Molybdenum sulfide

Molybdenum Sulfide IV. Inorganic compound with a lamellar structure and a graphite-like appearance, has exceptional anti-friction qualities. Its MoS 2 formula .

Summary

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  • 1 Story
  • 2 Structure and properties
  • 3 OKS Molybdenum Disulfide Dispersion
  • 4 OKS 300 concentrated disulfide dispersion
    • 1 Disulfide greases OKS 400/410
    • 2 Applications
  • 5 Sources

History

Molybdenum disulfide was known about 300 years ago when it was used by artisans in presses and tools. It was widely used during the Second World War to reduce friction and wear on war machinery. Since the 19th century it has been used as a lubricant for metal forging with regular adhesion and tool carburation problems in hot molding.

In the 1970s and 1980s there was an enormous volume of research and development on the subject of molybdenum disulfide lubrication, which was supported by national governments for the benefit of defense, aviation, or space activities.

Structure and properties

It is an inorganic solid with a lamellar structure and its properties make it unique and special in the field of tribology . It is a compound with a dark gray metallic appearance and a hardness 4 times lower than graphite . It is insoluble in water and dilute acids .

Its layered structure of three layers, a central Mo and two S sides that act as a strong ionic bond, thus resisting the roughness of the surfaces. The disulfide sheets are so thin that 1600 of them have a thickness of one micron, and their resistance to pressure exceeds the creep limit of known metals (30,000Kg / cm 2 ).

It has a graphite-like appearance but its density is more than double: 4.8g / cm3. It is non-conductive and diamagnetic. It is harmless, it does not attack the skin , it is insoluble in cold or hot water and it resists acids except nitric, aqua regia, fluorine and chlorine . It is thermally stable between -180ºC and + 450ºC; + 630 ° C without access of air and 1340 ° C + in atmosphere of argon .

Its great physical-chemical stability makes it not react in the presence of acids or gases at normal temperatures, being only attacked by Agua Regia, Sulfuric Acid and Hydrochloric acid at high temperatures. The MoS 2 temperature range is from -185º C to 450º C in the normal presence of air; up to 1,100º C with little air admission its melting point occurs at 1,650º C and in a hydrogen atmosphere it is reduced to metal at 900º C.

As a lubricant it has high friction and wear. It is very thermally stable and is not affected by radiation . Above 450ºC with air access it is transformed into gaseous CO 2 so that it does not show any abrasion phenomena .

It is semi-insulating diamagnetic, with a thermo-electric power in micro-volt degrees from 300 to 700º C at room temperature and its conductivity is positive or negative depending on the species: as a load conductor, it activates energy of 0.55, 0.14, 0.12, and 0.05 EV: The tenacious adherence of MoS 2 on metallic surfaces is of Physical- Chemical to Chemical-Mechanical origin and is directly proportional to the load.

The friction coefficient decreases with increasing loads. Its lubricating effect is explained by the strong bond of atoms of sulfur to metal surfaces and the ease of sliding of the lamellae. The property of disulfide of adhering to metal surfaces due to displacement due to mechanical demands is its greatest difference with respect to other solid lubricants, and in turn explains the reduction in the coefficient of friction.

The oxidation in the presence of oxygen begins in a remarkable way when exceeding 400ºC obtaining Molybdenum trioxide which acts as a protector of the lower layers of the lubricating film that remains unalterable.

After a purification process, a grade with strict specification is obtained in different grain sizes, with its MoS 2 formula .

OKS Molybdenum Disulfide Dispersion

Settlement is the initial phase of commissioning an internal combustion engine. It has not been possible to determine exactly when this period of reduction to a minimum of abrasion, oil and fuel consumption , that is, maximum engine performance, is met .

During the settling period welds, gears, and wear are produced by direct metallic contact. The most effective way to reduce the coefficient of friction, abrasion and damage caused by settling is the use of pure molybdenum disulfide. When the solid lubricant covers the actual contact area, cold welding cannot occur and the ridges of surface roughness are plastically deformed.

This dispersion added to motor oil provides a better quality of the bearing surfaces and an increase in performance, a longer life and better service conditions. Simultaneously treating the mechanical components exposed to friction with the OKS 200 paste when assembling the engine, an increase in power and a decrease in the temperature of the exhaust gases are obtained, regardless of whether the piston rings are chrome-plated or not, the type of engine nor the used lubricating oil.

The addition of OKS molybdenum disulfide dispersion to an internal combustion engine oil forms, during operation, a solid sliding film that protects against wear and reduces the coefficient of friction, thus giving an emergency lubrication, and evidencing an increase in performance, saving fuel and lubricant, facilitates start-up and smoother operation is observed.

Concentrated disulfide dispersion OKS 300

The automotive gears have been overloaded and therefore their lubrication has become difficult. Rolling and sliding friction have been combined more and more, giving rise to hypoid and worm gears and higher impact demands, contributing to a greater demand in the design of the lubricant.

The load and speed cause a greater friction in the differential and therefore a higher temperature that can exceed 150ºC and even 180ºC. The temperature destroys the EP chemical additives and therefore the seals and the pinion. The addition of the concentrated dispersion of molybdenum disulfide OKS 300 was then tested, achieving a significant decrease in temperature (48ºC), while reducing noise by 30%, obtaining a perfect pinion and crown condition. The same results have been achieved in synchronized gearboxes without affecting their operation at all.

Disulfide greases OKS 400/410

The decrease in wear on the chassis parts lubricated with OKS 400 has been verified, which led to the investigation of the decrease in the frequency of lubrication and therefore of the maintenance due to the long life lubrication incorporating molybdenum disulfide powder (OKS 110 ) to sintered iron components. In the front-wheel drive, the balls and tracks of the CV joints are treated with OKS 511 lacquer before assembly, and then the assembly and universal joints are lubricated with OKS 400.

Applications

  • It is used to make special MOLY-VEN® lubricants, it has a purity grade of 99.1% and the particles to which it is reduced range from 40 microns to 0.2 microns average, depending on the specific product to which it is intended.
  • Protects cylinders, rings, bearings, camshaft, guides and valve stems. It facilitates the movement of the rings in the piston grooves and seals the crankcase against the leakage of combustion gases. This additive does not settle or clog the filters, improves lubrication and increases the efficiency of the oils.
  • It has exceptional anti-friction qualities applied in the field of lubrication, as the following data translates: Coefficient of friction of 0.6, 0.3 to 0.05 depending on the product; withstands loads up to 400,000 PSI
  • On friction surfaces, protected with MoS 2, metal contact is reduced by up to 70%, significantly increasing, in some cases, up to 10 times the relubrication periods.
  • As a lubricant it has high friction and wear. It is very thermally stable and is not affected by radiation. Above 450ºC with airaccess it is transformed into gaseous CO 2 so that it does not present abrasion phenomena.

 

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