Understanding, preparation and application of nanometer tungsten oxide

Tungsten trioxide, whose molecular formula is WO3 and molecular weight is 231.85.

It is a kind of tungstic anhydride, tungstic acid products, tungsten oxide including tungsten trioxide and tungsten dioxide, there is no actual industrial production of tungsten dioxide products. According to the content of tungsten trioxide is divided into tungstate acid, sodium tungstate, calcium tungstate, ammonium paratungstate, ammonium metatungstate and other products.

In the W-O system, there are WO3, WO 2.9, WO 2.72, WO2 and other tungsten oxides. WO3(yellow) — WO2.90 (blue) -WO 2.72, (purple) that is, tungsten has three stable oxides: yellow oxide (WO3, VK-WO3), blue oxide (WO2.90, VK-WO29), and purple oxide (WO2.72, VK-WO27).

1, ammonium tungstate method tungsten concentrate by sodium hydroxide alkali hydrolysis, with hydrochloric acid neutralization, and then with ammonium chloride action, to generate ammonium tungstate, and then add hydrochloric acid acid hydrolysis reaction, to generate tungstate acid, and then after roasting decomposition, grinding, tungsten trioxide.

2. Hydrochloric acid decomposition of tungstate. The saturated aqueous solution of tungstate salts such as sodium Na2WO4 and calcium CaWO4 tungstate was heated, and the solution was slowly added to 2 ~ 3 times of excessive boiling concentrated hydrochloric acid by mole ratio. According to the above reaction, yellow tungstate acid is precipitated. At this time, if the droplet acceleration is too fast or the liquid temperature drops, it is easy to generate suspended or colloidal precipitation, which will bring difficulties to the next treatment. After continuous heating in the water bath for 1h, the precipitate becomes easy to filter. After standing, wash with 5% ammonium nitrate solution several times to completely remove the Cl-. After filtration, it is dried at 120℃ and finally heated up to 600℃. Tungstate acid is completely dehydrated into tungsten trioxide.

3. Thermal decomposition of ammonium paratungstate. The ammonium paratungstate (NH4)10W12O41·11H2O purified by recrystallization is put into a porcelain crucible and heated to about 400℃, when the ammonia evaporates, tungsten trioxide is obtained.

Morphology and application of segmented nanometer tungsten oxide

1. Nano-tungsten oxide — tungsten yellow (VK-WO3, 50nm)

Tungsten trioxide, yellow powder. Insoluble in water, soluble in alkali, slightly soluble in acid. Used for making high melting point alloy and hard alloy, tungsten wire and fireproof material. It can be obtained by adding acid after the eutectic of tungsten ore and soda soda.

Tungsten trioxide is a light yellow rhombic crystal powder. The color changes from light to dark when heated. Specific gravity of 7.16g/cm3, melting point of 1473℃, boiling point of 1750℃, 850℃ significantly sublimation, melting when green. Stable in air, insoluble in water and inorganic acids except hydrofluoric acid, slowly soluble in ammonia and concentrated hot sodium hydroxide solutions. Tungsten trioxide is easily reduced by various reducing agents. At room temperature, even small amounts of organic matter can reduce it and change its color. But when heated in the air, it returns to its original color. Tungsten trioxide is readily reduced by hydrogen, carbon monoxide and carbon to tungsten at 700~900℃.

Main applications:

1. Part of yellow tungsten oxide is used in the production of chemical products, such as paints and coatings, petroleum industry catalysts, etc.; But oxide is a kind of intermediate product, part is used in the production of metal tungsten powder and tungsten carbide powder, and then used in the production of metal tungsten products, and a large number of applications and production of tungsten alloy products, such as tungsten copper, tungsten nickel, tungsten nickel iron, tungsten silver, tungsten rhenium, tungsten thorium and so on.

2. Yellow tungsten oxide is used for many purposes in everyday life. Such as industrial X-ray screen phosphors produced from fireproof fabrics and gas sensors, tungstate.

3. Because of its rich yellow color, tungsten oxide is also used as a pigment in ceramics and paints.

4. At present, nanometer yellow tungsten oxide (VK-WO3 50nm) is more and more used in lithium battery anode materials, and for new energy vehicles.

Nano-tungsten oxide for lithium battery anode tungsten yellow (VK-WO3 50nm,)

In the field of energy storage research, tungsten oxide has become the focus of research in recent years because of its advantages such as good chemical stability, high chemical activity, large theoretical specific capacity and strong electrical conductivity. Tungsten oxide is a defective material. Oxygen holes on the surface can act as electron acceptors to guide the band, making the material an n-type semiconductor. Therefore, in practical application, the adsorption capacity of nano-tungsten oxide materials can be significantly improved by increasing the specific surface area and surface defects.

At present, researchers have prepared many kinds of nanometer tungsten oxide with crystal structure, such as nano hollow spheres, sea urchin-like nanoparticles, nanowires, mesoporous nanomaterials, etc. All of them have large specific surface area or surface defects, which can improve the physicochemical adsorption performance of lithium battery anode materials.

Nanometer tungsten oxide — violet tungsten (VK-WO27, 80-100nm)

Purple tungsten is divided into WO2.72(or W18O49). Because of its unique crystal structure, it has superior performance when used to make fine tungsten powder and fine tungsten carbide powder, and is soon applied in production.

Purple tungsten is a different form of tungsten oxide, with other tungsten oxide (blue tungsten) unique crystal structure, its properties are also very different. Large blue-tungsten particles have distinct edges and corners and are aggregated by small cubes. The surface is broken to different degrees and is full of cracks. The morphology of purple tungsten is obviously different from the other three, each large particle is a loose particle group composed of needle or rod-like grains. All the tungsten oxide pellets.

There are abundant cracks in the interior of the purple tungsten granules, and the internal particles are needle-like or rod-like. This structure of purple tungsten particles has a large gap, so that its loose density is low, conducive to the reduction process of hydrogen infiltration and water vapor escape, so that the reduction not only begins at the surface, but also can be carried out in the interior at the same time. The morphology of purple tungsten particles is rod-like, and the morphology of other tungsten oxide particles is nearly spherical. Purple tungsten particle size is the largest.

The purple tungsten can be divided into WO2.72 (or W18O49). The purple tungsten (TVO) powder has the largest mesoporous volume, the smallest micropore volume, the narrowest pore size distribution, the smallest fractional dimension and the largest average pore size, which is conducive to hydrogen reduction to produce ultramarine tungsten powder, but is not conducive to doping process. It is a unique crystal structure for the preparation of fine tungsten powder and fine tungsten carbide powder.

Main applications:

Purple tungsten oxide (VTO) is also known as tungsten purple oxide (TVO). Purplish tungsten oxide is produced during the calcination of ammonia metatungstate. The content of purple tungsten oxide produced by different manufacturers varies. It is not a chemical compound, but is made up of different components, such as arsenic trioxide, tungsten copper, and low levels of tungsten trioxide. The relative content of these compounds in purple tungsten oxide depends on the calcination parameters.

Purple tungsten oxide is a fine, powdered purple crystal. It is produced during the production of ammonia paratungstate at precisely controlled temperature reduction. Xiamen Zhongwu Online Technology Co., Ltd. produces two kinds of purple tungsten oxide with standard oxygen content. Purple tungsten oxide is mainly used in the production of metal tungsten powder and tungsten carbide. Purple tungsten oxide can also be used to make ultrafine tungsten powder and nano tungsten powder.

Nano tungsten oxide — violet tungsten for lithium cell (VK-WO27, 80-100nm)

Nanometer tungsten oxide — blue tungsten (VK-WO29, 80-100nm)

Blue tungsten is a class of dark blue compounds containing the mixed valence state of tungsten (Ⅵ) and tungsten (V). It’s usually formed in solution. The preparation method of pure tungsten compound with ammonium paratungstate, tungsten trioxide and sodium tungstate solution as raw materials.

Blue tungsten is a class of dark blue compounds containing the mixed valence state of tungsten (Ⅵ) and tungsten (V). It’s usually formed in solution. The suspension of tungsten oxide in hydrochloric acid can be reduced by zinc metal to obtain tungsten blue.

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