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.

Mechanism and kinetics of bubble formation in doped tungsten

Abstract: The mechanisms and kinetics of bubble formation that occur during annealing of tungsten doped with small amounts of K, Al, and Si compounds has been investigated by electron microscopy. Bubbles are present in the sintered ingot due to volatilization of the dope during the sintering treatment. As the ingot is worked down into wire, the bubbles present in the ingot become elongated. On annealing these elongated bubbles undergo shape changes which depend on the amount of working. Elongated bubbles with a length-to-width ratio of less than ten spheroidized while those with a length-to-width ratio greater than twenty are unstable and break up into a row of bubbles. If working has been sufficient to close up the elongated bubbles,e.g., in ribbon, 0.125 mm thick rolled from 0.9 mm diam wire, bubble formation results from the diffusion of vacancies to the volatile dopant particles.

Oxidation and dissolution of tungsten carbide powder in water

Abstract: The oxidation and dissolution of tungsten carbide powder dispersed in water was investigated using X-ray photoelectron spectroscopy (XPS) and leaching studies. We found that the WO 3 surface layer on the oxidised tungsten carbide powder dissolves readily at pH > 3 with the tungsten concentration increasing linearly with time. Adding cobalt powder to the tungsten carbide suspension resulted in a significant reduction of the dissolution rate at pH 3 solution chemistry and the Co 2+ adsorption at oxide/water interfaces.

Layered tungsten oxide-based organic-inorganic hybrid materials: an infrared and Raman study.

Abstract: Tungsten oxide-organic layered hybrid materials have been studied by infrared and Raman spectroscopy and demonstrate a difference in bonding nature as the length of the interlayer organic "spacer" molecule is increased. Ethylenediamine-tungsten oxide clearly displays a lack of terminal -NH3(+) ammonium groups which appear in hybrids with longer organic molecules, thus indicating that the longer chains are bound by electrostatic interactions as well as or in place of the hydrogen bonding that must be present in the shorter chain ethylenediamine hybrids. The presence of organic molecules between the tungsten oxide layers, compared with the layered tungstic acid H2WO4, shows a decrease in the apical W=O bond strength, as might be expected from the aforementioned electrostatic interaction.

Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscale-gap thermophotovoltaic power generators

Abstract: The impacts of radiative, electrical and thermal losses on the performances of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude- and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the cell absorption bandgap. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output due to thermal losses is determined. It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.