcite shows the beginning of the reaction at 560C with the formation of scheelite.
The intensive formation of scheelite is represented by the medium and wide endothermic peak at 740C. This is followed directly
by a large and sharp endothermic peak at 860C, representing the dissociation of unreacted calcite.
The DTA curve of tungsten trioxide shows three thermal effects. The sharp exothermic peak at 320C represents the oxidation
of tungsten oxide content of lower valency. The endothermic peaks at 750 and 1090C are related to polymorphic changes of
tungsten trioxide. The beginning of its sublimation is observed at temperature higher than 800C.
The DTA curves of sintering of tungsten trioxide with calcite or calcium oxide indicate that the intensive formation of scheelite
takes place by endothermic reactions at 660 and 545C respectively. The medium and small endothermic peaks at 520 and 730Con
the DTA curve of tungsten trioxide with calcium oxide represent the dehydration of calcium oxide and the loss of carbon dioxide
due to some carbonatization of calcium oxide with carbon dioxide from air, respectively.
The produced scheelite is colorless in thin sections, has distinct cleavage (101), crystallizes in the tetragonal system in
the form of tabular crystals and is optically positive.
The kinetics and mechanism of the dehydration and decomposition of heteropolyacids of molybdenum, tungsten and vanadium (H3+xYx+M12O40mH2O;
Y=Si, P; M=Mo, W) were studied. The data obtained on the dehydration kinetic parameters correlate with the expected structures,
of these crystal hydrates, the IR data and X-ray phase analysis.