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Molybdenum disulfide

 
Molybdenum Disulfide

 
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Molybdenum disulfide
 
 
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Molybdenum disulfide is the inorganic compound
Inorganic chemistry

Inorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry....
 with the formula
Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
 MoS2. This black crystalline sulfide
Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
 of molybdenum
Molybdenum

Molybdenum , is a Group 6 element chemical element with the symbol Mo and atomic number 42. It has the List of elements by melting point melting point of any element....
 occurs as the mineral molybdenite
Molybdenite

Molybdenite is a mineral of molybdenum disulfide, molybdenumsulfur2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure....
. Natural amorphous form is known as more rare mineral jordisite. More so than other transition metal
Transition metal

In chemistry, the term transition metal has two possible meanings:*It commonly refers to any element in the d-block of the periodic table, including the group 12 element elements zinc, cadmium and Mercury ....
 chalcogenide
Chalcogenide

A chalcogenide is a chemical compound consisting of at least one chalcogen ion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term is more commonly reserved for sulfides, selenides, and tellurides, rather than oxides....
s, MoS2 is unreactive, being unaffected by dilute acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
s. In its appearance and feel, molybdenum disulfide is similar to graphite
Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
 and indeed it is widely used as a solid lubricant because of its low friction properties, sometimes to relatively high temperatures.

bdenite ore is processed by flotation
Froth flotation

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries. Historically this was first used in the mining industry....
 to give relatively pure MoS2, the main contaminant being carbon.






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Encyclopedia


Molybdenum disulfide is the inorganic compound
Inorganic chemistry

Inorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry....
 with the formula
Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
 MoS2. This black crystalline sulfide
Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
 of molybdenum
Molybdenum

Molybdenum , is a Group 6 element chemical element with the symbol Mo and atomic number 42. It has the List of elements by melting point melting point of any element....
 occurs as the mineral molybdenite
Molybdenite

Molybdenite is a mineral of molybdenum disulfide, molybdenumsulfur2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure....
. Natural amorphous form is known as more rare mineral jordisite. More so than other transition metal
Transition metal

In chemistry, the term transition metal has two possible meanings:*It commonly refers to any element in the d-block of the periodic table, including the group 12 element elements zinc, cadmium and Mercury ....
 chalcogenide
Chalcogenide

A chalcogenide is a chemical compound consisting of at least one chalcogen ion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term is more commonly reserved for sulfides, selenides, and tellurides, rather than oxides....
s, MoS2 is unreactive, being unaffected by dilute acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
s. In its appearance and feel, molybdenum disulfide is similar to graphite
Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
 and indeed it is widely used as a solid lubricant because of its low friction properties, sometimes to relatively high temperatures.

Production

Molybdenite ore is processed by flotation
Froth flotation

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries. Historically this was first used in the mining industry....
 to give relatively pure MoS2, the main contaminant being carbon. MoS2 also arises by the thermal treatment of virtually all molybdenum compounds with hydrogen sulfide
Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the chemical formula Hydrogen2Sulfur. This colorless, toxic and flammable gas is partially responsible for the foul odor of egg and flatulence....
.

Structure and basic properties

In MoS2, each Mo(IV) center is trigonal prismatic, being bound to six sulfide ligands, each of which is pyramidal. The trigonal prisms are interconnected to give a layered structure, wherein molybdenum atoms are sandwiched between layers of sulfur atoms. Because of the weak van der Waals
Van der Waals force

In physical chemistry, the van der Waals force , named after The Netherlands scientist Johannes Diderik van der Waals, is the attractive or repulsive force between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules....
 interactions between the sheets of sulfide atoms, MoS2 has a low coefficient of friction, resulting in its lubricating properties. Other layered inorganic materials exhibit lubricating properties (collectively known as solid lubricants or dry lubricant
Dry lubricant

Dry lubricants or solid lubricants are materials which despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid media....
s) including graphite, which requires volatile additives, and hexagonal boron nitride
Boron nitride

Boron nitride is a binary compound, consisting of equal numbers of boron and nitrogen atoms. Its empirical formula is therefore BN. Boron nitride is isoelectronic with carbon and, like carbon, boron nitrides exists as various Polymorphism , one of which is analogous to diamond and one analogous to graphite....
.

MoS2 is diamagnetic and a semiconductor
Semiconductor

A semiconductor is a material that has electrical conductivity between those of a Electrical conductor and an electrical insulation; it can vary over that wide range either permanently or dynamically....
.

Use as lubricant

MoS2 with particle sizes in the range of 1-100 µm is a common dry lubricant
Dry lubricant

Dry lubricants or solid lubricants are materials which despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid media....
. 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 oil
Oil

An oil is a chemical substance that is in a viscosity liquid state at room temperature or slightly warmer, and is both hydrophobic and lipophilic ....
s and grease
Grease (lubricant)

The term grease is used to describe a number of Quasi-solid lubricants possessing a higher initial viscosity than oil. Although the word grease is also used to describe Rendering fat of animals, in the context of lubricants, it typically applies to a material consisting of a calcium, sodium or lithium soap base emulsion with mineral oi...
s are used, because they retain their lubricity even in cases of almost complete oil loss, thus finding a use in critical applications such as aircraft engine
Aircraft engine

An aircraft engine is a propulsion system for an aircraft. Aircraft engines are almost always either lightweight piston engines or gas turbines....
s. When added to plastic
Plastic

Plastic is the general common term for a wide range of synthetic or semisynthetic organic chemistry solid materials suitable for the manufacture of industrial products....
s, MoS2 forms a composite
Composite material

Composite materials are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure....
 with improved strength as well as reduced friction. Polymers that have been filled with MoS2 include nylon
Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides and first produced on February 28, 1935 by Wallace Carothers at DuPont....
 (with the trade name
Trade name

A trade name, also known as a trading name or a business name, is the name which a business trades under for commercial purposes, although its registered, Legal name , used for contracts and other formal situations, may be another....
 Nylatron
Nylatron

Nylatron is a tradename for nylon plastic, filled with molybdenum disulfide lubricant powder. It is used to cast plastic parts for machines, because of its mechanical properties and wear-resistance....
), Teflon, and Vespel. Self-lubricating composite coatings for high-temperature applications have been developed consisting of molybdenum disulfide and titanium nitride
Titanium nitride

Titanium nitride is an extremely hard ceramic material, often used as a coating on titanium alloy, steel, carbide, and aluminium components to improve the substrate's surface properties....
 by chemical vapor deposition
Chemical vapor deposition

Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films....
.

Specific uses
It is often used in two-stroke engines; e.g., motorcycle engines. MoS2 is also used in CV
Constant-velocity joint

Constant-velocity joints allow a rotating shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play....
 and universal joint
Universal joint

A universal joint, U joint, Gerolamo Cardano joint, Hardy-Clarence W. Spicer joint, or Hooke's joint is a joint in a rigid rod that allows the rod to 'bend' in any direction, and is commonly used in shafts that transmit rotary motion....
s. During the Vietnam War
Vietnam War

The Vietnam War, also known as the Second Indochina Wars, the Vietnam Conflict, or often in Vietnam the American War occurred in Vietnam, Laos and Cambodia from 1959 to April 30, 1975....
, the molybdenum disulfide product "Dri-Slide" was used to lubricate weapons, although it was supplied from private sources, not the military. MoS2-coatings allow bullet
Bullet

A bullet is a hard projectile propelled by a firearm, Sling , or air gun and is normally made from metal. A bullet does not contain explosives, but damages the intended target by tissue or mechanical disruption through impact or penetration....
s easier passage through the rifle barrel with less deformation and better ballistic accuracy.

Use in petrochemistry

Synthetic MoS2 is employed as a catalyst for desulfurization in petroleum refineries
Petrochemistry

Petrochemistry is the branch of chemistry that studies the transformation of crude oil and natural gas into useful products and raw materials....
; e.g., hydrodesulfurization
Hydrodesulfurization

Hydrodesulfurization is a catalytic chemical process widely used to remove sulfur from natural gas and from oil refinery such as gasoline, jet fuel, kerosene, diesel fuel, and fuel oils....
. The effectiveness of the MoS2 catalysts is enhanced by doping
Doping (semiconductor)

In semiconductor production, doping is the process of intentionally introducing impurities into an extremely pure semiconductor to change its electrical properties....
 with small amounts of cobalt or nickel and the intimate mixture is supported on alumina. Such catalysts are generated in situ by treating molybdate/cobalt or nickel-impregnated alumina with H2S or an equivalent reagent.

Future Developments


Lubrication

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 glaze
Compacted oxide layer glaze

Compacted oxide layer glaze describes the often shiny, wear-protective layer of oxide formed when two metals are slid against each other at high temperature in an oxygen-containing atmosphere....
s, 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.

Photocatalyst

A research group headed by Prof. L.I. Can with the Dalian Institute of Chemical Physics has claimed that when combined with Cadmium sulfide
Cadmium sulfide

Cadmium Sulfur is a chemical compound with the formula CdS. Cadmium sulfide is yellow in colour and is a semiconductor. It exists in nature as two different minerals, greenockite and hawleyite....
 it significantly increases the rate of photocatalytic hydrogen production .

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