Tungsten

About: Tungsten is a research topic. Over the lifetime, 35225 publications have been published within this topic receiving 456213 citations. The topic is also known as: W & element 74.

Tribological properties, phase generation and high temperature phase stability of tungsten- and vanadium-oxides deposited by reactive MSIP-PVD process for innovative lubrication applications

Abstract: The tungsten and vanadium oxides are promising to be usable as solid lubricants at elevated temperatures because of their ability to form oxygen deficient Magneli-phases. As a matter of fact, metal-oxides are interesting for tribological insets at atmospheric conditions because of their expected oxidation stability and low adhesion. The study reports about the deposition of tungsten and vanadium oxides in a reactive d.c. mode by the MSIP- (Magnetron Sputtering Ion Plating) PVD process and especially about the influence of the oxygen content in the sputtering atmosphere as well as the deposition temperature on the phase generation. A simplified ‘sputtering phase diagram’ of the binary systems V–O and W–O as a function of the deposition temperature (378–650 K) and the oxygen content (0–50%) was determined. Furthermore, it was shown that the tested vanadium-oxides are phase stable up to 878 K and the tungsten-oxides up to 1100 K (measured in a high-temperature XRD facility). Additionally tribological properties of the deposited oxide coatings, like the friction coefficient vs. steel, will be presented. For polished and WOx coated samples a friction coefficient of μ≈0.2 against steel was measured at room temperature. The coatings were analyzed by various testing methods to characterize the tribological, mechanical and structural properties, like SEM, nanoindentation, (high-temperature)-XRD and pin-on-disk.

Effect of substrates on the melting temperature of gold nanoparticles

Abstract: The size-dependent melting temperature of metallic nanoparticles (NPs) is generally examined on a solid substrate. However, most experimental works performed on a solid substrate were explained by a homogeneous particle model without considering the effect of the substrate. For example, in the previous studies, the melting temperatures of gold NPs were examined on carbon or tungsten substrates. However, the experimental results were described only by the surface tension of gold, without interfacial tension between gold and substrate. In the present work, the effect of the sorts of substrate on the melting temperatures of gold NPs was examined by using a thermodynamic model equilibrating the chemical potentials of liquid and solid particles. For this study, graphite, alumina and tungsten substrates were selected as typical ceramic and metallic substrates.

The influence of transition metal solutes on the dislocation core structure and values of the Peierls stress and barrier in tungsten

Abstract: Several transition metals were examined to evaluate their potential for improving the ductility of tungsten. The dislocation core structure and Peierls stress and barrier of 1/2〈111〉 screw dislocations in binary tungsten–transition metal alloys (W1−xTMx) were investigated using density functional theory calculations. The periodic quadrupole approach was applied to model the structure of the 1/2〈111〉 dislocation. Alloying with transition metals was modeled using the virtual crystal approximation and the applicability of this approach was assessed by calculating the equilibrium lattice parameter and elastic constants of the tungsten alloys. Reasonable agreement was obtained with experimental data and with results obtained from the conventional supercell approach. Increasing the concentration of a transition metal from the VIIIA group, i.e. the elements in columns headed by Fe, Co and Ni, leads to reduction of the C′ elastic constant and increase of the elastic anisotropy A = C44/C′. Alloying W with a group VIIIA transition metal changes the structure of the dislocation core from symmetric to asymmetric, similarly to results obtained for W1−xRex alloys in the earlier work of Romaner et al (2010 Phys. Rev. Lett. 104 195503). In addition to a change in the core symmetry, the values of the Peierls stress and barrier are reduced. The latter effect could lead to increased ductility in a tungsten-based alloy. Our results demonstrate that alloying with any of the transition metals from the VIIIA group should have a similar effect to alloying with Re.

R&D on full tungsten divertor and beryllium wall for JET ITER-like Wall Project

Abstract: The ITER reference materials have been tested separately in tokamaks, plasma simulators, ion beams and high heat flux test beds. In order to perform a fully integrated material test JET has launched the ITER-like Wall Project with the aim of installing a full metal wall during the next major shutdown. As a result of R&D projects in 2005-2006, bulk tungsten tiles are foreseen at the outer horizontal target and tungsten coating at the other divertor tiles. In some regions of the main chamber, beryllium coated Inconel tiles and bulk beryllium tiles are utilised which include marker tiles as erosion diagnostics. This paper gives an overview of the R&D carried out in the frame of the ITER-like Wall Project on the development of an inertially cooled bulk tungsten tile design and the characterization of tungsten and beryllium coating technologies.

Root Cause Analysis of Tungsten-Induced Protein Aggregation in Pre-filled Syringes

Abstract: Particles isolated from a pre-filled syringe containing a protein-based solution were identified as aggregated protein and tungsten. The origin of the tungsten was traced to the tungsten pins used in the supplier's syringe barrel forming process. A tungsten recovery study showed that the vacuum stopper placement process has a significant impact on the total amount of tungsten in solutions. The air gap formed in the syringe funnel area (rich in residual tungsten) becomes accessible to solutions when the vacuum is pulled. Leachable tungsten deposits that were not removed by the supplier's wash process are concentrated in this small area. Extraction procedures used to measure residual tungsten in empty syringes would under-report the tungsten quantity unless the funnel area is wetted during the extraction. Improved syringe barrel forming and washing processes at the supplier have lowered the residual tungsten content and significantly reduced the risk of protein aggregate formation. This experience demonstrates that packaging component manufacturing processes, which are outside the direct control of drug manufacturers, can have an impact on the drug product quality. Thus close technical communication with suppliers of product contact components plays an important role in making a successful biotherapeutic.