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Refractory metal molybdenum

Molybdenum is a refractory metal so its application is unique in high-temperature spheres. The page contains the description of this metal: physical and chemical properties, applications, grades, types of products.

Main information

Molybdenum is a chemical element with atomic number 42 in the periodical system; it is a forgeable iron-grey (compacted) or dark-grey (dispersed) transition metal. Density - 10.2 g/cm3, tmelt. = 2620°С, tboil. = 4630°С. Content in the earth’s crust - 3·10-4% (by weight). Molybdenum does not occur in free form. About 20 minerals containing molybdenum are known. The most important ones are molybdenite МоS2, powellite СаМоО4, molybdite Fe(MoO4)3·nH2O and wulfenite PbMoO4.


Molybdenum was discovered in 1778 by Swedish chemist Carl Scheele who generated oxide МоО3. In 1782 P. Hjelm was the first to generate molybdenum in metal form, but it was contaminated by carbon and molybdenum carbide. Pure metal was received in 1817 by Swedish chemist J. Berzelius.

The first attempts of using molybdenum in metallurgy were made at the end of the 19th century. Its industrial production began in 1909-1910 when specific properties of gun and armour steels alloyed with molybdenum and the technology of receiving compacted refractory metals by powder metallurgy methods was developed.

Molybdenum properties

Molybdenum and tungsten belong to the VI group of the Mendeleyev’s table, but molybdenum belongs to the 5th period. It usually stays in hexabasic condition, although there are some compounds with other basicity. Atomic number - 42; atomic weight - 95.95; density under room temperature - 10200 kg/m3. Molybdenum is a refractory transition metal. Its melting temperature is 2620±10°С, boiling temperature - approximately 4800 °С.

Molybdenum and its alloys also have a high modulus of elasticity, low thermal expansion coefficient, good heat stability, low thermal neutron capture cross section. This metal has a lower electric conductivity than copper, but this property is higher than iron has. It has a lower mechanical strength than tungsten, but is more pressurizable.

Physical and mechanical properties

Property Value
Atomic number 42
Atomic weight 95.94
Unit cell parameter, nm 0.31470
Atomic diameter, nm 0.272
Density under 20°С, g/cm3 10.2
Melting temperature, °С 2610
Boiling temperature, °С 4612
Melting heat, kJ/mole 28
Vaporization heat, kJ/mole: 590
Molecular volume, cm³/mole: 9.4
Specific heat, J/(g·K) 0,256
Heat conductivity, W/(m·К) 142
Linear expansion coefficient, 10-6 K-1 4.9
Resistance, µΩ·cm 5.70
Young’s modulus, HPa 336.3
Shear modulus, HPa 122
Poisson's ratio 0.30
Hardness, НВ 125
Spark colour Short yellow discrete flux of sparks
Group of metals Refractory metal

Chemical properties

Property Value
Covalent radius 130 pm
Ionic radius (+6e) 62 (+4e) 70 pm
Electronegativity (Pauling) 2.16
Electrolytic potential 0
Oxidation 6, 5, 4, 3, 2

Grades of molybdenum and its alloys

The most common molybdenum grades are MCh, MChVP, MRN, MK, TsM, MR and MV. There is clear molybdenum, molybdenum with different additives and alloys of molybdenum with other metals.
  • MCh - pure molybdenum without additives.
  • MChVP - vacuum-melted pure molybdenum without additives.
  • MRN - molybdenum of different applications without additives includes many admixtures if compared with MC and MCVP grades.
  • MK - contains silica alkaline additive.
  • TsM - contains zirconium and/or titanium additives.
  • MR - molybdenum-rhenium alloy.
  • MV - molybdenum-tungsten alloy.

Advantages / drawbacks

  • has a high melting point and good high-temperature resistance;
  • as the density of this metal (10200 kg/m3) is almost twice as low as tungsten has (19300 kg/m3), molybdenum-based alloys have a much higher strength-to-weight ratio (under temperatures below 1370 °С);
  • has a high modulus of elasticity;
  • low thermal expansion coefficient;
  • has a good heat stability;
  • low thermal neutron capture cross section;
  • high corrosive stability. This metal is stable in most alkaline solutions, sulphuric, hydrochloric and hydrofluoric acid under different temperatures and concentrations.
  • has a low scale formation;
  • high weld brittleness;
  • low plasticity under low temperatures;
  • mechanical hardening can be applied only up to 700-800 °С, but the metal is softened under higher temperatures due to recovery.

Molybdenum applications

Molybdenum and its alloys belong to refractory materials. There are two applications of refractory metals and their alloys in producing fuselage skin of re-entry cones and airplanes. In the first case these metals serve as heat shields that are separated from the main construction material with heat insulation. In the second case refractory metals and their alloys serve as the main construction material. Molybdenum lies in the second place after tungsten in strength properties. However, molybdenum and its alloys have the best strength-to-weight ratio under temperatures below 1350-1450°С. So molybdenum and niobium and their alloys serve as the most widely-used material for making fuselage skin and components of frames of rockets and supersonic aircraft as they have a higher strength-to-weight ratio under temperature up to 1370°С if compared with tantalum, tungsten and their alloys.

Molybdenum are used for making honeycombs for spacecraft, heat exchangers, shells of earth return rockets and capsules, heat shields, fuselage skin of trailing edges and stabilizers of supersonic aircraft. Some components of aeroducts of rocket and turbojet engines work in very harsh conditions (turbine blades, tail skirts, nozzle dampers, engine exits, flight control surfaces of solid propellant rockets). The material should not only have a high resistance to oxidation and gas erosion, but also high creep-rupture strength and shock resistance. Under temperature below 1370°С molybdenum and its alloys are used for making these parts.

Molybdenum is a promising material for making equipment working in sulphuric, hydrochloric and phosphoric acid. Due to high stability of this metal in melted glass it is widely used in glass industry, in particular for making electrodes for melting glass. Currently molybdenum alloys are used for producing press moulds and centerpieces for die casting machines intended for aluminium, zinc and copper alloys. High durability and hardness of such materials under increased temperatures determines their application as tools used in hot processing and pressurizing steel and alloys (piercer plugs, female moulds, extrusion rams).

Molybdenum improves the steel properties significantly. Molybdenum additive increases their hardenability. Slight molybdenum additives (0.15-0.8 %) to construction steels increase their durability, viscosity and corrosive stability so much that this allows using them for most critical components and products. For increasing the hardness molybdenum is added to cobalt and chrome alloys (stellites) that are used for facing wear (abrasion) component edges made of common steel. Also it is included into some heat- and acid-resistant nickel-, cobalt- and chrome-based alloys.

Another application is production of heaters of electric furnaces working in hydrogen under temperature up to 1600°С. Also molybdenum is widely used in electronic engineering and X-ray engineering for producing different components of vacuum-tubes, X-ray tubes and other vacuum devices.

Molybdenum compounds - sulphide, oxides, molybdates — serve as catalysts of chemical reactions, dye pigments, glaze components. Also this metal is included in fertilisers as a microadditive. Molybden hexafluoride is used in applying molybdenum on different materials. МоSi2 is used as a hard high-temperature lubricant. Pure monocrystal molybden is used for producing mirrors for powerful gasdynamic lasers. Molybdenum tellurides is a very good thermoelectric material for making thermoelectric generators (thermo-emf - 780 mkV/К). Molybdenum trioxide (molybdenum anhydride) is widely used as a positive electrode in lithium current sources. Molybden disulfide MoS2 and diselenide МоSе2 are used as lubricants of wearing pieces working under temperatures from -45 till +400°С. In paint and coatings industry and consumer goods industry several molybdenum compounds are applied as pigments for producing paints and varnishes for painting fabrics and furs.

Molybdenum products

There is a wide range of industrial products. The most common ones are molybdenum wire, rods, powder, billets, sheet.

Molybdenum rods wire and strip are applied in making heaters of high-temperature electric furnaces. Rods are used for making bushings of vacuum-tube devices. Wire is used in producing high-temperature thermocouples, filament lamps, receiving tubes and X-ray tubes. Sheets are used as a construction material for making products in the aircraft and space industry. Molybdenum powder is used as an alloying agent for different steels and alloys and as a primary raw material for compacted molybdenum.


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