Formation Of Vanadium Research Articles

V2O3/C composite fabricated by carboxylic acid-assisted sol\u2013gel synthesis as anode material for lithium-ion batteries

The potential battery electrode material V2O3/C has been prepared using a sol–gel thermolysis technique, employing vanadyl hydroxide as precursor and different organic acids as both chelating agents and carbon sources. Composition and morphology of resultant materials were characterized by X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopies, physical sorption, and elemental analysis. Stability and electronic properties of model composites with chemically and physically integrated carbon were studied by means of quantum-chemical calculations. All fabricated composites are hierarchically structured and consist of carbon-covered microparticles assembled of polyhedral V2O3 nanograins with intrusions of amorphous carbon at the grain boundaries. Such V2O3/C phase separation is thermodynamically favored while formation of vanadium (oxy)carbides or heavily doped V2O3 is highly unlikely. When used as anode for lithium-ion batteries, the nanocomposite V2O3/C fabricated with citric acid exhibits superior electrochemical performance with an excellent cycle stability and a specific charge capacity of 335 mAh g−1 in cycle 95 at 100 mA g−1. We also find that the used carbon source has only minor effects on the materials’ electrochemical performance.

Structure, chemical stability and electrical properties of BaCe0.9Y0.1O3\u2212\u03b4 modified with V2O5

Wet vacuum impregnation method was applied in order to evaluate the possibility of the formation of the material in BaCe0.9Y0.1O3−δ–V2O5 system. Single-phase BaCe0.9Y0.1O3−δ samples, synthesised by solid-state reaction method, were impregnated with the solution of vanadium(V) oxide precursor. Multi-step, multi-cycle impregnation procedure was applied to enhance the impregnation efficiency. Partial decomposition of Y-doped BaCeO3 in contact with the solution of the precursor, resulting in the formation of vanadium containing phases (CeVO4 and BaV2O6) on the materials surface, was observed. However, the presence of vanadium was also confirmed for the inner parts of the materials. The synthesised materials were submitted for exposition test to evaluate their chemical stability towards CO2/H2O. All BaCe0.9Y0.1O3-based materials modified by impregnation revealed higher chemical stability in comparison with single-phase un-modified BaCe0.9Y0.1O3−δ, since the amount of barium carbonate formed during the exposition was significantly lower. The total electrical conductivity of the received multi-phase materials was generally slightly lower than for the reference BaCe0.9Y0.1O3−δ sample, since the presence of the additional phases had a blocking effect on materials conductivity. The values of BaCeO3 lattice parameters and the Seebeck coefficient did not show the modification of the defects structure of Y-doped BaCeO3 during applied synthesis procedure.

Ultra-small V2O3 embedded N-doped porous carbon nanorods with superior cycle stability for sodium-ion capacitors

Abundant vanadium-based compounds with high theoretical capacity have attracted more attention for use as anodes in electrochemical energy storage. Herein, we report a two-step pyrolysis process on the formation of vanadium compound/N-doped porous carbon nanorods from a vanadium-based metal–organic framework. This process not only creates three different vanadium compounds (V8C7, V2O3 and VN), but also achieves the tunable N doping of carbon substrate. As anode materials for sodium storage, the optimized V2O3/N-doped porous carbon nanorods exhibit better long-term cycling performance (retention 74.4% after 3000 cycles at 1.0 A g−1) than others. The high cycle stability can be attributed to these superiorities in ultra-small V2O3, added N-doped porous carbon and the rich directional channels. Moreover, an asymmetric sodium-ion capacitor is assembled with a V2O3/N-doped porous carbon electrode and an activated carbon electrode, showing excellent cycling performance (retention 30.5 W h g−1 after 5000 cycles at 1.0 A g−1) and also enabling a high power density of 5805 W kg−1 with an energy density of 38.7 W h kg−1.

A concept of control of processes of vanadium, niobium and titanium carbonitrides forming by consecutive alloying

Base on laboratory and industrial experiments, as well as subsequent studies of the microstructure of steel samples alloyed with a certain sequence by vanadium, niobium, and titanium, a concept including compliance with the order of those microalloying elements introducing into steel developed and justified. According to the concept, the sequence of introduction is determined by the difference in the degree of their thermodynamic affinity to the nitrogen and carbon dissolved in the steel.Investigations of the microstructure of experimental microalloyed samples by an optical microscope, with a magnification x250, showed the most significant grain refinement with a consecutive additive – first vanadium with niobium and after 10 minutes of holding – titanium.The efficiency of the developed alloying method for the advanced formation of vanadium and niobium carbonitrides was evaluated by studies with the Mira3 Tescan electron scanning microscope having an X-ray energy dispersive microanalysis system X-Act (Oxford Instruments). When studying the compositions and the form of carbonitrides discovered in steel samples alloyed with a different sequence of additives, it was established, that during simultaneous additive of titanium, vanadium and niobium into steel, titanium carbonitrides account for a majority, while vanadium and niobium carbonitrides are not actually formed or are represented by single inclusions. Conversely, in steel samples alloyed with a consecutive additive to steel, first vanadium with niobium and later titanium, carbonitride of vanadium and niobium inclusions prevail. In this case, titanium carbonitrides are represented only by single and fine inclusions. Thus, first introducing of vanadium and niobium, allows them to react fully with stoichiometrically insufficient concentrations of nitrogen and carbon, ahead of the formation of titanium nitrides.Based on the results of the research in JSC “ArcelorMittal Temirtau”, using the developed concept of consecutive alloying by carbonitride-forming elements, the technology of 09G2FB grade steel production with a ferrite-bainite structure developed and implemented, fully meeting API Spec 5L requirements for steel of strength category X80.

Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

Effect of Al cocatalyst in ethylene polymerization using (imido)vanadium(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate moiety in 4-position (WCA-NHC), [V(N-2,6-Me2C6H3)Cl2(WCA-NHC)] [1; NHC=1,3-bis(2,6-dimethylphenyl)-imidazolin-2-ylidene], have been explored. The activities by 1 upon presence of AliBu3 in ethylene polymerization and in the copolymerization with norbornene (NBE) were higher than those in the presence of MAO, and the resultant poly(ethylene-co-NBE)s prepared by 1-AliBu3 catalyst possessed uniform molecular weight distributions and compositions. Formation of vanadium(III) species could be assumed upon presence of AliBu3, especially on the basis of both NMR and ESR spectra (silent) and certain significant changes in the V K-edge XANES (pre-edge and edge region) spectrum, whereas no significant changes in the XANES spectrum were observed from the toluene solution containing 1 upon addition of MAO. It is thus suggested that a difference in the catalyst performances between in the presence of MAO and AliBu3 should be due to a formation of different catalytically active species with different oxidation states.

Vanadium(IV/V) complexes of Triapine and related thiosemicarbazones: Synthesis, solution equilibrium and bioactivity

The stoichiometry and thermodynamic stability of vanadium(IV/V) complexes of Triapine and two related α(N)-heterocyclic thiosemicarbazones (TSCs) with potential antitumor activity have been determined by pH-potentiometry, EPR and 51V NMR spectroscopy in 30% (w/w) dimethyl sulfoxide/water solvent mixtures. In all cases, mono-ligand complexes in different protonation states were identified. Dimethylation of the terminal amino group resulted in the formation of vanadium(IV/V) complexes with considerably higher stability. Three of the most stable complexes were also synthesized in solid state and comprehensively characterized. The biological evaluation of the synthesized vanadium complexes in comparison to the metal-free ligands in different human cancer cell lines revealed only minimal influence of the metal ion. Thus, in addition the coordination ability of salicylaldehyde thiosemicarbazone (STSC) to vanadium(IV/V) ions was investigated. The exchange of the pyridine nitrogen of the α(N)-heterocyclic TSCs to a phenolate oxygen in STSC significantly increased the stability of the complexes in solution. Finally, this also resulted in increased cytotoxicity activity of a vanadium(V) complex of STSC compared to the metal-free ligand.

Solution studies of vanadium(IV), vanadium(V), and vanadium(IV,V) complexes with methionine in 3.0 mol L−1 KCl ionic medium at 25°C

A study of the H+–VO2+-methionine, H+––methionine, and H+––methionine (ligand, HL) systems by emf(H) measurements in 3.0 mol L−1 KCl ionic medium at 25°C is presented here. Data analysis using the LETAGROP program indicate formation of vanadium(IV) species [HVOL]2+, [VOL]+, and [H2VOL2]2+; vanadium(V) species [HVO2L]+ and VO2L; and the mix-valence vanadium(IV,V) species [H2V2O3L]4+, [V2O3L]2+, [OHV2O3L]+, (OH)2V2O3L, (OH)3V2O3L, [HV2O3L2]2+, [V2O3L2]+, and OHV2O3L2, whose stability constants βpqrs were determined according to the general reaction p H+ + q VO2+ + r + s L− . Selected structural parameters of some complexes formed in solution were determined using ab initio methods.

Structure of improved tribological properties of V–5at.%Ti alloys by nitrogen implantation at low energy

The aim of the present work was to study the morphological, structural, and chemical analysis as a function of depth in vanadium alloys with a 5 at.% of titanium implanted at 673 K with 1.2 keV N+ ions, by transmission electron microscopy (TEM), glow discharge (GD) analysis, and x-ray photoemission spectroscopy. These results are correlated with those of previously published nanoindentation tests, and the species and chemical states responsible for the increase in hardness are identified. The maximum increase in hardness corresponds to the highest N concentration, measured by both photoemission spectroscopy and GD. In addition, the thickness of the layer (≈1000 nm), where structural modifications are observed using TEM, can also be directly correlated with the thickness of the implanted layer, where an incremental increase in hardness has previously been measured. These findings support the conclusion that the formation of vanadium and titanium nitride/oxynitrides (–N–O,–O–N–H) compounds are responsible for the increased hardness of these V–5at.% Ti samples implanted with N at low ion energy and high sample temperature.

Structural and Spectroscopic Evidence for the Formation of Trinuclear and Tetranuclear Vanadium(III)/Carboxylate Complexes of Acetate and Related Derivatives in Aqueous Solution

The formation of vanadium(III) complexes with nuclearity greater than two is believed to occur in aqueous solution on the basis of potentiometric, electrochemical, and/or UV-vis spectroscopy titration measurements, although structural evidence for this is limited. Upon the addition of 1-2 equiv of acetate, propionate, chloroacetate, trifluoroacetate, or bromoacetate to an aqueous, acidic solution of vanadium(III), trinuclear and tetranuclear complexes are formed. The structures of [V4(mu-OH)4(mu-OOCCF3)4(OH2)8]Cl4.7.5H2O (1), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.CH3COOH.12H2O (2), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.3H2O (3), [V3(mu3-O)(mu-OOCCH2Br)6(OH2)3]CF3SO3.H2O (4), [V3(mu3-O)(mu-OOCCH2CH3)6(OH2)3]Cl.2H2O (5), [V3(mu3-O)(mu-OOCCH3)6(OH2)3]Cl.3.5H2O (6), and [V3(mu3-O)(mu-OOCCH2Cl)6(OH2)3]CF3SO3.H2O (7) have been determined by X-ray diffraction. Importantly, electrospray mass spectrometry and 1H NMR measurements suggest that these complexes are not purely solid-state phenomena but are also present in solution. For the vanadium(III)/acetate and vanadium(III)/propionate systems, two paramagnetic 1H NMR signals corresponding to two distinct complexes (species A and B) are observed in the 40-55 ppm region for 0.20 mol equiv of acetate or propionate, at pD 3.44. No corresponding signals are observed for the vanadium(III)/bromoacetate and vanadium(III)/chloroacetate systems under the same conditions or for the vanadium(III)/ trifluoroacetate system using 19F NMR spectroscopy. UV-vis spectra suggest that species B are structurally analogous for the vanadium(III)/acetate and vanadium(III)/propionate systems, whereas structurally different complexes are the major species for the other systems. Diffusion coefficients of species B for the vanadium(III)/acetate and vanadium(III)/propionate systems determined by pulsed-field-gradient spin-echo NMR spectroscopy measurements are (3.0 +/- 0.1) x 10-6 and (3.23 +/- 0.01) x 10-6 cm2 s-1, respectively, and are most consistent with species B being trimeric, rather than tetranuclear, complexes.

Vanadium staining in fired clay bricks

Abstract This paper reports on a series of efflorescence tests and instrumental techniques that have been used to determine the nature and mechanism of vanadium staining, and the effects of additions of magnesite, calcite, and fluorspar to the brick mix to eliminate the problem. Scanning electron microscopy, electron probe microanalysis, inductively coupled mass spectrometry (with laser ablation attachment), and X-ray photon spectrometry have been used to more fully understand the elemental composition, oxidation states, and formation of vanadium stains in fired clay bricks. It was found that the stains consist of V, K, Na, Mo, S, and O. Vanadium +4 compounds form initially within the brick and are slowly oxidised to vanadium +5 compounds as the water transports the potassium and sodium salts to the brick surface. X-ray diffraction led to a reasonably successful search match for a KVO(SO4)2 phase for the stains. Evolved gas analysis showed loss of vanadium compounds between 700 and 900° C which are most l...

Oxidation of Two ?-Hydroxy Acids by Vanadium(V)

The pathways for the oxidation of tartaric acid and citric acid by vanadium(V) in perchloric acid medium have been studied at 303 K by following the formation of vanadium(IV) spectrophotometrically at 760 nm. The oxidation reaction displays fractional order dependence with respect to both the α-hydroxy acids concentrations as well as fractional (tartaric acid) and first order (citric acid) dependencies with respect to the perchloric acid concentration. It does not matter at all whether the ionic strength was varied or was maintained constant. The reaction rate remains essentially constant with increasing ionic strength in the tartaric acid oxidation, but decreases slightly in the citric acid case. A decrease of the dielectric constant of the reaction medium results in a rate decrease in the tartaric acid oxidation and in a rate enhancement in the citric acid reaction. The activation parameters were obtained from studies of the reactions at different temperatures (293 to 313 K). Based on the experimentally determined rate laws oxidation mechanisms and theoretical rate laws were proposed.

Reduction of vanadium(v) by oxalic acid in aqueous acid solutions

The reduction of vanadium(V) to vanadium(IV) by oxalate in acidic media proceeds at 50 °C via two parallel pathways that involve activated states of compositions {VO2+; 2H+; 2C2O42−}≠ and {VO2+; 2H+; 3C2O42−}≠, resulting in an apparent change in the partial order on oxalate as its concentration increases and a maximum in the rate/pH profiles. The best explanation for these results assumes outer sphere electron transfer as the rate determining step in both pathways, without formation of vanadium(III). The implications for the bioinorganic chemistry of vanadium are discussed.

Thermal decomposition of oxovanadium(IV) complexes with N, N′-ethylenebis(amino acids)

Six oxovanadium(IV) complexes with N, N′-ethylenebis(amino acid) of general formula, [VO(XeX)(H 2O)]· nH 2O, where e and X represent ethylene group and ( S)-α-amino acid, respectively; and X=G (Gly) 1, ( S)-A (Ala) 2, ( S)-V (Val) 3·2H 2O, ( S)-P (Pro) 4, mG or G m (Sar or N-methylglycine) 5·H 2O and ( S)-M (Met) 6) were prepared. These complexes were characterized by means of TG, DTA, and XRD, and the thermal decomposition processes of these complexes up to 650°C were investigated. The thermal studies showed that the dehydration processes for 3 and 5 having water of crystallization were endothermic, whereas decompositions of all the complexes were exothermic. Calcinations of these complexes at 650°C resulted in the formation of vanadium(V) oxide V 2O 5. Choosing 1 as a leading example of the oxovanadium(IV) complexes, an over all reaction scheme for the thermal decomposition was proposed on the basis of IR and MS analyses of both the solid and the volatile decomposition products at different temperatures.

In-situ spectroscopic studies and modelling of crystallization processes of sulphuric acid catalysts

Deactivation processes of commercial and prototype sulphuric acid catalysts have been investigated in-situ both in highly converted and unconverted feed gases, using electron paramagnetic resonance (EPR) spectroscopy. The investigation revealed that the deactivation of catalysts for SO 2 oxidation is strongly dependent on physical and chemical parameters such as the pore structure of the support, the type of the alkali promoter as well as the SO 2 and SO 3 partial pressures. A hysteresis effect in catalytic activity could be observed during reheating of the deactivated catalysts. In this context indirect evidence was found of deactivation by the formation of vanadium(III) compounds. The various vanadium compounds in the oxidation state (IV) and with mixed valence (IV–V), formed during deactivation, have been characterized by EPR. The investigations showed no change in the vanadium oxidation state in the catalytic cycle under steady-state conditions, and at high SO 2 partial pressure even at low temperatures, indicating that the so-called ‘associative mechanism’ probably dominates in the catalytic SO 2 oxidation. A statistical lattice model was applied to describe the crystallization of binuclear complexes in the melt of sulphuric acid catalysts during deactivation while taking into account parameters such as temperature, the composition of the catalyst and SO 2 conversion.

Vanadium silicate xerogels in hydrogen peroxide catalyzed oxidations

Vanadium silicate xerogels (V 2O 5 SiO 2) were prepared by the sol-gel method by hydrolysis of vanadium and silicon alkoxides. The use of these xerogels as catalysts for oxidation of alkenes, alcohols and phenol was studied using 30% aqueous hydrogen peroxide as oxidant. It was found that the manner of xerogel preparation strongly influenced the catalytic activity of V 2O 5 SiO 2. Alcohols were the preferred solvents for the reaction and did not leach vanadium oxide into solution. For alkenes, epoxidation was the dominant oxidation reaction the yield and selectivity depending on the nucleophilicity and oxidizability of the substrate. For alkenes of intermediate nucleophilicity allylic oxidation was significant. Secondary alcohols were oxidized in low to fair yields whereas primary alcohols were inert. Phenol was oxidized selectively to a 2:1 mixture of hydroquinone/catechol. UV-vis and electron spin resonance spectra of V 2O 5 SiO 2 treated with hydrogen peroxide conclusively showed formation of vanadium-peroxo species with polarization of the O O bond as seen by formation of vanadium (IV) electron spin resonance spectra leading to oxidation by both heterolytic and homolytic cleavage.

Kinetics of iodine-catalyzed reduction of vanadium(V) by arsenic(III)

The kinetics of the iodine-catalysed reaction of vanadium(V) with arsenious acid in dilute H2SO4, leading to the formation of vanadium(IV) and arsenic acid, have been investigated spectrophotometrically. Plausible pathways consistent with the experimental rate law are discussed. An iodine bridged activated complex between reactant and substrate species is proposed to explain the electron mobility from arsenic to vanadium by ‘resonance transfer’. Applying other criteria, the heterolytic dissociation of the vanadium-iodine bond of the activated complex is considered rate-controlling.

Complex of vanadium(5+) with the dioxygen radical-anion in the catalyzed disproportionation of hydrogen peroxide

The intermediate formation of vanadium(5+) peroxo complexes was detected under conditions of the disproportionation of hydrogen peroxide in acetic acid catalyzed by ammonium metavanadate by51V NMR spectroscopy and the complex of vanadium(5+) ions with the dioxygen radical-anion was detected by ESR spectroscopy.

Chelates of vanadium(V) with organic hydroxy compounds in aqueous solutions

The formation of vanadium(V) complexes has been examined potentiometrically by the method of acidimetric titrations of aqueous solutions at pH 7-5. The composition has been determined and the formation constants have been calculated for the oxalate chelates VO2Ox23- and VO2Ox . (OH)2-, the maltol chelate VO2A2-, the ternary complex VO2OxA2-, and for binuclear and tetranuclear complexes with tartarate, glycolate, sorbitol, and mannitol. The structure of the complexes is discussed in terms of the consumption of protons for their formation.

Coordination rearrangement controlled electron transfer. 5. Formation of vanadium(III)-titanium(IV) and titanium(III)-titanium(IV) binuclear complexes in the cross reaction of titanium(hedta) and VO(hedta)-

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCoordination rearrangement controlled electron transfer. 5. Formation of vanadium(III)-titanium(IV) and titanium(III)-titanium(IV) binuclear complexes in the cross reaction of titanium(hedta) and VO(hedta)-Frank J. Kristine and Rex E. ShepherdCite this: Inorg. Chem. 1981, 20, 1, 215–222Publication Date (Print):January 1, 1981Publication History Published online1 May 2002Published inissue 1 January 1981https://doi.org/10.1021/ic50215a044RIGHTS & PERMISSIONSArticle Views77Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (964 KB) Get e-Alerts Get e-Alerts

On the borothermic preparation of some vanadium, niobium and tantalum borides

The formation of vanadium, niobium and tantalum diborides by the reactions of V 2O 3, Nb 2O 5 and Ta 2O 5 with elemental boron under vacuum in the temperature range 1000 °–1750 °C has been investigated. It has been established that niobium and tantalum diborides with a composition close to that of stoichiometric NbB 2 and TaB 2 are obtained after a heat treatment of the reactants at 1650 °C for 1 h. Borothermic reduction of V 2O 3 does not give a single-phase product but a mixture of VB 2 and VB. A method for the chemical analysis of NbB 2 − and TaB 2 samples has been proposed.