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[en] A new vanadium fluoride hydrate V2F6 . 4H2O was prepared by reacting vanadium metal with hexafluorosilicic acid solution. The crystal structure of the green compound was determined by X-ray diffraction. The identified structure of the CuMF6 . 4H2O-type (M = Ti, Zr) has not been found amongst vanadium fluoride hydrates to date. In addition, thermal decomposition behaviour and magnetic properties of V2F6 . 4H2O were studied. (orig.)
[en] A new lithium vanadium fluoride Li2VF6 was prepared by reacting lithium fluoride LiF with vanadium tetrafluoride VF4 in a monel capsule at 500 C. The crystal structure has been determined by means of powder X-ray diffraction. Trirutile-type dilithium hexafluorovanadate(IV) crystallizes in the tetragonal space group P42/mnm with lattice parameters a = 459.99(1), b = 459.99(1), c = 896.64(2) pm. The presence of a Jahn-Teller effect is discussed. (orig.)
[en] The problem studied here is the production of very high purity metallic vanadium. By analogy with the method used for silicon or germanium production in electronics, the one employed here involves preparing the tetrachloride from the impure metal, purifying it by distillation, an easy process, and finally reducing this tetrachloride with hydrogen to obtain the pure metal. By this technique it has been possible to reduce the impurity content from about 5000 ppm to under 500 ppm and, in particular, to eliminate almost completely the nitrogen which is not removed by the normal purification methods. The author has studied the changes in the morphology of the deposit obtained as a function of the operational conditions. He has determined in particular the conditions leading to the formation of a compact deposit. He has shown that the deposition kinetics are very probably governed by an adsorbed phase reaction at the metal surface, (author)
[fr]Le probleme aborde est celui de la production de vanadium metallique de tres haute purete, par analogie avec celle conduisant au silicium ou au germanium utilise en electronique. La methode utilisee consiste a preparer, a partir du metal impur, le tetrachlorure facilement distillable, a purifier celui-ci par distillation et enfin a le reduire par l'hydrogene pour regenerer le metal. Ce procede a permis de faire passer la teneur en impuretes d'environ 5000 ppm a moins de 500 et, en particulier, a eliminer presque totalement l'azote resistant aux traitements habituels de purification. L'auteur a etudie les variations de la morphologie du depot obtenu en fonction des conditions operatoires. Il a, en particulier, determine celles conduisant a un depot compact. Il a montre que la cinetique du depot est tres probablement reglee par une reaction en phase adsorbee a la surface du metal. (auteur)
[en] Evolution of bromine gas in the positive half cell of the Generation 2 (G2) vanadium bromide (V/Br) battery during charging is a concern which can be resolved by the use of bromine complexing agents. In this paper, for the first time, we report the effect of the addition of two quaternary ammonium bromides; N-ethyl-N-methyl-morpholinium bromide (MEM) and N-ethyl-N-methyl-pyrrolidinium bromide (MEP) to the positive and negative half cell electrolytes of the V/Br. Cyclic voltammetry (CV), linear sweep voltammetry and electrochemical impedance spectroscopy (EIS) studies showed that the addition of MEM–MEP effectively reduce Br2 vapours. Although the presence of MEM and MEP did not affect the mechanism of the electrode reactions, performance tests conducted in lab scale V/Br cells employing the VF11 cation exchange membrane resulted in lower average cell efficiencies possibly due to the increase in membrane resistance caused by membrane fouling
[en] Vanadium pentachloride and molybdenum and rhenium hexachloride are all thermally unstable but can be prepared by metathesis from the corresponding fluorides with BCl_3 at low temperatures. MoCl_6 is structurally related to β-WCl_6, and ReCl_6 to α-WCl_6. VCl_5 is a dimer in the solid state (see structure; V red, Cl green). (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] The electronic structure and bonding features of metal and transition metal fluorides in low oxidation states, GaF_3 and VF_3, have been studied from precise single crystal X-ray diffraction data using multipole and maximum entropy methods. The topology of the charge density is analyzed and the (3,−1) bond critical points are determined. Existences of ionic nature of bonding in low valent fluorine compounds are clearly evident. The spherical core of metal atom and aspherical or twisted core of transition metal atom reveal the fact that GaF_3 is much more rigid than VF_3. Aspherical cores of the polarized ligand atoms are also visible in the two-dimensional density distribution pictures. The true valence charge density surfaces with encapsulating the atomic basins maps are elucidated. An elongated saddle with mid-bond density of 0.6191 e/Å"3, observed in the compound VF_3, shows that its lattice is less rigid and has more ionic character than GaF_3.
[en] Highlights: ► A chemical thermodynamics review of V2O5 chlorination based on available thermodynamics data and software. ► Discuss the importance of ΔG° × T plots to study the viability of chlorination reactions. ► Reinforce the relationship between ΔG° × T and predominance diagrams, when plotted with thermodynamic consistency. ► Application of different computational methods with diverse complexity for studying the nature of equilibrium states. ► Speciation calculations to study the effect of temperature, partial pressure of O2 and Cl2 over chemical equilibrium. - Abstract: This work is mainly related to the thermodynamic study of the V2O5 carbon-chlorination. In this context, three different approaches of diverse complexity level were employed. First, the formation of individual vanadium chlorides and oxychlorides were considered on the basis of the well known ΔG° × T diagrams. It is suggested that these simple constructions can help in understanding the formation sequence of vanadium chlorinated species. Moreover, the relative stability of the most stable vanadium chloride (VCl4) and oxychloride (VOCl3) was addressed based on available thermodynamics data. Finally, a gas phase speciation calculation was performed in order to obtain, simultaneously, the concentration of all possible vanadium chlorides and oxychlorides as a function of temperature, Cl2 and O2 partial pressures. It is demonstrated that, although diverse in the complexity level, the three methods considered have a strong relation with each other, and converge to a better insight into the nature of the chemical equilibrium states achievable for the reaction system under study. The same approach can be applied to any other reaction system of technological importance
[en] The functional properties of quaternary I_2–II–IV–VI_4 nanomaterials, with potential interest in various technological fields, are highly sensitive to compositional variations, which is a challenging parameter to adjust. Here we demonstrate the presence of phosphonic acids to aid controlling the reactivity of the II element monomer to be incorporated in quaternary Cu_2ZnSnSe_4 nanoparticles and thus to provide a more reliable way to adjust the final nanoparticle metal ratios. Furthermore, we demonstrate the composition control in such multivalence nanoparticles to allow modifying charge carrier concentrations in nanomaterials produced from the assembly of these building blocks.
[en] The novel phase K2.5Cu5Cl(PO4)4(OH)0.5(VO2).H2O was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using low-temperature (100 K) single-crystal synchrotron diffraction data and refined against F2 to R = 0.035. The compound crystallizes in the tetragonal space group I4/mmm, with unit-cell parameters a =9.8120(8), c = 19.954(1) Aa, V = 1921.1(2) Aa3, and Z = 4. Both symmetrically independent Cu2+ sites show elongated square-pyramidal coordination. The V5+ ions reside in strongly distorted five-vertex VO5 polyhedra with 50% occupancy. The structure is based on a 3D anionic framework built from Cu- and V-centered five-vertex polyhedra and PO4 tetrahedra. Channels in the  and  directions accommodate large K atoms and H2O molecules. The compound is a new structural representative of the topology shown by the lavendulan group of copper arsenate and phosphate minerals. Their tetragonal or pseudotetragonal crystal structures are characterized by two types of 2D slabs alternating along one axis of their unit cells. One slab, described by the formula [Cu4X(TO4)4]8 (where X = Cl, O and T = As, P), is common to all phases, whereas the slab content of the other set differs among the group members. We suggest interpreting this family of compounds in terms of the modular concept and also consider the synthetic phase Ba(VO)Cu4(PO4)4 as a simplest member of this polysomatic series.