Performance Of Tungsten Research Articles

Performance of tungsten oxide/polypyrrole composite as cathode catalyst in single chamber microbial fuel cell

The Cathode catalyst with high catalytic activity for oxygen reduction reaction plays a vital role in the execution of microbial fuel cells over the years. In this study, the performance of tungsten oxide/polypyrrole (WO3/Ppy) composites as a cathode catalyst in a single chamber microbial fuel cell (SCMFC) was investigated. Electrochemical analysis viz. electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) of the composite indicates a ratio of 1:1 (WO3: Ppy) due to the synergistic effect of materials. WO3/Ppy composite with high surface area and the better structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field-emission scanning electron microscopy (FE-SEM), and Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The WO3: Ppy catalyst in MFC delivers a maximum power density of 0.571 W m−2 with a current density of 1.51 A m−2 at100 Ω, which is slightly lower than the platinum (Pt/C) coated carbon cloth (CC) (0.84 W m−2, 1.83 A m−2). The results suggest that the tungsten oxide/polypyrrole catalyst optimized for power output is an alternative to the expensive Pt/C in an air-cathode microbial fuel cell.

Photocatalytic landfill leachate treatment using P-type TiO2 nanoparticles under visible light irradiation

Landfill leachate treatment is a necessary measure for environmental protection and supporting sustainable development. Photocatalytic treatment method using N- or P-type TiO2 nanoparticles has been proposed as an efficient method for the treatment of recalcitrant pollutants. Since main oxidizing agents in the photocatalytic treatment by N- and P-type TiO2 are different, investigating their performance for the photocatalytic treatment of landfill leachate is necessary. Therefore, the purpose of this study is to evaluate the performance of P-type TiO2 nanoparticles for the photocatalytic treatment of landfill leachate under visible light irradiation. Silicon (Si) element was considered as TiO2 dopant, and Si-doped TiO2 nanoparticles were synthesized by sol–gel method. Four effective parameters on the photocatalytic treatment process, i.e., the dopant content of Si (Si wt.%), calcination temperature (T), pH, and exposure time, were considered as independent variables, and temporal normalized concentration of leachate residual COD was considered as dependent variable. Decision tree (M5P) model was applied for modeling the photocatalytic process of landfill leachate treatment using the data of 167 experiments. Based on the results, the optimum value of pH, calcination temperature, and dopant content for Si-doped TiO2 nanoparticles are 6, 500 °C, and 2.5 weight percentage, respectively, and the leachate COD removal efficiency at these conditions is about 85% for leachate with 600 mg/L initial COD. Therefore, Si dopant considerably enhances the photocatalytic activity of TiO2 nanoparticles under visible light irradiation. This photocatalytic process can be efficiently applied for landfill leachate treatment. Finally, the performance of Si-doped TiO2 nanoparticles as P-type TiO2 was compared with the performance of tungsten (W)-doped TiO2 nanoparticles as N-type TiO2 for leachate COD removal. Results showed that both types of nanoparticles have a similar performance for oxidizing the leachate COD, and there is no significant difference between them.

Impact of Thermal Aging on the SCR Performance of Tungsten Doped CeVO4 Mixed Oxides

The development of more thermally stable vanadia-based SCR catalysts for combined end-of-pipe technologies, i.e. selective catalytic reduction catalysts wash-coated on a particulate filter, has been considered in this study. The impact of thermal aging at 850 °C in wet atmosphere has been investigated on bulk W-doped CeVO4 catalysts. Strong detrimental effect on the specific surface area was observed delayed by the presence of tungsten. However, they preserve a significant selective conversion depending on the surface composition with an optimal tungsten composition.

The influence of plasma-surface interaction on the performance of tungsten at the ITER divertor vertical targets

The tungsten (W) material in the high heat flux regions of the ITER divertor will be exposed to high fluxes of low-energy particles (e.g. H, D, T, He, Ne and/or N). Combined with long-pulse operations, this implies fluences well in excess of the highest values reached in today’s tokamak experiments. Shaping of the individual monoblock top surface and tilting of the vertical targets for leading-edge protection lead to an increased surface heat flux, and thus increased surface temperature and a reduced margin to remain below the temperature at which recrystallization and grain growth begin. Significant morphology changes are known to occur on W after exposure to high fluences of low-energy particles, be it H or He. An analysis of the formation conditions of these morphology changes is made in relation to the conditions expected at the vertical targets during different phases of operations. It is concluded that both H and He-related effects can occur in ITER. In particular, the case of He-induced nanostructure (also known as ‘fuzz’) is reviewed. Fuzz formation appears possible over a limited region of the outer vertical target, the inner target being generally a net Be deposition area. A simple analysis of the fuzz growth rate including the effect of edge-localized modes (ELMs) and the reduced thermal conductivity of fuzz shows that the fuzz thickness is likely to be limited by the occurrence of annealing during ELM-induced thermal excursions. Not only the morphology, but the material mechanical and thermal properties can be modified by plasma exposure. A review of the existing literature is made, but the existing data are insufficient to conclude quantitatively on the importance and extent of these effects for ITER. As a consequence of the high surface temperatures in ITER, W recrystallization is an important effect to consider, since it leads to a decrease in material strength. An approach is proposed here to develop an operational budget for the W material, i.e. the time the divertor material can be operated at a given temperature before a significant fraction of the material is recrystallized. In general, while it is clear that significant surface damage can occur during ITER operations, the tolerable level of damage in terms of plasma operations currently remains unknown.

Synthesis and Performance of Tungsten Disulfide/Carbon (WS2/C) Composite as Anode Material

The precursors of an amorphous WS2/C composite were synthesized by a simple hydrothermal method using Na2WO4·2H2O and CH3CSNH2 as raw materials, polyethylene glycol as dispersant, and glucose as the carbon source. The as-synthesized precursors were further annealed at a low temperature in flowing argon to obtain the final materials (WS2/C composite). The structure and morphology of the WS2/C composite were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. The electrochemical properties were tested by galvanostatic charge/discharge testing and alternating current (AC) impedance measurements. The results show that the as-prepared amorphous WS2/C composite features both high specific capacity and good cycling performance at room temperature within the potential window from 3.0 V to 0.01 V (versus Li+/Li) at current density of 100 mAg−1. The achieved initial discharge capacity was 1080 mAhg−1, and 786 mAhg−1 was retained after 170 cycles. Furthermore, the amorphous WS2/C composite exhibited a lower charge/discharge plateau than bare WS2, which is more beneficial for use as an anode. The cyclic voltammetry and AC impedance testing further confirmed the change in the plateau and the decrease in the charge transfer resistance in the WS2/C composite. The chemical formation process and the electrochemical mechanism of the WS2/C composite are also presented. The amorphous WS2/C composite can be used as a new anode material for future applications.

Influence of the base temperature on the performance of tungsten under thermal and particle exposure

Tungsten, the plasma facing material (PFM) for the divertor in ITER, must sustain severe, distinct loading conditions. This broad array of exposure conditions necessitates comprehensive experiments that cover most of the expected loading parameters to predict qualitative statements about the performance and as a consequence thereof the intended operation time. However, comprehensive experiments are inherently difficult to realize due to the fact that there is no device that is capable of simulating all loading conditions simultaneously. Nevertheless, the linear plasma device PSI-2 enables experiments combining thermal and particle exposure at the same time. In this work, sequential and simultaneous loads on pure tungsten at different base temperatures were investigated to study not only the performance of the material, but also the influence of the experimental parameters. The detailed analysis and comparison of the obtained results showed different kinds of damage depending on the loading sequence, power density, microstructure of the samples, and base temperature. Finally, samples with transversal grain orientation (T) showed the weakest damage resistance and the increase of the base temperature could not compensate the detrimental impact of deuterium.

Impact of combined hydrogen plasma and transient heat loads on the performance of tungsten as plasma facing material

Experiments were performed in three different facilities in order to investigate the impact of combined steady state deuterium plasma exposure and ELM-like thermal shock events on the performance of ultra high purity tungsten. The electron beam facility JUDITH 1 was used to simulate pure thermal loads. In addition the linear plasma devices PSI-2 and Pilot-PSI have been used for successive as well as simultaneous exposure where the transient heat loads were applied by a high energy laser and the pulsed plasma operation, respectively. The results show that the damage behaviour strongly depends on the loading conditions and the sequence of the particle and heat flux exposure. This is due to hydrogen embrittlement and/or a higher defect concentration in the tungsten near surface region due to supersaturation of hydrogen. The different results in terms of damage formation from both linear plasma devices indicate that also the plasma parameters such as particle energy, flux and fluence, plasma impurities and the pulse shape have a strong influence on the damage performance. In addition, the different loading methods such as the scanning with the electron beam in contrast to the homogeneous exposure by the laser leads to an faster increase of the surface roughness due to plastic deformation.

Effect of iron(III) nitrate concentration on tungsten chemical-mechanical-planarization performance

Investigating the catalytic effect of Fe(NO3)3 on the performance of tungsten (W) chemical mechanical planarization in H2O2-based acidic slurries, we found that the trend of the polishing rate with increasing Fe(NO3)3 concentration was divided into two regions. The polishing rate in region I (<0.10wt%) increased rapidly because of the increase of the WO3 layer formed by the reaction of Fe(NO3)3 and H2O2. The polishing rate in region II (>0.10wt%), on the other hand, increased only slightly with increasing Fe(NO3)3 concentration. We suggest the excess ferric ions in the slurry were rapidly supplied to the W surface. Consequently, the addition of Fe(NO3)3 resulted in the rapid formation of the WO3 layer because of the decomposition of H2O2 into O2 by Fe3+ ion, and polishing rate increased with the Fe(NO3)3 concentration. This polishing trend was explained through the opposite trend of static etch rate, the confirmation of the surface morphology, the trend of the WO3 content on the W surface, and the trend of the corrosion potential and the corrosion current density.

Ruthenium and Tungsten as Contact Materials in Hermetically Plastic Sealed Telecom- and Signal-Relays

Palladium is the most frequently used contact material for telecommunication and signal relays. Good contact resistance stability and material transfer characteristics make it the most often used. The strong variation of the palladium price in recent years has made it necessary to look for alternatives. The development of gas-tight plastic sealed relay housings, which keep the gas filling inside the relay for a long time, e.g., more than 10 years for nitrogen and more than 100 years for sulfur-hexafluoride, allows nonprecious metal contact materials to be used, as an inert atmosphere can be kept for the entire life of the relay. Tests were performed with gold covered tungsten and ruthenium contacts mounted in a standard telecom relay filled with N/sub 2/ or SF/sub 6/. Although the contact resistance was always measured with dry circuit conditions applied, no relevant increase was observed during all electrical endurance tests. The ruthenium as well as the tungsten layer with a thickness of only 5 /spl mu/m withstood endurance tests at maximum loads at 30 W. As only minimum contact erosion and material transfer occurred, no contact sticking or bridging was observed. Overall the switching performance of tungsten and ruthenium is similar to PdRu10. As PdRu10 has superior performance especially when operating in an SF/sub 6/ atmosphere, the properties of Ru and W in N/sub 2/ as well as in SF/sub 6/ are at least comparable with all contact materials in current use. Gas-tight plastic sealed relay housings offer the advantages of hermetically sealed housings at an affordable cost.