Tungsten Concentration Research Articles

Assessing tungsten transport in the vadose zone: From dissolution studies to soil columns

This study investigates the dissolution, sorption, leachability, and plant uptake of tungsten and alloying metals from canister round munitions in the presence of model, well characterized soils. The source of tungsten was canister round munitions, composed mainly of tungsten (95%) with iron and nickel making up the remaining fraction. Three soils were chosen for the lysimeter studies while four model soils were selected for the adsorption studies. Lysimeter soils were representatives of the typical range of soils across the continental USA; muck-peat, clay-loamy and sandy-quartzose soil. Adsorption equilibrium data on the four model soils were modeled with Langmuir and linear isotherms and the model parameters were obtained. The adsorption affinity of soils for tungsten follows the order: Pahokee peat>kaolinite>montmorillonite>illite. A canister round munition dissolution study was also performed. After 24d, the measured dissolved concentrations were: 61.97, 3.56, 15.83mgL−1 for tungsten, iron and nickel, respectively. Lysimeter transport studies show muck peat and sandy quartzose soils having higher tungsten concentration, up to 150mgkg−1 in the upper layers of the lysimeters and a sharp decline with depth suggesting strong retardation processes along the soil profile. The concentrations of tungsten, iron and nickel in soil lysimeter effluents were very low in terms of posing any environmental concern; although no regulatory limits have been established for tungsten in natural waters. The substantial uptake of tungsten and nickel by ryegrass after 120d of exposure to soils containing canister round munition suggests the possibility of tungsten and nickel entering the food chain.

DIVIMP simulation of W transport in the SOL of JET H-mode plasmas

This study provides predictions of tungsten contamination extrapolated from an inter-edge localized mode phase of a high-triangularity, high-confinement, ITER-like wall (ILW) reference plasma without impurity seeding in JET. The tungsten concentrations for equivalent ILW plasmas are predicted for low, medium and high upstream densities, utilizing the Monte Carlo trace-impurity code DIVIMP on background plasmas calculated with the two-dimensional fluid code EDGE2D/EIRENE. It is observed that operation at the low-upstream-density plasma with a sheath-limited scrape-off layer leads to a core tungsten concentration of the order of 10−5. Increasing the density leads to a high-recycling scrape-off layer with sufficient divertor retention to ensure an acceptable core tungsten concentration that is less than 10−5. Sufficient divertor retention is achievable if the peak target electron temperature, Te, is below 10 eV. Achieving a significant reduction in tungsten sputtering by multiple charged impurity species (e.g. Be2+ and C4+) requires a peak target Te below 5 eV, which requires strong divertor radiation, achieved by impurity seeding in the ILW configuration.

Controlled tungsten melting and droplet ejection studies in ASDEX Upgrade

Tungsten rods of 1×1×3 mm3 were exposed in single H-mode discharges at the outer divertor target plate of ASDEX Upgrade using the divertor manipulator system. Melting of the W rod at a pre-defined time was induced by moving the initially far away outer strike point close to the W-rod position. Visible light emissions of both the W pin and consecutively ejected W droplets were recorded by two fast cameras with crossed viewing cones. The time evolution of the local W source at the pin location was measured by spectroscopic observation of the WI line emission at 400.9 nm and compared to the subsequent increase of tungsten concentration in the confined plasma derived from tungsten vacuum UV line emission. Combining these measurements with the total amount of released tungsten due to the pin melt events and ejected droplets allowed us to derive an estimate of the screening factor for this type of tungsten source. The resulting values of the tungsten divertor retention in the range 10–20 agree with those found in previous studies using a W source of sublimated W(CO)6 vapour at the same exposure location. Ejected droplets were found to be always accelerated in the general direction of the plasma flow, attributed to friction forces and to rocket forces. Furthermore, the vertically inclined target plates cause the droplets, which are repelled by the target plate surface potential due to their electric charge, to move upwards against gravity due to the centrifugal force component parallel to the target plate.

Water corrosion measurements on tungsten irradiated with high energy protons and spallation neutrons

A detailed analysis was performed on the degradation of a tungsten target under water cooling while being exposed to a 761MeV proton beam at an average current of 0.867mA to a maximum fluence of 1.3×1021protons/cm2. The target consisted of 3mm diameter tungsten rods arranged in bundles and cooled with deionized water flowing over their length. Degradation of the tungsten was measured through analyzing water resistivity, tungsten concentration in water samples that were taken during irradiation and through dimensional measurements on the rods after irradiation. Chemical analysis of irradiated water samples showed W concentrations up to 35μg/ml. Gamma analysis showed increases in concentrations of many isotopes including W-178, Lu-171, Tm-167, Tm-166, Yb-169 and Hf-175. Dimensional measurements performed after irradiation on the W rods revealed a decrease in diameter as a function of position that followed closely the Gaussian proton beam profile along the rod length and indicated a definite beam-effect. A general decrease in diameter, especially on the coolant-water entrance point where turbulent flow was likely, also suggests a chemically and mechanically-driven corrosion effect. A method to estimate the apparent corrosion rate based on proton fluence is presented and application of this method estimates the material loss rate at about 1.9W atoms/incident proton. From this result, the corrosion rate of tungsten in a 761MeV, 0.867mA proton beam was calculated to be 0.073cm/full power year. of irradiation.

EMC3-Eirene simulations of the spatial dependence of the tungsten divertor retention in ASDEX Upgrade

The Edge Monte Carlo 3D (EMC3)-Eirene code package is applied to simulate the deuterium plasma and neutral particle as well as the tungsten impurity transport in ASDEX Upgrade. Good agreement is found for the deuterium bulk plasma for an L-mode discharge both in the upstream and downstream profiles. The tungsten concentration in the core is computed for a point source placed at different positions around the outer strike point. Comparing the mean impurity residence time for divertor and main chamber sources yields the divertor retention factor R, which shows a very strong dependence on the location of the source relative to the strike point and also on the discharge parameters. While the tungsten transport is strongly suppressed directly at the strike point, it becomes much more efficient in the region 20–100 mm away from it in the far scrape-off layer.

Extension of the ECRH operational space with O2 and X3 heating schemes to control tungsten accumulation in ASDEX Upgrade

ASDEX Upgrade has been operated with tungsten-coated plasma-facing components for several years. H-mode operation with good confinement has been demonstrated. Nevertheless, purely neutral beam injection-heated H-modes with reduced gas puff, moderate heating power or/and increased triangularity tend to accumulate tungsten, followed by a radiative collapse. Under these conditions, central electron heating with electron cyclotron resonance heating (ECRH), usually in X2 polarization, changes the impurity transport in the plasma centre, reducing the central tungsten concentration and, in many cases, stabilizing the plasma. In order to extend the applicability of central ECRH to a wider range of magnetic field and plasma current additional ECRH schemes with reduced single-pass absorption have been implemented: X3 heating allows us to reduce the magnetic field by 30%, such that the first H-modes with an ITER-like value of the safety factor of q95 = 3 could be run in the tungsten-coated device. O2 heating increases the cutoff density by a factor of 2 allowing higher currents and triangularities to be addressed. For both schemes, scenarios have been developed to cope with the associated reduced absorption. In the case of central X3 heating, the X2 resonance lies close to the pedestal top at the high-field side of the plasma, serving as a beam dump. For O2, holographic mirrors have been developed which guarantee a second pass through the plasma centre. The beam position on these reflectors is controlled by fast thermocouples. Stray-radiation protection has been implemented using sniffer probes.

Microstructure and mechanical properties of W-C:H coatings deposited by pulsed reactive magnetron sputtering

Reported are results of microstructure, mechanical and tribological properties studies for thin, amorphous hydrogenated carbon based coatings with tungsten content from 4.7at.% up to 10.3at.%. Studied coatings have been deposited by pulsed, reactive magnetron sputtering on substrates under planetary rotation. Resulting coatings, characterized by transmission electron microscopy (TEM) also at high resolution (HREM), show multilayer structure consisting of sub-layers of W-C:H type, with alternately high and low tungsten concentration. Thickness and number of sub-layers depend on rotation speed of planetary substrate holder. An average tungsten concentration decreases with increasing partial pressure of reactive gas (C2H2) during deposition. More insight into the microstructure of coatings provided HREM analysis showing crystalline precipitations of about 1–2nm in size as well as tungsten-rich and tungsten-poor W-C:H sub-layers. Raman spectra confirm presence of amorphous, hydrogenated carbon (a-C:H) phase in the coatings. Microhardness of studied coatings depends on tungsten content and increases from 10.7GPa to 13.7GPa, for 5.1at.% and 10.3at.% of tungsten content, respectively. The highest cracking resistance and best adhesion (Lc2=78N and HF1) has been achieved for coatings containing 4.9at.% of tungsten and a sub-layer thickness of 5nm. Tribological processes occurring in the coating–coating contact zone are dominated by graphitization and oxidation of W-C:H coating. Very low friction coefficient (0.04) and low wear rate seems to be an effect gaseous micro-bearing by tribo-generated carbon oxides and methane as well as hydrogen released from the coating. In the W-C:H-steel contact zone a tribo-layer composed of iron and tungsten oxides mixed with graphite-like products is growing at the surface of steel counterpart. This tribo-layer becomes a barrier restricting direct contact of steel with the coating and thus preventing it from further intense wear.

Tissue Distribution of Tungsten in Mice Following Oral Exposure to Sodium Tungstate

Heavy metal tungsten alloys have replaced lead and depleted uranium in many munitions applications, due to public perception of these elements as environmentally unsafe. Tungsten materials left in the environment may become bioaccessible as tungstate, which might lead to population exposure through water and soil contamination. Although tungsten had been considered a relatively inert and toxicologically safe material, recent research findings have raised concerns about possible deleterious health effects after acute and chronic exposure to this metal. This investigation describes tissue distribution of tungsten in mice following oral exposure to sodium tungstate. Twenty-four 6-9 weeks-old C57BL/6 laboratory mice were exposed to different oral doses of sodium tungstate (0, 62.5, 125, and 200 mg/kg/d) for 28 days, and after one day, six organs were harvested for trace element analysis with inductively coupled plasma mass spectrometry (ICP-MS). Kidney, liver, colon, bone, brain, and spleen were analyzed by sector-field high-resolution ICP-MS. The results showed increasing tungsten levels in all organs with increased dose of exposure, with the highest concentration found in the bones and the lowest concentration found in brain tissue. Gender differences were noticed only in the spleen (higher concentration of tungsten in female animals), and increasing tungsten levels in this organ were correlated with increased iron levels, something that was not observed for any other organ or either of the two other metals analyzed (nickel and cobalt). These findings confirmed most of what has been published on tungsten tissue distribution; they also showed that the brain is relatively protected from oral exposure. Further studies are necessary to clarify the findings in splenic tissue, focusing on possible immunological effects of tungsten exposure.

Tribological properties of tertiary Al2O3/CNT/nanodiamond pulsed electrodeposited Ni–W nanocomposite

Wear resistance of electrodeposited tertiary alumina/carbon nanotube/nanodiamond nanocomposite using pulsed current has been studied in Ni–W binary alloy matrix. Electroplating process was performed in citrate based Ni–W bath, and the nanostructure of obtained compound layer was examined by AFM. The effects of process variables, i.e. tungsten concentration in electrolyte, treatment time, frequency and duty cycle, were experimentally studied. Statistical methods were used in order to provide the minimised wear rate. Finally, the contribution percentage of different effective factors was calculated and confirmation run revealed the validity of obtained results. Nanocomposite layers with higher density of nanoparticles will show better tribological properties.

Effect of tungsten addition on microstructure and high temperature strength of 9CrODS ferritic steel

Tungsten is an effective element for solid-solution strengthening and is a ferrite former in 9CrODS ferritic steel, however excessive tungsten leads to Laves phase formation. Appropriate tungsten concentration in 9CrODS ferritic steel was found to be around 2mass%, which produces high temperature strength without Laves phase precipitation. The stress increment due to solid-solution strengthening by tungsten was characterized as relatively small, compared to enhanced ferrite formation, the so called residual α-ferrite.

Induced tungsten melting events in the divertor of ASDEX Upgrade and their influence on plasma performance

Tungsten rods of 1×1×3mm were exposed at the outer divertor plate of ASDEX Upgrade using a manipulator system. Controlled melting of the W-rod in H-mode discharges was induced by moving the outer strike point towards the W-rod position. Visible light emission of ejected W droplets was recorded by fast camera systems. The resulting increase of tungsten concentration in the confined plasma was compared to that induced by W laser ablation into the outer main chamber boundary plasma. The resulting divertor retention expressed as ratio of tungsten core penetration probability from a divertor source to that of a main chamber source is ≈100. Ejected droplets are found to move always in general direction of the plasma flow. The measured magnitude of droplet acceleration shows that droplets are mainly subject to rocket forces and friction forces. Typical initial droplet size can be inferred from the time evolution of the droplet light emission to be ⩾100μm.

Characteristics of electrodeposited CoWP capping layers using alkali-metal-free precursors

CoWP films, used as a capping layer for a copper interconnection, were electrodeposited using alkali-metal-free precursors, and the effect of the electrolyte concentration on the film characteristics such as the thickness, composition, and microstructure was investigated. The current density and the film thickness increased with the concentration of cobalt, tungsten, and phosphorous precursors. When the cobalt ion concentration in the electrolyte was increased from 0.01 to 0.09M, the cobalt content in the film increased from 67 to 89 at%, while the tungsten and phosphorous contents decreased from 16 to 0.7 and 17 to 10 at%, respectively. The tungsten and phosphorous contents also increased as their corresponding concentrations increased in the electrolyte. Microstructural analyses showed that the tungsten and phosphorous content in the film greatly affected the crystallinity of the CoWP films electrodeposited using alkali-metal-free precursors.

Preparation, characterization and properties of thermochromic tungsten-doped vanadium dioxide by thermal reduction and annealing

Thermochromic tungsten-doped vanadium dioxide (VO 2) powders were successfully synthesized by thermal reduction using V 2O 5 as a vanadium precursor. The products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results indicated that W was successfully doped into the crystal lattice of VO 2 matrix, and prepared tungsten-doped VO 2 had a rod-like morphology. The effects of reducing temperature and annealing temperature on the crystallographic structures were also discussed. The phase transition temperature (Tt) of VO 2 could be simply tuned by changing the doping concentration of tungsten. When the doping concentration was 1.58 mol%, the Tt could be reduced to 37.8 °C from initial 69.5 °C, suggesting that tungsten-doped VO 2 possesses prominent thermochromic properties and optical switching characters. It has shown that this convenient and efficient approach could be applied in the mass-production of functional powders materials.

Catalytic adsorptive stripping voltammetry determination of ultra trace amount of tungsten using factorial design for optimization

A highly sensitive procedure is presented for the determination of ultra-trace concentration of tungsten by catalytic adsorptive stripping voltammetry. The method is based on adsorptive accumulation of the tungsten-pyrocatechol violet complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by chlorate. The influence of variables was completely studied by factorial design analysis. Optimum analytical conditions for the determination of tungsten were established. Tungsten can be determined in the range 0.06–12.0 ng/mL with a limit of detection of 0.02 ng/mL. The influence of potentially interfering ions on the determination of tungsten was studied. The procedure was applied to the determination of tungsten in one sandwich polyoxometalate and some synthetic samples similar to alloy compounds with satisfactory results.

Electrodeposition of nanocrystalline Co-W coatings from citrate electrolytes under conditions of controlled hydrodynamic: II. The electrodeposition rate and composition of the coatings

The influence of the ionic mass-transfer effects on the deposition rate, the current efficiency, and the composition and morphology of the coatings has been studied using a rotating cylindrical electrode in a citrate electrolyte containing CoSO4 (0,2 mol/l) and Na2WO4 (0.2 mol/l) (pH = 6.8) at the electrodeposition temperature of 60°C. It has been found that the decrease of the electrodeposition potential and the tungsten concentration in the coating with the current efficiency increase upon the Re number growth (Re ≥ 200) occur only under galvanostatic conditions. At the potentiostatic mode, similar of influence fails to be observed. It is shown that the estimated effects take place due to the electrodeposition through the nonstoichiometric surface coating layer with electronic conductivity, the composition components of which are in electrochemical equilibrium with the components of the solution at the film-solution boundary.

Hydrogenation of p-Chloronitrobenzene on Tungsten-Modified NiCoB Catalyst

NiCoB has been reported to be a good catalyst for the hydrogenation of p-chloronitrobenzene (p-CNB). However, it aggregates easily. In this study, a series of tungsten-modified NiCoB catalysts with various tungsten contents were synthesized by the chemical reduction method using NaBH4 as the reducing agent. The products were characterized by X-ray diffraction (XRD), N2 sorption, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The catalysts were tested for the liquid-phase hydrogenation of p-CNB. Ni, Co, W, and B were present in both elemental and oxidized states. The addition of tungsten could influence the surface composition of the catalyst. The electronic structures of Ni, Co, W, and B were also changed with changing content of tungsten. XPS showed that the elemental states of Ni, Co, W, and B formed an amorphous nanoalloy. The interactions of these species affected their electron densities and further influenced their catalytic activities. The tungsten oxide located among the NiCoB particles could act as a spacer that separates the NiCoB particles from their neighbors and inhibits aggregation. Compared to the unmodified NiCoB catalyst, the catalytic activity of tungsten-modified NiCoB exhibited an obvious increase, along with a slight decrease in the selectivity of p-chloroaniline (p-CAN). The differences in the atom radius and electronegativity of tungsten from those of the other elements in the alloy resulted in the formation of active sites for the catalytic reaction. The concentration of boron on the catalyst surface decreased with increasing tungsten concentration, which was responsible for the slight decrease in the selectivity of p-CAN. Considering the electronic effects, the structural effects, and the amount of B3+ (Lewis acid), good catalytic performance in the hydrogenation of p-CNB was achieved by modifying the NiCoB catalysts with the proper amount of tungsten. Tungsten species not only acted as a spacer to prevent NiCoB particles from aggregating, but also donated partial electrons to Ni and Co. An overdose of tungsten would cover the surface of Ni and result in low activity.

Tungsten-induced protein aggregation: Solution behavior

Tungsten has been associated with protein aggregation in prefilled syringes (PFSs). This study probed the relationship between PFSs, tungsten, visible particles, and protein aggregates. Experiments were carried out spiking solutions of two different model proteins with tungsten species obtained from the extraction of tungsten pins typically used in syringe manufacturing processes. These results were compared to those obtained with various soluble tungsten species from commercial sources. Although visible protein particles and aggregates were induced by tungsten from both sources, the extract from tungsten pins was more effective at inducing the formation of the soluble protein aggregates than the tungsten from other sources. Furthermore, our studies showed that the effect of tungsten on protein aggregation is dependent on the pH of the buffer used, the tungsten species, and the tungsten concentration present. The lower pH and increased tungsten concentration induced more protein aggregation. The protein molecules in the tungsten-induced aggregates had mostly nativelike structure, and aggregation was at least partly reversible. The aggregation was dependent on tungsten and protein concentration, and the ratio of these two and appears to arise through electrostatic interaction between protein and tungsten molecules. The level of tungsten required from the various sources was different, but in all cases it was at least an order of magnitude greater than the typical soluble tungsten levels measured in commercial PFS. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4695–4710, 2009

Radioisotope express analysis of tungsten carbide in the manufacture of high-strength cemented carbides

Radioisotope methods for express analysis of tungsten carbide in the manufacture of cobaltiferous powder mixture are described. Physically, this approach is based on an initial determination of tungsten in the powder mixture via registration of back-scattered beta radiation emitted by the radionuclide Sr90. The percentage of WC is measured by the product of concentration of tungsten and the ratio AWC/AW of atomic weights. A measurement system involving a standard specimen is developed capable of accelerated determination of the percentage of WC. This highly express method is capable of exercising real-time control over the process of mixing of alloy components (WC + Co).

Influence of speciation on tungsten toxicity

Information on tungsten ecotoxicology is very limited. Moreover, it is an even larger lack of information linking tungsten environmental speciation and environmental effects. Soluble tungsten compounds can be released into the environment after corrosion and dissolution of tungsten containing alloys and minerals. Tungsten aquatic chemistry is quite complicated; tungsten anions may polymerize (depending upon concentration and aquatic geochemistry) in aquatic systems at environmentally relevant pHs. However, our present knowledge of tungsten toxicological effects is entirely based on the data obtained in experiments with monotungstates. Here we report experimental results demonstrating that polytungstates are significantly more toxic than monotungstates. Toxicological effects of sodium tungstate and metatungstate have been examined in the standard OECD toxicological tests for Daphnia, algae and earthworms. LD50 and EC50 values for sodium tungstate are more than 10 times larger than those for sodium metatungstate, when expressed in terms of tungsten concentration. This difference increases 12-fold more when LD50 and EC50 are expressed in terms of molecular concentrations. These toxicity patterns have also been observed in the experiment with laboratory aquatic ecosystems. At the ecosystem level, mono- and polytungstates also affect the nitrogen cycle. These findings stress the need for further studies of both environmental speciation of tungsten and toxicity of different tungsten compounds.

Manufacture, microstructure and mechanical properties of Mo–W–N nanostructured hard films

Mo 1− x W x N y ( x = 0–0.67) hard films were fabricated on wafers of silicon and high speed steel by dc magnetron sputtering technique. The effect of tungsten concentration on the phase composition, microstructure, surface morphology, hardness, adhesion, and corrosion resistance of the films was studied by X-ray diffraction, scanning electron microscopy, nano-indentation, and scratch test. It was found that if the W concentration ( x) in the film is in the range of 0–0.52, the films exhibit fcc (Mo,W)N y single phase where larger W atoms substituted Mo atoms in fcc MoN y . At higher x values ( x > 0.52) the films exhibit a two-phase structure consisting of fcc (Mo,W)N y and pure bcc tungsten phase. The hardness of the Mo 1− x W x N y films increases at first with increasing x, and then decreases after passing a maximum. The maximum hardness of 47 GPa is obtained at x = 0.37 corresponding to an adhesion strength of 60 N. The Mo–W–N coated high speed steel has a lower corrosion current density and higher corrosion potential than the bare high speed steel substrates.