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.

Flexible electrochromic reflectance device based on tungsten oxide for infrared emissivity control

Abstract: Instead of the usual sputtered anhydrous tungsten oxide thin films, a powder of monohydrated tungsten oxide (WO3.H2O) was used for the making of an electrochromic infrared emissivity modulator. The WO3.H2O powder was embedded in a porous plastic matrix before being laminated with other appropriate layers of the battery-like device, leading then to a complete flexible emissivity modulator. The widely open structure of the hydrated tungsten oxide makes lithium intercalation easier, which is particularly suitable for the realization of plasticized devices. Compared to a classical battery assembly, a porous plastic graphite layer laminated with a conductive grid was sandwiched between the WO3.H2O and the electrolyte layers. Such an original device allowed both a perfect uniformity in current collection and a sufficient porosity for the liquid electrolyte displacement. The complete device demonstrated a satisfying electrochemical behavior under 1 mV/s potential sweeps, allowing the insertion of a large amount of lithium ions into the WO3.H2O structure. Hemispherical reflectance measurements were carried out both over the VIS/NIR (0.4–2.5 μm) and the mid-infrared (2.5–25 μm) spectral ranges. Reflectance over the 2.5–25 μm spectral range was found to switch from 2% to 32% upon intercalation of 0.65 Li per tungsten. This value is comparable to previous literature results obtained for rigid devices.

Effects of sequential tungsten and helium ion implantation on nano-indentation hardness of tungsten

Abstract: To simulate neutron and helium damage in a fusion reactor first wall sequential self-ion implantation up to 13 dpa followed by helium-ion implantation up to 3000 appm was performed to produce damaged layers of ∼2 μm depth in pure tungsten. The hardness of these layers was measured using nanoindentation and was studied using transmission electron microscopy. Substantial hardness increases were seen in helium implanted regions, with smaller hardness increases in regions which had already been self-ion implanted, thus, containing pre-existing dislocation loops. This suggests that, for the same helium content, helium trapped in distributed vacancies gives stronger hardening than helium trapped in vacancies condensed into dislocation loops.

Thermal Conductivity of Clear Fused Silica at High Temperatures

Abstract: The thermal conductivity of clear fused silica was measured over the temperature range 300–2100°K in an experiment which minimized radiative energy transport. This was a steady‐state experiment involving the measurement of the electric current and voltage drop through a fine tungsten wire which was embedded along the axis of a cylindrical silica rod. The wire served both as a heating element and as a resistance thermometer. Thermal conductivities were calculated by graphical evaluation of the rate of change of electric power with temperature at different temperatures. The experiment yielded thermal conductivities between 2.6×10−3 and 2.9×10−3 cal/cm sec°K at room temperature, and between 4.5×10−3 and 5.5×10−3 cal/cm sec°K over the temperature range 1000–2100°K.

Dislocations mediate hydrogen retention in tungsten

Abstract: In this letter, a comprehensive mechanism for the nucleation and growth of bubbles on dislocations under plasma exposure of tungsten is proposed. The mechanism reconciles long-standing experimental observations of hydrogen isotopes retention, essentially defined by material microstructure, and so far not fully explained. Hence, this work provides an important link to unify material's modelling with experimental assessment of W and W-based alloys as candidates for plasma facing components.

Enhanced low-temperature sintering of tungsten

Abstract: The effects of various transition metal additions on the sintering of a well-characterized, fine tungsten powder were analyzed using both isothermal and constant heating rate experiments in the temperature range 900 to 1400°C. Approximately four atomic mono-layers of palladium on the tungsten powder surface were found to be the optimal enhancer, followed by nickel, cobalt, platinum, and iron. The addition of Cu to the tungsten had no appreciable effect on the sintering kinetics. Sintering enhancement by these transition metals is related to their periodic chart position (i.e., electron structure). An overall non-Arrhenius shrinkage temperature dependence is attributed to grain growth in the activator-treated specimens. The activation energy for tungsten densification was determined to be 430 to 450 kJ/mol, which is in general agreement with a grain boundary diffusion process.