Vanadium Foil Research Articles

Fabrication and operational considerations of hydrogen permeable Mo2C/V metal membranes and improvement with application of Pd

Mo2C has previously been demonstrated as an effective catalyst layer to enable stable H2 permeation through vanadium foils at high temperatures. In this study, this approach was extended to several group V metal foils (V, Nb, and Ta) as well as mixed gas testing. The best permeability was achieved with V, and an activation process was developed to recover the performance of V foils displaying evidence of oxidation. Nb foils yielded ~ 20% the permeability of V, while Ta was too brittle to operate effectively. Mo2C/V membranes were operated at feed conditions well above the ductile-to-brittle transition pressure without embrittlement; however, the H2 permeability of Mo2C/V membranes was significantly attenuated at lower temperatures (< 600°C). H2 permeation was also severely inhibited by the presence of N2 or CO2 in mixed gas environments due to strong competitive adsorption. The addition of a Pd catalyst layer on top of Mo2C improved mixed gas stability and increased H2 permeability to 2 × 10−8molm−1s−1Pa−0.5 at 500°C for V based membranes. As an interlayer, Mo2C was demonstrated to be a stable barrier preventing Pd-V interdiffusion at 500°C while simultaneously allowing significant H2 permeation.

Mechanical properties of laser beam welded similar and dissimilar aluminum alloys

Two approaches were used for laser beam welding of similar and dissimilar joints of AA7075 and AA5182 that aim to overcome the weldability problems of high-strength Al-Zn-Mg-Cu alloys. The first approach implies the use of vanadium foil as additional filler material, while the second implies the use of a fiber laser with a large beam diameter and a top-hat beam profile. Although both approaches result in an improved weld quality, in terms of weld appearance, porosity and cracking, the resulting mechanical properties differ considerably. The addition of vanadium leads to a local increase of microhardness in the fusion zone. However, the tensile strength of these joints is lower as for fiber laser welded joints. In direct comparison fiber laser welded joints exhibit also higher formability as the joints welded with vanadium foil. The highest formability is obtained for dissimilar joints with the medium-strength Al-Mg alloy. Due to the unavoidable softening in the weld zone of heat treatable aluminum alloys, the formability of the joints is inferior in comparison to the base materials. In addition, the positive effect of post-weld heat treatment, surface milling and warm forming on the resulting mechanical properties of similar and dissimilar joints is discussed.

Synthesis of vanadia nanorod arrays and their novel applications as alco-sensors

Vanadia (V2O5) nanorod arrays were grown by oxidizing vanadium foil at five different voltages for 3h through electrochemical anodic oxidation method. Dense aligned nanorods with L/D ratio 4.75-4.88 (diameter D≈40–45nm and length≈190–220nm) were grown at the optimized voltage 55V. The dominant existence of V2O5 phase and its layered structure were verified by XPS and Raman spectrum analysis respectively. Linear I–V characteristic curve of the sensor based on V2O5 nanorod arrays confirms its Ohmic contact with the electrodes. Gas sensing investigations of the sensor reveals its n-type behavior with the average response magnitude of 6.13 in N2 atmosphere, which signifies the industrial application of the sensor in a gaseous atmosphere. The sensor shows remarkable static response towards ethanol with lower detection threshold of 800ppb and a maximum response magnitude of 7.27 at 500ppm. Based on variable resistance model, a suitable gas sensing mechanism is also established.

X-ray diffraction measurements of plasticity in shock-compressed vanadium in the region of 10–70 GPa

We report experiments in which powder-diffraction data were recorded from polycrystalline vanadium foils, shock-compressed to pressures in the range of 10–70 GPa. Anisotropic strain in the compressed material is inferred from the asymmetry of Debye-Scherrer diffraction images and used to infer residual strain and yield strength (residual von Mises stress) of the vanadium sample material. We find residual anisotropic strain corresponding to yield strength in the range of 1.2 GPa–1.8 GPa for shock pressures below 30 GPa, but significantly less anisotropy of strain in the range of shock pressures above this. This is in contrast to our simulations of the experimental data using a multi-scale crystal plasticity strength model, where a significant yield strength persists up to the highest pressures we access in the experiment. Possible mechanisms that could contribute to the dynamic response of vanadium that we observe for shock pressures ≥30 GPa are discussed.

Self-assembled V2O5 interconnected microspheres produced in a fish-water electrolyte medium as a high-performance lithium-ion-battery cathode

Interconnected microspheres of V2O5 composed of ultra-long nanobelts are synthesized in an environmental friendly way by adopting a conventional anodization process combined with annealing. The synthesis process is simple and low-cost because it does not require any additional chemicals or reagents. Commercial fish-water is used as an electrolyte medium to anodize vanadium foil for the first time. Electron microscopy investigation reveals that each belt consists of numerous nanofibers with free space between them. Therefore, this novel nanostructure demonstrates many outstanding features during electrochemical operation. This structure prevents self-aggregation of active materials and fully utilizes the advantage of active materials by maintaining a large effective contact area between active materials, conductive additives, and electrolyte, which is a key challenge for most nanomaterials. The electrodes exhibit promising electrochemical performance with a stable discharge capacity of 227 mAh·g–1 at 1C after 200 cycles. The rate capability of the electrode is outstanding, and the obtained capacity is as high as 278 at 0.5C, 259 at 1C, 240 at 2C, 206 at 5C, and 166 mAh·g–1 at 10C. Overall, this novel structure could be one of the most favorable nanostructures of vanadium oxide-based cathodes for Li-ion batteries.

Water adsorption on polycrystalline vanadium from ultra-high vacuum to ambient relative humidity

We have studied the reaction of water vapor with a polycrystalline vanadium surface using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) which allows the investigation of the chemical composition of the vanadium/water vapor interface at p(H2O) in the Torr range. Water dissociation on the vanadium surface was studied under isobaric conditions at p(H2O) ranging from 0.01 to 0.50Torr and temperatures from 625K to 260K, i.e. up to a relative humidity (RH) of ~15%. Water vapor exposure leads to oxidation and hydroxylation of the vanadium foil already at a pressure of 1×10−6Torr at 300K (RH~4×10−6%). The vanadium oxide layer on the surface has a stoichiometry of V2O3. Initial adsorption of molecular water on the surface is observed at RH>0.001%. Above a RH of 0.5% the amount of adsorbed water increases markedly. Experiments at increasing temperatures show that the water adsorption process is reversible. Depth profile measurements show a thickness for the vanadium oxide layer of 3–5 mono layers (ML) and for vanadium hydroxide of 1–1.5 ML over the whole RH range in the isobar experiments. The thickness of the adsorbed water layer was found to be in the sub-ML range for the investigated RH's.

Vanadium pentoxide cathode materials for high-performance lithium-ion batteries enabled by a hierarchical nanoflower structure via an electrochemical process

Hierarchical vanadium oxide nanoflowers (V10O24·nH2O) were synthesized via a simple, high throughput method employing a fast electrochemical reaction of vanadium foil in NaCl aqueous solution, followed by an aging treatment at room temperature. During the electrochemical process, the anodic vanadium foil is dissolved in the form of multi-valence vanadium ions into the solution, driven by the applied electrical field. After being oxidized, the VO2+ and VO2+ ions instantly react with the OH− in the electrolyte to form uniformly distributed vanadium oxide nanoparticles at a high solution temperature due to the exothermic nature of the reaction. Finally, nucleation and growth of one dimensional nanoribbons takes place on the surface of the nanoparticles during the aging process to form unique hierarchical V10O24·nH2O nanoflowers. Upon heat treatment, the hierarchical architecture of the vanadium pentoxide nanoflower morphology is maintained. Such a material provides porous channels, which facilitate fast ion diffusion and effective strain relaxation upon Li ion charge–discharge cycling. The electrochemical tests reveal that the V2O5 nanoflowers cathode could deliver high reversible specific capacities with 100% coulombic efficiency, especially at high C rates (e.g., 140 mAh g−1 at 10 C).

Atomistically observing real-space structure of composition modulated (Nb0.94V0.06)10(SixGe1−x)7 nanowires with ultralow resistivity

We have synthesized quaternary single crystalline (Nb0.94V0.06)10(SixGe1−x)7 nanowires (NWs) (0.1 ≤ x ≤ 0.5) in high density by flowing a NbCl5 precursor and placing vanadium (V) foil on a mixture of Si, Ge, and C powder. The composition of Si (x) in the NW could be modulated from 0.1 to 0.5 by changing the substrate temperature. We have investigated how the atoms comprising the quaternary NWs are arranged in a real-space using a spherical aberration corrected scanning transmission electron microscope. The filling of Si and Ge atoms in Ge atom columns is analyzed by comparing experiments and simulations. Electrical transport measurements show that (Nb0.94V0.06)10(Si0.5Ge0.5)7 NWs have an ultralow resistivity of ∼8.5 μΩ cm, lower than that of most conducting metal silicides, as well as a high failure current density of 1.1 × 108 A cm−2 at room temperature. The synthesis of quaternary single crystalline (Nb0.94V0.06)10(SixGe1−x)7 NWs (0.1 ≤ x ≤ 0.5) shows that Si and Ge composition can be easily modulated in metal germanosilicide nanostructures. The quaternary NWs may supply high quality nanoscale materials for the gate and interconnect in SiGe based nanoelectronics.

Mechanistic studies of hydrogen transport through [formula omitted]/V composite membranes

Composite membranes comprised of vanadium foils coated with molybdenum carbide catalyst layers were recently introduced as alternatives to palladium for high temperature separation of H2. Experiments using D2/H2 mixtures unambiguously show that the mechanism involves dissociation, proton transport, and subsequent recombination. Temperature-dependent measurements of H2 flux were performed on sets of membranes in which the thickness of both the V foil and the Mo2C layers were varied in order to provide insight into the underlying transport mechanisms. It is shown that hydrogen transport through the carbide itself can be limiting for catalyst layers >20nm. At temperatures <750°C the flux is highly activated, suggesting that dissociation of H2 on the carbide surface is the rate limiting step. At higher temperature the permeability decreases with temperature in good agreement with the theoretical predictions of the permeability of the underlying V metal. The permeability of these composite membranes significantly exceeds that of pure Pd, with values as high as 5.9×10−8molm/m2sPa0.5 at 750°C.

ChemInform Abstract: Synthesis and Visible Light Photocatalytic Activity of β‐AgVO3 Nanowires.

AbstractThe title nanowires with diameters of about 200—700 nm and lengths up to 300 μm are hydrothermally synthesized from AgNO3 powder, vanadium foil, and H2O (autoclave, 200 °C, 20 h).

Abnormally deep penetration of hydrogen into niobium under the influence of the pulse high-temperature plasma

The process of storing and redistributing hydrogen atoms under the action of pulse high-temperature hydrogen plasma obtained on the PF-4 plasma focus (PF) plant in an assembly of three high-purity niobium foils is studied by the elastic recoil detection (ERD) method. It is determined that, as the number of hydrogen plasma pulses increases, the implanted hydrogen atoms are redistributed at larger depths in an assembly of niobium foils which significantly exceed the projected range of hydrogen ions (when their maximal velocity reaches ∼108 cm/s). A maximum hydrogen concentration of up to 60 at % is reached in the nearest (to PF-4) surface of the third Nb foil under the action of 20 hydrogen plasma pulses. The observed phenomenon can be attributed to the ejections of implanted hydrogen atoms under the action of high-power shock waves created in niobium foils by the pulse hydrogen plasma and/or by the accelerating diffusion of hydrogen atoms under the action of compression-straining waves at the front of the shock wave with redistributions of hydrogen atoms at larger depths. Similar behavior is found in assemblies of two or three and more nickel, vanadium, niobium, and tantalum foils of different thicknesses, including foil assemblies made of heterogeneous materials, which were also studied.

Revealing the 3D internal structure of natural polymer microcomposites using X-ray ultra microtomography

Properties of composite materials are directly affected by the spatial arrangement of reinforcement and matrix. In this research, partially hydrolysed cellulose microcrystals were used to fabricate polycaprolactone microcomposites. The spatial distribution of cellulose microcrystals was characterized by a newly developed technique of X-ray ultra microscopy and microtomography. The phase and absorption contrast imaging of X-ray ultra microscopy revealed two-dimensional and three-dimensional information on CMC distribution in polymer matrices. The highest contrast and flux (signal-to-noise ratio) were obtained using vanadium foil targets with the accelerating voltage of 30 keV and beam current of >200 nA. The spatial distribution of cellulose microcrystals was correlated to the mechanical properties of the microcomposites. It was observed that heterogeneous distribution and clustering of cellulose microcrystals resulted in degradation of tensile strength and elastic modulus of composites. The utilization of X-ray ultra microscopy can open up new opportunities for composite researchers to explore the internal structure of microcomposites. X-ray ultra microscopy sample preparation is relatively simple in comparison to transmission electron microscopy and the spatial information is gathered at much larger scale.

Monochromatic x-ray radiography for areal-density measurement of inertial fusion energy fuel in fast ignition experiment

Ultrafast, two-dimensional x-ray imaging is an important diagnostics for the inertial fusion energy research, especially in investigating implosion dynamics at the final stage of the fuel compression. Although x-ray radiography was applied to observing the implosion dynamics, intense x-rays emitted from the high temperature and dense fuel core itself are often superimposed on the radiograph. This problem can be solved by coupling the x-ray radiography with monochromatic x-ray imaging technique. In the experiment, 2.8 or 5.2 keV backlight x-rays emitted from laser-irradiated polyvinyl chloride or vanadium foils were selectively imaged by spherically bent quartz crystals with discriminating the out-of-band emission from the fuel core. This x-ray radiography system achieved 24 μm and 100 ps of spatial and temporal resolutions, respectively.

Mechanical characterization of hotplate synthesized vanadium oxide nanobelts

Vanadium oxide nanobelts have been synthesized on Si or SiN substrates by simply heating vanadium foils on a hotplate. As-grown nanobelts were characterized as V 2O 5· nH 2O (0.3 < n < 1.7) layer structures containing water molecular intercalation. Using an electromechanical resonance method, the Young’s modulus of the nanobelts was measured in situ in a scanning electron microscope. It was found that the Young’s modulus of as-grown nanobelts varied between 5.6 and 98 GPa, with a typical Q-factor of 120. Such scattered values were attributed to the different contents of water molecules in the nanobelts. After annealing at 450 °C in vacuum, the nanobelts were converted to α-V 2O 5 phase and a polycrystalline structure was observed. The Young’s modulus of the annealed nanobelts showed more consistent values at an average of 28.9 GPa, lower than the calculated modulus of bulk α-V 2O 5 at 68 GPa.

Morphology-Tuned Synthesis of Single-Crystalline V5Si3 Nanotubes and Nanowires

We report the morphology-tuned synthesis of single-crystalline V 5 Si 3 nanotubes and nanowires. Free-standing hexagonal V 5 Si 3 nanostructures are grown on a vanadium foil substrate placed on Si powder by a chemical vapor deposition method. By controlling the reaction time and substrate temperature, we have succeeded in morphology tuning of V 5 Si 3 nanotubes and nanowires. When the downstream temperature is fixed at 950 °C, V 5 Si 3 nanotubes are formed with the reaction time of 5 min and V 5 Si 3 nanowires are obtained with the reaction time of 15 min. With the downstream temperature of 950 °C and the reaction time of 15 min, when Si powder is mixed with carbon powder to the Si composition of 10—50%, both nanotubes and nanowires are simultaneously formed on the vanadium foil along the temperature gradient. Single-crystalline V 5 Si 3 nanotubes thus synthesized are the first metal silicide nanotubes reported so far.

Oxidation of vanadium with reactive oxygen plasma: A photoelectron spectroscopy study of the initial stages of the oxide growth process

We report on the oxidation of vanadium surface in a low-temperature oxygen plasma studied by in-situ photoelectron spectroscopy (XPS, UPS). Pure vanadium foil was exposed to the oxygen plasma for different time intervals allowing to investigate early stages of the oxide–metal interface formation process and the oxide film growth. Upon increasing the exposure time to the oxygen plasma we identify two regimes with respect to the vanadium oxidation state: formation of 4+ state on the early stages of growth and in saturated regime vanadium was found to be predominantly in the 5+ oxidation state. Angle-resolved XPS was used to perform an in-depth distribution analysis of chemical composition in outermost layers of the oxide. We found that plasma oxidation produces a well-pronounced interface with a transition layer thickness of about 1.3 nm.

クロムめっき処理したＳＵＳ３０４Ｌとチタンのパルス通電圧接

Joints composed of stainless steel and Ti were fabricated from Cr-plated SUS304L alloy rods and Ti rods using vanadium foil as an insert metal, in a process using pulsed current hot pressing (PCHP) equipment. The effects of the bonding temperature and the thickness of the Cr-plate layer on the mechanical properties of the joints were investigated. Tensile testing at 300 K and microstructural observations were carried out. The joints fabricated at 1173 K from 20 μm thick Cr-plated SUS304L rods and Ti rods showed the highest tensile strength of 340 MPa. SEM-EDS analyses revealed that the Cr-plate layer was left after PCHP process and no intermetallic compounds formed at the bonding interfaces. The cracks originally existed in the Cr layer plated on SUS304L rods disappeared perfectly during PCHP process at 1273 K. In contrast, the joints fabricated from 5 μm thick Cr-plated SUS304L rods and Ti rods showed the lowest tensile strength because of the formation of FeV intermetallic compound in the bonded interlayer.

High-brightness, narrowband, and compact soft x-ray Cherenkov sources in the water window

Narrowband, soft x-ray Cherenkov radiation at energies of 453 and 512 eV has been generated by 10 MeV electrons in, respectively, titanium and vanadium foils. The measured spectral and angular distribution of the radiation, and the measured total yield (≈10−4 photon per electron) are in agreement with theoretical predictions based on refractive index data. We show that the brightness that can be achieved using a small electron accelerator is sufficient for practical x-ray microscopy in the water-window spectral region.

Development of Eutectic Free Cladding Materials for Metallic Fuel

Historically, it is well known that U base metallic fuel has a lower eutectic temperature with stainless steel cladding. In the phase diagram for the U-Fe binary system, the eutectic temperature is 998K. The eutectic reaction is a limiting factor for raising reactor operation temperature.For the purpose of development of eutectic-free cladding materials, three kinds of diffusion-couple tests with 10mass%Zr alloy were conducted at a temperature of 1027K for 2250hrs.We selected the following materials: (a) nitrogen charged zirconium foils, (b) vanadium foils of commercial grade, and (c) nitrogen charged ferritic stainless steel (HT-9).The results showed that typical Zr rich layer was observed in all of these materials. Zr rich layer appeared to act as a barrier against inter-diffusion of U, Fe. The barrier provided immunity to the eutectic reaction.Discussion was made on C-14 problems in relation to another desirable thermodynamic characteristics of Zr such as carbon-14 immobilization.EPMA analysis indicated relatively high nitrogen concentration at the barrier. The barrier is probably composed of ZrN.

Crystal Structure of Elongated Thin Foils of Fe and V

Kiritani et al. have recently reported that a large number of vacancy clusters are formed in plastically elongated thin foil of fcc metals and that no dislocations at all are observed in the thin portion of the elongated film. These findings suggest that elongation proceeds by atom transportation accompanied by generation of vacancies. In the present work, strips of prototype bcc metals of iron and vanadium were elongated to fracture, and thin portions that can be observed under TEM; i.e. , fractured edges, were observed by electron microscopy. The results show that iron thin foils that had been elongated in pure helium gas reacted with residual oxygen atoms such that the thin portions transformed to α-Fe 2 O 3 . Iron thin foil that had been elongated under a 10 −6 Pa vacuum showed usual bcc structure, and void-like defects were observed. Strips of vanadium were elongated to fracture at 77 K and 293 K, and large number of void-like defects were observed in as-elongated specimens. In thin vanadium foil that had been elongated at 673 K, TEM visible defects were not observed initially, and void like defects appeared after 200 keV electron illumination for 60 minutes. Stereo-microscopic examination showed that void-like defects had formed inside vanadium thin foil.