Vanadium Powder Research Articles

Microwave-synthesized V2O5 nanoparticles for ammonia sensing at room temperature

We introduce a process for synthesizing V2O5 nano particles directly from vanadium powder using a microwave oven in just 5 min. These nanoparticles are oval-shaped with an average diameter of 9 nm. These V2O5 nanoparticles are capable of detecting 1 ppm NH3 at room temperature with the response of 1.16 and the response/recovery times of 15 s and 326 s, respectively. Notably, the NH3 sensing characteristics of these V2O5 nanoparticles are almost unaffected by the humidity in the air and remain unchanged after at least 60 days of measurement. Therefore, V2O5 nanoparticles synthesized using microwave techniques are a material with great potential for application as low-energy NH3 sensors.

Structure and tribological properties of “carbon steel – VC containing coating” compositions formed by non-vacuum electron-beam surfacing of vanadium-containing powder mixtures

Vanadium carbides are known as efficient reinforcing components for surface layers of steel parts. They provide good tribological characteristics of material under sliding friction conditions and against dry abrasive particles. Since wear conditions usually are quite severe, a thick coating is needed to provide the reliable protection of the part. The majority of currently used surfacing technologies ensure the coatings of insufficient thickness. For this reason, the non-vacuum electron beam cladding which is able to provide thick coatings is a reasonable alternative to other surfacing methods. This paper presents an analysis of the microstructure, micro- and nanohardness, elasticity, and tribological characteristics of coatings formed by non-vacuum electron-beam surfacing of vanadium and graphite-containing powder mixtures. In the course of the study, coatings with the average thicknesses of 1.8, 2.5, 2.6, 3.4 mm were formed on the surface of blanks made of medium‑carbon steel. Hardness of cladding layers was significantly improved compared to the low-carbon steel (by the factor of 5–7). The wear resistance of coatings under conditions of sliding friction was 5.8 times higher than the wear resistance of the base metal after quenching and tempering; the wear resistance of coatings under conditions of friction against fixed and loosely fixed abrasive particles was ∼2 and ∼4.8 times higher, respectively. Surface hardening of steel alloyed with vanadium and carbon derives from the presence of a martensitic matrix, ledeburite precipitates and a high volume fraction (14.5–29.5 vol%) of vanadium carbide particles of a dendritic form, which act as rigid barriers.

Direct additive manufacturing as spring of new tool steels

Additive manufacturing (AM) is now common in production of metallic matrixes with/without reinforcements (nanoprecipitates) to improve functional and structural mechanical properties of 3D objects. The presence of liquid phase in direct processes allows the possibility to change the conventional chemical composition of materials homogeneously. Powder Bed Fusion (PBF), in which the high nonequilibrium solidification nature resembles a localized high cooling rate but allowing, still the formation nanocarbides in-situ. Thus, it will be the suitable technology to tailor novel functionally gradient metallic materials. Nevertheless, this character is only present in the upper layers due to the shaping being made layer by layer. During shaping, the previous layers undergo post heat treatments contributing for growing the carbide dimension. Hence, metallic alloys can be developed simultaneously with the processing stage by changing the chemical composition by addition of fundamental elements to the matrix powder. In tool steel the improvement of hardening carbide content can contribute to a better performance concerning hardness and abrasion wear resistance. The present study concerns the addition of vanadium powder and allotropes of carbon, in correlation with the partition coefficient between vanadium and carbon in the steel selected - AISI H13, processed by selective laser melting (PBF/SLM), without requiring adjusting the processing parameters. The hardness attained is analogous to high speed steels, since this allows layers with a similar matrix to the wrought tool steel but with higher content of hardening carbide (VxCy). The sustainability of the final product is evident.

Vanadium as co-catalyst for exceptionally boosted Fenton and Fenton-like oxidation: Vanadium species mediated direct and indirect routes

In this study, vanadium powder (V) was employed as a cocatalyst to enhance the Fenton-like system. The V-Fe(III)/H2O2 system can rapidly produce hydroxyl radicals and completely oxidize chloramphenicol with exceptionally high stability for long-term operation. The low-valent vanadium sites on the surface during the stepwise oxidation of vanadium from V0 to V(IV) can donate electrons for direct H2O2 activation and indirect Fenton reaction by reducing Fe(III) to produce hydroxyl radicals. Meanwhile, density functional theory (DFT) calculation unveils that low-valent vanadium sites of vanadium can lengthen Fe-O bonds of FeOH2+ to elevate the oxidation potential of Fe(III) and promote Fe(III) reduction induced by H2O2. The self-cleaning effect of vanadium under acidic conditions can maintain reactive sites for sustainable electron donation and long-lasting enhanced Fenton oxidation. This study provides a novel enhanced Fenton oxidation for water remediation and the first mechanistic insights into the origins of V-based advanced oxidation technologies, it may also be beneficial to treat vanadium-contained wastewater.

INFLUENCE OF THE COMPOSITION OF THE SATURATING MIXTURE DURING CHROME VANADIZING OF STEEL ON THE STRUCTURE AND PROPERTIES OF THE COATING

The article presents the results of laboratory studies on the joint thermal diffusion saturation of steel X35CrNi2-3 with chromium and vanadium at a temperature of 1000°C for 24 hours. In the experiments, vanadium was used as the second saturating component, both in the form of ferrovanadium and pure metal with a fraction of up to 150 μm, introduced in amounts of 10 and 15 % (wt.). A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using a JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The obtained data shows that the composition of the saturating mixture has a signifi-cant effect on the structure and morphology of the outer diffusion layer. In the case of using pure vanadium powder, both the outer coating and the underlying metal under it become loose, porous, which degrades the surface quality. When using ferrovanadium, the coating is devoid of such disadvantages. The depth of chromium diffusion in all vari-ants of chromium vanadization is lower than with the one-component saturation.

Synthesis of vanadium powder by magnesiothermic reduction of V2O3 in a reactive molten salt

Synthesis of vanadium powder by magnesiothermic reduction of V2O3 in a reactive molten salt

Preparation of vanadium by the magnesiothermic self-propagating reduction and process control

Abstract A new process for preparing vanadium by direct reduction of V2O5 from the Mg–V2O5 self-propagating system is proposed in this article. The reaction behavior and path of V2O5 in the magnesiothermic reduction process were investigated using the XRD, SEM-EDS, laser particle size analyzer, and specific surface area analyzer. The experimental results show that the reaction of the V2O5–Mg system is a solid-solid reaction, and the initial reaction temperature is 570°C. Although the formation of MgV2O4 spinel cannot be predicted via the calculation of thermodynamics, the presence of MgV2O4 spinel is of great significance to the V2O5 reduction process. Taking into account the characteristics of the gradual reduction of V2O5 by Mg and the appearance of the MgV2O4 spinel phase, the limiting link of the reaction may be the transition from MgV2O4 to V. A reduction path of V2O5 beyond the thermodynamic prediction is proposed: V2O5 → V3O5 → MgV2O4 → V. The reaction temperature and the phase transformation process can be effectively controlled by adjusting the ratio of reactants and additives, and element V can be obtained by a one-step rapid self-propagating reaction and breaking through the reaction restriction link. In this experiment, the vanadium powder with a porous structure, a specific surface area of 3.44 m2 g−1, and the oxygen content of 4.86 wt% were obtained.

Effect on Microstructure and Mechanical Properties of Microwave-Assisted Sintered H13 Steel Powder with Different Vanadium Contents.

The present work demonstrated the first-ever preparation of block specimens by the microwave sintering of H13 alloy powder. Varying proportions of vanadium powder (1.5%, 2.5%, 3.5%, 4.5%, and 5.5% on a mass basis) were added to H13 mold steel and these mixtures were sintered using microwaves. X-ray fluorescence spectroscopy was employed to determine the compositions of the resulting specimens and vanadium percentages of 1.56%, 2.04%, 3.10%, 4.06%, and 4.20% were determined. These results demonstrate a clear trend, with significantly lower vanadium amounts than expected based on the nominal values at higher vanadium loadings. Different samples were also found to exhibit different degrees of ablation, and this effect was related to the presence of voids in the materials. The surface compositions of these specimens were examined by laser-induced breakdown spectroscopy and were found to be relatively uniform. The microstructures as well as the hardness properties of the materials were assessed. Microwave sintering of 100 g specimens at 1300 °C for 10-min generated samples with hardness values ranging from 205 HV (at the lowest vanadium content) to 175.2 HV (at the highest vanadium content). The wear behavior of samples prepared by microwave sintering H13 die steel with different vanadium contents at room temperature has been studied. The results showed that 1.5% vanadium content is the best mass ratio.

From Microurchins to V2O5 Nanowalls: Improved Synthesis through Vanadium Powder and Fast, Selective Adsorption of Methylene Blue.

Research on synthesizing micro- and nanosized materials directly from metals has attracted considerable attention because of its simplicity, ability to synthesize in large quantities, and high uniformity. This study proposes a simple method to synthesize high-uniformity or high-density V2O5 microurchins and nanowalls directly from vanadium powder. Remarkably, the synthesis condition of 60 °C for 1 h is considered to be an optimal condition to convert metals into micro- or nano-oxides. The as-synthesized V2O5 nanowalls can adsorb nearly 90% of methylene blue in the dark in 3 min. The adsorption selectivity of these samples with several pigments is investigated.

Synthesis of VO2 thin films from vanadium powder and determination of room-temperature NH3 sensing properties

VO2 nanomaterials were synthesized directly from vanadium powder and NH4OH solution. The effect of annealing temperature on the formation of VO2 and V2O5 phases of materials after synthesis was investigated and analyzed. The material is composed of nanoparticles with an average size of about 2 nm. The gas sensing properties of VO2 samples at room temperature were studied. The VO2 nanomaterial was selective toward NH3 at 25 °C among other test gases such as C2H5OH, CH3COCH3, and C3H8. The effects of moisture, stability, and gas-sensing mechanism of VO2 nanomaterials were also investigated and discussed. VO2 nanomaterials have simple fabrication and superior air sensitivity and thus have great potential as NH3 sensors at room temperature.

From vanadium powder to vanadium pentoxide rolled-up nanosheets: Hydrothermal synthesis and its ethanol sensing properties

Vanadium pentoxide is recently known as a material with good gas sensing properties. This study proposes a simple method of synthesizing rolled sheet V2O5 nanomaterials directly from vanadium metal. By adjusting the processing temperature, the dimension of the nanosheet can be controlled. Analytical techniques such as SEM, TEM, XRD, UV–Vis, Raman were used to study the morphology and structure of the fabricated material. The rolled-up nanosheets exhibited good ethanol sensitivity compared to several ethanol-sensitive materials over the past two years. The gas sensing model explaining the superiority and suitability of the material structure in the application of gas sensor was proposed and discussed.

Mechanical and structural behaviour of TiAlV nanocrystalline elaborated by mechanical milling technique

The aim of this study is to fabricate the Ti50Al40X10 nanostructured alloy (X: V) from pure titanium, aluminium, and vanadium powders by using a high-energy planetary ball mill with increasing milling time from 10 to 80 h. Morphology, structural, and mechanical properties of this alloy were investigated by a SEM, XRD, and nano-indentation testing. The effect of milling time on structural, morphological, and mechanical properties has been investigated. Microstructural characterisation showed a decrease of average particle size during milling time. Crystallite size decreased from 49 to 6.02 nm and lattice strain increased from 0.15% to about 0.89% during mechanical alloying. In addition, the mechanical properties of Ti50Al40V10 nanostructured materials were strongly depended on the microstructure and crystallite size of new phases that appear during mechanical milling. Microhardness of the Ti50Al40V10 alloy increases with milling time from 261 to 738 Hv. These changes could be attributed to the crystallite size and the strain variations during milling.

Synthesis, Structure and Properties of Material Based on V2AlC MAX Phase

Abstract–A material based on the V2AlC MAX phase has been obtained for the first time by the method of self-propagating high-temperature synthesis (SHS) using a reaction mixture of vanadium oxide(V) and (IV) powders with aluminum and carbon (graphite). The obtained material was characterized by X-ray diffraction and energy-dispersive X-ray spectroscopy. The Rietveld method was used to perform quantitative analysis. The synthesized material based on the V2AlC MAX phase is an electrical conductor that demonstrates the metallic behavior of conductivity in the entire measured temperature range of 300–1300 K in the vacuum of 2 × 10–3 Pa. It has been suggested that the V2AlC phase makes a decisive contribution to the electrical resistance of the synthesized material that may be caused by the formation of V2AlC nanolaminate grains contacting with each other in the bulk of the material.

A novel approach to synthesize surface composite by in-situ grown VC reinforcement in steel matrix via TIG arcing

Tungsten Inert Gas (TIG) arcing is a surface modification process and can be used for some specific applications. In the present work, in-situ grown vanadium carbide particle coating was manufactured by initially applying the coating of finely ground vanadium and graphite powder on the steel substrate and subsequently fused the mixture by TIG arcing. Various reactions occurring in the fusion zone and the formation of different phases were thermodynamically predicted and related to the experimental observations. The modified surface was found to be free from micro-cracks and porosity. Microstructural characterization of the modified layer was performed by different techniques like the field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) etc. The results showed that the microstructure of the modified surface was consisted of vanadium carbide particles formed in-situ within the martensite matrix developed due to rapid cooling during TIG arcing. Further, the shape and size of these particles were evaluated by carbon replica method and characterized in scanning transmission electron microscopy (STEM) imaging mode available in the HRTEM. STEM analysis shows the formation of micron size vanadium carbide particles in cuboidal and rod shape as well as fine nanoprecipitations in a cuboidal shape. A significant increase in hardness of the modified region was observed which can be due to the combined effect of in situ formation of fine vanadium carbide in the martensite matrix.

Enhanced optical and structural properties of V-doped binary SnS2 buffer layer

Recently tin disulfide (SnS2) has attracted considerable attention due to its n-type semiconductor property with a tunable bandgap similar to CdS and In2S3, Tin disulfide (SnS2) and doped vanadium (V) powder were successfully prepared by a simple hydrothermal method. The crystallographic, morphological, elemental conformation and optical properties were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersion microscopy (EDS), Atomic force microscopy (AFM), UV–Vis spectroscopy and electrochemical analysis, respectively. The XRD analysis revealed the polycrystalline nature of the films. Raman spectroscopy indicated a prominent peak at ~315 cm−1 along with two small peaks after the incorporation of V contents. The AFM analysis showed the big grain and the rough surface of the films. The optical absorption indicates a remarkable shift to the lower wavelength and optical bandgap was found to vary from 2.42 to 2.02 eV with V-doped contents. The photocurrents response of the V-doped SnS2 films was conducted by three-electrode configuration which demonstrating good photoresponse, three times higher than pure SnS2 photoanode. The results reveal that the V- doping with SnS2 is a very promising compound for effectively photovoltaic application.

Micro-abrasive Wear Behavior of Nitrided and Multilayer Coated High Vanadium Powder Metallurgy Alloy

The micro-abrasive behavior of plasma nitrided Vanadis 10, a high vanadium powder metallurgy alloy, combined with TiCN/AlTiN/CrAlTiN/CrN multilayer film was evaluated and compared with different treatment conditions. Microstructural evolution with treatments was evaluated. The tribological behavior was accessed using the fixed ball micro-abrasion test and SiC as abrasive. The counter-body was an AISI 52100 steel sphere (O 25.4 mm), the SiC abrasive slurry concentration was 0.50 g/cm3, the rotary speed was set at 75 rpm, and the applied load was 0.49 N. The wear crater was characterized by scanning electron microscopy (SEM). Results indicated that the film is effective in reducing the wear coefficient in more than 80 pct for all conditions compared with Vanadis 10. Nitriding treatments impaired the samples’ wear resistance because of the presence of cracks in this layer. Sliding/grooving abrasion was observed for the conditions with higher wear coefficients. The change in the micro-abrasion wear mechanism from grooving abrasion to rolling abrasion is attributed to the protection of the surface by the hard multilayer coating, producing a reduction in the wear coefficient.

Phase transformation in spark plasma sintered ZrB2–V–C composites at different temperatures

Spark plasma sintering was employed for the fabrication of ZrB2–V–C composites at different consolidation temperatures (1800, 1900 and 2000 °C) using an external pressure of 40 MPa for 7 min under vacuum atmosphere. Vanadium powders and graphite nano-flakes were applied as metallic and carbonaceous sinter additives, respectively, in the ZrB2 matrix ultrahigh temperature ceramic composites. All composites approached their theoretical densities as the relative density values were >99%. The in-situ synthesis of VB2 and ZrC compounds, during the reactive sintering process at all temperatures, was verified by phase and microstructural analyses. It was found that vanadium and graphite were entirely consumed via reaction with the matrix by sintering at 1900 °C, while the majority of them were left intact at the temperature of 1800 °C. However, the compounds of VB2 and ZrC were partially reacted together, at 2000 °C, which led to the synthesis of extra complex phases of V1.54B50 and V3Zr3C. The hardness of composites slightly decreased with increasing the sintering temperature, while the fracture toughness was remarkably enhanced.

Preparation of vanadium powders by calcium vapor reduction of V2O3 under vacuum

A novel process for synthesizing vanadium powders via calcium vapor reduction of V2O3 under 10 Pa was investigated. The mixture of vanadium trioxide powders and calcium chloride as a flux was the feed preform, and was then reduced by calcium vapor. After reduction, the reduction samples was subjected to a leaching process, the vanadium powders was synthesized by drying and dehydrogenating of the leaching products. The XRD and SEM results of the dehydrogenation products indicated that vanadium were produced and the V particles transformed into clear antler-shaped particles. Vanadium powders (98 wt% V) with 25 ppm H, 1300 ppm N, 1500 ppm O was finally obtained after a dehydrogenation process by Oxygen-nitrogen combined tester (ONH-2000).

The Study on Sintering Capabilities of High Purity Metal Vanadium Powder

High purity metal vanadium powder was milled by high energy ball milling, and the grain size and morphology of vanadium powder was observed by electron probe, and the stress-strain curve was measured by CMT5305 universal testing machine for research of the mechanical property. In order to investigate the effect of sintering process on the property of product, the vanadium powder was sintered by the hot pressing sintering process and the cold isostatic pressing with vacuum sintering process respectively. The experimental results show that for the cold isostatic pressing with vacuum sintering process, the density of raw compact increases with the increase of pressing pressure. When the pressure increases to 280 MPa, the density and relative density of raw compact are 3.99 g·cm-3 and 66.94% respectively, the density and relative density of product after sintering are 5.28 g·cm-3 and 88.59% respectively. With the pressure increasing from 80 MPa to 200 MPa, the compressive strength increases significantly from 0.4 MPa to 6.0 MPa, the pressure increases to 280 MPa, the compressive strength slowly increases to 7.4 MPa. For the hot pressing sintering process, the relative density of product is higher than that of cold isostatic pressing with vacuum sintering process, and the density and relative density reach to 5.51 g·cm-3 and 92.91% respectively under 280 MPa pressure.

Nanosized Vanadium Diboride: Synthesis, Structure, and Properties

X-ray diffraction, scanning electron microscopic, and X-ray photoelectron spectroscopic examinations, as well as energy dispersive X-ray and elemental analyses revealed the formation of single-phase VB2 with the average particle sizes of 20–35 nm from the reaction between vanadium(III) chloride and sodium borohydride at a molar ratio of 1: 10 in the temperature range of 595–930°C in an argon atmosphere at a contact time of 14–28 h. The reaction between amorphous boron and vanadium powders at 800°C in an argon atmosphere at a contact time of 32 h in Na2B4O7 and KCl ionic melts gave VB2 with the average particle size of ~90 nm.