
| Molybdenum disulfide is the inorganic compound with the formula MoS2. This black crystalline sulfide of molybdenum occurs as the mineral molybdenite. More so than other transition metal chalcogenides, MoS2 is unreactive, being unaffected by dilute acids. In terms of its appearance and feel, molybdenum disulfide is similar to graphite and indeed it is widely used as a solid lubricant [1][2] due to its low friction properties, sometimes to relatively high temperatures. MoS2 with particle sizes in the range of 1-100 µm is a common dry lubricant. Few alternatives exist that can confer the high lubricity and stability up to 350 °C in oxidizing environments. Sliding friction tests of MoS2 using a pin on disc tester at low loads (0.1-2 N) give friction coefficient values of <0.1. Molybdenum disulfide is often a component of blends and composites where low friction is sought. A variety of oils and greases are used, since they retain their lubricity even in cases of almost complete oil loss, thus finding a use in critical applications such as aircraft engines. When added to plastics, MoS2 forms a composite with improved strength as well as reduced friction. Polymers that have been filled with MoS2 include nylon, with the trade name Nylatron, Teflon, and Vespel. Self-lubricating composite coatings for high-temperature applications have been developed consisting of molybdenum disulfide and titanium nitride by chemical vapor deposition. Specific uses There are currently no clear lubrication alternatives to molybdenum disulfide or the very similar tungsten disulfide that can resist temperatures higher than 350°C in oxidizing environments. Research has been conducted on compacted oxide layer glazes, which form during metallic surface sliding wear at several hundred degrees Celsius. However, because these oxide layers are physically-unstable, their use has currently not proven practical.
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