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Tungsten Oxide Nanowires

詳細: カテゴリ: Tungsten Information; 2015年2月05日（木曜）11:03に公開; 参照数: 1432

Tungsten oxide nanowires were prepared by a vapor transport method using yellow tungsten oxide powder as a raw material. The crystal structure and morphology of WO3 nanowires were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The obtained nanowires were hexagonal WO3.

The major factors that influenced the morphology were the furnace temperature and the substrate position. The diameter of the nanowires decreased as the distance of the substrate from the raw material increased. Sensors were fabricated by pouring a few drops of nanowire-suspended ethanol onto oxidized Silicon substrates equipped with a pair of interdigitated Pt electrodes. The sensor made of the nanowires as thin as 50 nm showed the highest response to NO2 at a low operating temperature of 100 °C. The temperature dependence of the response was discussed in relation to the formation of NO2− and NO3− ions on the surface of WO3. The response slightly increased with decreasing diameter if the nanowires are regional depleted in NO2, while it largely increased if the nanowires are in volume depletion. A theoretical calculations based on assumptions were proposed in order to clarify the correlation between the nanowire response and their diameter.

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Yellow Tungsten Oxide

詳細: カテゴリ: Tungsten Information; 2015年2月05日（木曜）10:56に公開; 参照数: 1430

Yellow tungsten oxide (WO3) is a chemical compound containing the transition metal tungsten and oxygen. It is obtained as an intermediate in the recovery of tungsten from its minerals. To a large extent, exact time and temperature control determines the physical characteristics of the tungsten oxide. Yellow tungsten oxide is a finely divided yellow crystalline powder.

Tungsten oxide is used for the production of tungsten metal powder or as a pigment for ceramics and paints due to its rich yellow color. Yellow tungsten oxide (WO3) is also used as material for tungsten oxide nanowires. Tungsten oxide nanowires were prepared by a vapor transport method using yellow tungsten oxide powder as a raw material.

Two commercial grades are available:

1. Tungsten blue oxide WO2.97 has a deep blue colour.

2. Tungsten yellow oxide WO3 has a yellow to bright green colour.

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Influence of Synthesis Conditions on Tungsten Oxide Functional Properties

詳細: カテゴリ: Tungsten Information; 2015年2月05日（木曜）10:51に公開; 参照数: 1366

Knowledge of the relation between the synthesis conditions of specific metal oxide and its functional properties is important for the possible application of metal oxides in advanced technologies. The chemical and physical properties of tungsten oxide are generally dependent on the route of their synthesis.

Tungsten oxide and its hydrates can be synthesized using various chemical methods, such as ‘wet’ chemical precipitation, hydrolysis of tungsten alkoxide or thermal decomposition of tungsten salts. The WO3 films on various substrates can also be prepared using various vacuum techniques. Modification of the chemical or physical route within the same method also influences the resulting properties of the synthesized material.

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Where Is Tungsten Oxide From?

詳細: カテゴリ: Tungsten Information; 2015年2月05日（木曜）10:43に公開; 参照数: 1326

Tungsten oxide is obtained from the minerals scheelite, wolframite, ferberite. It is insoluble in H2O and acids, but soluble in hot alkalis.

Intermediates, such as tungsten trioxide, tungsten blue oxide, tungstic acid, and ammonium metatungstate can be derived from APT, either by partial or complete thermal decomposition or by chemical attack.

Stoichiometric compounds such as W20O58, W18O49 or WO2 are formed intermediately during the reduction process and can be isolated by interrupting the reduction process at the selected reduction state.

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Violet Tungsten Oxide Nano Powders

詳細: カテゴリ: Tungsten Information; 2015年2月03日（火曜）19:42に公開; 参照数: 1306

1. Product Name: WO3-x

2. Particle size:50-60nm

3. Purity: 99.9%

4. Appearance: Violet powder, the color depend on its tightness of oxygen index particles and the L/D ratio of the needle (SEM)

Violet tungsten oxide is a finely divided violet crystalline powder. It is produced by rotary calcining ammonium paratungstate at closely controlled temperatures in a reducing atmosphere. Violet tungsten oxide is used primarily for the production of tungsten metal powder and tungsten carbide.

Violet tungsten oxide nano powders is made from ammonium paratungstate (APT), The smaller the particle size of the raw material is, the smaller particle size of the violet tungsten produced is. Violet tungsten oxide is important material of manufacting super-fine tungsten powders and tungsten carbide nano powders.

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Tungsten Oxides Colours (IV)

詳細: カテゴリ: Tungsten Information; 2015年2月03日（火曜）19:38に公開; 参照数: 1416

Colours can also change with the temperature of the material due to alterations in the reflectivity of the oxides. Thermochromism is the property of substances to change colour due to a change in temperature and WO3 is an attractive example for this property. On cooling the oxide by liquid nitrogen down to -196°C, a sudden change occurs from yellow to white, which then alters to a bluishwhite colour between -50 and -27°C. At room temperature it becomes pale lemon-yellow again. On further heating to 200-300°C, WO3 becomes dark yellow, changing to a deep orange colour at 400 to 500°C. These reversible colour changes are linked to changes in the electronic properties of WO3 which alter due to changes of the internal symmetry of the WO3 crystals (through alterations of the lattice arrangements).

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Tungsten Oxides Colours (III)

詳細: カテゴリ: Tungsten Information; 2015年2月03日（火曜）19:32に公開; 参照数: 1626

The colours of the tungsten oxides are a result of the fact that the absorption and emission of photons (light) are dependent on wavelength. If the material has a low reflectivity at the short wavelength end of the spectrum (460-480 nm) it appears yellow to orange, because only the green and yellow part of the light is reflected. If it has a low reflectivity at the long wavelength end of the spectrum (550-700 nm), it appears blue or violet. If all components of the white light are absorbed and not re-emitted, the material appears black.

Colours can significantly change with different valence states within an oxide structure, although the parent structure of differently coloured oxides basically appears the same (due to changes in absorption and reflection and/or transmission). Inherent colours also change with the size of the particles, and the colours of powders therefore can significantly differ from those of single crystals. Thin films of tungsten trioxide are even transparent, but can be readily coloured by impurities which are used today for electronic devices.

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Tungsten Oxides Colours (II)

詳細: カテゴリ: Tungsten Information; 2015年2月03日（火曜）19:28に公開; 参照数: 1539

Stoichiometric compounds such as W20O58, W18O49 or WO2 are formed intermediately during the reduction process and can be isolated by interrupting the reduction process at the selected reduction state.

All , characteristic crystal symmetries, and also peculiar crystal forms. They are commonly not visible to the naked eye, as the powder particles are too small for a simple visual detection.

However, they can be made visible by looking at the powders with the help of an electron microscope where distinct differences of the crystal forms can be clearly recognised.

Colours of the tungsten oxides, prepared by interrupting the reduction process at selected reduction stages: yellow WO3, blue W20O58, violet W18O49, chocolate-brown WO2, and grey W metal.

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Images of Tungsten Oxides and Tungsten Metal

詳細: カテゴリ: Tungsten Information; 2015年2月02日（月曜）18:33に公開; 参照数: 1412

Electron-microscopical images of tungsten oxides and tungsten metal, formed during hydrogen reduction of WO3. The reason for the significant change in form of the powder particles is a result of a chemical vapour transport (CVT) of tungsten via the volatile tungsten hydroxide WO2(OH)2; by courtesy of Prof. Roland Haubner; Vienna University of Technology. tungsten oxides，tungsten metal

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Tungsten Oxides Colours (I)

詳細: カテゴリ: Tungsten Information; 2015年2月02日（月曜）18:22に公開; 参照数: 1443

There are several tungsten oxides, but only four of them are of major importance. They all have attractive colours: the yellow WO3, the dark blue W20O58 (WO2.9), the violet W18O49 (W2.72) and the chocolate brown WO2. So-called higher tungsten oxides are structurally related to both the WO3 and W20O58 structures and exhibit chemical formulas between WO2.99 and WO2.889. They belong to the group of non-stoichiometric tungsten oxides, and are of interest mainly to structural chemists. They exhibit colours from yellow to green to very dark blue. The colour changes are a result of a slight loss of oxygen which generates an additional valence state in the WO3 parent structure, either W5+ or W4+. Cation-to-cation charge transfer between the parent W6+ and a reduced ion is responsible for the change in colour.

Tungsten oxides are important starting materials for the production of tungsten metal powder by hydrogen reduction. These oxides are formed out of ammonium paratungstate by a thermal decomposition process called “calcination” and are depending on the decomposition conditions (more or less reducing), a mixture of different higher tungsten oxides, including amorphous oxide phases. As described before, they exhibit colours between yellow and dark blue (TBO,“Tungsten Blue Oxide”).

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絶縁ガラス用Cs 0.32 WO 3粒子

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絶縁ガラス用Cs 0.32 WO 3粒子