Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur

Overview of Molybdenum Disulfide

Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is MoS2. This compound is classified as a transition metal dihalide. It is a silver-black solid in the form of molybdenite (the main ore of molybdenum). MoS2 is relatively unresponsive. It is not affected by dilute acid and oxygen. In appearance and feel, molybdenum disulfide is similar to graphite. Because of its low friction and robustness, it is widely used as a dry lubricant. Bulk MoS2 is a diamagnetic, indirect bandgap semiconductor similar to silicon, with a bandgap of 1.23 eV. MoS2 is naturally found as pyroxene (a crystalline mineral) or pyroxene (a rare low-temperature form of pyroxene). The molybdenite is processed by flotation to obtain relatively pure MoS2. The main pollutant is carbon. Almost all molybdenum compounds are produced by heat treatment with hydrogen sulfide or elemental sulfur, and can also be produced by the metathesis reaction of molybdenum pentachloride. Unlike graphite, MoS2 does not depend on adsorbed water or other vapours for its lubricant properties. It can be used at temperatures as high as 350 ºC in oxidizing environments and up to 1100 ºC in nonoxidizing environments. Its stability makes it useful in high-temperature applications in which oils and greases are not practical.

 MoS2 is particularly suitable as a lubricating material due to its layered structure and low friction coefficient. When the shear stress is applied to the material, the sliding between the layers will dissipate energy. Extensive work has been done to characterize the friction coefficient and shear strength of MoS2 in various atmospheres. The shear strength of MoS2 increases with the increase in the friction coefficient. This characteristic is called superlubricity. Under environmental conditions, the friction coefficient of MoS2 is determined to be 0.150, and the corresponding estimated shear strength is 56.0 MPa. The method of directly measuring the shear strength shows that the value is closer to 25.3MPa. Various forms of MoS2 have a layered structure in which the plane of molybdenum atoms is sandwiched by the plane of sulfide ions. These three layers form a single layer of MoS 2. Bulk MoS2 consists of stacked single layers that are held together by weak Van der Waals interactions.

Applications of Molybdenum Disulfide

Molybdenum disulfide is an important solid oxidant, especially suitable for high temperature and high pressure. It also has diamagnetism, converts linear photoconductors and semiconductors that display P-type or N-type conductivity, and has the functions of rectification and energy conversion. The main function of molybdenum disulfide used in friction materials is to reduce friction at low temperatures and increase friction at high temperatures, with a small loss on ignition and volatile in friction materials.

Anti-friction

The disulfide micro-particle size formed by supersonic jet pulverization can reach 325-2500 mesh, the micro-particle hardness is 1-1.5, and the friction coefficient is 0.05-0.1, so it can use the anti-friction effect in friction materials.

Increased friction

Molybdenum disulfide is not conductive, and there are molybdenum disulfide, molybdenum trisulfide and molybdenum trioxide silicon carbide. When the temperature of the friction material rises sharply due to friction, the shrinking molybdenum trioxide particles gradually heat up and expand, which increases the friction in the axial direction;

Anti-oxidation: Molybdenum disulfide is obtained through a comprehensive reaction of chemical purification, and its PH value changes 7-8, slightly alkaline. It covers the surface of the friction material to protect other materials and prevent them from being oxidized, especially to make other materials difficult to shift and increase adhesion.

Lubricant

Due to the weak van der Waals interaction between sulfide atoms in MoS, the friction coefficient is very low. Molybdenum sulfide 2 particles with a particle size of 1–100 µm are a common dry lubricant. In an oxidizing environment, there are few other options that can provide high lubricity and stability at temperatures up to 350°C. MoS sliding friction test 2 uses a pin on a disc tester to obtain a friction coefficient value of less than 0.1 under low load (0.1-2 N). It requires low-friction blends and composite components. When added to the plastic, molybdenum sulfide 2 forms a composite material with enhanced strength and reduced friction. Polymers that can be filled with MoS2 include nylon, Teflon and Vespel.

Catalytic

MoS2 is used as a co-catalyst for desulfurization (such as hydrodesulfurization) in petrochemistry. Doping a small amount of cobalt or nickel can enhance the catalyst. An intimate mixture of these sulfides is supported on alumina. Such catalysts or equivalent reagents are produced in situ by processing alumina impregnated with molybdate/cobalt or nickel. The catalysis does not occur in the regular flaky areas of the crystallites but at the edges of these planes. MoS 2 is used as a hydrogenation catalyst for organic synthesis. It is derived from a common transition metal rather than the tenth metal, because when the main consideration is catalyst price or sulfur poisoning, it is many alternatives, so MoS2 should be chosen. MoS2 can effectively hydrogenate nitro compounds to amines and can be used to generate secondary amines through reductive alkylation reactions. The catalyst can also carry out the hydrogenolysis of organic sulfur compounds, aldehydes, ketones, phenols and carboxylic acids. However, the catalyst has relatively low activity and usually requires a hydrogen pressure higher than 95 atm and a temperature higher than 185°C.

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