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By Dr.Zhang from Nanjing Normal University | 13 June 2019 | 0 Comments

Know more about Molybdenum disulfide!

Know more about Molybdenum disulfide!
 

1. What is MoS2?
Molybdenum disulfide, a kind of black solid powder with metallic luster, is the main ingredient of molybdenite. It is an inorganic compound composed of molybdenum and sulfur and its chemical formula is MoS2. Besides, its melting point is 1185℃, its density is 4.80g/cm3(14℃) and its Mohs rating is 1.0~1.5. Molybdenum disulfide is insoluble in water, dilute acid and concentrated sulfuric acid. Generally, it is also insoluble in other acids, bases and organic solvents, but soluble in aqua regia and boiling concentrated sulfuric acid.
2. Preparation
Heating the hydrochloric acid and hydrofluoric acid under direct steam and stirring them repeatedly, washing them with hot water, centrifuging, drying and grinding, then molybdenite concentrate can be prepared. Ammonium molybdate is made by adding hydrogen sulfide gas into ammonium molybdate solution. Then, transforms ammonium molybdate into molybdenum trisulfide precipitation by adding hydrochloric acid, after that centrifuging, washing, drying and grinding the precipitation and  heating it to 950 °C for desulfurization. Finally, molybdenum disulfidecan is made.
3. Applications
  • Lubricant
Due to the weak van der Waals interaction between the sulfide atoms, the friction coefficient of MoS2 is very low. Molybdenum disulfide in the particle size range of 1-100 µm is a common dry lubricant. Few alternatives can provide high lubricity and stability in oxidation conditions up to 350°C.
Molybdenum disulfide is usually a component of blends and composites that requires low friction. For example, it is added to graphite to improve bonding. Besides, using various oils and greases, it can retain its lubricity even when oil is almost completely lost. Therefore, it has been applied in key applications such as aircraft engines. When added to plastics, molybdenum disulfide forms a composite material that enhances strength and reduces friction.
Polymers containing molybdenum disulfide include nylon, Teflon and Vespel.
  • Catalysis
In petroleum chemistry, molybdenum disulfide is used as an auxiliary for desulfurization, such as hydrodesulphurization. Doping a little cobalt or nickel can improve the catalytic performance of molybdenum disulfide catalyst. The mixture of sulfides is supported by alumina. The catalyst is produced by in situ treatment of molybdate/cobalt or nickel impregnated alumina with hydrogen sulfide or similar reagents. The catalysis does not occur in the regular sheet areas of the crystal, but at the edges of these planes.
4. Pros and cons
Pros:
(1) It can save a lot of grease.
(2) It can reduce mechanical wear, prolong the service life of friction equipment, reduce the loss of equipment parts, and improve the attendance of equipment.
(3) The application of molybdenum disulfide lubrication can improve the work efficiency and accuracy.
Cons:
(1) Low thermal conductivity.
(2)Poor permeability.
5.
Safeguards
(1) Engineering control: enclosed operation, local ventilation.
(2) Eyes protection: wear chemical safety glasses.
(3) Body protection: Wear protective overalls on infiltration.
(4) Hands protection: wear latex gloves.
(5) Respiratory protection: when the dust concentration in the air exceeds the standard, it is recommended to wear self-suction filter dust mask. Air respirator should be worn during emergency rescue or evacuation.

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