What is the magic of tungsten sulfide, which is the smoothest among thousands of materials?

wallpapers Industry 2021-04-01
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, which is a dark gray orthorhombic crystalline solid with a relative density of 7.510. The layered structure is easy to dissociate and has similar lubricating properties to graphite.
Physical and chemical properties of tungsten disulfide
Tungsten disulfide is slightly soluble in cold water and 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.
Tungsten disulfide can be used as a lubricant.
Tungsten disulfide can be used as a lubricant, with better performance than molybdenum disulfide, lower friction coefficient, higher compressive strength, and lubricity at 1316°C. Used as a high-temperature solid lubricant, used alone for high-temperature, high-pressure, high-speed, high-load, and transport equipment in chemically active media. The forging and stamping lubricants configured with other materials can extend the life of the mold and improve the finish of the product. Filling materials formulated with polytetrafluoroethylene and nylon can be used to make self-lubricating parts. Tungstic acid reacts with ammonia water to generate ammonium tungstate and then reacts with hydrogen sulfide to generate ammonium tetrathiotungstate, which is decomposed into tungsten disulfide after high-temperature roasting.
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