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.

Influence of proton insertion on the conductivity, structural and optical properties of amorphous and crystalline electrochromic WO3 films

Abstract: Amorphous and crystalline tungsten oxide films were RF-sputtered from a metallic target in oxygen/argon atmosphere onto un-heated and heated substrates. Upon cyclic electrochemical treatment in 0.1 M H2SO4 aqueous solution, both types of films showed good electrochromic reversibility beyond 1000 cycles. The crystallinity changes of both types of films were studied by XRD. For c-WO3, the results showed that hydrogen insertion enhance the degree of crystallinity with the clear appearance of tungsten bronze diffraction peaks due to the formation of H0.1WO3, with tetragonal crystalline structure. For a-WO3, coloration weakens the amorphous features and increases the crystallinity properties. The DC electrical conductivity increases, in a reversible way, with four order of magnitudes namely from 10−7 to 10−3 (Ω cm)−1 for bleached and colored films, respectively. Both types of films exhibit remarkable solar transmission modulation, about 51%, which is adequate for smart windows applications. In contrast to amorphous films, crystalline tungsten oxide films show reflection modulation in the NIR reaching 25% upon charge insertion. The Drude reflectance edge arises for colored films suggesting that coloration in c-WO3 is attributed to a scattering mechanism of Drude-like free electron, while coloration of a-WO3 is attributed to a hopping mechanism of small polaron. The visible, infrared and solar modulations are given for both types of films. Coloration/bleaching were found to be faster for amorphous films. Self-bleaching process in different oxidative environments involves a redox cycle aided by water polarity. Crystalline WO3 showed pronounced coloring persistence relative to amorphous films which is attributed to different binding energy related to large and small polarons.

Volatility of the Oxides of Tungsten and Molybdenum in the Presence of Water Vapour

Abstract: ACCORDING to L. Wohler and O. Balz1,2, the oxides WO3, W2O5 (W4O11) and WO2 volatilize considerably above 800–900° C., and the vapour pressure of tungsten trioxide is, according to O. Ruff and Grieger3,2, 0·206 mm. at 1,023° C. It is generally believed that this phenomenon explains the formation of much larger metal grains during the reduction of tungsten trioxide in hydrogen at 800–900° C. from much finer oxide grains.

Compositions of corrosion-resistant Fe-based amorphous metals suitable for producing thermal spray coatings

Abstract: A method of coating a surface comprising providing a source of amorphous metal that contains manganese (1 to 3 atomic %), yttrium (01 to 10 atomic %), and silicon (03 to 31 atomic %) in the range of composition given in parentheses; and that contains the following elements in the specified range of composition given in parentheses: chromium (15 to 20 atomic %), molybdenum (2 to 15 atomic %), tungsten (1 to 3 atomic %), boron (5 to 16 atomic %), carbon (3 to 16 atomic %), and the balance iron; and applying said amorphous metal to the surface by a spray

On the Eu3+ Fluorescence in Mixed Metal Oxides. III. Energy Transfer in Eu3+‐Activated Tungstates and Molybdates of the Type Ln2WO6 and Ln2MoO6

Abstract: The fluorescence of unactivated and rare‐earth‐activated materials of the type Ln2WO6, Ln2MoO6, and Y2W1−xMoxO6 (0≤x≤0.1) has been studied. From the experiments on unactivated materials it follows that energy transfer from tungstate to tungstate or mobyldate group takes place, whereas there is no transfer from molybdate to molybdate or tungstate group. Arguments in favor of exchange‐regulated energy transfer from tungstate or molybdate group to rare‐earth ion are put forward. The efficiencies of the rare‐earth‐activated tungstates and molybdates can be qualitatively understood assuming a strong dependence of the energy transfer on the angle tungsten (molybdenum)—oxygen—rare earth. In Y2W1−xMoxO6:Eu the molybdate group acts as a killer of the fluorescence under short‐wave uv excitation and as a sensitizer under long‐wave uv excitation.