Vanadium Molybdenum Research Articles

Estimation of oxide scale growth and temperature increase of high (9–12%) chromium martensitic steels of superheater tubes

The improved ferritic steels that have very good creep strength such as grades 91 and 92 have been widely used for power plant applications. For example, a chromium–molybdenum–vanadium steel tube (SA213-T91) has been available in the market for two decades. The SA213-T91 material has better high temperature strength and oxidation resistance than those of the more widely used materials such as T11 and T22. In this paper, estimations of the oxide scale growth and temperature increase of 9–12% Cr martensitic steels of superheater tubes are carried out using an incremental procedure, utilizing the finite element simulations and the relation between the Larson Miller Parameter (LMP) and the scale thickness over a period of time. In order to show the superiority of T91 steels over T22 steels, two different steam temperatures are considered in the models for comparisons. The estimations showed as expected that the oxide scale growth and temperature increase of the 9–12% Cr steels were significantly lower compared to those of 2.25% Cr steels.

Electrochemical behaviour and sulfur tolerance of V x Mo (1−x) O y as solid oxide fuel cell anode

Abstract Vanadium molybdenum oxide system (V x Mo (1− x ) O y for x ≤0.13) is synthesized through reducing acidified vanadate and molybdate solution at 60 °C by passing hydrogen sulfide gas through the solution. The electrochemical performance of the mixed oxide is tested at various operation temperatures as an anode material for intermediate temperature solid oxide fuel cell (IT-SOFC) under pure and 50 ppm H 2 S-containing hydrogen fuel. The highest cell performance of 0.18 W cm −2 peak power is reached at an operation temperature of 750 °C for dry H 2 . It is found that the addition of 50 ppm H 2 S to the anode gas causes a 22% decrease in the cell peak power. The loss in the cell performance is attributed to both gas conversion and diffusion. Short-term regeneration tests indicate that 1 h-exposure to sulfur-free gas is insufficient for the reactivation of the cell performance.

Hybrid Laminar Organic-Inorganic Semiconducting Nanocomposites

Hybrid two-dimensional nanocomposites of transition metal semiconductors based on molybdenum disulfide, zinc oxide, and vanadium pentoxide, in which ultra-thin sheets of the inorganic component are stabilized by insertion into a bilayer of organic amphiphiles, are described. The resulting solids are commensurate species with characteristic stoichiometries, extremely high aspect ratio, and large organic-inorganic interfaces. Synthesis procedures and changes in the properties of the nanocomposites with respect to those of their components, depend on the structural nature of the pristine semiconductor. Derivatives of the laminar semiconductor MoS2 are obtained by quasi-topotactic intercalation of amphiphiles into the layered inorganic matrix, being changes in the properties mainly associated to guest-host charge transfer without altering significantly the electronic structure of the sulfide. In the case of the structurally isotropic ZnO bottom-up sol-gel synthesis procedures, it is necessary to use amphiphiles as templates, producing the two dimensional confinement with significant changes in the band gap of the semiconductor. Vanadium oxide, because of bonding asymmetry, may be easily intercalated. However due to its low laying conduction band, this leads to mixed valence species. Beyond size and dimension induced bang-gap changes, the optical properties of the products, as appreciated in their absorption and emission spectra, are in general qualitatively similar to those of pristine semiconductors.

Liquation Cracks in Hot Upset Low Alloy Steel Screw Heads

Abstract A thermally upset screw head had numerous cracks at the intersection screw head / screw shaft. The screw consisted of steel that usually does not tend to hot crack. The screw failed when tightening it by applying a torque lower than the nominal torque. The screw head was simply sheared off. A hot crack has clearly been identified as damage-causing mechanism of the material, or, more precisely, liquation cracks. Other damage hypotheses such as liquid metal induced stress corrosion cracking have reliably been excluded in the course of examinations. The material used was 1.7711, 40CrMoV4–6, a material especially used for creep resistant fasteners such as screws and nuts for operating temperatures up to 540°C. This material belongs to the group of low alloy chromium molybdenum vanadium steels. It is typically used in the tempered condition. In Europe, it corresponds to standard EN 10269. In the USA, this steel is known as ASTM A193 GR B16.

Bis[tris(ethylenediamine-κ2N,N′)cobalt(III)] octakis-μ-3-oxido-hexadeca-μ2-oxido-tetradecaoxido-μ12-tetraoxosilicato-octamolybdenum(VI)hexavanadium(IV,V) hexahydrate

The title compound, [Co(C2H8N2)3]2[SiMo8V4O40(VO)2]·6H2O, was prepared under hydro­thermal conditions. The asymmetric unit consists of a transition metal complex [Co(en)3]3+ cation (en is ethyl­enediamine), one half of an [SiMo8V4O40(VO)2]6− heteropolyanion, two solvent water mol­ecules in general positions and two half-mol­ecules of water located on a mirror plane. In the complex cation, the Co3+ ion is in a distorted octa­hedral coordination environment formed by six N atoms of the three chelating en ligands. One of the en ligands exhibits disorder of its aliphatic chain over two sets of sites of equal occupancy. The [SiMo8V4O40(VO)2]6− heteropolyanion is a four-electron reduced bivanadyl-capped α-Keggin-type molybdenum–vanadium–oxide cluster. In the crystal, it is located on a mirror plane, which results in disorder of the central tetra­hedral SiO4 group: the O atoms of this group occupy two sets of sites related by a mirror plane. Furthermore, all of the eight μ2-oxide groups are also disordered over two sets of sites with equal occupancy. There are extensive inter­molecular N—H⋯O hydrogen bonds between the complex cations and inorganic polyoxidoanions, leading to a three-dimensional supra­molecular network.

Influence of mechanochemical activation on structure and some properties of mixed vanadium–molybdenum oxides

Mechanochemical activation of individual V2O5, MoO3 and mixed vanadium-molybdenum oxide system in various media (air, water, and ethanol) has been studied. Powder X-ray diffraction, nitrogen adsorption–desorption, thermogravimetric and chemical analysis, FTIR and Raman spectroscopy, and scanning electron microscopy have been used for research of prepared milled samples. The electrokinetic properties (dependence zeta potential—pH, position of isoelectric point) of individual V2O5, MoO3 and mixed vanadium–molybdenum oxide system, synthesized via mechanochemical treatment in various medium, in aqueous solutions of electrolytes also have been determined. Initial, milled, and spent samples are characterized with the help of XRD, FTIR and Raman spectroscopy, and SEM and adsorption of nitrogen. The catalytic properties of vanadium–molybdenum oxide composition activated in different media have been investigated in reaction of oxidation dehydrogenation of propane.

A weak mixed mobile ion effect in vanadium–tellurite oxide glass modified by silver and lithium cations

The effect of the partial replacement of lithium oxide by silver oxide in a glassy vanadium–molybdenum–tellurite oxides matrix is analyzed by means of impedance spectroscopy. We find that a weak mixed mobile ion effect (MMIE) is due to the different kind of modifications silver and lithium oxides induce in the glass of formula 0.7[ x Ag 2O (1 − x) Li 2O] 0.3[0.5 V 2O 5 0.5 MoO 3] 2 TeO 2.

Two dumbbell-like polyoxometalates constructed from capped molybdovanadate and transition metal complexes

Self assembly of NaVO 3, Na 2MoO 4·2H 2O and NiCl 2·6H 2O with the assistance of organic liginds under hydrothermal conditions results in two molybdovanadates [Ni(enMe) 2] 4{[Ni(enMe) 2(H 2O)] 2[Ni(enMe) 2][(V VMo VI 8V 4 IVO 40)(V IVO) 2] 2}·10H 2O ( 1) and [Ni(enMe) 2] 5{[Ni(enMe) 2] 2[(V VMo VI 4Mo V 4V 4 IVO 40)(V IVO) 4] 2}·2H 2O ( 2), (enMe = 1,2-diaminopropane), which have been characterized by single crystal X-ray diffraction analysis, IR spectroscopy, and elemental analysis. Both of the two compounds exhibit dumbbell-like structures constructed from capped polyoxomolybdovanadates and [Ni(enMe) 2] 2+ complexes. Polyoxoxanion 1 is composed of two bicapped Keggin-type anions [(V VMo 8V 4 IVO 40)(V IVO) 2] 7−, one [Ni(enMe) 2] 2+ bridging fragment and two decorated nickel(II) complexes. Polyxoxanion 2 consists of two tetracapped molybdenum–vanadium polyoxoanions [(V VMo VI 4Mo V 4V 4 IVO 40)(V IVO) 4] 7−, one [Ni(enMe) 2] 2+ bridging fragment and a nickel(II) decorated fragment. Polyxoxanions 1 and 2 are further linked to form three-dimensional supramolecular networks through extensive hydrogen bonding interactions. In addition, photocatalysis properties of these two compounds have been investigated.

A transition-metal-templated 3-D supramolecular framework based on molybdenum–vanadium polyoxoanions

A polyoxometalate [Co(phen)3][Co(en)3][Co(en)2(H2O)2][Co(en)2]0.5[O40(VIVO)2] · 6H2O (1) (en = ethylenediamine, phen = 1,10-phenanthroline) has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR, electron paramagnetic resonance, X-ray photoelectron spectroscopy, elemental analyses, and thermogravimetry. The structure is an interesting 3-D supramolecular network containing bi-capped Keggin-type molybdenum–vanadium clusters with transition metal complexes generated in situ under mild hydrothermal conditions. Compound 1 contains four different counteractions being coordinated complexes of cobalt. The magnetic properties of 1 have also been studied in the temperature range of 4–300 K, and its magnetic susceptibility obeys the Curie–Weiss law, showing ferromagnetic coupling.

10.1007/s11451-008-1009-0

It is demonstrated that 50% substitution of vanadium for molybdenum in the pyrochlore lattice of the complex oxide Y2(V x Mo1 − x )2O7 results in a transition from the spin-glass ground state (at x = 0) to the ferromagnetic state in Y2VMoO7 (a = 10.1645(2) Å, T C = 55 K). The Gd2V0.67Mo1.33O7 compound (a = 10.2862(3) Å) is a ferromagnet with T C (84 K) exceeding that of undoped Gd2MnO2O7.

Nanoscaled rutile active phase in Mo–V–Nb–O supported catalysts for the oxidation of propane to acrylic acid

Alumina-stabilized nanosized rutile Mo–V–Nb–O oxide phases are prepared, characterized and used for the selective oxidation of propane to acrylic acid. Coverage on alumina support, atomic Mo/V molar ratio and calcination conditions (inert vs. oxidizing) affect the structure and catalytic performance. The effect of Mo/V ratio is opposite depending on calcination atmosphere. Segregated molybdenum oxides are not efficient while partially reduced rutile-type mixed molybdenum–vanadium oxide phases are efficient for the conversion of propane to acrylic acid. Niobium species would have a structural effect, stabilizing mixed molybdenum–vanadium oxide phases.

Preparation, characterization and catalytic performance of Mo–V–O oxide layers linked by alkylamines

Thin layers of alkylamine-stabilized molybdenum vanadium complex oxide were prepared under hydrothermal condition; these materials exhibited 10-60 times higher catalytic activities than pure crystalline Mo-V-O oxide in the selective oxidation of alcohols.

Studies of nanostructures and conductivity in the system V xMo 1− xO y

Synthesis and characterization of the tailored nanostructured vanadium molybdenum oxide (V x Mo 1− x O y ) system is reported. TEM studies clearly show the formation of varying morphologies at vanadium and molybdenum rich ends. The effect of these differing morphologies on the surface area is presented. It is shown that compositions with x < 0.40 have electronic conductivity and a reduced contribution of ionic conductivity. Possible explanations for this observation are discussed. The VMO system shows promise for application as electrode materials in fields such as supercapacitors.

Two new polyoxometalate tri-supported transition metal complexes constructed from bi-capped Keggin molybdenum–vanadium clusters and copper complex fragments

Two new molybdenum–vanadium polyoxometalate tri-supported transition metal complexes [Cu(2,2 ′-bipy)] [Cu(2,2 ′-bipy) 2] 2[PMo 8V 6O 42]· nH 2O ( n = 1.5 ( 1) and n = 2 ( 2); 2,2 ′-bipy = 2,2 ′-bipyridine) have been hydrothermally synthesized and characterized by elemental analyses, IR, XPS and single-crystal X-ray diffraction analyses. Both compound 1 and compound 2 contain molybdenum–vanadium polyoxometalates, each of which support one [Cu(2,2 ′-bipy)] 2+ cation and two [Cu(2,2 ′-bipy) 2] 2+ cations, respectively. The difference between compound 1 and compound 2 is that the polyoxoanion of 1 is a bi-capped α-Keggin cluster and that of 2 is a bi-capped pseudo-Keggin one. Studies of magnetic properties indicated the presence of ferromagnetic behaviors for compounds 1 and 2.

Selective Oxidation of Alcohols by Orthorhombic Mo–V–O Phase with Molecular Oxygen

Abstract We have investigated heterogeneous oxidation of alcohols using crystalline molybdenum vanadium oxide (Mo–V–O) as catalyst with molecular oxygen as oxidant. The major product from primary alcohol was aldehyde, the secondary alcohol was mainly dehydrated to olefin, and the oxidation of cyclic alcohols chiefly afforded ketones. A Hammett plot suggested that hydride abstraction might be involved in the reaction step. We have discussed possible reaction mechanism based on substrate adsorption and activation on catalytically active sites.

Magnetic properties of the Gd2V0.67Mo1.33O7 and Y2VMoO7 pyrochlore compounds

It is demonstrated that 50% substitution of vanadium for molybdenum in the pyrochlore lattice of the complex oxide Y2(V x Mo1 − x )2O7 results in a transition from the spin-glass ground state (at x = 0) to the ferromagnetic state in Y2VMoO7 (a = 10.1645(2) A, T C = 55 K). The Gd2V0.67Mo1.33O7 compound (a = 10.2862(3) A) is a ferromagnet with T C (84 K) exceeding that of undoped Gd2MnO2O7.

Low‐Alkali Metal Content in β‐Vanadium Mixed Bronzes: The Crystal Structures of β‐Kx(V,Mo)6O15 (x = 0.23 and 0.32) by Single‐Crystal X‐Ray Diffraction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Magnetic ordering of V n/Mo(0 0 1) systems: Ab-initio calculations

A density-functional theory (DFT) study is performed using a full-potential linearized-augmented-plane-waves (FP-LAPW) method to investigate the magnetic structure of vanadium–molybdenum systems (V n /Mo(0 0 1), n = 1, 2). The topmost V layers relax inward in both systems with a larger contraction in V 2/Mo(0 0 1) system. A p(1 × 1) in-plane ferromagnetic ordering with appreciable magnetic moments is obtained on V overlayers, which is found to be the ground state in both systems. The layers below the surface exhibit induced magnetism with antiferromagnetic interlayer coupling.

Rotationally resolved spectra of jet-cooled VMo

The authors report the first gas-phase spectroscopic investigation of diatomic vanadium molybdenum (VMo). The molecules were produced by laser ablation of a VMo alloy disk and cooled in a helium supersonic expansion. The jet-cooled VMo molecules were studied using resonant two-photon ionization spectroscopy. The ground state has been demonstrated to be of (2)Delta(52) symmetry, deriving from the dsigma(2)dpi(4)ddelta(3)ssigma(2) electronic configuration. Rotational analysis has established the ground state bond length and rotational constant as r(0) (")=1.876 57(23) A and B(0) (")=0.142 861(35) cm(-1), respectively, for (51)V(98)Mo (1sigma error limits). Transitions to states with Omega(')=2.5, Omega(')=3.5, and Omega(')=1.5 have been recorded and rotationally analyzed. A band system originating at 15 091 cm(-1) has been found to exhibit a vibrational progression with omega(e) (')=752.7 cm(-1), omega(e) (')x(e) (')=12.8 cm(-1), and r(0) (')=1.90 A for (51)V(98)Mo. The measured bond lengths (r(0)) of V(2), VNb, Nb(2), Cr(2), CrMo, Mo(2), VCr, NbCr, and VMo have been used to derive multiple bonding radii for these elements of r(V)=0.8919 A, r(Nb)=1.0424 A, r(Cr)=0.8440 A, and r(Mo)=0.9725 A. These values reproduce the bond lengths of all nine diatomics to an accuracy of +/-0.012 A or better.

Potassium magnesium and potassium cobalt molybdates: Synthesis and ion conductivity

Potassium magnesium and potassium cobalt molybdates of composition K2M2II (MoO4)3 (M = Mg, Co) and the products of their heterovalent doping by scandium(III) and vanadium(V) ions have been studied by impedance spectroscopy, powder X-ray diffraction, and electron microscopy. The compounds have high ion conductivity. Partial heterovalent substitutions of scandium for magnesium or vanadium for molybdenum additionally increases ion conductivity. The high conductivity of potassium magnesium and potassium cobalt molybdates allows us to consider them as promising solid electrolytes with potassium conductivity.