Overview of tungsten disulfide
Tungsten disulfide is an inorganic compound with a molecular formula of WS2 and a molecular weight of 247.97.
It is a small gray crystal or powder with metallic luster, belonging to the hexagonal crystal system, semi-conducting and diamagnetic. The natural mineral is tungstenite. The layered structure is easy to dissociate and has similar lubricating properties to graphite. , Such as for aerosols.
Physical and chemical properties
Dark gray powder, appears as tungstenite in nature, it is dark gray orthorhombic crystalline solid.
Slightly soluble in cold water, soluble in hot water. It is insoluble in hydrochloric acid and alkali (except for the mixture of concentrated nitric acid and hydrofluoric acid). Soluble in molten alkali, insoluble in alcohol. The density is 7.6g·cm-3. It is reductive and can react with hot concentrated sulfuric acid, nitric acid, aqua regia and other strong oxidants. It can be converted into WO3 by heating in air or oxygen. It is decomposed into tungsten and sulfur when heated to 1250°C in a vacuum. In a dry stream of pure nitrogen, the mixture of tungsten trisulfide and sulfur is heated to 900°C to sublime the excess sulfur, and the residue is tungsten disulfide.
Preparation
1. Tungstic acid reacts with ammonia water under stirring at 57～60℃ for 3h, keeps warm and naturally settles for more than 16h, the generated ammonium tungstate reacts with hydrogen sulfide gas to generate ammonium tetrathiotungstate, which is roasted at high temperature and decomposed into tungsten disulfide .
2. Tungsten reacts very slowly with liquid sulfur. WS2 can be formed by passing sulfur vapor to red hot tungsten. Tungsten is mixed with stoichiometric sulphur bloom and reacted in a nitrogen atmosphere at 800°C for 24 hours to form WS2, such as reacting at 6MPa and 1800°C to form orthorhombic WS2.
3. Using ammonium tetrathiotungstate as the raw material, heating and decomposing the ammonium tetrathiotungstate under the condition of isolating the air, the temperature rises from room temperature to 700-1200℃ with a temperature gradient of 100-200℃/hour during heating. After being kept at this temperature for 24 to 48 hours, it is then reduced to room temperature with a temperature gradient of 30 to 110°C/hour, and the material is discharged and crushed.
The preparation method of ultrafine scaly crystal tungsten disulfide used for lubricants has simple process equipment, does not pollute the environment, and is safe and reliable in operation, and can produce tungsten disulfide with stable quality, high purity, and ultrafine crystal structure of hexagonal crystal system.
Tungsten Disulfide for Petroleum Catalyst
Like ammonium metatungstate, nano-tungsten disulfide powder (WS2) can also be used as a petroleum catalyst, that is, as a catalyst for hydrodesulfurization and polymerization, reforming, hydration, dehydration, and hydroxylation. This is mainly because it It has the characteristics of good cracking performance, high catalytic activity, reliable stability and long service life.
Specifically, in the presence of a tungsten disulfide catalyst, the process of high-temperature cracking of petroleum hydrocarbons to produce ethylene, propylene, butene and other low-carbon olefins is easier than without catalysts, and it also contributes to the production of light aromatics. . This is mainly due to the fact that WS2 can lower the reaction temperature. WS2 powder has higher catalytic activity due to its smaller particle size and special layered structure.
Because of the strong covalent bond in the layer, WS2 powder has excellent chemical stability. It is slightly soluble in cold water, insoluble in hydrochloric acid and alkali (except for the mixture of concentrated nitric acid and hydrofluoric acid), and insoluble in alcohol. Therefore, it is suitable as a new generation of petroleum catalyst, which can effectively reduce the occurrence of adverse reactions during use, and can also extend the service life of the product.
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