Molybdenum 101

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Molybdenum Molybdenum is a Group 6 chemical element with the symbol Mo and atomic number 42. The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys. Molybdenum does not occur as a free metal on Earth, but rather in various oxidation states in minerals. Industrially, molybdenum compounds are used in high-pressure and high-temperature applications, as pigments and catalysts.

History

Molybdenite - the principal ore from which molybdenum is now extracted - was previously known as molybdena. Molybdena was confused with and often utilised as though it were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant. Even when molybdena was distinguishable from graphite, it was still confused with the common lead ore PbS (now called galena).

It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized that molybdena was neither graphite nor lead. He and other chemists then correctly assumed that it was the ore of a distinct new element, named molybdenum for the mineral in which it was discovered. Peter Jacob Hjelm successfully isolated molybdenum by using carbon and linseed oil in 1781.

For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of appropriate metallurgical techniques. In 1913, Frank E. Elmore developed a flotation process to recover molybdenite from ores; flotation remains the primary isolation process.

Occurrence
Molybdenum
This bubble map shows the global distribution of molybdenum output in 2005 as a percentage of the top producer (USA - 56,900 tonnes).

Molybdenum The world's largest producers of molybdenum materials are the United States, China, Chile, Peru and Canada. Though molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4), the main commercial source of molybdenum is molybdenite (MoS2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining. Large mines in Colorado (such as the Henderson mine and the now-inactive Climax mine) and in British Columbia yield molybdenite as their primary product, while many porphyry copper deposits such as the Bingham Canyon Mine in Utah and the Chuquicamata mine in northern Chile produce molybdenum as a byproduct of copper mining.

Molybdenum is the 54th most abundant element in the Earth's crust and the 25th most abundant element in the oceans, with an average of 10 parts per billion; it is the 42nd most abundant element in the Universe.

Applications

Alloys

The ability of molybdenum to withstand extreme temperatures without significantly expanding or softening makes it useful in applications that involve intense heat, including the manufacture of armour, aircraft parts, electrical contacts, industrial motors and filaments.

Most high-strength steel alloys contain 0.25% to 8% molybdenum. Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steels, tool steels, cast irons and high-temperature superalloys.

Molybdenum is also used in steel alloys for its high corrosion resistance and weldability.

Because of its lower density and more stable price, molybdenum is sometimes used instead of tungsten. Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2,623 °C (4,753 °F), molybdenum rapidly oxidizes at temperatures above 760 °C (1,400 °F) making it better-suited for use in vacuum environments.

Other applications as catalyst and compounds
  • Molybdenum-99 is a parent radioisotope to the daughter radioisotope technetium-99m, which is used in many medical procedures.
  • Molybdenum disulfide (MoS2) is used as a solid lubricant and a high-pressure high-temperature (HPHT) antiwear agent. It forms strong films on metallic surfaces and is a common additive to HPHT greases. It also has semiconducting properties with distinct advantages over traditional silicon or graphene in electronics applications. MoS2 is also used as a catalyst in hydrocracking of petroleum fractions which contain nitrogen, sulfur and oxygen.
  • Molybdenum disilicide (MoSi2) is an electrically conducting ceramic with primary use in heating elements operating at temperatures above 1500 C in air.
  • Molybdenum trioxide (MoO3) is used as an adhesive between enamels and metals.
  • Lead molybdate (wulfenite) co-precipitated with lead chromate and lead sulfate is a bright-orange pigment used with ceramics and plastics.
  • Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.
  • The element is also used in NO, NO2, NOx analyzers in power plants for pollution controls. At 350 C (662 F) the element acts as a catalyst for NO2/NOx to form only NO molecules for consistent readings by infrared light.
  • Ammonium heptamolybdate is used in biological staining procedures.
  • Molybdenum coated soda lime glass is used for CIGS solar cell fabrication.
  • Phosphomolybdic acid is a stain used in thin layer chromatography.

Additional Resources

International Molydenum Association (IOMA)
http://www.imoa.info/

London Metals Exchange
http://www.lme.com/minormetals/molybdenum.asp

USGS Minerals Information
http://minerals.usgs.gov/minerals/pubs/commodity/molybdenum/

Molybdenum in the News

Metals Market Place
http://metalsplace.com/news/molybdenum/

Mining.com
http://www.mining.com/tag/molybdenum/

Infomine.com
http://www.infomine.com/commodities/molybdenum.asp