Review on the Effectiveness of Tungsten Disulfide and Molybdenum Disulfide Lubricant

 Solid lubrication is a method of coating or plating on the surface of the friction pairs to form a thin film and reducing friction.

tungsten disulfide and molybdenum disulfide image

The technique of using solid lubricants to lubricate is called solid lubrication. Tungsten disulfide and molybdenum disulfide are excellent solid lubricating materials, in the field of ultra-solid lubrication has a very high value, this technology is applied to the hard disk drive bearing of computer, such as rotation and sliding in ultra high vacuum system.

Molybdenum disulfide has a graphite-like structure, molybdenum and sulfur through the covalent bond to form a hexagonal structure, each molybdenum is surrounded by six sulfur atoms, the molecular layer surface only sulfur atoms, each layer molecular layer thickness of 0.626nm. The thermal stability of MoS2 is better in the air environment lower than 400 degrees. When the temperature is higher than 400 degrees, MoS2 will be oxidized to MoS3 in a short time, MoS3 is a granular material with higher hardness, attached to the friction surface of abrasive formation. But in a vacuum and inert gas environment, the structure of MoS2 at 1100 DEG C can keep steady.

Tungsten disulfide WS2 also has a hexagonal lamellar structure similar to molybdenum disulfide. Tungsten atoms and sulfur atoms covalently bonded, the molecular layer surface only sulfur atoms, between the sulfur atoms between the weak molecular bonds. WS2 is insoluble in almost all media, including acids, alkalis, oils and water, but is sensitive to free gaseous fluoride, hydrofluoric acid and hot sulphuric acid. Compared with MoS2, the thermal stability of WS2 is better than that of MoS2, and the decomposition temperature of WS2 is 510 °C in the air. In 539 degrees will be rapid oxidation, decomposition temperature in vacuum and inert gas is 1150 DEG C. Compared to the molybdenum disulfide, more widely applicable temperature range WS2.

Several domestic and foreign lubricant manufacturers have tungsten disulfide, molybdenum disulfide and graphene three lubrication performance comparison, through the test found that tungsten disulfide is not only stronger than molybdenum disulfide, stronger than graphene. In addition, in the high radiation operating environment, tungsten disulfide has a higher anti-radiation properties, can adapt to more complex operating environment, therefore, the major manufacturers are tungsten disulfide lubricant showed a more intense interest in production.

In the United States, aerospace industry, mainly used as MoS2 solid lubricating material, this is because the United States is the production of molybdenum power, convenience with local resources. In China, we have not only molybdenum more tungsten, relative to molybdenum, tungsten, whether it is heat resistance, physical and chemical stability, or radiation resistance are better than molybdenum, so tungsten disulfide lubricant will be better choice.

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