[en] Literary data on vapor composition above niobium pentafluoride are analyzed and incorrectness of the value of vaporization heat of NbF₅ monomeric molecules, given in the Glushko reference book, is shown. Heat capacities of NbF₅ gas for monomeric, two-dimensional, three-dimensional and four-dimensional NbF₅ molecules are estimated and the vaporization heats of monomeric and polymeric forms at the melting temperature (in kJ/mol): 79.3(5.0)-NbF₅, 71.0(6.7)-(NbF₅)₂, 53.9(4.6)-(NbF₅)₃, 44.5(6.7)-(NbF₅)₄, are calculated

[en] A liquid-liquid extraction process for the extraction of tantalum and niobium, and their separation from each other is provided. A solution of the fluoride complexes of tantalum and niobium is firstly formed and tantalum extracted therefrom using a selective organic extractant in an amount of not more than 1 mole of extractant per mole of tantalum present. A second tantalum extraction is then carried similarly, but using not more than 0,2 moles of extractant per mole of tantalum originally present. Niobium is then extracted in a similar way. The tantalum and niobium rich organic phases are optionally washed with acid and subjected to stripping to recover tantalum and niobium, generally in a precipitated form

[en] Main statistic parameters of the process of rectification separation of niobium and tantalum in the form of their pentafluorides and pentachlorides are calculated. Comparison of the data obtained shows that niobium pentafluoride rectification efficiency is 5 time less according to the value of interstage flow than the rectification of their pentachlorides. To illustrate the possibilities of rectification separation and purification of niobium and tantalum pentafluorides a number of experiments have been carried out. Experiments have grounded that the use of high-efficiency rectification coulomus is necessary for the fine separation of pentafluoride data and for their purification from a number of impurities. Behaviour of impurities during rectification purification of pentafluorides is in correlation with the data on liquid-vapor phase equilibria in studied systems of pentafluorides-impurity (TiF₄, AlF₃, WF₆, WOF₄, MoOF₄, MoF₆)

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[en] Doping can result in energy band rearrangement, high carrier concentration and fast carrier separation in semiconductor materials. Consequently, great enhancement in the photocatalytic performance can be achieved. In this work, Al³⁺-doped niobium oxyfluoride (Nb₃O₇F) was synthesized by a facile hydrothermal approach for the first time. A series of characterization tools were used to investigate the phase, composition, microstructure, chemical state, spectrum response and band gap. The influence of Al doping on the photocatalytic performance was also investigated by varying the molar ratios of Al/Nb. The results confirmed that Al atoms have been successfully incorporated into the Nb₃O₇F lattice. Al doping led to slightly lowering of the band gap of Nb₃O₇F from 3.08 to 2.99 eV. Moreover, Nb₃O₇F with 0.06 mol% Al doping exhibited the highest degradation efficiency for methyl blue under visible light irradiation. Crystal defects generated by appropriate Al-doping increased the specific surface area and the optimized band gap could be responsible for the improved photocatalytic activity. (author)

[en] A study was made on the reasons of increased oxygen content in electrolytic niobium by investigation into thermal stability of potassium heptafluoroniobate and the products of its hydrolysis. Methods of infrared spectroscopy, X-ray phase and crystal optical analyses were used for investigation. It was shown that KNbO₃ which thermal decomposition results in separation of free oxygen represents one of the products of K₂NbF₇ pyrohydrolysis. This process is responsible for the high corrosivity of the melt as well as the oxidation of cathode deposite. One of the possible ways of metal protection from oxidation lies in the use of other niobium compound instead of K₂ NbF₇ as electrolyte component, which doesn't form the niobate of alkali metal during its thermal decomposition

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