The synthesis and some properties of new compound Cu13Fe4V10O44

A new compound with the formula Cu₁₃Fe₄V₁₀O₄₄ has been obtained as a result of a solid-state reactions occurring during heating the mixtures both of oxides: CuO, V₂O₅, Fe₂O₃ and vanadates: Cu₅V₂O₁₀, Cu₃Fe₄V₆O₂₄. The DTA measurements were used to choose the heating temperatures as well as for determination of thermal stability of the new compound. Cu₁₃Fe₄V₁₀O₄₄ melts incongruently at 790?±?5?°C. The new phase crystallizes in the monoclinic system. The indexing results and the calculated unit cell parameters for Cu₁₃Fe₄V₁₀O₄₄ are given. Its infra-red spectrum and image obtained by means of an electron scanning microscope are presented.     

Monolayer V2O5/TiO2–ZrO2 catalysts for selective oxidation of o-xylene: preparation and characterization

A series of TiO₂?CZrO₂ supported V₂O₅ catalysts with vanadia loadings ranging from 4 to 12 wt% were synthesized by a wet impregnation technique and subjected to various thermal treatments at temperatures ranging from 773 to 1,073?K to understand the dispersion and thermal stability of the catalysts. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area, oxygen uptake, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results of 773?K calcined samples conferred an amorphous nature of the mixed oxide support and a highly dispersed form of vanadium oxide. Oxygen uptake measurements supported the formation of a monolayer of vanadium oxide over the thermally stable TiO₂?CZrO₂ support. The O 1s, Ti 2p, Zr 3d, and V 2p core level photoelectron peaks of TiO₂?CZrO₂ and V₂O₅/TiO₂?CZrO₂ catalysts are sensitive to the calcination temperature. No significant changes in the oxidation states of Ti⁴⁺ and Zr⁴⁺ were noted with increasing thermal treatments. Vanadium oxide stabilized as V⁴⁺ at lower temperatures, and the presence of V⁵⁺ is observed at 1,073?K. The synthesized catalysts were evaluated for selective oxidation of o-xylene under normal atmospheric pressure in the temperature range of 600?C708?K. The TiO₂?CZrO₂ support exhibits very less conversion of o-xylene, while 12 wt% V₂O₅ loaded sample exhibited a good conversion and a high product selectivity towards the desired product, phthalic anhydride.     

Preparation and properties of homogeneous V2O5-SiO2 xerogel composite based on interpenetrating polymer network

In this paper, we report the conducting and electrochemical properties of a homogeneous V₂O₅-SiO₂ xerogel composite obtained from the simultaneous polymerization in both inorganic components (Si-O and V-O based polymers) forming an interpenetrating polymer network, where a mutual “solubility” due to cross-links and entanglements was observed. The presence of V₂O₅ inside the silica matrix has a strong effect on electrical conductivity; measurements showed room temperature conductivity almost 1000 times higher than what is found in the literature. In addition, the electrochemical behavior is quite similar to that found in V₂O₅ xerogel. Moreover, the effects of thermal treatment on the conducting and electrochemical properties were investigated. It was found that both properties were improved with no significant effect on V₂O₅ xerogel layered structure.     

Phase equilibria up to the solidus line in the V2O5-CrVMoO7 system

The phase equilibria being established in the V₂O₅-CrVMoO₇ system in the solid state and the whole component concentration range have been studied by the X-ray powder diffraction and thermal analysis methods. The measurements have shown that the V₂O₅-CrVMoO₇ system is not a real two-component system in the subsolidus area.

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Zusammenfassung Mittels Thermoanalyse und Debye-Scherrer-Verfahren wurde das Phasengleichgewicht im Feststoffsystem V₂O₅-CrVMoO₇ im gesamten Konzentrationsbereich untersucht. Die Messungen zeigen, daß es sich bei dem System V₂O₅-CrMoO₇ im Bereich unter Solidus um kein echtes Zweikomponentensystem handelt.

     

Thermal properties of hydrated lanthanum and yttrium polyvanadates

The study of thermal properties of La(HV₆O₁₆)₃.19.5H₂O and Y(HV₆O₁₆)₃.22H₂O showed, that the dehydration of both compounds is discontinuous. After release of last water amount, the parent structure is destabilized and products of thermal decomposition, V₂O₅ and corresponding orthovanadates, start to be formed. The decomposition of La(HV₆O₁₆)₃.19.5H₂O results in formation of V₂O₅ and LaVO₄, the temperatures of crystallization of which differ. The decomposition products of yttrium salt crystallize simultaneously. All compounds formed melt at 685°C. By crystallization of the melt, the mixtures V₂O₅-LaVO₄ and V₂O₅-YVO₄, respectively, are formed which are stable up to 1000°C.     

Enhanced thermal degradation of 2,2′-dichlorodiethyl sulfide (sulfur mustard,HD) with the presence of metal oxides

Thermal degradation of sulfur mustard (2,2′-dichlorodiethyl sulfide, HD) in the presence of metal oxide adsorbents was investigated by thermal desorption in conjunction with gas chromatography–mass spectrometry (GC-MS). Zr(OH)₄, Al₂O₃, Al₂CoO₄, MgO, CeO₂, and V₂O₅ were used as metal oxide adsorbents. Neat HD was spiked onto the metal oxides packed in glass tubes, which were kept at room temperature and then heated at moderately elevated temperatures of 100°C by a thermal desorption system. The products of thermal degradation were directly transferred and analyzed by GC-MS. 1,4-Dithiane and 1,4-oxathiane were characterized as the major products of the thermal degradation of HD in the presence of Zr(OH)₄, Al₂O₃, Al₂CoO₄, and CeO₂ adsorbents. No effective degradation was observed with MgO and V₂O₅. Of particular note is Zr(OH)₄, which extremely enhanced the thermal degradation of HD.     

Evolution des tenseurs de dilatation thermique en fonction de la température. III. Etude expérimentale des oxydes PbO1,57, PbWO4, V2O5 et V2O3 et analyse des résultats

The evolution of thermal expansion tensor versus temperature has been measured by powder X-ray diffraction for PbO_1,57 (in the range 77–636°K), PbWO₄ (95–800°K), V₂O₅ (77–773°K) and V₂O₃ (77–600°K). Tensor anisotropy is explained considering structure and chemical bonds (V₂O₅, PbWO₄). We verified that the evolution of anisotropy (measured by aspherism index) is much different, according to whether the oxide presents a continuous phase transition (V₂O₃) or not (PbO_1,57, PbWO₄, V₂O₅).     

Electrical Resistivity, Magnetic Susceptibility, X-Ray Photoelectron Spectroscopy, and Electronic Band Structure Studies of Cu2.33−xV4O11

The electronic and physical properties of Cu_2.33V₄O₁₁ were characterized by electrical resistivity, magnetic susceptibility and X-ray photoelectron spectroscopy (XPS) measurements and by tight-binding electronic band structure calculations. Attempts to prepare Cu_2.33−xV₄O₁₁ outside its narrow homogeneity range led to a mixture of Cu_2.33V₄O₁₁, CuVO₃ and β-Cu_xV₂O₅. The magnetic susceptibility data show no evidence for a magnetic/structural transition around 300 K. The XPS spectra of Cu_2.33V₄O₁₁ reveal the presence of mixed valence in both Cu and V. The [Cu⁺]/[Cu²⁺] ratio is estimated to be 1.11 from the Cu 2p_3/2 peak areas, so [V⁴⁺]/[V⁵⁺]=0.56 by the charge balance. Our electronic structure calculations suggest that the oxidation state of the Cu ions is +2 in the channels of CuO₄ tetrahedra, and +1 in the channels of linear CuO₂ and trigonal planar CuO₃ units. This predicts that [Cu⁺]/[Cu²⁺]=1.33 and [V⁴⁺]/[V⁵⁺]=0.50, in good agreement with those deduced from the XPS study.     

Synthesis, structure and magnetic properties of V4O9—A missing link in binary vanadium oxides

V₄O₉: A missing link of Wadsley phases has been successfully synthesized by using sulfur as a reducing agent at a low temperature and its structure has been determined by combining electron, X-ray and neutron diffractions. V₄O₉ has an orthorhombic Cmcm structure and the lattice parameters are a=10.356(2) Å, b=8.174(1) Å and c=16.559(3) Å at room temperature. The structure is composed of shared edges and corners of three types of polyhedra; a VO₆ distorted octahedron, a VO₅ pyramid and a VO₄ tetrahedron. The structure of V₄O₉ is very similar to that of vanadyl pyrophosphate (VO)₂P₂O₇ which has PO₄ tetrahedra instead of VO₄ tetrahedra. This indicates that V₄O₉ is a salt of pyro-ion [V₂O₇]^4-; (VO)₂V₂O₇. The magnetic properties of V₄O₉ have been investigated by magnetic susceptibility, high-field magnetization and inelastic neutron scattering measurements. V₄O₉ is a quantum spin system with a spin-gapped ground state. The excitation gap between the singlet ground state and the excited triplet state is approximately 73 K. The magnetic susceptibility behavior suggests that V₄O₉ is a spin-1/2 dimer system with significant interdimer interactions, as opposed to (VO)₂P₂O₇, which is an alternating spin-1/2 chain system. This difference is thought to be due to the fact that VO₄-mediated interactions are considerably weaker than PO₄-mediated interactions.     

Thermal decomposition of ammonium metavanadate supported on Al2O3

The thermal decomposition of ammonium metavanadate supported on aluminium oxide was investigated using DTA, TG and X-ray diffraction techniques.The results obtained revealed that ammonium vanadate decomposed at 225–250°C giving an intermediate compound ((NH₄)₂V₆O₁₆) which decomposed readily at 335–360°C producing V₂O₅. Alumina was found to chance the formation of the intermediate compound and retard its decomposition. Some of the V⁵⁺ ions of V₂O₅ lattice seemed to be reduced into V⁴⁺ and V³⁺ ions by heating in air at 450°C in the presence of Al₂O₃. Such a reaction was attributed to dissolution of some Al³⁺ ions in the V₂O₅ lattice via location in interstitial positions and/or in cationic vacancies. Al₂O₃ was found to interact with V₂O₅ at 650° C giving well-crystalline A1VO₄ which decomposed at about 750°C forming well-crystalline δ-Al₂O₃ and V₂O₅,. Pure Al₂O₃, heated in air at 1000°C, existed in the form of the κ-phase which, on mixing with V₂O₅ (0.5 V₂O₅:1 Al₂O₃) and heating in air at 1000°C, was converted entirely to the well-crystalline α-Al₂O₃ phase.     

Zur Bildung und Umwandlung von Oxidphasen im quasibinären System V2O5?Nb2O5

Formation and Transformation of Oxide Phases in the Quasibinary System V₂O₅? Nb₂O₅ In the quasibinary system V₂O₅? Nb₂O₅ three phases exist in addition to the boundary phases: VNbO₅, V₂Nb₉O_27.5, and VNb₉O₂₅. Only the latter phase is a thermodynamically stable one. The metastable phases VNbO₅ and V₂Nb₉O_27.5 are formed by thermal decomposition of freeze-dryed products of alkoxide hydrolysis. VNb₉O₂₅ can be formed by thermal treatment of a metastable solid solution with TT-Nb₂O₅ structure or, beside V₂O₅, by thermal decomposition of the other metastable phases. A reaction scheme of formation and decomposition of phases in the quasi- binary system is given and discussed.     

On Electrical Conductivity Measurement for Lithium-Vanadium Bronze

Lithium-vanadium bronze Li_1+xV₃O₈ was produced by the solid-phase method and its electrical conductivity was measured with silver and platinum electrodes. X-ray diffraction and thermal analyses demonstrated that Li_1+xV₃O₈ interacts at a temperature of 480°C with metallic silver to give AgV₂O₅ and AgV₃O₈, which is responsible for the poor reproducibility of results in electrical conductivity measurements with silver electrodes.     

Reactivity of the oxides in the ternary V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CuO-α-Sb<Subscript>2</Subscript>O<Subscript>4</Subscript> system in air

In this work it has been established which compounds finally are formed in air in the two-component CuO-V₂O₅ and CuO-α-Sb₂O₄ systems. Unknown thermal properties of CuV₂O₆, Cu₂V₂O₇ and Cu₁₁V₆O₂₆ have been established. Reactivity of the oxides and phase relations in the ternary V₂O₅-CuO-α-Sb₂O₄ system in air have been studied by using XRD and DTA methods. The results have showed the reaction of V₂O₅, CuO with α-Sb₂O₄ does not produce any compound where all the three oxides would be involved. It has been established that the α-Sb₂O₄ reacts and forms binary phases independently with CuO or V₂O₅. On the base of these results the investigated system was divided into subsidiary subsystem in which CuSb₂O₆ remains at equilibrium in the solid state with other phases formed in corresponding binary systems.     

Study of thermal properties of potassium μ-hydroxo-bis(oxo-diperoxovanadate)(V)

The thermal decomposition of K₃[OH{VO(O₂)₂}₂]·H₂O was studied under dynamic conditions up to 350°C and also isothermally at 150°±3°C in self-generated atmosphere. K₄[V₂O₆(O₂)] is formed as the reaction intermediate. The final products of thermal decomposition of K₃[OH{VO(O₂)₂}₂]·H₂O are KVO₃ and K₄V₂O₇.

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Zusammenfassung Unter dynamischen Bedingungen bis 350°C und isotherm bei 1503°C in selbsterzeugter Atmosphäre wurde die thermische Zersetzung von K₃[OH{VO(O₂)₂}₂]H₂O untersucht. Als Zwischenprodukt der Reaktion wird K₄[V₂O₆(O₂)] gebildet. Die Endzersetzungsprodukte von K₃[OH{VO(O₂)₂}₂]H₂O sind KVO₃ und K₄V₂O₇.

     

Cryoscopic studies on some Tungstates and Vanadates in Molten KNO3

The depression of the freezing point of molten KNO₃, as solvent, was measured after the addition of small concentrations of the solutes: 1. WO₃, K₂WO₄, K₂W₂O₇ and 2. V₂O₅, Cs₂V₆O₁₆ and Rb₂V₆O₁₆. DTA-apparatus was used in the measurements. The results showed that the investigated tungstates and vanadates were dissociated in the melt with the formation of monotungstate (WO₄)^2? and orthovanadate (VO₄)^3?-ions.     

Ion state of atoms and the properties of perovskite-like compound CaCu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

The binding energies and valence state of atoms in the perovskite-like compound CaCu₃V₄O₁₂ have been determined using XPS spectroscopy. The stoichiometry of this phase is formulated as Ca²⁺Cu²⁺Cu ₂ ⁺ (V ₂ ⁵⁺ V ₂ ⁴⁺ O₁₂). Under an air atmosphere, the phase interacts with water vapor and oxygen. As a result, Ca(OH)₂ is formed on its surface, the Cu⁺ and V⁴⁺ ion concentrations decrease, and the Cu²⁺ and V⁵⁺ concentrations increase in association. Raman spectra show shortened cation-anion bond lengths and cation-anion-cation bond angles in CaCu₃V₄O₁₂ compared to perovskite CuVO₃; the two structures are alike. The electrical conductivity, magnetic susceptibility, thermal and sensor properties of CaCu₃V₄O₁₂ in aqueous salt solutions have been studied.     

Preparation and studies of a new ammonium vanadium bronze, (NH4)xV2O5

A new bronze-type phase of composition (NH₄)_0.40±0.02V₂O₅ is obtained around 230°C during the thermal decomposition of NH₄VO₃ in hydrogen atmosphere. The bronze intermediate is characterized by X-ray diffraction, electrical conductivity, magnetic susceptibility, and ESR studies. It is found to be isostructural with other known β-type vanadium bronzes of general formula M_xV₂O₅, where M is usually a monovalent metal. Electrical conductivity and magnetic studies indicate the localized character of conduction electrons at V⁺⁴ sites. At high temperatures (>400°C), the bronze undergoes decomposition and subsequent reduction to V₂O₃ in hydrogen atmosphere.     

Effect of thermal transformations of constituent polyhedra of the crystal structure on the properties of Cd2V2O7

Analysis of variations in the linear and angular parameters of constituent polyhedra of the cadmium pyrovanadate Cd₂V₂O₇ structure, namely, VO₄ tetrahedra and CdO₆ octahedra, as calculated from the results of in situ high-temperature X-ray diffraction experiments in the range from 25 to 900°C, showed that, in the range from 600 to 720°C, the thermal expansion coefficient (tec) of CdO₆ polyhedra is near zero, whereas VO₄ tetrahedra increase in volume, although less strongly than in other temperature ranges. A structural interpretation is given to anomalous temperature dependences of cadmium ion emission and electrical conductivity on the basis of different thermal behavior patterns of the constituent polyhedra of the Cd₂V₂O₇ structure.     

Crystal growth,structural and electrical properties of rubidium and cesium vanadium oxide bronzes

Crystals of the following compounds were grown by cathodic reduction of CsV⁵⁺O or RbV⁵⁺O metls: Cs_0.3V₂O₅ (A), Cs₂V₅O₁₃ (B), CsV₂O₅ (C), Rb_0.4V₂O₅ (D), Rb_0.37V₂O_∼4.8 (E) (a new orthorhombic compound) and Rb_2−xV_3+2xO_8+2x (F). The crystal symmetry and cell parameters of the Rb compounds (which were known for F only) were determined, as well as those of Rb_0.3V₂O₅, which has the structure of A. Magnetic susceptibility and ESR measurements confirm the intermediate valence in E. A, C, and E are semiconductors with activation energies in the range 0.07–0.2 eV. Cs_0.3V₂O₅ (A), in which V⁴⁺ and V⁵⁺ do not occupy distinct crystallographic sites, has the highest electrical conductivity.     

Thermal decomposition of potassium carbonatooxoperoxovanadate(V)

The thermal decomposition of K₃[V(CO₃)O(O₂)₂] was studied under isothermal, dynamic and quasi-isobaric-isothermal condition. A mixture of K₄V₂O₇ and K₂CO₃ was identified as the primary product of thermal decomposition. Under experimental conditions not allowing a continuous loss of volatile products, the reaction of K₄V₂O₇ with CO₂ gives KVO₃ and K₂CO₃.

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Zusammenfassung Unter isothermen, dynamischen und quasi-isobaren Bedingungen wurde die thermische Zersetzung von K₃[V(CO₃)O(O₂)₂] untersucht. Als Primärprodukt der thermischen Zersetzungsreaktion wurde ein Gemisch aus K₄V₂O₇ und K₂CO₃ festgestellt. Wird unter experimentellen Bedingungen das Entweichen flüchtiger Produkte verhindert, so gibt die Reaktion von K₄V₂O₇ mit CO₂ die Produkte KVO₃ und K₂CO₃.