Substitution Of Tungsten Research Articles

Optimized energy storage with hydrothermally synthesized metal sulfide nanocomposite electrodes

Supercapacitors exhibit impressive energy storage capabilities, providing high power density and quick charge/discharge cycles across various applications, including electronics and renewable energy systems. Molybdenum disulfide (MoS2) plays a crucial role in enhancing supercapacitor performance through its high surface area, conductivity, and electrochemical stability. Recent reports have shown that manipulating phase transitions and incorporating dopants or substitutions can significantly enhance the performance of 2D materials. The present study investigated the influence of tungsten substitution on the phase changes and electrochemical properties of MoS2. The hydrothermal synthesis process involved the substitution of tungsten with different concentration, leading to a notable phase change from 2 H to 1 T, as confirmed by X-ray diffraction (XRD) analysis. Morphological studies using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) revealed modifications in the morphological structure. The electrochemical performance of pristine MoS2 and MoS2/WS2 composites were evaluated using cyclic voltammetry (CV), chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS). The determined specific capacitances of MoS2/WS2 composites exhibited higher values compared to pristine MoS2. Specifically, the sample with 15 mol% tungsten addition demonstrated a maximum specific capacitance of 333 F g−1, surpassing that of pristine MoS2 and other samples at a current density of 1 A g−1. This research provides valuable insights into the phase-dependent electrochemical behaviour of MoS2 with tungsten substitution, offering a better understanding of its potential for applications in high-performance energy storage devices.

High‐performance bismuth titanate‐ferrite (Bi5Ti3FeO15) for high‐temperature piezoelectric applications

AbstractAdvancing the development of high‐temperature piezoelectric sensors requires high‐performance piezoelectric materials with high Curie temperatures, wherein the charge signals can be efficiently collected at elevated temperatures. The bismuth layer‐structured ferroelectric (BLSF) bismuth titanate‐ferrite (Bi5Ti3FeO15, BTF) has recently attracted considerable attention because of its high Curie temperature (TC) of ∼761°C. However, the piezoelectric properties of BTF‐based compounds have not been extensively investigated because of their extremely poor piezoelectric performances and low electrical resistivities at elevated temperatures. Herein, tungsten‐substituted BTF (BTF‐100xW) ceramics were synthesized using a solid‐state reaction method. X‐ray diffraction refinement results confirmed the lattice distortion of the BO6 octahedron, while piezoelectric force microscopy images verified an increase in the domain wall density with tungsten modification, both of which contribute to significant enhancement of the piezoelectric properties of BTF‐100xW as intrinsic and extrinsic contributions, respectively. Remarkably, BTF‐3W exhibits a high TC of 793°C and a large piezoelectric constant (d33) of 24.3 pC/N, which is over three times that of BTF (7.1 pC/N). Importantly, the substitution of tungsten decreases the concentration of oxygen vacancies, increases the direct current electrical resistivity, and improves the electrical homogeneity at high temperatures, resulting in extremely stable piezoelectric and electromechanical properties at high temperatures, with a high in‐situ relative d33 of >90% at 400°C and a small variation in the electromechanical coupling factor (kp) of <8% at temperatures up to 450°C. These results suggest that the tungsten‐substituted BTF is a potential candidate for high‐temperature piezoelectric ceramics, and is a promising material for applications in high‐temperature piezoelectric sensors.

Enhanced rate capability and mitigated capacity decay of ultrahigh-nickel cobalt-free LiNi0.9Mn0.1O2 cathode at high-voltage by selective tungsten substitution

Owing to the further requirement for electric vehicle market, it is appropriate to lower the cost and improve the energy density of lithium-ion batteries by adopting the Co-free and Ni-rich layered cathodes. However, their practical application is severely limited by structural instability and slow kinetics. Herein, ultrahigh-nickel cobalt-free LiNi0.9Mn0.1O2 cathode is elaborate designed via in-situ trace substitution of tungsten by a wet co-precipitation method following by high-temperature sintering. It is revealed that the in-situ doping strategy of high valence W6+ can effectively improve the structure stability by reducing irreversible phase transition and suppressing the formation of microcracks. Moreover, the transformed fine particles determined by W-doping can facilitate the kinetic characteristics by shortening Li+ diffusion paths. As expected, 0.3 mol% W-doped LiNi0.9Mn0.1O2 cathode exhibits a high specific capacity of 143.5 mAh/g after 200 cycles at high rate of 5 C in the wide potential range of 2.8-4.5 V, representing a potential next-generation cathode with low-cost, high energy-density and fast-charging capabilities.

Enhanced electrochemical properties of W-doped Na3V2(PO4)2F3@C as cathode material in sodium ion batteries

Sodium super ion conductors (NASICON) based structures are being explored as cathode materials for application in sodium ion battery technology. Na3V2(PO4)2F3 has been established as an important candidate in this category but suffers from low electronic conductivity. In this work, the effect of the substitution of Tungsten (W) in place of Vanadium on the electrochemical performance of Na3V2(PO4)2F3@C in sodium ion battery (SIB) has been elucidated in detail. The crucial role played by the synthesis method and the product morphology on the electrochemical property of the cathode material has been highlighted. The Na3V1.96W0.04(PO4)2F3@C cathode synthesized using sonochemically assisted sol gel followed by ball milling method exhibits improved structural integrity and enhanced Na-ion mobility. The cathode delivers a high reversible capacity of 153 mAh g−1 at 0.1C. Theoretical studies indicate that incorporation of W reduces the band gap and improves the interfacial resistance of Na3V2(PO4)2F3@C.

Improved mechanical properties by nanosize tungsten-molybdenum carbides in tungsten containing hot work die steels

AISI H13 die steel with substitution of tungsten for vanadium (H13–W) was produced through vacuum induction melting and forging, followed by 1050°C-quenching and 600°C-tempering. Through 10–40 h of 600°C-tempering, H13–W exhibits superior red hardness as compared to H13 steel. The increments of hardness (4-6HRC) as well as yield strength were deducted to the precipitated M6C-type carbides with sizes ranging from 10 nm to 400 nm. Two classifications of carbides are identified. Type I of carbides has the nano size of 8–50 nm, and type II of undissolved primary carbides ((Fe1.34Mo1.62 Cr2.95W0.09)C) has the bigger size of 100–400 nm. The yield strength increments (Δσy) were modeled by a bivariate distribution of nano and undissolved precipitates. The calculated major strengthening effects from type I nano carbides in H13–W/H13 steels were close to the deduced values by Hall-Petch theory, they were 1053 MPa and 965.8 MPa, respectively. According to the calculation on equilibrium solubility of precipitations of MoC/Mo2C and WC/W2C, it was testified that MoC, Mo2C, WC and W2C were wholly dissolved into austenite at 1050 °C of quenching, followed by precipitating in large quantities in the form of nanosize carbides at 600oC-tempering.

Zirconium alloyed tungsten borides synthesized by spark plasma sintering

Tungsten borides (WBx; x = 2.5 or 4.5) with an increasing substitution of tungsten by zirconium from 0 to 24 at.% were synthesized by spark plasma sintering (SPS) for the first time. The influence of the holding time (2.5–30 min) on the densification behavior, microstructure evolution and development of the properties of W–Zr–B compounds were studied. The samples were characterized using scanning electron microscopy (SEM) for microstructure analysis, X-ray diffraction (XRD) for phase identification, Vickers micro-indentation for microhardness measurements, tribological tests to determine the coefficient of friction and specific wear rate, as well as measurements of electrical conductivity. The XRD results confirm the presence of the WB4 phase in the microstructure, despite the high sintering temperature (1800 °C) and small overstoichiometric excess of boron (4.5) addition in the sintered samples. This is caused by the high heating rate (400 °C/min), short holding time (2.5 min) and addition of zirconium. The Vickers hardness (HV) values measured at 1 N are 24.8 ± 2.0 and 26.6 ± 1.8 GPa for 24 at.% zirconium in WB2.5 and for 0 at.% zirconium in WB4.5, respectively. In addition, the hardest sample (W0.76Zr0.24B2.5) showed electrical conductivity up to 3.961·106 S/m, which is similar to WC–Co cemented carbides. The friction and wear test results reveal the formation of a boron-based film which seems to play the role of a solid lubricant.

Li1.5La1.5MO6 (M\u2009=\u2009W6+, Te6+) as a new series of lithium-rich double perovskites for all-solid-state lithium-ion batteries

Solid-state batteries are a proposed route to safely achieving high energy densities, yet this architecture faces challenges arising from interfacial issues between the electrode and solid electrolyte. Here we develop a novel family of double perovskites, Li1.5La1.5MO6 (M = W6+, Te6+), where an uncommon lithium-ion distribution enables macroscopic ion diffusion and tailored design of the composition allows us to switch functionality to either a negative electrode or a solid electrolyte. Introduction of tungsten allows reversible lithium-ion intercalation below 1 V, enabling application as an anode (initial specific capacity >200 mAh g-1 with remarkably low volume change of ∼0.2%). By contrast, substitution of tungsten with tellurium induces redox stability, directing the functionality of the perovskite towards a solid-state electrolyte with electrochemical stability up to 5 V and a low activation energy barrier (<0.2 eV) for microscopic lithium-ion diffusion. Characterisation across multiple length- and time-scales allows interrogation of the structure-property relationships in these materials and preliminary examination of a solid-state cell employing both compositions suggests lattice-matching avenues show promise for all-solid-state batteries.

Кристаллическая структура и диэлектрические свойства керамических материалов на основе AgNbO3

Using the data of qualitative X-ray phase analysis, it was shown that in a wide concentration range at 1223 K compounds based on silver niobate are formed in the condition of the heterovalent substitution of tungsten(VI) ions for niobium(V) ions. These compounds are isomorphic to a perovskite-type structure. Microprobe analysis data allows to determine the homogeneity of the analyzed samples and the correspondence of their experimental compositions to the theoretical ones for the formula Ag1-xNb1-xWxO3. Using the data of X-ray diffraction analysis (Rietveld method) in the Crystallography Data Analysis Software – GSAS, the crystal structure of the obtained compounds was refined. The surface morphology of samples having been obtained at 1373 K was investigated by scanning electron microscopy (SEM). It was shown that with an increase of Nb5+ to W6+ substitution degree for Ag1-xNb1-xWxO3 ceramic samples in the range of the (0.2≤x≤0.8) molar ratio, the average particle size for the studied compositions grows from 1.3 to 5.2 μm, respectively. For the obtained ceramic compounds based on silver niobate with a perovskite-like structure (tetragonal distortion), the temperature-frequency dependences of dielectric parameters in the range 300-900 K were studied. It was found that samples slowly cooled from 1373 K are characterized by low values of (ε ~ 10) and loss (tgδ ~ 0.004 at f = 1 kHz) at room temperature. The ceramics obtained are characterized by relatively high values of dielectric permittivity ε at low frequencies and/or high temperatures. The dielectric parameters of the obtained ceramics are similar to the characteristics of so-called "colossal" dielectric constant materials. The revealed features of the dielectric characteristics of quenched ceramics apparently result from Maxwell-Wagner relaxation at intercrystalline contacts.

Effect of partial substitution of iron by tungsten on the crystal structure and electronic properties of WB3

Polycrystalline samples of the W1-xFexB3 (x = 0.00, 0.15) were synthesized by the first time by arc melting. The effect of the chemical pressure due to the substitution of tungsten by iron atoms on the crystal structure and electronic properties were studied by X-ray diffraction, electron microscopy, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and Density Functional Theory calculations. Rietveld refinement analysis indicate the presence of transition metal vacancies in the structure. The Mössbauer spectroscopy shows the presence of two non-equivalent crystallographic sites with different chemical environments, which are symptomatic of a charge density redistribution for one of the two iron sites and suggesting a vacancies formation mechanism. X-ray photoelectron spectroscopy and Density Functional Theory calculations show a similar density charge behavior for the tungsten atoms. Finally, an increment of electronic states at the Fermi level was predicted due to the partial iron substitution in the highest boride of tungsten.

Extension of the A nB nO3 n+2 Slicing/Oxidizing Process from 2D Layered to 1D Columnar Perovskites: The La7W7-xM xO30 Structural Family with Di-, Tri-, and Tetravalent Transition Metal M Substitutes to Tungsten.

The A7B7O30 structural type is a columnar-perovskite-type arrangement originally evidenced in La7Mo7O30 [Goutenoire et al. J. Solid State Chem. 1999, 142, 228], an intermediate reduction product of fast oxide-ion conductor La2Mo2O9. Subsequently, this new structural family has been extended to La7W6+4M5+3O30 (M = Nb, Ta) [Goutenoire et al. J. Solid State Chem. 2005, 178, 2811]. Here we show that it is possible to further extend the solid solution through partial substitution of hexavalent tungsten by di-, tri-, or tetravalent transition metals. The general formula is La3+7W6+7- xM m+ xO30 with x = 3/(6 - m), or m = 6 - 3/ x. Single phase samples with M m+ = Zn2+, Fe3+, and Ti4+ have been prepared, and their crystal structure refined using X-ray powder diffraction. In the structure, the transition metal with lower valence is preferentially located in the octahedral site shared by consecutive trans-connected perovskite cages, whose diagonal runs along the threefold axis of the structure. Close similarities are noticed with the cationic repartition and distortion of coordination polyhedra in compounds belonging to the A nB nO3 n+2 series of layered perovskites. A rationale is proposed, which includes the A7B7O30 structural type as a subsequent 1D step to the 3D → 2D A nB nO3 n+2 scheme of perovskite framework slicing by progressive oxygen insertion through decreasing n.

Synthesis and Properties of Vanadium Substituted Bismuth Tungstates with Fluorite-like Structure

The samples of vanadium substituted bismuth tungstates with a cubic structure were obtained by solid state method. The unit cell volume of the compounds slightly contracts with increasing tungsten content and in case of vanadium doping. Thermal expansion coefficient of bismuth tungstate is equal to 13×10-6 °C-1. The electrical conductivity was investigated using ac impedance spectroscopy. The results showed that the substitution of tungsten with vanadium ions increased electrical conductivity values by one order of magnitude.

Superhard Tungsten Diboride-Based Solid Solutions.

Solid solutions of tungsten diboride (WB2) with increasing substitution of tungsten (W) by tantalum (Ta) and niobium (Nb)-ranging from 0 to 50 at. % on a metals basis-were synthesized through resistive arc melting. Samples were characterized using a combination of powder X-ray diffraction (PXRD) for phase identification, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy for elemental composition, Vickers microindentation for hardness measurements, and thermogravimetric analysis for thermal stability. The solubility limit was found to be less than 8 at. % for Nb and less than 10 at. % for Ta, as determined by PXRD. Vickers hardness ( Hv) values were measured to be 40.3 ± 1.6 and 41.0 ± 1.2 GPa at 0.49 N for 6 at. % Nb and for 8 at. % Ta substitution, respectively. In addition, the hardest solid solution (W0.92Ta0.08B2) showed oxidation resistance up to ∼570 °C, approximately 70 °C higher than that of tungsten carbide (WC). Although pure WB2 is known not to be superhard, these results demonstrate the formation of superhard solid solutions through the substitution of tungsten by small amounts of transition metals. This increase in hardness can be attributed to solid solution hardening.

Understanding the Influence of Lattice Composition on the Photocatalytic Activity of Defect‐Pyrochlore‐Structured Semiconductor Mixed Oxides

The defect‐pyrochlore‐structured photocatalyst CsTaWO6 is an ideal starting material for anion doping from the gas phase, and is known to be highly active for solar hydrogen generation under simulated sunlight without co‐catalysts. To investigate the active site of CsTaWO6 for hydrogen generation and to understand the effects of the two d0 elements in the compound, systematic and successive element substitution of tantalum and tungsten on the crystallographic 16c sites of the starting material has been performed. Substituting lattice tantalum with niobium hardly changes the band gap of the resulting compounds CsTa(1 −x)Nb x WO6, but the photocatalytic activity for hydrogen generation and oxidation reactions is strongly influenced. By investigating the surface reactivity toward adsorption, surface effects altering the activity are identified. In contrast, substituting lattice tungsten with molybdenum reduces the band gap of CsTaWO6 into the visible‐light range. Materials containing Mo are however not able to generate hydrogen anymore, due to the altered conduction band positions proven by density functional theory calculations. CsTaMoO6 exhibits a band gap of 2.9 eV and evolves oxygen efficiently under UV light irradiation after CoPi co‐catalyst deposition, and even under visible light small amounts of oxygen.

Effects of Partial Replacement of Iron with Tungsten on Microstructure, Electrical, Magnetic and Humidity Properties of Copper-Zinc Ferrite Material

This paper presents the analysis of the influence of partial replacement of iron with tungsten on the properties of copper-zinc spinel ferrite material. The samples of Cu0.5Zn0.5WxFe2−xO4 spinel powder ferrites were prepared by using a sol–gel self-combustion technology. The ferrite samples were treated for 30 min at 1000°C. The x-ray diffraction was used in order to establish the differences between the phase compositions of ferrites with different tungsten content. Scanning electron microscopy was used to highlight the influence of the tungsten content on the crystallites. All the samples of Cu0.5Zn0.5WxFe2−xO4 were subject to investigation of the influence of the substitution of tungsten upon their electrical and magnetic properties. The measurements of the electrical properties were performed in different humidity conditions, in order to highlight the effect of moisture conditions on the electrical properties of the material and to analyze the applicability of Cu0.5Zn0.5WxFe2−xO4 ferrite for resistive or capacitive humidity sensors.

Influence of partial substitution of Fe3+ with W3+ on the microstructure, humidity sensitivity, magnetic and electrical properties of barium hexaferrite

This paper investigates the influence of partial substitution of iron with tungsten on the properties of barium hexaferrite. The BaWxFe12−xO19 hexaferrite samples were prepared by using a sol–gel autocombustion technology. The powder ferrites were heat treated for 30min at 1000°C. The samples were investigated by using X-ray diffraction in order to highlight the differences between the phase compositions of comparative samples. The influence of the substitution of tungsten ions on the size and shape of the crystallites was revealed by the scanning electron microscopy. The investigations of the substitution of tungsten were focused mainly on magnetic and electrical properties of the BaWxFe12−xO19 ferrites; the measurements of electrical properties were performed in different humidity conditions, aimed at obtaining a ferrite useful as a material support for capacitive or resistive humidity sensors. In this respect, the partial substitution of iron with tungsten contributes to an increasing of permittivity and to a reduced electrical resistivity of the material, without significantly lowering its sensitivity to humidity.

Study on Mesoporous PW/SBA-15 for Isomerization of α-Pinene

SBA-15 supported phosphotungstic acid has been synthesized under hydrothermal conditions via pH adjustment and characterized with various analytical and spectroscopic techniques including X-ray diffraction (XRD), N2 adsorption, transmission electron micrographs (TEM). XRD results indicate that the substitution of tungsten occurs in the silicate framework structure of SBA-15. Study on the catalytic activity of mesoporous PW/SBA-15 catalyst through the isomerization of the a-pinene was investigated. The best reactive conditions of a-pinene isomerization were follows: reaction temperature 130°C, dosage of PW/SBA-15 catalyst 2 %, reactive time 2 h. Then the rate of a-pinene conversion could achieve 94.56 %, the selectivity of camphene could achieve 48.5%.

P74: Novel human mitochondrial enzyme can transform nitrite into nitric oxide

Endogenous metabolism of nitrate to nitrite to nitric oxide (NO) affects numerous biological events in humans, such as blood pressure control and hypoxic vasodilation, yet the molecular mechanism of this transformation remains uncertain and controversial. Nitrate and nitrite conversion to NO are reductive processes, requiring electron and proton transfer reactions, suggesting that oxidoreductase enzymes are involved. Nitrate reduction may occur through a combination of endogenous (i.e. human enzymes) and exogenous (i.e. commensal bacteria) nitrate reductase enzymes, while nitrite reduction to nitric oxide is likely catalyzed by endogenous nitrite reductase enzymes. Several mechanisms have been investigated, yet no conclusive data are available to support a single enzyme as an indispensable component for reduction of nitrite to NO in human tissue. It is likely that different enzyme systems are active in specific tissues under differential hypoxia, pH and co-factor regulatory control. We have identified a novel human nitrite reductase enzyme, which we hypothesize may contribute to mitochondrial reduction of nitrite to NO. The mitochondria amidoxime reducing component (mARC) enzyme is widely expressed in human tissue, but has an undefined physiological function. We hypothesize that mARC catalyzes the NADH-dependent reduction of nitrite to NO. To test this hypothesis the kinetics of nitrite reduction to NO by human mARC was investigated. Recombinant mARC was generated using standard molecular biology techniques, and then isolated using metal affinity chromatography. Site directed mutagenesis was used to change the active site cysteine into alanine. Human cytochrome b5 and cytochrome b5 reductase were also isolated to determine if mARC can utilize NADH as an electron source in conjunction with these enzymes. Nitric oxide chemiluminescence spectroscopy was used to measure NO-formation rates under anaerobic conditions. Our study established that mARC can generate NO from nitrite in the presence of NADH, cytochrome b5, and cytochrome b5 reductase at pH 7.4. The maximum velocity (Vmax) of NO-formation measured was 5 nmoles NO s−1 mg−1 protein. Moreover, mutation of the putative active site cysteine residue to alanine, and substitution of tungsten for molybdenum, completely abolished enzyme activity. The kinetic data supports our hypothesis and establishes that human mARC is capable of catalyzing reduction of nitrite to NO. Moreover, these data suggest that cysteine 270 and molybdenum are important in the transformation of nitrite to NO. Disclosure Supported by institution training grant (T32).

Diiron(III)‐Containing 23‐Tungsto‐2‐Borate: First Evidence of 3d Metal Substitution in the {BW13} Framework

AbstractThe reaction of [HBW11O39]8–, (WO4)2–, and Fe3+ (1:2:3 ratio) in water at pH 1.5 resulted in [{FeIII(H2O)3}2(WO2)(HBW11O39)2]8– (1), the first 3d‐metal‐substituted tungstoborate whose structure differs from that of a monosubstituted Keggin framework. Polyanion 1 is composed of an unprecedented 23‐tungsto‐2‐borate subunit stabilized by FeIII coordination at the external positions. The linkage mode of the 11‐tungstoborate fragments in 1 evidences that substitution of tungsten by 3d metals can occur in the capping positions of the {BW13} skeleton.

Synthesis, Characterization and Catalytic Application of Mesoporous PW/SBA-15 for Epoxidation of α-Pinene

Supported phosphotungstic acid SBA-15 were synthesized under hydrothermal conditions and characterized by X-ray diffraction (XRD), N2 adsorption, transmission electron micrographs (TEM), scanning electron micrographs (SEM), Fourier-transform infrared spectroscopy (FT-IR). XRD and FT-IR results indicated that the substitution of tungsten occurs in the silicate framework structure of SBA-15. TEM and SEM investigations confirmed the presence of ordered high degree ordering hexagonal structure in the novel PW/SBA-15 material. Their catalytic activity was evaluated in the epoxidation of α-pinene. 2,3-epoxypinane was the main product. The results of epoxidation of α-pinene by PW(40)/SBA-15 were fellows: the conversion rate of α-pinene and the selectivity were 87.61% and 79.90% respectively.

In Situ X‐ray Absorption Spectroscopy/Energy‐Dispersive X‐ray Diffraction Studies on the Hydrothermal Formation of Bi2W1–xMoxO6 Nanomaterials

AbstractBi2WO6 has attracted considerable interest as a visible‐light‐driven photocatalyst with a layered Aurivillius structure. The catalytic performance of bismuth tungstate is notably enhanced through the partial substitution of tungsten with molybdenum. Whereas hydrothermally obtained Bi2W1–xMoxO6 solid solutions maintain the Bi2WO6 structure, their morphologies vary with the molybdenum content. Lower Mo contents (x &lt; 0.5) favor the formation of hierarchically nanostructured microspheres that consist of sheet‐like building blocks. Their disintegration is observed for greater extents of W/Mo substitution, hand in hand with a decrease in the surface area. Raman spectra furthermore indicate changes in the local structure of the octahedral W/Mo moieties upon variation of the Mo content. As little is known about the growth kinetics and hydrothermal formation processes of nanostructured Bi2W1–xMoxO6 catalysts, in situ XAS investigations were performed to determine the onset of their hydrothermal formation from Bi(NO3)3·5H2O, K2WO4 andNa2MoO4. In situ energy‐dispersive X‐ray diffraction (EDXRD) experiments revealed a correlation between particle shape, Mo content and formation pathway of the Bi2W1–xMoxO6 nanomaterials. The results are compared to related in situ studies on hierarchically structured W/Mo oxides.