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.

Development of W/Cu—functionally graded materials☆

Abstract: Plasma facing components (PFCs) consist of a plasma facing and a heat sink material. These have to fulfil different functions that require different material properties, for example the coefficient of thermal expansion (CTE) of tungsten and copper. Joining of these materials (e.g. by brazing or HIPing) results in the formation of thermal-induced stresses at the interface. Functionally graded materials (FGMs), used as an interlayer, reduce these thermally induced stresses. Two different methods, laser sintering and plasma spraying, have been investigated as a means to produce W/Cu FGMs to be used in PFCs of next step confinement experiments. In addition to mixtures of tungsten and copper powders, 40 wt.% Cu-coated W powder was used to produce W/Cu composites with a content of either 25 or 60 vol.% Cu. The composite microstructure has been analyzed according to Cu content, particle distribution and layer structure. The difference in the behavior of powder mixtures and coated powder is outlined. A comparison of plasma sprayed to commercially produced Cu-infiltrated W samples is made and the results of thermomechanical and thermophysical testing are discussed with respect to different microstructures.

Influence of impurities on the fracture behaviour of tungsten

Abstract: Ten tungsten materials with different impurity concentrations and different microstructures have been investigated by Auger electron spectroscopy and scanning electron microscopy with respect to their fracture behaviour. For almost all samples, both inter- and transgranular fracture are observed, and the proportion of each type varies. Due to the difference in their impurity content and grain boundary area, a large variation in the grain boundary impurities can be expected. By analysing the fracture surfaces the effect of grain boundary impurities, especially phosphorous and oxygen, on the fracture resistance of the boundaries was determined. The results indicate that for the analysed tungsten materials, grain boundary impurities do not have a significant influence on the fracture resistance of the boundaries. Other factors such as the size and shape of the grains, the amount of deformation and therefore the density of dislocations within the grains have a greater impact on the fracture behaviour of tungsten.

Synthesis and characterization of W–Cu nanocomposites developed by mechanical alloying

Abstract: In the present investigation, attempts have been made to synthesize W–Cu nanocomposites by mechanical alloying (MA) and the results show that MA is a very good processing technique in making these nanocomposites. Elemental tungsten and copper are also milled. Characterization techniques like XRD, TEM and SEM have been used to study the crystallite size, r.m.s. strain and their morphology changes on milling. Crystallite size of tungsten was found to 15 nm and that of copper as 40 nm after 20 h of milling. Tungsten being brittle has lower crystallite sizes than copper on milling. Copper being ductile has good cushioning effect and tungsten crystallite sizes are relatively higher in the as-milled W–Cu samples when the fraction of copper is higher in W–Cu system. Elemental tungsten, elemental copper and W–Cu nanocomposites obtained after milling for 20 h were subjected to annealing at 400, 600, and 800 °C for 2 h and the phase transformation in these powders was studied.

Oxidation of Tungsten

Abstract: Two oxide layers form during the oxidation of tungsten between 700° and 1000°C. The outer layer is porous, powdery, yellow tungstic oxide, , and the inner layer is a dense, thin, dark‐blue, tightly adherent oxide of uncertain composition. The oxidation reaction follows initially the parabolic rate law, but eventually there is a transition to the linear rate law. The rate of formation of the inner oxide is presumably inversely proportional to its thickness. The inner oxide seems to transform to the outer oxide at a constant rate. Upon combining the rate laws of the two individual processes, an overall rate equation covering the whole range is obtained. The thickness of the inner layer tends to a limiting value when the rate of its formation is equal to the rate of transformation to the outer layer.

Review on Recent Progress in the Development of Tungsten Oxide Based Electrodes for Electrochemical Energy Storage.

Abstract: Current progress in the advancement of energy-storage devices is the most important factor that will allow the scientific community to develop resources to meet the global energy demands of the 21st century. Nanostructured materials can be used as effective electrodes for energy-storage devices because they offer various promising features, including high surface-to-volume ratios, exceptional charge-transport features, and good physicochemical properties. Until now, the successful research frontrunners have focused on the preparation of positive electrode materials for energy-storage applications; nevertheless, the electrochemical performance of negative electrodes is less frequently reported. This review mainly focuses on the current progress in the development of tungsten oxide-based electrodes for energy-storage applications, primarily supercapacitors (SCs) and batteries. Tungsten is found in various stoichiometric and nonstoichiometric oxides. Among the different tungsten oxide materials, tungsten trioxide (WO3 ) has been intensively investigated as an electrode material for different applications because of its excellent charge-transport features, unique physicochemical properties, and good resistance to corrosion. Various WO3 composites, such as WO3 /carbon, WO3 /polymers, WO3 /metal oxides, and tungsten-based binary metal oxides, have been used for application in SCs and batteries. However, pristine WO3 suffers from a relatively low specific surface area and low energy density. Therefore, it is crucial to thoroughly summarize recent progress in utilizing WO3 -based materials from various perspectives to enhance their performance. Herein, the potential- and pH-dependent behavior of tungsten in aqueous media is discussed. Recent progress in the advancement of nanostructured WO3 and tungsten oxide-based composites, along with related charge-storage mechanisms and their electrochemical performances in SCs and batteries, is systematically summarized. Finally, remarks are made on future research challenges and the prospect of using tungsten oxide-based materials to further upgrade energy-storage devices.