The separation for tungsten and molybdenum was carried out using anion exchange separation (Dowex 1×10; 200–400 mesh).
Irradiation was carried out in a swimming pool reactor at a thermal flux of about 1–2×1013 n·cm−2·sec−1 for 15 hours.
The samples and standard were allowed to cool for 5–6 hours before chemical processing. the high concentration of calcium
in plants (up to 40 mg/g dry material), the use of hydrofluoric acid for a good absorption and quantitative recovery of tungsten
led us to dissolve the samples with Ht−H2O2 mixtures containing boric acid to prevent the precipitation of fluorides.
Authors:A. Garrido Pedrosa, M. Souza, S. Lima, Dulce Melo, A. Souza, and A. Araújo
bifunctional catalysts were synthesized using impregnation and polymeric precursor
methods. After the synthesis process the samples were calcined at 600, 700
and 800C and characterized by X-ray diffraction, nitrogen adsorption
and temperature programmed reduction study by thermogravimetry. DTG-TPR profiles
showed between three and five reduction events at different temperatures attributed
to platinum reduction and to different stages of tungsten species reduction.
A comparative study of the synthesis method influence on the DTG-TPR curves
Authors:M. Pavlova, N. Jordanov, M. Michailov, and S. Gabrovska
A simple neutron-activation method for the determination of rhenium based on a preliminary extractive separation of the latter
from molybdenum and tungsten is described. The sample is decomposed with sodium peroxide, a small amount of water is added
and the resulting pulp is extracted with pyridine. The extract is evaporated to dryness, the residue is dissolved in water
and the solution is passed through a column packed with Dowex 50WX8 in H+ form to eliminate the metal impurities. The HReO4 passed, after neutralization with ammonia, is evaporated to dryness in penals, which then are irradiated with thermal neutrons.
Uranium analysis at trace levels from geological samples was performed by K X-ray fluorescence using a semiconductor detector
and radioisotope excitation. The exciting57Co-source was constructed in such a way as to produce a high peak to background ratio. Using 10 minutes counting times the
detection limit with a 0.26 GBq source was 24 μg/g improving to about 9 μg/g with a ten times stronger source. The detection
limits for tin, cerium, tungsten and thorium were also measured.
An analytical method, SSMS, for the determination of trace impurities in cobalt is described. This element is used as raw material for the production of60Co in Embalse Nuclear Power Station. Tin, aluminum, lead, silicon, molybdenum, calcium, vanadium, boron, chromium, zirconium, tungsten, nickel, magnesium, iron, zinc and copper were determined. Manganese, analyzed by AAS, was used as an internal standard. The measurements were semiquantitative. The accuracy of the results was compared with that of emission spectrography and atomic absorption spectrometry, the agreement was found to be satisfactory.
INAA technique for the determination of impurities (O, F, Na, Mg, Al, Si, P, S, K, Sc, Cr, Mn, Fe, Co, Ni, etc.) and of some doping elements in molybdenum and tungsten with detections limits between 10–12 and 10–6g/g by using a nuclear reactor and a neutron generator have been developed. The methods have been used to control the products of processing of refractory materials, to study the dynamics of impurities and doping elements at all stages of the production process.
The long-lived -radionuclidic impurities in the columns of spent99Mo/99mTc generators one year after the calibration date have been determined by -spectrometry. Three radionuclidic impuritiesfission products (103Ru,106Ru and125Sb) were detected. Also in the majority of samples three radioisotopes of tungsten (181W,185W and188W) were also present. The contents of the impurities were found to vary greatly. According to the activity, energy and half-life, the main contribution to the residual activity in the spent generators is due to the presence of125Sb.
Authors:K. Lilius, M. Gasik, V. Järvelä, and S. Strömberg
A technique named ‘apparent thermogravimetry’ (ATG) has been developed for studying infiltration phenomena. It has been used
for investigating of infiltration of copper, cast iron, and cobalt alloys into porous tungsten, sintered steel, and tungsten
carbide. A description of ATG signal behaviour has been obtained, taking into account ‘internal’ (capillary, viscous, gravitational,
end-drag) and ‘external’ (wetting, buoyancy, Archimedean) forces. Dependencies of Archimedean foroe and wetting angle on different
parameters are described in relation to the infiltration mechanism. The ATG method can be used to determine surface tension
or contact angle.
Authors:I. Konstantinov, B. Zatolokin, N. Krasnov, Yu. Sevastyanov, and L. Volkova
Procedures for determining traces of calcium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum and tungsten
in tantalum are described utilizing 11 MeV proton activation. The instrumental method of analysis with the use of a Ge(Li)
detector and the radiochemical separation of the corresponding fractions are described. The formula for the calculation of
the concentration of traces with the use of thick target yields is given. Experimental data on the thick target yields of
radioisotopes44Sc,52Mn,56Co,65Zn,93mMo,96Tc are presented. Based on the experimental data, the detection limits are estimated at 1–10 ppb for the above mentioned metal
traces in tantalum. The successful solution of the task of the simultaneous determination of nine elements in tantalum confirms
the wide applicability of proton activation analysis.
The chlorination kinetics of alkali-added (K and Li) tungsten trioxide were studied by thermogravimetry, using gaseous CCl4 as chlorinating agent. The reactivity of the modified samples was compared to the results on the chlorination of pure WO3. Similar apparent activation energies were found for the pure and alkali-added samples. However, potassium additive resulted in a strong decrease of the initial reaction rate, while surface lithium has no influence on it.