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Introduction Over the years, an ever-increasing research interest in chemistry of niobium has aroused not only from the striking structural novelties and complexities exhibited by niobium compounds but also from their unique

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migrated into the channels, decreasing the amount of Br⊘nsted acid sites. In this study, the effect of the introduction of niobium carbide was studied on the dehydro-aromatization of methane over molybdenum containing HMCM-22 zeolite at 973 K. This

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Journal of Thermal Analysis and Calorimetry
Authors: Aleksandr Knyazev, Mirosław Mączka, Nataliya Kuznetsova, Jerzy Hanuza, and Aleksey Markin

Abstract  

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
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$C_{\text{p}}^{\text{o}} (T),$$ \end{document}
enthalpy
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$H^{\text{o}} ({\rm T}) - H^{\text{o}} (0)$$ \end{document}
, entropy
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$S^{\text{o}} (T) - S^{\text{o}} \left( 0 \right)$$ \end{document}
, and Gibbs function
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$G^{{^{\text{o}} }} ({\rm T}) - H^{{^{\text{o}} }} (0)$$ \end{document}
, 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.
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Abstract  

Radiolysis of nitrobenzene solution of cobalt(III) dicarbollide, which is used for solvent extraction of cesium from fission products results in enhanced extraction of niobium-95. The isomeric nitrophenols, 2,4-dinitrophenol, p-nitrosophenol and m-aminophenol exhibit antergism towards extraction of niobium cations. Synergistic effect is exhibited by 2,5-dinitrophenol, o- and p-aminophenol, o-nitroaniline and 2,4,6-trinitrophenol which are among the products of two-phase systems with nitrobenzene radiolysis. Two competing processes, complexation of niobium and protonation of ligand, both depending on the ligand benzene ring substituents, are discussed.

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Abstract  

Destructive and non-destructive procedures have been developed for the determination of titanium by photon activation analysis. The non-destructive analyses with an internal standard method are performed on niobium and tantalum oxides while destructive determinations, including non-isotope addition and radiochemical separation, are applied to yttrium oxide samples.

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Abstract  

A solvent extraction procedure for the separation of niobium and tantalum has been developed. The method consists of extracting tantalum from its aqueous mixture with niobium, with the help of di(2-ethylhexyl)phosphoric acid (HDEHP) in n-heptane. The aqueous feed consists of niobium and tantalum in an aqueous medium containing hydrochloric and oxalic acids. The concentrations of niobium and tantalum were raised to 1 mg/ml in the aqueous solution. The extraction efficiency of tantalum under these conditions was found to be 85%. Effects of chloride and oxalate ions as well as those of the concentration of HDEHP on the extraction efficiency were studied and discussed in detail.

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Abstract  

Ammonium niobium oxalate was prepared and characterized by elemental analysis, XRD and FTIR spectroscopy analysis, which confirmed that the molecular formula of the complex is NH4(NbO(C2O4)2(H2O)2)(H2O)3. Dynamic TG analysis under air was used to investigate the thermal decomposition process of synthetic ammonium niobium oxalate. It shows that the thermal decomposition occurs in three stages and the corresponding apparent activation energies were calculated with the Ozawa–Flynn–Wall and the Friedman methods. The most probable kinetic models of the first two steps decomposition of the complex have been estimated by Coats–Redfern integral and the Achar–Bridly–Sharp differential methods.

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Abstract  

A95mTc tracer with an excellent quality was prepared by a simple sublimation method after α-bombardment of niobium metal. Technetium-95m produced by the93Nb(α,2n)95mTc reaction was separated from the niobium targets in a quartz tube by heating at 1100°C in an oxygen gas flow. Technetium-95m sublimed as an oxide was deposited on the inner wall of the quartz tube outside an electric furnace, and then collected as a pertechnetate solution by washing with water. The ICP-MS analysis of the95mTc solution revealed its excellent quality, compared to a95mTc solution prepared from the same targets through a wet chemical separation method and a commercial95mTc solution. With this tracer, the precision of ICP-MS analysis of99Tc in environmental samples are highly improved.

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Abstract  

Two radiochemical neutron activation analysis techniques capable for the determination of Ag, Au, Cd, Co, Cr, Cs, Cu, Fe, Hf, Ir, K, Mn, Mo, Na, Ni, Pd, Pt, Rb, Sc, Se, Ta, Th, Sn, W, Zn, and Zr in niobium via medium- and long-lived indicator radionuclides were developed. They involve two different irradiation and cooling times as well as two different group separation schemes based on extraction and ion exchange. The achievable limits of detection are between 10−7 g/g and 10−13 g/g. The techniques were applied to analysis of niobium of different purity grades. For a number of elements, the results of these techniques are compared with those of other techniques.

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