Vanadium Content Research Articles

Rational optimization of substituted α‐MnO2 cathode for aqueous zinc‐ion battery

AbstractDensity functional theory (DFT) is utilized to explore the effects of increasing concentrations of vanadium (V) and chromium (Cr) substitution on the discharge of α‐MnO2 cathode in hydrated zinc‐ion batteries (ZIBs). During H+‐intercalation and Zn2+‐intercalation, Cr‐substitution proves to be more effective than V‐substitution in promoting discharge behaviors. Transitioning from Mn0.875Cr0.125O2, Mn0.75Cr0.25O2 to Mn0.625Cr0.375O2 is found to consistently enhance the discharge voltage, along with improved tunnel structure retention and volume expansion suppression. In comparison, the promoting effect of increasing V‐substitution is relatively small at initial discharge stages and leads to degradation at later stages, primarily due to an increased concentration of unstable Mn2+ ion. The superior effect of Cr‐substitution is attributed to the unique atomic and electronic structures of substituted Cr4+ and reduced Cr3+ ions during discharge. These ions serve as active electron acceptors to limit the formation of Mn3+ and Mn2+ ions, and as anchors to stabilize the α‐MnO2 framework and intercalated H+/Zn2+ ions, respectively. Our study highlights fine‐tuning through substitution to enhance the performance of α‐MnO2‐based cathode materials in ZIBs.

Stability of Vanadium Doped Transition Metal Dichalcogenides under Etching Atmosphere

Two‐dimensional (2D) transition metal dichalcogenides (TMDs) have attracted intensive interests for its unique electronic, optical, and thermal properties. Doping is necessary to expand the application. However, the stability of doped materials has been overlooked. This study focuses on the stability of monolayer‐doped MoS2 with different vanadium (V) concentrations. It provides a quantitative assessment of the etching results. Findings indicate that the stability of MoS2 under different etching atmospheres follows the series of lightly doped MoS2 (LD), pristine MoS2 (PR), moderately doped MoS2 (MD), and highly doped MoS2 (HD). Our research indicates that the stability of the material is linked to the bonding energy of cations and anions, as well as the amount of lattice distortion, which competes with one another. Low levels of V doping do not lead to significant lattice distortion, and the binding energy between sulfur (S) and V surpasses that of molybdenum (Mo), which is the primary factor. Excessive doping results in lattice distortion, which leads to a multitude of defects and a reduction in durability. This work is important for guiding the assessment of the reliability, the protection of degradation, and application scenarios of TMDs.This article is protected by copyright. All rights reserved.

Investigating the structural, electronic, and magnetic properties of Cd1-xVxTe: Insights from First-Principles calculations

In our study, we aim to investigate the structural, electronic, and magnetic properties of CdVTe, a diluted magnetic semiconductor with a Cadmium telluride (CdTe) structure. To achieve this, we employ the full potential linear augmented plane wave method implemented in the CASTEP code, which allows us to accurately simulate the behavior of the system. To describe the electronic exchange and correlation effects, we adopt the generalized gradient approximation (GGA) within the density functional theory (DFT) framework. This choice of methodology ensures reliable and accurate calculations of the electronic and magnetic properties of Cd1-xVxTe. Our results reveal that the substitution of Vanadium (V) into the Cadmium (Cd) site of the CdTe lattice does not alter the zinc blende crystal structure, demonstrating the stability and structural integrity of the system. Furthermore, our calculations demonstrate that the introduction of Vanadium impurities leads to spin polarization within the material, resulting in the emergence of a magnetic moment. Notably, we find that a Vanadium concentration of approximately x≈0.12 exhibits the strongest magnetic properties, characterized by a significant magnetic moment. These findings provide valuable insights into the behavior and potential applications of CdVTe as a diluted magnetic semiconductor, shedding light on the interplay between structural, electronic, and magnetic properties in this material.

Effects of Vanadium Doping on the Optical Response and Electronic Structure of WS2 Monolayers

Abstract2D dilute magnetic semiconductors have been recently reported in transition metal dichalcogenides doped with spin‐polarized transition metal atoms, for example vanadium‐doped WS2 monolayers, which exhibit room‐temperature ferromagnetic ordering. However, a broadband characterization of the electronic band structure of these doped WS2 monolayers and its dependence on vanadium concentration is still lacking. Therefore, power‐dependent photoluminescence, resonant four‐wave mixing, and differential reflectance spectroscopies are performed here to study optical transitions close to the A exciton energy of vanadium‐doped WS2 monolayers at three different doping levels. Instead of a single A exciton peak, vanadium‐doped samples exhibit two photoluminescence peaks associated with transitions from a donor‐like level and the conduction band minima. Moreover, resonant Raman and second‐harmonic generation experiments reveal a blueshift in the B exciton energy but no energy change in the C exciton after vanadium doping. Density functional theory calculations show that the band structure is sensitive to the Hubbard U correction for vanadium, and several scenarios are proposed to explain the two photoluminescence peaks around the A exciton energy region. This work provides the first broadband optical characterization of these 2D dilute magnetic semiconductors, shedding light on the novel and tunable electronic features of V‐doped WS2 monolayers.

A detailed kinetic model for the methanol oxidative dehydrogenation on vanadia-based catalysts: Aggregation state role and active site requirements

A kinetic model was derived for the methanol oxidative dehydrogenation to formaldehyde, methyl formate and dimethoxymethane on sub-monolayer and multilayer V2O5/TiO2 catalysts. Considering a hemiacetal intermediate, the model combines Langmuir-Hinshelwood/Eley-Rideal/Mars-van Krevelen mechanisms, accounting for lattice oxygen redox sites and Brønsted acid sites. The fitted model depends on 4 thermodynamically consistent parameters, adequately simulating yield trends with temperature, residence time, and partial pressure of methanol, oxygen and added water. Oxidation steps follow a Mars-van Krevelen redox cycle, while the dimethoxymethane formation is reversible, as the water addition favored the hemiacetal intermediate. The catalyst with higher vanadia surface density was intrinsically more active (lower activation energy of the rate limiting step), attributed to its higher reducibility, while showing weaker methanol adsorption (lower enthalpy of chemisorption). The increase in reducibility correlates with the transition from monomers to polymers to crystalline vanadia when vanadium content increases, as observed by XRD, Raman spectroscopy and DRS-UV–vis.

Effect of manganese and vanadium additions on the microstructures and two-body abrasive wear behaviors of Fe–B hardfacing alloys

Fe–B wear-resistant alloys often exhibit brittleness and suboptimal wear resistance, making them unsuitable for severe operational conditions. In this study, we incorporated ferromanganese powder and ferrovanadium powder were compounded into the Fe–B wear-resistant alloy by plasma cladding technology. The results indicate that the addition of a minor percentage of vanadium, such as about 2 wt%, does not induce any changes in the phase composition. The alloy layer primarily consists of (Mn,Fe)2B and γ-Fe, with vanadium predominantly dissolving in the primary (Mn,Fe)2B phase. This dissolution enhances the toughness of the hard phase and refines the grain structure. At around 4 wt% vanadium, a spherical VB phase precipitates. This inclusion elevates the impact toughness of the alloy layer. The impact toughness of the high manganese content with 4.69 wt% vanadium is the highest, up to 39.11 J/cm2, which is about 30 %higher than that of the sample without vanadium. As vanadium content rises, both the hardness and wear resistance of the alloy layer improve. The most optimal performance was observed with a manganese content of 20.15 wt% and vanadium at 4.69 wt%, achieving a hardness of 65.5 HRC and wear amounts of 48.1 mg (24 N load) and 85.0 mg (48 N load).

Preparation of V2O3 by a short process of ammonium salt reduction and its electrocatalytic properties investigation

Ammonium salt vanadium precipitation is the main method of vanadium metallurgy at home and abroad, but the traditional ammonium precipitation of vanadium can only obtain high valence of V2O5, and the NH3 produced in the calcination process cannot be fully utilized. And the preparation of low-valence vanadium oxide V2O3 is long and costly. Self-reduction of thermal decomposition of nitrogen-containing precipitation products to produce V2O3 is a novel and short process method that can achieve full utilization of ammonia. NaVO3 was used as the vanadium source, choline chloride (C5H14ClNO (ChCl)) was used as the vanadium precipitation reagent, and the vanadium concentration was 30 g/L, n(ChCl)/n(V) = 1.5, the initial pH was 1.5, the temperature was 85°C, the time was 2 h, and the vanadium precipitation efficiency could reach 97.05%. V2O3 with purity of 97.98% can be obtained by calcination at 550°C for 3 h in an argon atmosphere. XRD, FTIR, XPS, SEM-EDS were used to characterize the product, which further proved that the final product was V2O3. The electrocatalytic hydrogen evolution reaction (HER) of V2O3 in acidic media showed high stability after 1000 cyclic voltammetry (CV) cycles, with a low Tafel slope of 88.5 mVdec−1. The electrochemical double layer capacitance (EDLC) was measured by CV at different scan rates, and the EDLC of V2O3 was 1.104 mFcm−2. This study provides a short-flow preparation method for V2O3 and can provide predictions for the application of V2O3 in HER and supercapacitors.

Associations between maternal blood metal concentrations during the first trimester and spontaneous preterm birth: a nested case-control study

BackgroundFew studies have utilized whole blood samples to investigate the association between metal mixture exposure during early pregnancy and spontaneous preterm birth (SPB). We conduct this nested case–control study to investigate both the independent and joint effect of each metal, and identify critical metals in the metal mixture.ResultsA total of 120 pregnant women with SPB and 120 pregnant women with full-term delivery were selected from the prospective birth cohort. We measured 14 metal concentrations in maternal blood collected during 10–13 weeks gestation. Conditional logistic regression showed that high concentrations of vanadium (V), magnesium, and copper were positively associated with SPB (Adjusted OR = 5.76 (95% CI 2.46–13.53), 3.64 (95% CI 1.64–8.09), 2.88 (95% CI 1.29–6.41), respectively). Moderate manganese (Mn) concentration (50th–75th percentile) group had the lowest estimated OR (Adjusted OR = 0.32 (95% CI 0.13–0.76)). The high level of strontium (Sr) was negatively associated with SPB (Adjusted OR = 0.39 (95% CI 0.17–0.91)). The BKMR model showed a significant positive joint effect of metal mixture exposure on SPB, while V was the most important metal. The non-linear effects of V and lead (Pb) on SPB, and the interaction effects between V–Pb, Sr–Mn were also revealed.ConclusionsMaternal blood metal mixtures in the first trimester were found to be positively associated with SPB, with V exhibiting the strongest independent association. Mn had a potential U-shaped association with SPB. Elimination of metal contamination in the environment has a positive impact on maternal and child health.

Highly efficient recovery of vanadium from Abu Zeneima ferruginous siltstone, Southwestern Sinai, Egypt, by a novel polyimine‐based chelating ligand

AbstractTo extract V5+ ions from the ferruginous siltstone in the Abu Zeneima region of Southwestern Sinai, Egypt, a chelating polyimine ligand (PVAm‐Ben) was synthesized via a condensation reaction involving polyvinyl amine and α‐hydroxy ketone (Benzoin). The structure of PVAm‐Ben underwent comprehensive characterization employing various techniques, namely; FT‐IR, 1H‐NMR, 13C‐NMR, and GC/MS analyses. Experimental factors controlling such as pH, time, initial concentration, dosage, temperature, and stripping, were systematically optimized to enhance measurement accuracy. Under conditions of 25°C, 0.015 mol/L, and 30 minutes, PVAm‐Ben/C2H4Cl2 exhibited remarkable retention capacity at pH 3. Linear regression analysis results suggested the release of a mole of H+ during the extraction process. The stability constant (log β = 2.1882) of the PVAm‐Ben/V5+ complex was determined, yielding a value of 154.24. The stoichiometry mechanism between PVAm‐Ben and V5+ ions displayed a linear correlation (slope: 0.9922), signifying 1 mole of PVAm‐Ben reacting with 1 mole of vanadium. The pseudo‐second‐order kinetic model indicated an exothermic, spontaneous, and advantageous extraction process at low temperatures. Efficient stripping of PVAm‐Ben/C2H4Cl2 loaded with vanadium was achieved using 0.05 M NaOH with a 99% efficiency rate. Ultimately, enhanced variables were employed to yield a V2O5 concentrate with a vanadium content of 55% and a purity level of 98.21%.

Transcriptome analysis reveals vanadium reduction mechanisms in a bacterium of Pseudomonas balearica

The continuously elevated concentration of vanadium (V) in the environment is of great concern due to its potential risks to organisms. Microbial reduction is considered a green way to remediate the V-contaminated sites. This study presents the first demonstration of Pseudomonas balearica, a bacterium flourishing in vanadium-titanium magnetite tailings, exhibiting the capacity to reduce pentavalent V [V(V)]. We found that P. balearica exhibited strong tolerance to high V(V) levels, despite lacking known V(V)-reducing genes. After 48 h of incubation, the reduction rates of V(V) by P. balearica under 0.5 mM and 10 mM V(V) stress reached 81.1% and 60.6%, respectively. The phosphorus group and carboxyl group on the bacterial cell surface contributed to V(V) binding and reduction. Both extracellular and intracellular V(V) reduction was significantly facilitated by many critical V-induced differentially expressed genes (DEGs) encoding nitrate/nitrite reductases, ABC transporters, NADH, and c-type cytochromes. In addition, up-regulation of DEGs associated with reactive oxygen species (ROS)-scavenging enzymes, such as glutathione peroxidase, superoxide dismutase, and catalase, was observed as a protective response to oxidative stress triggered by V(V). Moreover, some up-regulated DEGs (ureC, ureE, ureA, and ureG) encoding urease subunit or urease accessory proteins significantly enriched in the nickel cation binding pathway, indicating that P. balearica may be resistant to Ni stress by regulating urease activity. This study will help to more thoroughly elucidate the characteristics and mechanisms of V(V) reduction by microbes and provide a native bacterium flourishing in tailings for potential bioremediation of V pollution and bioleaching of V-sources.

Efficient reduction of vanadium (V) with biochar and experimental parameters optimized by response surface methodology

Water pollution deteriorates ecosystems and has a great threaten to the environment. The environmental benefits of wastewater treatment are extremely important to minimize pollutants. Here, the biochar purchased from the related industry was used to treat the wastewater which contained high concentration of vanadium (V). The concentration of vanadium was measured by the IC-OES and the results showed that 96.1% vanadium (V) was reduced at selected reaction conditions: the mass ratio of biochar to vanadium of 5.4, reaction temperature of 90 °C, reaction time at 60 min and concentration of H2SO4 of 10 g/L, respectively. Response surface methodology confirmed that all the experimental parameters had positive effect on the reduction of vanadium (V), which could improve the reduction efficiency of vanadium (V) as increased. The influence of each parameter on the reduction process followed the order: A (Concentration of H2SO4) > C (mass ratio of biochar to vanadium) > B (mass ratio of biochar to vanadium). Especially, the mass ratio of biochar to vanadium and concentration of H2SO4 had the greatest influence on the reduction process. This paper provides a versatile strategy for the treatment of wastewater containing vanadium (V) and shows a bright tomorrow for wastewater treatment.

Time-specific impact of trace metals on breast density of adolescent girls in Santiago, Chile.

Whether trace metals modify breast density, the strongest predictor for breast cancer, during critical developmental stages such as puberty remains understudied. Our study prospectively evaluated the association between trace metals at Tanner breast stage B1 (n = 291) and at stages both B1 and B4 (n = 253) and breast density at 2 years post-menarche among Chilean girls from the Growth and Obesity Cohort Study. Dual-energy x-ray absorptiometry assessed the volume of dense breast tissue (absolute fibroglandular volume [FGV]) and percent breast density (%FGV). Urine trace metals included arsenic, barium, cadmium, cobalt, cesium, copper, magnesium, manganese, molybdenum, nickel, lead, antimony, selenium, tin, thallium, vanadium, and zinc. At B1, a doubling of thallium concentration resulted in 13.69 cm3 increase in absolute FGV (β: 13.69, 95% confidence interval [CI]: 2.81, 24.52), while a doubling of lead concentration resulted in a 7.76 cm3 decrease in absolute FGV (β: -7.76, 95%CI: -14.71, -0.73). At B4, a doubling of barium concentration was associated with a 10.06 cm3 increase (β: 10.06, 95% CI: 1.44, 18.60), copper concentration with a 12.29 cm3 increase (β: 12.29, 95% CI: 2.78, 21.56), lead concentration with a 9.86 cm3 increase (β: 9.86, 95% CI: 0.73, 18.98), antimony concentration with a 12.97 cm3 increase (β: 12.97, 95% CI: 1.98, 23.79) and vanadium concentration with a 13.14 cm3 increase in absolute FGV (β: 13.14, 95% CI: 2.73, 23.58). Trace metals may affect pubertal breast density at varying developmental stages with implications for increased susceptibility for breast cancer.

Studies on chemically prepared Zn1-2xSnxVxO nanoparticles for supercapacitor application

The present study reports the preparation of Zn1–2xSnxVxO (0≤x≤0.10) nanoparticles synthesized by the co-precipitation method. Phase determination and structural properties are carried out using the X-ray diffraction technique. Young's modulus, bond length and bond angles are examined. The change in the crystallite size, texture coefficient and bond length indicates that the dopants Sn and V are successfully incorporated in the Zn lattice. The average crystallite size ranges from ∼32 – 19 nm for various doping concentrations of tin & vanadium. The texture coefficient increases due to the addition of the dopant. The band gap is 3.253 eV when x=0.00 and the same is 3.229 eV when x=0.10. Due to the addition of dopants, a red-shifted band gap is observed. The charge carrier concentration increases as the doping concentration of tin & vanadium increases and the prepared nanoparticles are p-type in nature. More vacancies and more defects are observed from the dielectric studies. The doping increases the specific capacitance and a maximum specific energy density of 11,372 J/kg is observed.

A Non-Stabilized Supersaturated High-Energy-Density Storage Concept for the Redox Flow Battery and Its Demonstration in an H2-V System

Redox Flow Batteries are ideal for grid-scale energy storage but have low energy density. In an effort to resolve this issue, this work presents an H2-vanadium RFB system that operates with the catholyte above the solubility limit of vanadium ions in the supersaturated regime without the use of chemical stabilizers, necessary for the operation of a novel solid/liquid storage concept. Initial charge/discharge testing was performed at constant potential (1.35 V charge and 0.65 V discharge) increasing Vanadium concentrations from 1.5 M to 2.5 M. Coulometric capacity increased 67% (40.2 Ah l−1 to 67.0 Ah l−1) while average current density decreased 35% (48 mA cm−2 to 31 mA cm−2) with charge/discharge limited to SOC (20%–80%). Continuing charge/discharge with a cutoff current of 5.56 mA cm−2 increased coulombic capacity by 43% (36.4 Ah l−1 to 51.9 Ah l−1) while average current density decreased 17% (27.7 mA cm−2 to 22.9 mA cm−2). Additional testing was performed with constant current charge/discharge (75 mA cm−2), limited by cutoff potential (1.35 V charge and 0.60 V discharge). Coulometric capacity increased 73.5% (26.5 Ah l−1 to 46.0 Ah l−1) with higher working potential for the 2.5 M Vanadium solution. Energy capacity increased 79.1% (25.3 Wh l−1 to 45.3 Wh l−1) with minimal change in charge/discharge power (90.7/−70.9 mW cm−2 to 92.1/−72.8 mW cm−2) and efficiency (77.1% to 78.4%).

Influence of aluminum and vanadium oxides on copper borate glass: A physical/radiological study

Due to the radiation released by commonly used isotopes, many nuclear, medical, and industrial facilities require proper radiation shielding. In this work, distinct copper borate glasses intercalated with varied aluminum and vanadium oxide (Al2O3 and V2O5) content have been synthesized and used against radiation (gamma rays and fast/thermal neutrons). The different percents were as follows: [60% B2O3 + 35% CuO + (5-x)% Al2O3 + xV2O5], where x = 0, 1, and 2.5 wt.%, which was coded as BCu(5-x)Al:xV. The synthesized glass samples were characterized using Fourier transforms, infrared, and X-Raydiffraction analysis. Experimentally, the radiation shielding possessions of the samples were established using an HPGe detector at the gamma energy lines 0.356 MeV, 0.661 MeV, 1.173 MeV, and 1.332 MeV. Also, the prepared glasses were investigated theoretically using the Monte Carlo code (MCNP5) at photon energies of 0.015–15 MeV. Also, the fast and thermal neutron macroscopic effective removal cross-sections were calculated using MRCsC and JANIS-4.1 software, respectively. The prepared sample BCu2.5Al:2.5V, which has a vanadium and aluminum content of 2.5%, has the highest linear attenuation coefficient as well as the highest removal cross-section for fast, and thermal neutrons.

Effect of tempering temperature on stress corrosion resistance of a low alloy high strength steel with high vanadium content

The stress corrosion resistance of a low alloy high strength steel with high vanadium content, tempered at different temperatures, was examined by electrochemical measurements and slow strain rate tensile test under different environments. Combined with scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), the results show that three different tempering temperatures had an influence on the microstructure of this steel as well as its electrochemical behavior and stress corrosion sensitivity. With the increase of tempering temperature, the ferrite grains coarsened, the average dislocation density lowered as well as the number of vanadium carbide also decreased, though the size of vanadium carbide increased. However, the interface distortion between vanadium carbide and matrix exacerbated, resulting in the increase of the local dislocation density. Therefore, the corrosion potential and impedance decreased, meantime, the stress corrosion sensitivity aggravated.

Effects of vanadium content on the microstructure and tensile properties of NbTiVxZr high-entropy alloys

Vanadium boasts a relatively small atomic radius among numerous refractory alloying elements, yet its effects on the microstructure and mechanical behavior of refractory alloys remain enigmatic. In this work, a series of NbTiVxZr high-entropy alloys (HEAs) with low density were formulated to explore the evolution of microstructures and mechanical properties with varying vanadium content. When the vanadium content was low, the matrix exhibited the single-phase body-centered cubic structure. Excessive vanadium contents (NbTiV0.75Zr, NbTiVZr) disrupted phase stability and tended to aggregate at grain boundaries, forming V-rich and Zr-rich phases. These precipitated phases pinned grain boundaries, impeding grain growth and resulting in both grain boundary strengthening and precipitation strengthening, albeit at the expense of grain boundary cohesion, ultimately leading to brittleness. However, these deleterious phases were redissolved, and fracture elongation increased more than 2 times after water quenching at 1200 °C. The microstructural changes induced by heat treatment were corroborated by alterations in grain boundary relaxation behavior, where the redissolution of precipitated phases after water quenching caused a shift of the grain boundary relaxation internal friction peak to a lower temperature and an increase in peak height. This study elucidates the intrinsic relationship between mechanical properties and microstructures with vanadium content in NbTiVxZr alloys, offering insights for the design of TiV-based lightweight refractory HEAs with high strength and excellent ductility.

The incidence of upper respiratory infections in children is related to the concentration of vanadium in indoor dust aggregates.

It has been reported that the disease-initiated and disease-mediated effects of aerosol pollutants can be related to concentration, site of deposition, duration of exposure, as well as the specific chemical composition of pollutants. To investigate the microelemental composition of dust aggregates in primary schools of Vilnius and determine trace elements related to acute upper respiratory infections among 6-to 11-year-old children. Microelemental analysis of aerosol pollution was performed using dust samples collected in the classrooms of 11 primary schools in Vilnius from 2016 to 2020. Sites included areas of its natural accumulation behind the radiator heaters and from the surface of high cupboards. The concentrations of heavy metals (Pb, W, Sb, Sn, Zr, Zn, Cu, Ni, Mn, Cr, V, and As) in dust samples were analyzed using a SPECTRO XEPOS spectrometer. The annual incidence rates of respiratory diseases in children of each school were calculated based on data from medical records. The mean annual incidence of physician-diagnosed acute upper respiratory infections (J00-J06 according to ICD-10A) among younger school-age children was between 25.1 and 71.3% per school. A significant correlation was found between vanadium concentration and the number of episodes of acute upper respiratory infections during each study year from 2016 to 2020. The lowest was r = 0.67 (p = 0.024), and the highest was r = 0.82 (p = 0.002). The concentration of vanadium in the samples of dust aggregates varied from 12.7 to 52.1 parts per million (ppm). No significant correlations between the other trace elements and the incidence of upper respiratory infections were found, which could be caused by a small number of study schools and relatively low concentrations of other heavy metals found in the samples of indoor dust aggregates. A significant and replicable correlation was found between the concentration of vanadium in the samples of natural dust aggregates collected in primary schools and the incidence of acute upper respiratory infections in children. Monitoring the concentration of heavy metals in the indoor environment can be an important instrument for the prevention and control of respiratory morbidity in children.

Influence of V on the Microstructure and Precipitation Behavior of High-Carbon Hardline Steel during Continuous Cooling.

High-carbon hardline steels are primarily used for the manufacture of tire beads for both automobiles and aircraft, and vanadium (V) microalloying is an important means of adjusting the microstructure of high-carbon hardline steels. Using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the microstructure and precipitation phases of continuous cooled high-carbon steels were characterized, and the vanadium content, carbon diffusion coefficient, and critical precipitation temperature were calculated. The results showed that as the V content increased to 0.06 wt.%, the interlamellar spacing (ILS) of the pearlite in the experimental steel decreased to 0.110 μm, and the carbon diffusion coefficient in the experimental steel decreased to 0.98 × 10-3 cm2·s-1. The pearlite content in the experimental steel with 0.02 wt.% V reached its maximum at a cooling rate of 5 °C·s-1, and a small amount of bainite was observed in the experimental steel at a cooling rate of 10 °C·s-1. The precipitated phase was VC with a diameter of ~24.73 nm, and the misfit between ferrite and VC was 5.02%, forming a semi-coherent interface between the two. Atoms gradually adjust their positions to allow the growth of VC along the ferrite direction. As the V content increased to 0.06 wt.%, the precipitation-temperature-time curve (PTT) shifted to the left, and the critical nucleation temperature for homogeneous nucleation, grain boundary nucleation, and dislocation line nucleation increased from 570.6, 676.9, and 692.4 °C to 634.6, 748.5, and 755.5 °C, respectively.

Insight studies on the deactivation of sulfuric acid regeneration catalyst

The SAR unit is used for regenerating spent sulfuric acid for alkylation reactions. In the SAR unit, the converter employs a potassium and vanadium-based catalyst for conversion of SO2 to SO3. The multiple bed fixed bed reactor is there to ensure that almost entire amount of SO2 is converted to SO3. On observing the generation of large amounts of fines in the reactor catalyst, the spent catalyst and fines are collected for insight studies. The current study enlightens the possible causes of catalyst deactivation and fines generation. Structural changes in potassium/vanadium based catalyst during the oxidation of sulfur dioxide identified as the major cause of catalyst deactivation. Such structural changes and their impact on catalyst property were determined using various physico-chemical characterization methods like crushing strength, Loss on drying (LOD), XRF, XRD, FTIR and XPS analysis. LOD analysis shows the higher moisture and volatile content in spent and fines compared to fresh catalyst. High moisture content in spent catalyst decreases hardness of catalyst resulting in leaching of vanadium salt and carrier degradation due to thermal cycling. Chemical analysis data found to show the active vanadium content in fines is higher compared to spent which indicates vanadium has leached out from fresh catalyst and is deposited on fines. These observations are further correlated with XRD and XPS results. XPS analysis shows the relative distribution of V4+ and V5+ species on the catalyst surface are altered and found very low concentration of V4+ sites on spent catalyst. The XRD analysis demonstrates the leaching of the active component, potassium vanadyl sulfate K(VO2) (SO4)·3H2O, which then accumulated in the fines fraction. FT-IR and XRD results further shows increase in sulfate accumulation on spent catalyst surface along with phase changes. FTIR analysis of simulated spent catalyst are well correlated with these findings.