Influence Of Tungsten Research Articles

Reduction of nitrates in Cucumis sativus L. seedlings I. Influence of tungsten and vanadium on absorption and reduction of nitrates

Investigations were conducted on the influence of tungsten (Na<sub>2</sub>WO<sub>4</sub>) and meta-vanadate (NaVO<sub>3</sub>) on uptake and reduction of nitrates by cucumber seedlings. Tungsten and vanadium almost completely inhibited nitrate reductase activity (NR) after treating the plants for 24 hours with nitrates in the presence of 10<sup>-4</sup> M WO<sub>4</sub><sup>-2</sup> and 10<sup>-3</sup> M VO<sub>3</sub><sup>-</sup>. Uptake of NO<sub>3</sub><sup>-</sup> in the presence of WO<sub>4</sub><sup>-2</sup> in this same period of time was lowered by about 50 %, while in the presence of VO<sub>3</sub><sup>-</sup> by seventy percent. The ratio of NO<sub>3</sub><sup>-</sup> absorbed to that reducted in control plants was around 3, whereas in the presence of WO<sub>4</sub><sup>-2</sup> and VO<sub>3</sub><sup>-</sup> 9 and 8 respectively. The effect of NR inhibiting activity by WO<sub>4</sub><sup>-2</sup> and VO<sub>3</sub><sup>-</sup> was significant but somewhat weaker if both inhibitors were applied to the plants 24 hours after formation of the NR system, whereas NO<sub>3</sub><sup>-</sup> uptake was subject to a slight lowering. The above data suggest that WO<sub>4</sub><sup>-2</sup> and VO<sub>3</sub><sup>-</sup> after a 24 hour application of these inhibitors to plants, primary inhibit biosynthesis and activity of NR and to a lesser extent effect NO<sub>3</sub><sup>-</sup> absorption. On the basis of results reached the Butz and Jackson (1977) hypothesis concerning the model of NO<sub>3</sub><sup>-</sup> uptake and reduction by plant tissues is discussed.

Reduction of nitrates in Cucumis sativus L. seedlings II. Influence of tungsten and vanadium on nitrate reductase and adenosine triphosphatase activities

ATPases isolated from the roots of cucumber seedlings activated by Mg<sup>+2</sup> ions in experiments in vitro, were fairly distinctly inhibited by Ca<sup>-2</sup> ions, very slightly inhibited by fluorides and molybdenum ions while NO<sub>3</sub><sup>-</sup> anions had no effect on the level of ATPase activity studied. Introduction into the nutrient of 10<sup>-4</sup> M Na<sub>2</sub>WO<sub>4</sub> or 10<sup>-3</sup> M Na VO<sub>3</sub> (inhibitors of nitrate reductase NR) distinctly inhibited activity of the ATPase under study especially of fractions IIa and III, and inhibited NR activity and lowered uptake of NO<sub>3</sub><sup>-</sup>. WO<sub>4</sub><sup>-2</sup> and VO<sub>3</sub><sup></sup> inhibited to the same extent absorption and reduction of NO<sub>3</sub><sup>-</sup> in the initial phase of NR induction, whereas at a later stage both inhibitors checked reduction to a greater degree than uptake of NO<sub>3</sub><sup>-</sup>. The results indicate the possibility of certain ATPase participation in assimilating nitrates, and suggest that in the initial stage of biosynthesis of the NR enzyme system, activity of the enzyme is distinctly dependent upon NO<sub>3</sub><sup>-</sup> transport and the level of NR activity limited by the amount of nitrate taken up. At a later an additional mechanism of NO<sub>3</sub><sup>-</sup> transport probably functions, not connected with simultaneous reduction of nitrates. On the basis of results the Butz and Jackson (1977) hypothesis concerning a model for the absorption and reduction of NO<sub>3</sub><sup>-</sup> by plant tissues is discussed.

Effect of tungsten on tensile properties and flow behaviour of RAFM steel

Effect of tungsten in the range of 1–2wt.% on tensile properties and flow behaviour of 9Cr–W–Ta–V Reduced Activation Ferritic–Martensitic (RAFM) steel has been investigated. The tungsten in the investigated range was found to have only minor effect on the tensile properties of the steel over the temperature range of 300–873K and at a strain rate of 3×10−3s−1. The tensile flow behaviour of the RAFM steels was adequately described by the Voce’s constitutive equation. The tensile strength of the steels were predicted well from the parameters of the Voce’s constitutive equation. The Voce’s strain hardening parameter ‘nv’ was found to be quite sensitive to the tungsten content and predicted the onset of dislocation climbing process at relatively higher testing temperature with the increase in tungsten content. The equivalence between tensile and creep deformations and the influence of tungsten have been discussed.

Influence of Tungsten and Titanium on the Structure of Chromium Cast Iron

Influence of Tungsten and Titanium on the Structure of Chromium Cast Iron The paper analyses the as-cast state structure of chromium cast iron designed for operation under harsh impact-abrasive conditions. In the process of chromium iron castings manufacture, very strong influence on the structure of this material have the parameters of the technological process. Among others, adding to the Fe-Cr-C alloy the alloying elements like tungsten and titanium leads to the formation of additional carbides in the structure of this cast iron, which may favourably affect the casting properties, including the resistance to abrasive wear.

Influence of tungsten and molybdenum on seed germination and early seedling growth of wheat - a comparative study

Fifty one promising landraces of rice cultivars of three districts viz. Nadia, 24 Parganas(N) and MA comparative study on the effect of tungsten and molybdenum on seed germination and early seedling growth of wheat was carried out. Both W and Mo influenced the seedling growth in similar fashion. W and Mo enhanced the germination relative index at lower application. Relative yield increased at lower applied doses of W as well as Mo whereas at higher application it decreased. Lower applied doses of W and Mo showed maximum index of metal tolerance. Higher applied doses of both metals showed toxic effect on plant growth. A highly significant (p= 0.01 in W and p = 0.001 in Mo) increment in grade of growth inhibition (GG) at the higher administration of W and Mo was observed. The toxic effect of tungsten on wheat was more marked than molybdenum.

Influence of tungsten on the emission features of Nd 3+, Sm 3+ and Eu 3+ ions in ZnF 2–WO 3–TeO 2 glasses

The glasses of the composition (45− x)ZnF 2– xWO 3–49TeO 2:1.0Nd 2O 3/Sm 2O 3/Eu 2O 3 with x varying from 5 to 20 mol% were synthesized. Optical absorption, fluorescence spectra (in the spectral range 400–2300 nm) and also fluorescence decay were studied at ambient temperature. The Judd–Ofelt theory analysis was applied to characterize the absorption and luminescence spectra of Ln 3+ ions in these glasses. Following the luminescence spectra, various radiative properties like transition probability A, branching ratio β and the radiative life time τ for 4F 3/2 → 4I 11/2, 4G 5/2 → 6H 7/2, 5D 0 → 7F 2 emission levels respectively for Nd 3+, Sm 3+ and Eu 3+ doped glasses of these glasses have been evaluated. The variations observed in these parameters were discussed following of varying co-ordinations (tetrahedral and octahedral positions) and the valence states of tungsten ions in the glass network. A significant enhancement in the intensities of 4F 3/2 → 4I 11/2 (Nd 3+), 4G 5/2 → 6H 7/2 (Sm 3+) and 5D 0 → 7F 2 (Eu 3+) emission lines has been observed with increase of WO 3 content; this is attributed to the increase in the concentration W 5+ ions in the glass network that acts as modifiers. The quantitative analysis of these results (with the aid of the data on ESR, IR and Raman spectral studies) has indicated that the glasses mixed with around 15 mol% of WO 3 have the optimum concentration for yielding the highest quantum efficiency with low phonon losses for the above-mentioned principal transitions.

ChemInform Abstract: The Influence of Tungsten Alloying Additions on the Passivity of Aluminum.

Transition metals such as Mo, W, Ta, Cr, and W can be used to significantly enhance the localized corrosion resistance of Al. Since these elements exhibit very low solubilities in aluminum, a nonequilibrium alloying method, such as sputter deposition, must be used to produce single-phase alloys. The addition of approximately 9 atom percent W to Al can shift its pitting potential in the positive direction as much as 2600 mV. Heat-treatment of these nonequilibrium alloys results in the precipitation of a second phase that is detrimental, but not catastrophic, to corrosion performance. Surface analysis of the Al-W passive film formed as a function of applied anodic potential reveals that it remains thin throughout the polarization sequence and contains very little oxidized solute, regardless of the applied potential. The oxidized W present in the film is in the form of WO{sub 2} and WO{sub 3} (or WO{sup {minus}2}{sub 4}). The results of this paper reveal that the electrostatic-repulsion or oxidized-solute barrier-layer mechanisms are not responsible for the dramatic enhancement in the passivity of Al with the addition of W. Instead, the small amount of oxidized W in the passive film may interact synergistically with the hydrated aluminum oxide structure to formmore » a more protective film.« less

The influence of tungsten on the thermal stability and mechanical behavior of electrodeposited nickel MEMS structures

The thermal stability and mechanical behavior of LIGA Ni–W alloys with 5 and 15 at.% W were investigated. The strength of these alloys exceeds that of pure LIGA Ni, and the underlying microstructures of the Ni–W alloys are stable to 700 °C. The Ni–W alloys are brittle as-deposited, but annealed samples exhibited a promising balance of strength and ductility. W-alloyed LIGA Ni offers increased thermal stability and strength, as well as opportunities for tailoring mechanical properties with heat treatment.

The role of tungsten in the coarsening behaviour of M23C6 carbide in 9Cr–W steels at 600 °C

Tungsten is sometimes used as a solute in the so called 9Cr creep-resistant steels for use in the power generation industry, in part because of its ability to reduce the coarsening rate of M23C6 carbides. The mechanism by which it does so is not fully understood and indeed has been shown to be inconsistent with multicomponent coarsening theory, which predicts an opposite effect. This makes the role of tungsten to the coarsening behaviour of the carbide remain unsolved over decades. The work presented here is an attempt to show that the influence of tungsten can be reconciled with experiments, if kinetic study ignores the presence of Laves phase (Fe2W) in the system.

Influence of tungsten on the carbon nanotubes growth by CVD process

The effect of tungsten (W) on the growth of multi-walled carbon nanotubes (MWNTs) using the chemical vapour deposition (CVD) process over a metal Fe–W catalyst incorporated into a silica matrix is reported. A W molar content in Fe/SiO 2 up to 10% was studied. The incorporation of only 2% of W substantially modifies the crystalline phases and the crystalline degree of the catalyst during the MWNTs synthesis. This fact seems to have a strong influence on the type and yield of the carbonaceous species obtained by the CVD of acetylene, at 600 °C and 180 Torr, over each catalyst. Tungsten interacts with iron within the matrix, diminishing the catalytic activity of the metal nanoparticles, and both, carbon nanotubes and carbon nanofibers, are obtained when tungsten is present. The results obtained support the hypothesis of a base growth model for carbon nanotubes indicating a strong interaction between silica matrix and Fe/W nanoparticles, independently of the content of W.

The influence of tungsten on structure and activity of Mo–V–W-mixed oxide catalysts for acrolein oxidation

Abstract For the partial oxidation of acrolein to acrylic acid, a series of catalysts with the general formula Mo 8 V 2 W c O x and a varying amount of tungsten (0 ≤ c ≤ 5) was investigated. Catalysts were prepared starting from aqueous solutions of ammonium heptamolybdate, metavanadate and metatungstate, which were dried, employing spray drying and crystallisation followed by calcination. The resulting precursors and catalysts were characterised by XRD, SEM and TG/DTA–MS. Additionally, kinetic experiments were applied. Spray drying results in the formation of amorphous structures, whose temperature stability shows a tendency to rise with an increasing amount of tungsten. Spray dried samples in general show a better catalytic performance than crystallised ones. In TP-reactions the spray dried mixed oxides were investigated with regard to their catalytic properties: conversion of acrolein, yield and selectivity regarding the partial oxidation to acrylic acid. The best performance could be assigned to the minor tungsten doped catalysts. The oxygen pathways were investigated with the so-called steady state isotopic transient kinetic analysis (SSITKA). After the replacement of 16 O 2 against 18 O 2 in the feed gas, the rate of oxygen incorporation into the reactants and the isotopic distribution of the oxidation products were analysed depending on temperature and tungsten content. Tungsten doping has a significant influence on the amount of 16 O removed from the catalyst under 18 O 2 . The amount of oxygen made available by the catalysts correlates with the catalysts’ activity.

Influence of tungsten on microstructure of mechanically alloyed γ‐TiAl

This article presents preliminary results of the processing and characterization of gamma-TiAl alloy modified by W addition. An alloy with the target chemical composition of TiAl-5W (at.%) was synthesized by mechanical alloying. Two methods were used for powder compaction: hot pressing at 1300 degrees C and hot extrusion at 1100 degrees C. Hot extrusion turned out to be a superior consolidation technique over hot pressing. The matrix of final alloy was composed of a phase based on TiAl and a minor amount of Ti(3)Al. The grain size in the extruded alloy was much smaller than in the hot-pressed one. Minute W particles formed a dispersoid.

Influence of Film Composition on the Structure and Dielectric Properties of Anodic Films on Ti–W Alloys

The influence of tungsten on an amorphous-to-crystalline transition, leading to formation of anatase, and dielectric properties is examined for anodic oxides on Ti–W alloys. The structural change, which occurs at voltages of on high-purity titanium, and provides sites for generation of high-pressure gas oxygen bubbles, is suppressed to progressively increased voltages by increasing tungsten content of the film. Phosphorus species, derived from the electrolyte, also hinder the change. The tungsten species are located in the inner of the film thickness as result of the faster migration of ions relative to that of ions in the growing oxide. Although the reported permittivity of anodic tungsten oxide is higher than that of amorphous anodic titania, the permittivity of the films on alloys decreases gradually with increasing tungsten content.

The Influence of Tungsten on the Chemical Composition of a Temporally Evolving Nanostructure of a Model Ni-Al-Cr Superalloy

The influence of W on the temporal evolution of gamma' precipitation toward equilibrium in a model Ni-Al-Cr alloy is investigated by three-dimensional atom-probe (3DAP) microscopy and transmission electron microscopy (TEM). We report on the alloys Ni-10 Al-8.5 Cr (at.%) and Ni-10 Al-8.5 Cr-2 W (at.%), which were aged isothermally in the gamma + gamma' two-phase field at 1073 K, for times ranging from 0.25 to 264 h. Spheroidal-shaped gamma' precipitates, 5-15 nm diameter, form during quenching from above the solvus temperature in both alloys at a high number density (approximately 1023 m-3). As gamma' precipitates grow with aging at 1073 K, a transition from spheroidal- to cuboidal-shaped precipitates is observed in both alloys. The elemental partitioning and spatially resolved concentration profiles across the gamma' precipitates are obtained as a function of aging time from three-dimensional atom-by-atom reconstructions. Proximity histogram concentration profiles (Hellman et al., 2000) of the quaternary alloy demonstrate that W concentration gradients exist in gamma' precipitates in the as-quenched and 0.25-h aging states, which disappear after 1 h of aging. The diffusion coefficient of W in gamma' is estimated to be 6.2 x 10-20 m2 s-1 at 1073 K. The W addition decreases the coarsening rate constant, and leads to stronger partitioning of Al to gamma' and Cr to gamma.

Influence of tungsten and rhenium concentration on creep properties of a second generation superalloy

Creep properties at three different temperatures (1123, 1253 and 1373 K) for five single crystal alloys with varying Re and W content are presented. Tungsten content has been varied between 3.0 and 3.6 wt.%, rhenium between 2.3 and 2.9 wt.%. Creep properties, such as minimum creep rate, time to reach 1, or 2% strain and time to failure have been evaluated. For the low temperature regime, two parts of rhenium can be replaced by one part of tungsten. In the intermediate range, the ratio c W/ c Re≈1.3 has to be fulfilled with the constraint that c Re≥2.3 wt.%. At high temperature the sum of W plus Re concentration determines the time to failure.

The Peculiarities of Tungsten's Influence on Phase Transformations and Mechanical Properties of the Directionally Solidified HCR Nickel-Base Alloy

The application of the directional solidification (DS) increases the life of turbine blades. But this technology demands a new alloying approach, especially for the nickel-base, hot corrosion resistant (HCR) alloys. Such an approach was undertaken in this investigation. The influence of tungsten on the microstructure, phase content, phase transformations, and mechanical properties of the HCR nickel-base alloys were studied both in equiaxially and directionally solidified conditions. Tungsten content was varied between 3 to 9%. Samples with equiaxially and directionally solidified structures were obtained in a High Gradient Directional Solidification Unit with the liquid metal coolant (LMC). The LMC was molten aluminium. It was shown that tungsten has the effect of strengthening the dendrites, which further promotes the DS. The maximum mechanical properties of the directionally solidified alloy were obtained at tungsten content of 7% versus 5% for the conventionally solidified alloy.

The Influence of Tungsten (W) on Properties in High Nitrogen Stainless Steels

Superaustenitic stainless steels with about 6% molybdenum (Mo) have now been used successfully for over twenty years because of their high corrosion resistance. Requirements for even better performance have resulted in more highly alloyed superaustenitic steels, also with high nitrogen (N) levels. Substituting W for Mo in stainless steels has been claimed to have both negative and positive effects. To investigate these effects, especially on corrosion resistance in high Mo superaustenitic stainless steels, a series of eight experimental steels was produced. The heats were designed to investigate the effects of substitution of W for Mo in a base alloy containing 24% chromium (Cr), 22% nickel (Ni) and 0.5% nitrogen (N). To achieve this Mo and W were varied between 5 to 7% and 0 to 5% respectively. The microstructures and resistance to localised corrosion were investigated for solution annealed and sensitised samples. Addition of W improved the resistance towards localised corrosion in a similar way as Mo. However, the structural stability was decreased on replacing Mo by W. This negative effect was observed in the whole temperature range studied and had also a negative influence on the crevice corrosion resistance.

The influence of tungsten alloying on the mechanical properties of tantalum

Pour des alliages de tantale-tungsten ayant des compositions nominales de tantale entre 0 et 10% en poids, de tests mecaniques a des temperatures entre 77 et 400 K, et des taux d'elongation variant de 0.000016 a 6800 s −1 , l'addition de tungsten reduit de maniere notable la dependance du fluage du tantale sur le taux d'elongation au voisinnage de la deformation plastique. Le comportement du taux d'elongation sur le durcissement de l'alliage change de maniere subtile, le rendant plus proche du comportement du cuivre, un metal c.f.c. Ces effets se font sentir dans les contraintes limitantes de deformation plastiques uniformes calculees a partir de nos courbes de fluage: pour le tantale sans elements d'alliage, la containte d'instabilite semble diminuer de maniere dramatique pour des taux d'elongation superieurs a environ 0.005 s −1 , alors que pour les alliages de tungsten, elle reste inchangee ou augmente faiblement

Influence of tungsten, carbon and nitrogen on toughness and weldability of low activation austenitic high manganese stainless steels

The effect of alloying elements of tungsten, carbon and nitrogen on high temperature strength, toughness and weldability of Fe12Cr15Mn alloy has been investigated. The high temperature stregth of Fe12Cr15Mn0.2C0.1N at 873 K increases with the addition of 2–300W without affecting ductility. The toughness as estimated by Charpy tests, is also not influenced by the addition of 2–3%W, while the increase of carbon content decreases the absorbed energy. The transition temperature shifts to higher temperature by aging at 873 K for 3600 ks, but it is still lower than room temperature. The degradation of tougheness after aging is considered to be related to the precipitation of M23C6 on grain boundaries. The weldability evaluated by hot cracking susceptibility is not affected by alloying of tungsten and carbon in this alloy system. It is noted that the alloys studied show less hot cracking susceptibility than commercial AISI 316L stainless steel.

ChemInform Abstract: The Influence of Tungsten on the Pitting of Aluminum Films.

AbstractAl‐8.5% W and Al‐10.3% W alloy films are prepared by co‐sputter deposition and their corrosion behavior is studied by potentiodynamic polarization in 0.1 M KCl.