Increasing Vanadium Content Research Articles

Toward the Optimization of a Cr‐V Bimetallic Catalyst for Producing Bimodal Polyethylene: Effect of Vanadium Content and Calcination Temperature

AbstractThis work covers the synthesis of bimodal polyethylene with a SiO2‐supported vanadium‐oxide/silyl‐chromate (Cr‐V) bimetallic catalyst, which is prepared by using the residual hydroxyl groups on the VOx/SiO2 catalyst precursor to support chromium species. The effects of vanadium content and calcination temperature of the support on catalyst activity and polymer properties are investigated in detail. It is found that increasing vanadium content in the Cr‐V catalyst leads to the decline of catalyst activity, while the molecular weight of the resulting polyethylene is raised. On the other hand, the decline of catalytic activity at high vanadium content in the Cr‐V catalyst can be remedied by decreasing the calcination temperature of the support, and the molecular weight of the polymers is reduced at the same time. However, too low a calcination temperature is not beneficial for catalyst activity due to the poisoning effect of the excess hydroxyl groups on the active sites, and this would cause the increase of molecular weight as well.

Testing Baked Anodes with an Increased Vanadium Content

Results are given for testing baked anodes for aluminum electrolyzers prepared from high-sulfur petroleum coke. In anodes of these cokes, there is an increase in vanadium content to 600 ppm that contaminates aluminum. By boriding aluminum, the possibility is established of using high-sulfur petroleum coke with a high heavy-metal content in production. It is shown that introduction of micro-additions of boron into molten electrolyte and aluminum makes it possible to reduce the vanadium content in metal from 200–220 to 100–120 ppm. The production regime in test electrolyzers remained stable for the test period. An associated effect of boriding melts is a fixed reduction in voltage loss in the cathode by about 30 mV that corresponds to a reduction in electrical energy of about 1700 US$ per year per electrolyzer (with a price of 0.02 US$/kW·h).

Phosphomolybdovanadic acid catalyzed oxidation of 2,6-dimethylphenol into para-quinone in a biphasic system

In this paper, we disclose the results of our extended investigations on the reactivity of modified-type vanadium-containing heteropoly acids $${\text{H}}_{\text{a}} {\text{P}}_{\text{z}} {\text{Mo}}_{\text{y}} {\text{V}}_{{{\text{x}}^{\prime}}} {\text{O}}_{\text{b}}$$ (HPA-x′) towards the oxidation of 2,6-dimethylphenol (2,6-Me2P). This reaction is of great value as an effective way to the corresponding 2,6-dimethyl-1,4-benzoquinone (2,6-Me2BQ), practically avoiding the formation of diphenoquinone, which is interesting from the standpoint of its potential application as a sensitizer and ‘platform molecule’. The overall process is based on two reactions: the oxidation of 2,6-Me2P by $${\text{V}}^{\text{V}} {\text{O}}_{2}^{ + } \leftrightarrow {\text{V}}^{\text{V}} {\text{ - HPA}}$$ and the oxidation of reduced VIV-HPA ↔ VIVO2+ by dioxygen to the initial state. Special attention was given to the former process with regard to the influence of the reaction parameters on the product distribution. The desired quinone was efficiently synthesized in good yield (95%) at total substrate conversion, carrying out the oxidation in a biphasic water–trichloroethene system at 70 °C under nitrogen atmosphere in the presence of HPA-10′ solution (H17P3Mo16V10O89). The increase in vanadium content favored the selectivity of 2,6-Me2BQ due to faster electron transfer. The multicycle tests of catalyst showed its stability to V2O5·nH2O deposition.

Transformation from conducting ferromagnetic to insulating diamagnetic in vanadium doped ZnO nanoparticles

A simple cost effective approach of solution combustion method is chosen to prepare the vanadium doped ZnO nanoparticles. X-ray diffraction and Raman spectroscopy affirm the single phase formation of ZnO and evolution of secondary phase upon increasing vanadium concentration. Further lattice irregularity due to vanadium substitution is clearly manifested. Morphological aspects explored using SEM and TEM implies the alteration of hexagonal grain boundaries to spherical ones. A systematic study on the grain boundary reformation of the ZnO nanograins due to vanadium is undertaken using structural, morphological and spectroscopic characterizations. Electrical studies illustrate the individual contributions of grain and grain boundary towards the resistance of the material. Magnetization decreases with increasing vanadium concentration. Possible interplay between defect/doping and conductivity is proposed so as to explain the underlying mechanism of magnetic interactions.

Investigation on the oxidation behavior of AlCrVxN thin films by means of synchrotron radiation and influence on the high temperature friction

Abstract Friction minimization is an important topic which is pursued in research and industry. In addition to the use of lubricants, friction-reducing oxide phases can be utilized which occur during. These oxides are called Magneli phases and especially vanadium oxides exhibit good friction reducing properties. Thereby, the lubrication effect can be traced back to oxygen deficiencies. AlCrN thin films are being used as coatings for tools which have to withstand high temperatures. A further improvement of AlCrN thin films concerning their friction properties is possible by incorporation of vanadium. This study analyzes the temperature dependent oxidation behavior of magnetron sputtered AlCrVN thin films with different vanadium contents up to 13.5 at.-% by means of X-ray diffraction and X-ray absorption near-edge spectroscopy. Up to 400 °C the coatings show no oxidation. A higher temperature of 700 °C leads to an oxidation and formation of Magneli phases of the coatings with vanadium contents above 10.7 at.-%. Friction coefficients, measured by ball-on-disk test are correlated with the oxide formation in order to figure out the effect of vanadium oxides. At 700 °C a decrease of the friction coefficient with increasing vanadium content can be observed, due to the formation of VO 2 , V 2 O 3 and the Magneli phase V 4 O 7 .

The effect of Ar-ion irradiation on nanomechanical and structural properties of ODS RAF steels manufactured by using HIP technique

The influence of low energy ion irradiation on mechanical and structural properties of Oxide Dispersion Strengthened (ODS) Reduced Activation Ferritic (RAF) steels were investigated using Nanoindentation (NI), High Resolution Scanning Electron Microscopy (HR SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques. ODS samples were manufactured by means of High Isostatic Pressing (HIP) technique and irradiated at room temperature with 320 keV Ar2+ ions up to fluences reaching 1 × 1016 cm−2. The results revealed fast increase of nanohardness in the function of two dependencies: (i) vanadium addition and (ii) ion fluence range. Furthermore, along with increasing vanadium content, the increase in the number of ∼100 nm sized precipitates consisting of Cr-O-V and Cr-C-V with small amounts of alloying elements (Ti, Al, W) have been observed. Simultaneously, the presence of nano-precipitates, with average size below 10 nm has been recorded. Conducted research confirms that their number decreases with increasing V content. The reported hardening effect is most probably related to: (i) quantity and size of precipitates identified as chromium-vanadium oxides and carbides with addition of alloying elements and (ii) level of damage created by ion irradiation.

Investigation of the influence of the vanadium content on the high temperature tribo-mechanical properties of DC magnetron sputtered AlCrVN thin films

The forming of high-strength steels or new aluminum alloys leads to a steady increase of the load of tools and coatings. One approach is to positively influence the manufacturing process by using thin solid films with self-lubricating features, provided by oxides at high temperatures with low decohesion energies. For the purpose of this study, AlCrN provides the matrix, while vanadium oxides are used to enhance the frictional and wear properties. However, it is not yet clear which minimum amount of vanadium has to be incorporated in DC magnetron sputtered AlCrN coatings to improve the tribological behavior. Therefore, in this study, AlCrVN coatings are synthesized with an increasing vanadium content by means of reactive DC magnetron sputtering. Additionally, a vanadium-free AlCrN coating is used as reference for the tribo-mechanical investigations. The coatings were synthesized up to a vanadium content of 13.5at.-% and no phase change could be detected by means of x-ray diffraction. Moreover, no hexagonal AlN phase, which reduces the mechanical properties and the oxidation resistance, was formed. In contrast to the vanadium-free coating, the hardness of the coatings containing vanadium is slightly reduced. The coating with the smallest vanadium content shows the highest hardness of all analyzed coatings. A heat treatment at 400°C does not lead to any significant changes with respect to mechanical properties, but at 700°C hardness, modulus of elasticity and critical load decreased for all coatings, indicating a significant change in mechanical properties. The ball-on-disc test at room-temperature, 400°C, and 700°C shows the highest wear coefficient for the coating with the lowest vanadium content, due to the poor adhesion of the coating, although this coating shows the highest H/E-ratio.

Anatase to rutile phase transition promoted by vanadium substitution in TiO2: A structural, vibrational and optoelectronic study

Abstract The anatase to rutile phase transition of TiO 2 which normally occurs at 750 °C, is reduced to temperatures below 600 °C by vanadium doping. The structural transformation is observed by a systematic study in the temperature range from 450 °C to 750 °C. The introduction of vanadium in rutile lattice is found to have impact on lattice parameters and particle size. This substitution also helps to reduce the bandgap of rutile TiO 2 to 1.76 eV from 3.04 eV upon 6 at% of vanadium doping. Vanadium induces additional donor level in forbidden region. XANES study confirms that vanadium is in mixed valence state of V 4+ and V 5+ and concentration of V 4+ increases with increasing doping amount and in the band gap region donor level due to V 4+ takes deeper position than V 5+ . As a result, the effective band gap decreases with increasing vanadium concentration. Anharmonicity of vibrational modes systimatically increases which indicates increasing phonon-phonon interaction with increasing doping concentration.

V-containing ZrO2 inorganic yellow nano-pigments prepared by hydrothermal approach

Recent results on the preparation, characterization and color properties of the V-containing ZrO2 inorganic yellow nano-pigment are reported. A series of monoclinic V-ZrO2 solid solution nanocrystals (VxZr1-xO2, being x = 0, 0.1, 0.02, 0.03, 0.04, 0.05, 0.065, 0.08 and 0.1) were prepared straightforward by hydrothermal processing of mixtures of zirconyl nitrate and ammonium metavanadate in water. Interestingly, the crystalline precipitated obtained by hydrothermal processing at 140 °C for 3 d was almost entirely V-containing ZrO2 nanocrystals with the structure of monoclinic zirconia for the whole range of compositions. Lattice parameters changes along the series of prepared samples annealed at 700 °C indicated the increase of vanadium content inside the monoclinic vanadium-zirconia crystalline phase up to the nominal amount of vanadium of x = 0.05. Transmission and scanning electron micrographs of the hydrothermal precipitates showed the formation of defined sets of loosely assembled primary nanocrystals sized 3–4 nm in a disc-like larger motif sized in the range between 25 and 70 nm, depending on the nominal amount of vanadium dopant. Further annealing at 700 °C for 1 h gave rise to compact, discrete, morphologically well-defined secondary nanocrystals without size changes and with improved chromatic coordinates. The high stability in aqueous dispersion and the structural and microstructural characteristics of the prepared and annealed nanocrystals up to 1200 °C made them good candidates as nano-pigments for digital decoration.Finally, the advantages of the hydrothermal approach against other non-conventional methods for the preparation of V-ZrO2 nano-pigments, such as sol-gel and polyol, will be discussed.

Effect of heat treatment on the structure and hardness of high-entropy alloys CoCrFeNiMnV x (x = 0.25, 0.5, 0.75, 1)

High-entropy alloys CoCrFeNiMnVKharkov Institute of Physics and Technology, ul. Akademicheskaya 1, Kharkov 61108 (Kharkov Institute of Physics and Technology, ul. Akademicheskaya 1, Kharkov 61108 = 0.25, 0.5, 0.75, 1) were prepared by vacuum arc melting. The structure and microhardness of the alloys have been studied in the cast state and after annealing at temperatures of 700–1100°C. It has been found that the alloys consist of the fcc (γ) solid solution and intermetallic sigma (σ) phase. The volume fraction of the σ phase increases with increasing vanadium content. As a result of annealing, phase transformations occur, including the precipitation of σ particles from the γ phase and, vice versa, the precipitation of γ particles from the σ phase. It has been shown that the change in the volume fraction of the σ phase upon annealing occurs due to the changes in the total content of σ-forming elements, chromium and vanadium, in accordance with the lever rule. With increasing temperature, the volume fraction of the σ phase varies nonmonotonically; first, it increases, then it decreases. The microhardness of the alloys correlates well with the change in the volume fraction of the σ phase. The mechanisms of the phase transformations and quantitative relationships between chemical and phase compositions of the alloys and their hardness are discussed.

Hyperfine properties of La(V1−xFex)O3 compounds

LaV1−xFexO3 perovskites were synthesized in the vanadium-rich concentration range (i.e., x < 0.5) and characterized structurally and for the hyperfine properties of the iron nuclear probe. The aim of this investigation was to better understand the physical transformations that take place in the undoped compound (LaVO3) at low temperatures. For that, X-ray diffraction analysis and, more extensively, 57Fe Mossbauer spectroscopy were applied. The results revealed that the LaV1-xFexO3 vanadium-rich perovskites are orthorhombic at RT, and their lattice parameters decrease with increasing vanadium concentration. Lowering the temperature, the system becomes magnetic, with the iron moment freezing progressively. The presence of two magnetic subspectral components obtained at the lowest measurement temperatures suggests that the vanadium-rich samples, including LaVO3, undergo a phase transition from an orthorhombic to a monoclinic structure at low temperatures.

Effect of Vanadium Doping on Microstructure and Dielectric Behavior of CaCu&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;Ti&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;12&amp;lt;/sub&amp;gt; Ceramics

In this work, effect of vanadium doping of CaCu₃Ti₄O₁₂ (CCTO) on microstructure and complex dielectric constant over wide frequency (100 Hz-1 MHz) and temperature (0°C – 160°C) ranges has been studied. The vanadium doping of CCTO system results in an increase of grain size, the grains being surrounded by melted-like grain boundaries. Real parts of dielectric constant of all samples are similar at low frequency (<1 kHz). In doped samples, above 1 kHz, a relaxation appears which is evidenced by a drop of real part of permittivity and a peak of its imaginary part. This relaxation phenomenon is very significant at relatively low doping rates and then decreases again as vanadium content increases. AC conductivity behavior of vanadium-doped CCTO can be divided in three regions depending on conduction processes. The calculated activation energies were close to 0.46 eV.

Evaluation of additive formulations to inhibit precipitation of positive electrolyte in vanadium battery

A comprehensive study has been performed to develop blended additive formulations based on organic and inorganic compounds to prevent the precipitation of supersaturated V(V) species in the Vanadium Flow Battery at high temperatures around 50 °C. It was found that organic formulations are oxidized by the strong oxidizing effect of V(V) species and are hence ineffective. The inorganic additive formulation KS11 which consists of 1 wt% of K3PO4+ 1 wt% of SHMP appears to be very effective with a vanadium solution of composition 3.5 M V(V) in total sulphate/bisulphate concentration of 5.7 M up to a temperature of 40 °C. The phosphate ions (PO43−) released from K3PO4 and PO3− ions from SHMP (NaPO3)6 are believed to adsorb onto the nucleating ions, thus inhibiting the precipitation of scale forming species, or adsorption onto the growing crystals, deforming and/or inhibiting further formation of vanadium crystals. Although the electrochemical activity of 3.5 M V solutions was unaffected in the presence of the KS11, increasing vanadium concentration above 3.5 M and total sulphate/bisulphate concentration above 6 M is probably increasing the formation of electrochemically inactive complexes of vanadium-sulphate and polyvanadic species. This results in increased solution viscosity and subsequently reduces the electrochemical activity exponentially.

Effect of Variable Oxidation States of Vanadium on the Structural, Optical, and Dielectric Properties of B2O3-Li2O-ZnO-V2O5 Glasses.

In the present study, the effect of variable vanadium oxidation states on the structural, optical, and dielectric properties of vanadium oxide containing lithium borate glasses has been investigated. Electron paramagnetic resonance studies indicate that vanadium in these glasses is mostly in the V4+ state, having a tetragonal symmetry. As the glass composition of V2O5 increases, tetragonality also increases at the cost of octahedral symmetry. The photoluminescence (PL) spectra of these glasses are dominated by zinc oxide transition, whereas the peaks pertaining to the vanadyl group are not visible in the PL spectra. The optical absorption spectra show a single wide absorption band, which is attributed to V4+ ions in these glasses. The ac conductivity of the glasses increases with an increase in vanadium content. The highest electrical conductivity observed is ∼10-5 S cm-1 at 250 °C for the glass with 2.5 mol % V2O5. Electrical conductivity is dominated by electron conduction, as indicated by the activation energy calculation.

Effects of Cr and V additions on the microstructure and properties of high-vanadium wear-resistant alloy steel

The effects of chromium and vanadium additions on the microstructure, hardness and wear resistance of high-vanadium alloy steel (containing 5–10 wt-% V and 2–10 wt-% Cr) were studied by means of optical microscopy, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness and Rockwell-hardness tester & M-200 ring block wear tester. Researching results showed that the solidification structure of high-vanadium wear-resistant alloy steel was mainly consisted α-Fe (martensite), vanadium carbide (VC), M3C and M7C3. Vanadium is mainly distributed over VC, and certain amount of vanadium exists in the matrix and M7C3 type eutectic carbide. Chromium is mainly distributed over the M7C3, and the matrix also contains a small quantity of chromium. It is found that the content of VC increases with the increase of vanadium content when carbon and chromium contents are constant. The change of micro- and macro-hardness was not obvious with the increase of vanadium content. The content of M7C3 type eutectic carbides increases gradually with the increase of chromium content when carbon and vanadium contents are constant. The micro- and macro-hardness increases with the increase of chromium content. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The change of chromium content had no obvious effect on wear resistance of high-vanadium alloy steel when carbon and vanadium contents. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The wear resistance of as-cast high-vanadium alloy steel is the best when the content of vanadium and chromium is 10 wt-% and 5 wt-% respectively.

Optical and electrical studies of borosilicate glass containing vanadium and cobalt ions for smart windows applications

Borosilicate glass with different concentrations of vanadium and cobalt of the composition (mol%) 40 Na2B4O7- 40 SiO2- (20–x) V2O5- x Co2O3, with x=0, 1, 3 and 5mol% were prepared by melt quenching technique at 1373K and investigated by X-ray diffraction (XRD) and FTIR spectroscopy. Optical properties of the obtained borosilicate glasses in the UV–vis range were also investigated. Urbach theory has been used to analyze the optical data. The dc electrical conductivity was investigated for all samples in the temperature range from 298K to 700K. The ac electrical conductivity was measured in the frequency range from 50Hz to 2MHz from 298 to 523K. Guntini's theory has been used to analyze the electrical data. It was found that Urbach energy decreases with the increase of vanadium content, the sample with x=0 shows the highest absorption in the visible and IR region and an electrical conductivity in the order of 10−2Scm−1. The frequency exponent was calculated. A semiconducting behavior has been assessed for the studied glasses. The sample with x=0 has the highest IR absorption, the highest conductivity, at 323K at different frequencies, and the lowest activation energy; these features are promising for smart windows applications.

Ferromagnetic signature in vanadium doped ZnO thin films grown by pulsed laser deposition

Abstract

Effect of the vanadium concentration on structural and photoluminescence of YP1−xVxO4: 1 at. % Tb3+ nanophosphors

Simple sol-gel method was used to synthesize nanoscale yttrium phosphate-vanadates with general formula YP1−xVxO4: 1 at. % Tb3+ (x = 0–1.0). The nanopowder samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and room temperature steady and time resolved photoluminescence spectroscopy. The structural analysis reveals that the volume, the crystallite size of the nanophosphors increases with increasing vanadium content and their morphologies, changes from spherical, for low vanadium content, to rods for high content. Blue and green PL emissions of Tb3+and (VO4)3− were observed in YP1−xVxO4 and investigated in details. In addition, the role of Inter-Valence Charge transfer IVCT band in the quenching process of Tb3+ emission in YP1−xVxO4 is highlighted.

Features of the composition of vanadyl porphyrins in the crude extract of asphaltenes of heavy oil with high vanadium content

ABSTRACTFeatures of changes in the content of nickel and vanadium in heavy oils and their asphaltenes are shown for various fields of Volga-Ural region (Russia). The change in the content of vanadyl complexes in the studied asphaltenes upon increase of vanadium content was demonstrated. Several polar solvents (acetone, N,N-dimethylformamide, isopropanol, acetonitrile) are compared as extractants to obtain crude extracts of vanadyl porphyrins from asphaltenes with vanadium content of 0.44 wt%. The opportunity of more efficient extraction of vanadyl porphyrins from asphaltenes is shown by deposition extraction method, particularly when using N,N-dimethylformamide. Absorption spectra and matrix-assisted laser desorption/ionization (MALDI) mass spectra of the extracts obtained were analyzed. For extracts with maximum content of vanadyl porphyrins, the presence of mainly etio- and deoxophylloerythroetioporphyrins was revealed. It was shown that proportion of etio-type vanadyl porphyrins does not exceed 75% of the amount of porphyrins of DPEP-type. A maximum of molecular weight distribution in both types falls on a homologue of vanadyl porphyrin C31 containing nine carbon atoms in the alkyl substituents.

Effects of vanadium content on the microstructure and dry sand abrasive wear of a eutectic Cr-Fe-C hardfacing alloy

In this study, the effects of vanadium on the morphology and wear behavior of a eutectic Cr-Fe-C hardfacing alloy were discussed. The alloys tested contained different amounts of vanadium, ranging from 0 to 2.39 wt%. A fibrous V4C3 was found when the alloy contained 0.93 wt% vanadium. The addition of vanadium was found to decrease the fraction of eutectic M23C6 and increase the width of the interspaces between the eutectic cells. The DTA results revealed that V4C3 formed just before the eutectic α+M23C6 during solidification. The surface hardness was shown to increase with increasing vanadium content, which also caused the hardness deviation and wear loss to decrease; however, the addition of vanadium was not shown to affect the hardness of eutectic α+M23C6. The V4C3 could be scratched off during the wear test due to the increase in the width of the interspaces between the eutectic cells; therefore, the alloys that contained 0.93 and 2.39 wt% vanadium exhibited similar wear loss results.