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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.


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TL;DR: In this paper, a simple sonochemical synthesis of nanostructured molybdenum carbide from the ultrasonic irradiation of hexacarbonyl was presented.
Abstract: The preparation of nanophase materials has been the focus of intense study in materials science1,2 A variety of chemical and physical preparative methods have been applied to produce materials with nanometer structure, including metal evaporation,3 decomposition of organometallic compounds,4 and reduction of metal salts5,6 Sonochemical decomposition of transition metal carbonyl compounds has also been proven to be a useful technique to generate nanophase transition metals7,8 Recently, molybdenum and tungsten carbides have been examined as heterogeneous catalysts because their activity is often similar to that of the platinum group metals9-11 For catalytic applications, high surface area materials are generally needed; the preparation of interstitial carbides of molybdenum and tungsten with high surface areas, however, is very difficult We present here a simple sonochemical synthesis of nanostructured molybdenum carbide from the ultrasonic irradiation of molybdenum hexacarbonyl In addition, we have examined the catalytic activity and selectivity of these materials for the dehydrogenation of alkanes The chemical effects of ultrasound arise from acoustic cavitation: the formation, growth, and implosive collapse of bubbles in a liquid12,13 The collapse of bubbles generates localized hot spots through adiabatic compression or shock wave formation within the gas of the collapsing bubble This local heating produces a wide range of high-energy chemistry The conditions formed in these hot spots have been experimentally determined, with transient temperatures of ∼5000 K, pressures of∼1800 atm, and cooling rates in excess of 1010 K/s14,15 Using these extreme conditions, we have explored a variety of applications of ultrasound to materials chemistry16 A slurry of molybdenum hexacarbonyl (1 g in 50 mL of hexadecane) was sonicated with a high-intensity ultrasonic horn (Sonic and Materials, model VC-600, 05 in Ti horn, 20 kHz, 100 W cm-2) at 90 °C for 3 h under argon to yield a black powder The powder was filtered inside an inert atmosphere box (Vacuum Atmospheres, <1 ppm O2), washed several times with purified, degassed pentane, and heated at 100 °C under vacuum X-ray powder diffraction17 (XRD) showed extremely broad peaks centered at a d spacing of 24, 15, and 13 A (Figure 1), which did not match body-centered cubic (bcc) lines of molybdenum metal After the heat treatment at 450 °C under helium flow for 12 h, sharper peaks in the XRD were observed at d spacing values of 239, 149, and 127 A which accurately correspond to face-centered cubic (fcc) molybdenum carbide, Mo2C (Figure 1) The synthesis of Mo2C is particularly prone to substantial oxygen contamination9 Even after heat treatment at 450 °C under helium, oxygen was still present at about 4 wt % Since the presence of oxygen could poison the catalytic activity, it was removed prior to catalytic studies by heating in a flowing 1:1 CH4/H2 mixture at 300 °C for 1 h, then at 400 °C for 1 h, and finally at 500 °C for 48 h The flow rate of the CH4/H2 mixture was 275 cm3 (STP)/min After this carburization, excess carbon, hydrogen, and oxygen had been largely removed The elemental analysis results showed the sample was very pure (theoretical for Mo2C, 9411 % Mo, 589 % C; exptl, 9386 % Mo, 568 % C, 008 % H, 006 % N), which corresponds to a stoichiometry of Mo2C097 The XRD was essentially unchanged by carburization

256 citations

Journal ArticleDOI
TL;DR: Transition metal oxides (TMOs) based on conversion reactions are attractive candidate anode materials for lithium-ion batteries (LIBs) because of their high theoretical capacity and safety characteristics as mentioned in this paper.
Abstract: Transition metal oxides (TMOs) based on conversion reactions are attractive candidate anode materials for lithium-ion batteries (LIBs) because of their high theoretical capacity and safety characteristics. In this review, we have summarized recent progress in the rational design and efficient synthesis of TMOs with controllable morphologies, compositions, and micro-/nanostructures, along with their Li storage behaviors. Single metal oxides of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), ruthenium (Ru), chromium (Cr), molybdenum (Mo), and tungsten (W) and their common binary metal oxides have been discussed in this review. Finally, the less well-known merits of conversion reactions are put forward, and the design of metal oxide electrodes making full use of these merits has been proposed.

253 citations

Journal ArticleDOI
TL;DR: It has been shown that the as-prepared tungsten oxide ceramic nanofibers have a quick response to ammonia with various concentrations, suggesting potential applications of the electrospun tungsteins oxide nan ofibers as a sensor material for gas detection.
Abstract: We describe the fabrication and characterization of tungsten oxide nanofibers using the electrospinning technique and sol-gel chemistry. Tungsten isopropoxide sol-gel precursor was incorporated into poly(vinyl acetate)(PVAc)/DMF solutions and electrospun to form composite nanofibers. The as-spun composite nanofibers were subsequently calcinated to obtain pure tungsten oxide nanofibers with controllable diameters of around 100 nm. SEM and TEM were utilized to investigate the structure and morphology of tungsten oxide nanofibers before and after calcination. The relationship between solution concentration and ceramic nanofiber morphology has been studied. A synchrotron-based in situ XRD method was employed to study the dynamic structure evolution of the tungsten oxide nanofibers during the calcination process. It has been shown that the as-prepared tungsten oxide ceramic nanofibers have a quick response to ammonia with various concentrations, suggesting potential applications of the electrospun tungsten oxide nanofibers as a sensor material for gas detection.

251 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,055
20222,162
2021902
20201,216
20191,447
20181,372