Solid Solution Of Vanadium Research Articles

Coating Reactions on Vanadium and V-Si-B Alloys during Powder Pack-Cementation.

Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materials for high temperature applications. Presently, the main attention is focused on three-phase alloy compositions that consist of a vanadium solid solution phase and the two intermetallic phases V3Si and V5SiB2. Similar to other refractory metal alloys, a major drawback is the poor oxidation resistance. In this study, initial pack-cementation experiments were performed on commercially available pure vanadium and a three-phase alloy V-9Si-5B to achieve an oxidation protection for this new type of high temperature material. This advance in oxidation resistance now enables the attractive mechanical properties of V-Si-B alloys to be used for high temperature structural applications.

Influence of Nb, Ti and Mo on Microstructure and Mechanical Properties of Vanadium Solid Solutions

The present study addresses the microstructural evolution and mechanical properties of three different cast V-5X (X = Nb, Ti and Mo) alloys. All alloy compositions are located in the vanadium solid solution (VSS) phase field in their respective phase diagrams. While the alloys V-5Ti and V-5Nb solidified as single-phase VSS after arc-melting, the alloy V-5Mo additionally shows some amount of molybdenum solid solution (MoSS) in the resulting as-cast microstructure. To improve the mechanical database on vanadium-based alloys, room temperature compression tests were performed and microhardness measurements were carried out by the Vickers indentation method. The lattice parameters were determined by X-ray diffraction analysis and they were calculated using the density functional theory. By carrying out these experiments, the data available for vanadium-based alloys were extended being now available for further optimization of novel V-Si-B high temperature alloys.

Experimental Study of Phase Composition of B‐Fe‐Mn‐V Alloys and Thermodynamic Calculations of Phase Equilibria in the B‐Mn‐V and B‐Fe‐Mn‐V Systems

Phase compositions of B‐Fe‐Mn‐V alloys were studied by several experimental methods (DTA measurement, X‐ray diffractions, and scanning electron microscopy). Besides the experimental study of the quaternary system, thermodynamic modelling of the ternary B‐Mn‐V system by the Calphad method and thermodynamic calculations for the quaternary B‐Fe‐Mn‐V system were performed. Calculations for the quaternary system are based on the ternary subsystems (B‐Mn‐V, B‐Fe‐V, B‐Fe‐Mn, and Fe‐Mn‐V). Boron is modelled as an interstitial element in all solid solutions of vanadium, manganese, and iron. Very good agreement between experimental results and thermodynamic calculations was achieved. The created thermodynamic database is suitable for thermodynamic calculations of phase diagrams for all the ternary subsystems and also for the B‐Fe‐Mn‐V quaternary system.

Process-Oriented Microstructure Evolution of Vss-V3Si-V5SiB2 Materials

Abstract Vanadium silicide alloys are potentially interesting high temperature materials, since they combine high mechanical strength at temperatures of up to 1 000 °C with a low density. In this study, the microstructures of innovative V-Si-B high temperature materials are examined using different analytical methods. The selected V-9Si-13B model alloy was manufactured using a powder metallurgical process route as well as an ingot metallurgical process. The alloys show a vanadium solid solution phase as well as the high-strength silicide phases V3Si and V5SiB2. Especially for the powder metallurgically fabricated alloy, showing finely dispersed phases, the quantification of microstructural constituents is difficult. The phases, however, can be separated from one another via computer tomography.

FORMATION OF CARBIDE TYPE COATING IN THE PROCESS OF MICROARC STEEL VANADATION

The high-energy impact on the material surface is used for the intensifi cation of surface diff usion saturation of steel. The article describes the process of microarc thermochemical treatment in which a steel product was immersed in a container fi lled with coal powder, and was heated by passing electric current. Microdischarges are formed in a powder environment. They are concentrated around the product and create a region of gas discharge. This leads to surface heating of the product and the surrounding powder environment. The pyrolysis of coal in a container formed a carbon-containing environment, which enables to carry out carburizing of steel. In addition, there is a possi bility of formation of carbide type surface due to the simultaneous diff usion of carbon and alloying element. Its source is a conductive coating containing the powder of diff usant. The authors have investigated the possibility of forming the coatings of carbide type by diff usion saturation of low carbon steel with vanadium. The cylindrical samples of steel 20 with a diameter of 12 mm and length 35 mm were used. The powder of low carbon ferrovanadium was used as the source of diff usant. The current density on the surface of the samples was 0.53 A/cm 2 , the temperature was increased from ambient to 1250 °С. To study the structure and phase composition of the diff usion layer optical microscopy, scanning electron microscope with energy dispersive microanalysis system, X-ray phase analysis, atomic force microscopy, microhardness analysis were used. After treatment for 3 min it was detected the formation of the diff usion layer with thickness of 170 – 180 μm. The basis of the diff usion layer is a solid solution of vanadium in α-iron with a vanadium concentration of 3 – 4 wt. % and the ratio of the number of atoms in the unit cell is 9:1, corresponding to α-Fe9 V with microhardness of 8.0 – 9.0 GPa. The layer base comprises the multiple nanoscale carbide inclusions, as well as carbides of the VC 0.863 type with the size up to 10 microns with vanadium concentration about 64 wt. % and microhardness of 21.65 – 25.75 GPa, undergoing the atomic ordering with the formation of the cubic V 8 C 7 superstructure.

Hydride phase equilibria in V–Ti–Ni alloy membranes

Vanadium is highly permeable to hydrogen which makes it one of the leading alternatives to Pd alloys for hydrogen-selective alloy membrane applications, but it is prone to brittle failure through excessive hydrogen absorption and transitions between the BCC α and BCT β phases. V–Ti–Ni alloys are a prospective class of alloy for hydrogen-selective membrane applications, comprising a highly-permeable vanadium solid solution and several interdendritic Ni–Ti compounds. These Ni–Ti compounds are thought to stabilise the alloy against brittle failure. This hypothesis was investigated through a systematic study of V70Ti15Ni15 by hydrogen absorption and X-ray diffraction under conditions relevant to membrane operation. Dissolved hydrogen concentration in the bulk alloy and component phases, phase identification, thermal and hydrogen-induced expansion, phase quantification and hydride phase transitions under a range of pressures and temperatures have been determined. The vanadium phase passes through three different phase fields (BCC, BCC+BCT, BCT+BCT) during cooling under H2 from 400 to 30°C. Dissolution of Ni and Ti into the vanadium phase increases the critical temperature for β-hydride formation from <200 to>400°C. Furthermore, the Ni–Ti phases also exhibit several phase transitions meaning their ability to stabilise the alloy is questionable. We conclude that this alloy is significantly inferior to V with respect to its stability when used as a hydrogen-selective membrane, but the hydride phase transitions suggest potential application for high-temperature hydrogen and thermal energy storage.

The effect of Ti on hydrogen absorption and diffusivity in V–Ti–Al alloy membranes

The ongoing development of H2-selective alloy membranes is gradually increasing the competitiveness of membrane-based H2/CO2 separation against established H2/CO2 separation technologies. Continued advances in terms of their flux, cost and durability, however, will be required before they are widely adopted. Palladium-based alloy membranes have appeared on the market in recent years in the form of thin, supported, alloy films which minimise the Pd consumption (and therefore, cost). Vanadium-based alloys are an emerging alternative to these Pd membranes, and while they potentially offer high H2 flux at much lower cost, they lag behind Pd-based alloy membranes in terms of robustness. The challenge remains to improve the mechanical stability of vanadium (primarily by reducing hydrogen absorption) while minimising the associated permeability penalty. A number of prospective alloying elements have been identified, including Ni, Al, Cr and Ti. This work has shown that substitution of V by Ti increases hydrogen absorption and decreases hydrogen diffusivity, with the overall effect being a negligible change in permeability, but greater hydrogen absorption brings the penalty of poorer mechanical properties. As this is the opposite of the preferred case (i.e., reduced absorption and higher diffusivity), Ti is therefore an unfavourable addition to the base V90Al10 alloy. These findings are in contrast to previous work on V–Ti–Ni alloys, in which the segregation of V, Ti and Ni between multiple phases had the overall effect of increasing hydrogen diffusivity relative to the base V90Ni10 alloy. Whereas the true role of Ti was masked in the V–Ti–Ni system, the single-phase V–Ti–Al system examined here provides a clear illustration of the negative impact of Ti on vanadium solid solution alloy membranes.

The effect of Ti on the microstructure, hydrogen absorption and diffusivity of V–Ni alloy membranes

Vanadium is highly permeable to hydrogen which makes it one of the leading alternatives to Pd alloys for hydrogen-selective alloy membrane applications. The tendency of vanadium to embrittle can be reduced through alloying, thereby enabling V-based membranes to be developed for specific operating regimes. Foremost amongst these alloying additives are Ni and Ti. Ni is known to form V–Ni solid solutions with decreased hydrogen absorption and diffusivity compared to V. The influence of Ti is more complex due to phase segregation, and this work focuses the influence of Ti on the microstructural and chemical properties of hydrogenated vanadium–nickel solid solution alloys. Alloy membranes of the compositions V90−xTixNi10 (where 2≤x≤10) were prepared by the sectioning arc-melted ingots and the deposition of a Pd dissociation/recombination catalyst at each surface. Hydrogen permeation measurements were undertaken using the constant pressure method, with feed pressures ranging from 1 to 10 bar, permeate pressures <0.05 bar via use of a sweep gas, and temperatures of 350 and 400 °C. Hydrogen absorption of these same alloys was measured under corresponding conditions using the Sieverts' method. The microstructures featured a dendritic (branched) body-centred cubic vanadium solid solution matrix with interdendritic Ni–Ti compounds. The Ti content in the matrix increased, while the Ni content decreased, with increasing bulk Ti content. Hydrogen diffusivity increased with increasing bulk Ti content and increasing dissolved hydrogen concentration. The Ni–Ti compounds, known for being weakly hydrogen absorbing, also scavenge oxygen from the vanadium matrix, both of which are important in enhancing the embrittlement resistance of these alloys. This work has shown that Ti is a favourable additive for vanadium–nickel alloy membranes when added in the amount of ∼10 at%, with a hydrogen diffusivity (DH) equal to 4.2×10−8 m2 s−1 and hydrogen permeability of 1.2×10−7 mol−1 s−1 Pa−0.5 corresponding to a feed pressure of 10 bar and temperature of 400 °C.

Low‐Temperature Preparation and Magnetic Properties of V‐Doped SnO2 Nanoparticles

A solid solution of vanadium (V)‐doped tin oxide (SnO2) particles of average diameter 2 nm and V content of 19 at.% was prepared at normal pressure and low temperature (100°C) by mixing wet SnO2 gel SnO2·xH2O with a boiling solution of vanadium oxide (V2O5). Experimental characterizations using X‐ray, electron diffraction, and transmission electron microscope show evidence of a pure single phase. The nanoparticles exhibit a mixed magnetic behavior, namely paramagnetic and ferromagnetic. Their thermal stability is also investigated. At higher temperature, 850°C, some amount of Fe precipitates from the solid solution.

Microstructures and Mechanical Properties of in-situ V-V3B2 Composites

AbstractA series of binary V-B alloys, with compositions spanning the eutectic, were produced by arc melting and drop casting. Microstructural examination revealed that the fully eutectic structure occurs at V-11B rather than V-15B as reported in the V-B phase diagram (all compositions in at.%). The V-11B eutectic was directionally solidified in an optical floating zone furnace, resulting in a composite microstructure consisting of a V matrix and flake or trigonal shaped V3B2 phase. The boride flake spacing (ë) decreases with increasing growth rate (R), following the relation ë2.56R=C, where C is a constant. TEM observations showed that the orientation relationship between the V and V3B2 phases is given by: [001]V // [001]V3B2 and (100)V // (100)V3B2. The growth direction and the V/V3B2 interface are parallel to the [001] direction and (100) planes in the two phases, respectively. Tensile tests were used to investigate the temperature dependence of the strength and ductility of the composite. At temperatures to 600°C, the yield strength of the eutectic is about 140 MPa higher than that of a commonly used vanadium solid-solution alloy, V-4Cr-4Ti. Surprisingly, the eutectic shows 5% tensile ductility at room temperature which increases to 10% as the test temperature is raised to 800°C.

Search for new materials in sputtered V 1− xC x films

In this work, the vanadium–carbon system has been explored in a wide range of atomic carbon content x (0.01< x<0.69) with the aim of obtaining films of new materials. V 1− x C x films were prepared by reactive dc diode magnetron sputtering and Electron Probe Micro-Analysis (EPMA) was used to determine their composition. The structures of as-sputtered films were identified by X-ray and Transmission Electron Microscopy (TEM). It is shown that they strongly depend on the carbon content x and several interesting facts can be underlined. If most of the films are crystalline and contain phases related to the phase diagram, a glass forming ability (GFA), located around x=0.32, permits to obtain a mainly amorphous film. This value is in the carbon content range of the hemicarbide V 2C. Below x=0.32, films are composed of the bcc vanadium solid solution which can be considerably extended (up to 0.17) inducing a lattice parameter expansion. Above x=0.32, films are first wholly made up of the substoichiometric VC monocarbide and then contain additional amorphous carbon. For x=0.32, TEM images and associated diffraction patterns suggest a nanocomposite material with numerous little crystals of carbide embedded in an amorphous matrix. A special attention has been devoted to this composition and a crystallization study has been undertaken. All these results show the capability of the binary V–C system combined with a sputtering process to generate promising films and coatings.

Electrorefining of carbonitrothermic vanadium in a fused salt electrolytic bath

Electrorefining of impure vanadium was carried out in a fused LiCl–KCl–VCl2 bath. The impure vanadium, a solid solution of vanadium, nitrogen, carbon and oxygen (V,N,C,O), was prepared by carbonitrothermic reduction of V2O5. The major impurities present in (V,N,C,O) were: (wt.%) carbon 1.6, oxygen 1.2 and nitrogen 2.5. The maximum purity, current efficiency and metal yield, after refining, were 99.85, 90 and 86 wt.% respectively. The evaluation and characterization of the electrodeposited vanadium were carried out by chemical analysis, scanning electron microscopy, optical microscopy and hardness measurements.

Metastable Hexagonal Vanadium Molybdate Study

The solid solution of vanadium in hexagonal molybdenum oxide has never previously been completely studied; no information has been given about the solubility limit or the thermal stability of the system. In this work, we have determined that the solubility limit is reached with the following composition: (NH4)0.13V0.13Mo0.87O3. Our samples have been obtained by a soft chemistry method. The obtained precipitates have been processed and analyzed with several techniques. We have shown that the introduction of vanadium in the h-MoO3 structure has several effects, on the thermal stability of the metastable mixed oxide, on the morphology, as well as on the lattice parameters.

Differentiation between the Green and Turkish Blue Solid Solutions of Vanadium in a Zircon Lattice Obtained by the Sol-Gel Process

In this communication, zircon containing vanadium samples which gradually turn greenish have been prepared by controlling the composition (fluoride addition) and the method of preparation (sol-gel, ceramic and solid impregnation) in order to investigate how to affect the shape and size of the vanadium particles, and their location, clustering and distribution. The level of green color, and consequently the amount of V5+ in the sample, could be associated with the development of an Si-O-Si network in the zircon lattice, bonding with the highly reactive zirconium precursors.

Phase equilibria in vanadium-rich alloys of the V-Ni-Al system

Vanadium-rich alloys of the V-Ni-Al system were studied by the methods of metallographic, x-ray diffraction, and electron beam microprobe analysis. The boundaries of the phases, and the vertices of the conoidal triangle αβσ, in the vanadium corne, of the 1200°C isothermal section were determined. The maximum solubility of aluminum in the σ-phase is 6 at. %. The homogeneity range of the NiAl-based β-phase is very broad; the maximum solubility of vanadium in β reaches 41.5 at. %. The maximum solubility of nickel in the vanadium solid solution is 25 at. %. Alloys containing 15–20 % Al and 20–30% Ni exhibit a tendency to dispersion haraen and, therefore, might serve as a basis for the development of a new generation of radiation-resistant materials.

Fracture Behavior of Vanadium/Vanadium Silicide In-Situ Composites

The fracture behavior of V-V{sub 3}Si in-situ composite alloys has been evaluated for intermetallic phase fractions of 30, 50, and 70 volume percent. In addition, the mechanical properties of the ductile constituent in these composites have been evaluated from two alloys containing silicon at its solubility-limit in vanadium at the eutectic temperature and at 1400{degrees}C. The fracture toughness was found to increase monotonically with increasing volume fraction of ductile phase. Fractography has shown evidence of crack bridging by the vanadium solid solution phase and increased ductility within the composite relative to bulk measurements. The toughness results are compared with predictions based on an existing model of ductile-phase toughening using our measurements of component properties.

Investigation of vanadium solid solution and zeta phase regions of the vanadium-carbon system

The vanadium-rich solvus of the V-C system was determined for the temperature range of 1100–1650 °C. The solubility decreases from a maximum of 4.3 at.% C at 1650 °C to 0.5 at.% C at 1100 °C. The heat of solution for carbon in vanadium was determined to be 83.7 kJ mol −1. No evidence was found for the postulated ordered phase V 64C from transmission electron microscopy, optical microscopy or electron diffraction studies. The existence of a zeta phase having the stoichiometry V 4C 3− x where x = 0.33 was confirmed by X-ray and metallographic evidence. Its peritectoid decomposition temperature was determined by differential thermal analysis to be 1320 ± 10 ° C. The hardness of quenched V-C alloys increases monotonically with carbon content over the range 0.02–0.64 at.% C. Quenched alloys aged at 300 °C for various times show a maximum in the hardness on aging for about 1 h.

Studies of V−Mo−O systems with small vanadium content in acrolein oxidation

A solid solution of vanadium in MoO3 with a solubility limit of about 3 mol.% V2O5 is shown to be formed. Its catalytic properties are discussed.

Physicochemical and mechanical properties of vanadium-titanium alloys

1. We investigated the strength, electrical resistivity, density, and corrosion rate of vanadium-titanium alloys in a series of organic and inorganic acids at different temperatures. 2. Anomalous changes in the electrical resistivity and strength characteristics were noted in the region of dilute solid solutions of vanadium, which are due to the presence of interstitial impurities in alloys of this system. 3. We determined the region of composition for alloys with a low corrosion rate (<0.1 mm/year) and high strength and ductility, which makes these alloys promising as corrosion-resistant materials.

Electrical and magnetic properties of solid solutions of vanadium and titanium disilicides in chromium disilicide

1. A study was made of the influence of temperature on the electrical resistivity (20–950°C), a differential thermal emf (20–350°C), and magnetic susceptibility (20–800°C of chromium disilicide, as well as of solid solutions of VSi2 (0–100 mol.%) and TiSi2 (0–80 mol.%) in chromium disilicide. 2. On the basis of experimental data it is shown that the chromium, vanadium, and titanium atoms in the solid solutions investigated are in a tetravalent state. The atomic orbits of vanadium alone have a single electron with an uncompensated spin, whereas neither chromium nor titanium atoms have such electrons. 3. It has been established that, with increasing concentration of VSi2 and TiSi2 in chromium disilicide, the overlapping of the wave functions of the metal atoms is intensified, and a gradual change from typically semiconducting to metallic properties is observed. 4. The characteristics of the valence and zone models of solid solutions based on chromium disilicide are examined. It is noted that the concentration dependence of the properties of these solid solutions at substantial VSi2 and TiSi2 concentrations is responsible for changes in the density of states near the Fermi surface rather than changes in the degree of filling of the valence band.