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Journal of Thermal Analysis and Calorimetry
Authors: A. Derafa, M.-C. Record, D. Mangelinck, R. Halimi, and A. Bouabellou

formation in Mo–W–Si thin films and the corresponding ternary phase diagram. The binary and ternary phase diagrams Tungsten and molybdenum elements show great similarity both in electronic and structural properties. They belong to

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Abstract  

The present investigation has been revealed that homogeneous silver-tungsten (Ag–W) composite powders doped with cobalt as sinter aid can be produced by the two-stage reduction of co-precipitated tungstate. The sintering of the powders has been studied using dilatometry and the results showed that the critical level for activated sintering is of the order of 0.3 mass percent cobalt with respect to the tungsten content of the compact powder. This critical level is equivalent to approximately six to seven atomic layer coverage of the tungsten particles by cobalt. The levels of cobalt addition above the critical amount leads to the formation of cobalt tungsten (CoW3) intermetallic compound precipitates, which become trapped within the silver phase in the sintered composite material. Microstructural evaluation of sintered specimens has been carried out using optical and electron microscopy. Transmission electron microscopy results revealed the neck formation between adjacent tungsten particles along with the presence of silver around the tungsten particles. Energy dispersive X-ray (EDX) analysis also confirmed that amounts of cobalt was 0.3 mass percent, in the region containing the silver at the tungsten particle interface which agreed with the level of activated sintering.

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The preparation, and thermal characterization and ion exchanger behavior of hydrous tungsten oxides obtained from purified tungsten trioxide, by processing of a Brazilian scheelite ore were described. By an alkaline fusion of tungsten trioxide with an excess of sodium carbonate at 900C an intermediate tungstate product is obtained. Acid lixiviation of the tungstate intermediary in different experimental conditions produces two different hydrous tungsten oxides I and II respectively. A third material was produced by thermal treatment of II, yielding the material IIA, a monohydrate species. The materials prepared were characterized by TG/DTG, X-ray diffractometry and by surface area measurements. Their ion exchange behavior was studied too, using Na+ and K+ ions as the exchanged species. The inorganic exchanger materials were partially regenerated and may be used consecutively.

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Methods were developed for the separation of tungsten from molybdenum by liquid-liquid extraction and extraction chromatography using thiocyanate and a quaternary ammonium salt, Zephiramine. Tungsten was extracted into chloroform as an ion associate of tungsten(V)-thiocyanate complex and Zephiramine cation was retained on a column of Teflon powder coated with Zephiramine, but molybdenum(III) was neither extracted nor retained. The extraction chromatographic method was successfully applied to the determination of trace amounts of tungsten in molybdenum by neutron activation analysis.

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A simple, rapid and non-destructive method is described for determining molybdenum and tungsten in steels over the concentration range 0.07 to about 20% by mass. The method uses high resolution spectrometry of the low energy gamma-rays induced by 5 MeV alpha-particle beams. The precision for molybdenum is 2.7% and for tungsten is 0.55% using respectively the 204 and 100.1 keV gamma-rays. Results obtained by Ge(Li) and intrinsic germanium detectors are compared. The extent of interference from other elements is discussed.

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Abstract  

The possible determination of tungsten in low grade ores from Northern India, Rajasthan State has been explored by energy dispersive X-ray fluorescence analysis /EDXRF/ technique using radioisotope based excitation of W L X-rays and high resolution Si/Li/ detector system. Finely powdered ore has been diluted with optimal quantity of cellulose and converted into pellets to make it suitable for X-ray analysis after homogenization. The experiments have shown the minimum detectable limit of 33 ppm in diluted matrix. The results are compared with the spectrophotometric stannous chloride-thiocyanate method. EDXRF appears to be encouraging for routine and precise analysis of tungsten in low grade ores.

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The present paper is concerned with the isotope exchange between185W and tungsten, and32P and phosphorus respectively, in uranium(IV) trivacant Keggin and Dawson polyoxotungstophosphate complexes, in water. These studies were carried out at different concentrations and temperature. The isotope exchange rate increases with the temperature and the reagents' concentration. The experimental results show that the complexes are labile kinetically.

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Abstract  

A radiochemical separation method using an anion exchange resin has been applied to 4N grade tungsten for determining U, Th and 4 other elements. While tungsten remained in the resin, Na, K and As were separated with 0.05M HCl and 1M HF and then U, Th and Cr were eluted with 1M HCl and 1M HF. The separation yield of neptunium (U) was influenced largely by the amount of thorium, but this influence could be neglected as the concentration of the thorium was below 0.5g/ml. The content of these elements were calculated by a single comparator method using monitors, gold and cobalt. The detection limits of U and Th are 4.0 and 1.2 ppb, respectively.

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Abstract  

Methods for the analysis of potassium, holmium and lanthanum in their tungsten bronzes, MxWO3, are described. Simultaneous thermal neutron activation of samples and comparison standards was followed by counting with Ge(Li) diodes. Analysis was performed by comparing appropriate full energy peaks in the spectra of the three elements with peaks in the187W spectrum for sample and standard. Results with accuracy of 1 to 3% were obtained.

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Nanopages
Authors: E. Horváth, P. L. Neumann, A. L. Tóth, É. Vázsonyi, A. A. Koós, Z. E. Horváth, P. Fürjes, C. Dücső, and L. P. Biró

The deposition of nanowires for interconnects in nanoelectronic devices werestudied morphologically by scanning electron microscopy (SEM), atomic force microscopy (AFM) and by in-situ resistance measurements. The deposition and basic characterization of nanometer size tungsten wires by gas injection (GIS) and focused ion beams (FIB) was carried out in-situ in a LEO 1540 XB workstation. The I(V) measurement showed that the deposited W wires have ohmic characteristic. The variation of the resistance during an ex-situ heating was linear with a low thermal coefficient (4% of the pure metallic W).

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