A method for the substoichiometric determination of tungsten by thermal neutron activation analysis has been developed based
on the selective extraction of the tungsten dithiol complex into amyl acetate. The method is simple, rapid and accurate. It
has been used in the determination of tungsten in alloy steel, meteorites and biological standard kale.
Authors:Aleksandr Knyazev, Mirosław Mączka, Nataliya Kuznetsova, Jerzy Hanuza, and Aleksey Markin
In the present work temperature dependence of heat capacity of rubidium niobium tungsten oxide has been measured first in
the range from 7 to 395 K and then between 390 and 650 K, respectively, by precision adiabatic vacuum and dynamic calorimetry.
The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity
, for the range from T→0 to 650 K. The high-temperature X-ray diffraction and the differential scanning calorimetry were used for the determination
of temperature and decomposition products of RbNbWO6.
The instrumental neutron activation analysis /INAA/ of tungsten in various steel samples has been done with a 2 Ci252Cf fission neutron source having an integrated neutron flux of 1010 ns–1 and measuring the -activity of187W on a 4 K multi-channel analyzer /MCA/ coupled to a high purity germanium /HPGe/ detector. The tungsten content of various steel samples was between 0.017 and 0.024%.
The aim of the present work was to provide arguments to the almost ‘hystorical’ problem of what β-tungsten is.
WO3was reduced in dry H2gas atmosphere in order to examine, whether β-tungsten formed in such a way contains oxygen as part of the lattice described
as WxO (e.g. W20O) or is a pure metallic phase of tungsten.
As a result of thermoanalytical measurements and of chemical analysis for oxygen, the assumption is supported that in the
600-800C temperature range of metal formation not the WxO (β-W)→W(α-W) transformation but the β-W→α-W structural rearrangement of materials with identical chemical composition is
the most probable process.
The earlier opinion that the formation of the β-W structure requires the presence of oxygen atoms was not verified by our
The absorption of rhenium(VII) and tungsten(VI) ions on Al2O3 from HCl, HClO4, HNO3, H2SO4, H3PO4, NaOH, NH4OH, NaCl, NaF, and Na-tartarate solutions by batch equilibration, as well as by passage through a chromatographic column,
has been studied. The results show that rhenium(VII) can be effectively separated from tungsten(VI) using any of the acid
or salt solutions investigated. The experimental data allowed to develop a simple procedure for the radiochemical separation
of rhenium isotopes from an irradiated WO3 sample.
A rapid method has been developed for the determination of tungsten, especially in rocks. The reaction182W(n, γ)183mW (T=5.3 sec), with a thermal neutron capture cross-section of 0.5 b was used. The samples were irradiated in the fast pneumatic
system of the FRM, which is described briefly. The low-energy γ-rays of the isomer183mW were measured by a high-resolving Ge(Li) detector. The sensitivity of the method is 0.1 mg tungsten with an accuracy of
about 5%; the minimum concentration is 0.1–0.2% W in geological samples. The analysis time is 2 min per sample.
A simple, rapid and non-destructive method is described for determining tungsten in steels over the concentration range 0.08 to about 3% by mass. The method uses the low energy gamma-rays induced in183W by neutrons from the 3 MeV bombardment of beryllium with deuterons. The precision is normally better than 10%.
Authors:I. Szilágyi, Judit Pfeifer, C. Balázsi, A. Tóth, Katalin Varga-Josepovits, J. Madarász, and G. Pokol
We studied the thermal stability of different hexagonal tungsten trioxide, h-WO3 samples, which were prepared either by annealing hexagonal ammonium tungsten bronze, (NH4)0.33−xWO3−y, or by soft chemical synthesis from Na2WO4. The structure and composition of the samples were studied by powder XRD, SEM-EDX, XPS and 1H-MAS NMR. The thermal properties were investigated by simultaneous TG/DTA, on-line evolved gas analysis (TG/DAT-MS), SEM
and in situ powder XRD. The preparative routes influenced the thermal properties of h-WO3 samples, i.e. the course of water release, the exothermic collapse of the hexagonal framework and the phase transformations
were all affected.
Authors:J. L. Vučina, D. M. Lukić, S. K. Milonjić, and M. M. Stoiljković
The sorption of tungstate anions on alumina from aqueous solutions of sodium chloride was investigated in dynamic conditions.
The breakthrough curves as the function of W and NaCl concentrations, pH and the flow rates were determined. The breakthrough
capacities, the capacities at C/C0=0.5, the total column sorption capacities and the utilization degrees or column efficiencies, were determined. The obtained
tungstate anion sorption data fit with a Langmuir-type isotherm. The values of the breakthrough capacity, Q0,9max,the Langmuir equilibrium constant or affinity parameter, KL, and the free energy change, ΔG, of tungsten sorption were also determined.
Authors:C. Ribeiro, W. de Souza, Marisa Crespi, J. Gomes Neto, and F. Fertonani
Tungsten carbide, WC, has shown dissimilar thermal behavior when it is heated on changeable heating rate and flow of oxidant
atmosphere. The oxidation of WC to WO3 tends to be in a single and slow kinetic step on slow heating rate and/or low flux of air. Kinetic parameters, on non-isothermal
condition, could be evaluated to the oxidation of WC to heating rate below 15°C min−1 or low flow of air (10 mL min−1). The reaction is governed by nucleation and growth at 5 to 10°C min−1 then the tendency is to be autocatalytic, JMA and SB, respectively.