What Is Molybdenum Disulfide?
Molybdenum disulfide is a compound of molybdenum and sulfur, with the chemical formula MoS2.
Also known as molybdenum (IV) sulfide, it is identified by the CAS registration number 1317-33-5. This compound features a hexagonal, layered structure that facilitates its lubricious properties. Molybdenum disulfide is typically extracted from natural ores through purification processes.
It is classified as a hazardous substance under the Industrial Safety and Health Law and as a Class I Designated Chemical Substance under the PRTR Law.
Uses of Molybdenum Disulfide
Molybdenum disulfide is primarily used as a lubricant, a steel additive, and a precursor for synthesizing molybdates.
1. Lubricants
As a solid lubricant, molybdenum disulfide is commonly added to grease, particularly for use in environments where dust contamination of grease is a concern, such as construction sites.
2. Additive
It also serves as an additive to various materials (e.g., sintered alloys, brakes, friction materials, plastics, rubber) to reduce friction. For instance, adding molybdenum disulfide to brake materials can prevent seizing while preserving the coefficient of friction.
3. Dry Film
Additionally, it is employed in the production of dry films, where it is mixed with resin to create a coating. Unlike oil-based lubricants, molybdenum disulfide does not evaporate and effectively reduces shear force on frictional surfaces.
Properties of Molybdenum Disulfide
Molybdenum disulfide has a molecular weight of 160.07, melts at 2,375°C, and boils at 1,450°C. It appears as a black solid at room temperature and pressure, with a density of 5.06 g/mL. Insoluble in water, most acids, alkalis, and organic solvents, it dissolves in concentrated nitric acid and aqua regia.
Types of Molybdenum Disulfide
Available for both research and industrial use, molybdenum disulfide is sold in various forms.
1. Reagent Products for Research and Development
For R&D purposes, it comes in manageable sizes like 25g, 100g, and 500g, suitable for laboratory use and storable at room temperature.
2. Industrial Materials
In industrial settings, it is available in forms such as powder and crystals, used in applications like solid lubricants and additives. Single crystals are also utilized in research for AFM, STM, and thin film coatings. Supply quantities vary by manufacturer, typically starting from 25 kg to accommodate factory use. Powders come in a range of particle sizes, requiring selection based on specific needs.
Other Information on Molybdenum Disulfide
1. Chemical Reaction of Molybdenum Disulfide
Upon heating in oxygen, molybdenum disulfide yields molybdenum oxide. It reacts with chlorine gas to produce molybdenum chloride (V). While stable under normal conditions, it decomposes at high temperatures to emit sulfur oxide, posing an explosion risk with potassium nitride and magnesium upon heating or friction. Molybdenum trioxide, another industrially significant compound, is derived from roasting molybdenum disulfide.
2. Crystal Structure of Molybdenum Disulfide
The hexagonal layered structure of molybdenum (IV) sulfide consists of molybdenum layers sandwiched between sulfur atoms. The Mo=S bonds are strong, whereas the bonds between sulfur atoms across layers are weak, facilitating easy slippage under shear forces. This characteristic is fundamental to its low friction and excellent lubrication properties.