AskDefine | Define molybdenum

Dictionary Definition

molybdenum n : a polyvalent metallic element that resembles chromium and tungsten in its properties; used to strengthen and harden steel [syn: Mo, atomic number 42]

User Contributed Dictionary

English

Noun

  1. a metallic chemical element (symbol Mo) with an atomic number of 42.

Translations

External links

For etymology and more information refer to: http://elements.vanderkrogt.net/elem/mo.html (A lot of the translations were taken from that site with permission from the author)

Extensive Definition

Molybdenum (, from the Greek meaning "lead-like"), is a Group 6 chemical element with the symbol Mo and atomic number 42. It has the sixth-highest melting point of any element, and for this reason it is often used in high-strength steel alloys. Molybdenum is found in trace amounts in plants and animals, although excess molybdenum can be toxic in some animals. Molybdenum was discovered in 1778 by Carl Wilhelm Scheele and first isolated in 1781 by Peter Jacob Hjelm.

Characteristics

Molybdenum is a transition metal with an electronegativity of 1.8 on the Pauling scale and an atomic mass of 95.9 g/mole. It does not react with oxygen or water at room temperature. At elevated temperatures, molybdenum trioxide is formed in the reaction 2Mo + 3O2 → 2MoO3.
In its pure metal form, molybdenum is silvery white with a Mohs hardness of 5.5, though it is somewhat more ductile than tungsten. It has a melting point of 2623°C, and only tantalum, osmium, rhenium, and tungsten have higher melting points. It also has the lowest heating expansion of any commercially used metal.

Isotopes

There are 35 known isotopes of molybdenum ranging in atomic mass from 83 to 117, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, five are stable, with atomic masses from 94 to 98. All unstable isotopes of molybdenum decay into isotopes of niobium, technetium, and ruthenium.
Molybdenum-92 and molybdenum-100 are the only naturally occurring isotopes that are not stable. Molybdenum-100 has a half-life of approximately 1×1019 y and undergoes double beta decay into ruthenium-100. Molybdenum-98 is the most common isotope, comprising 24.14% of all molybdenum. Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately .15 μs.
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.
A side product of molybdenum mining is rhenium. As it is always present in small varying quantities in molybdenite, the only commercial source for rhenium is molybdenum mines.

Compounds

Molybdenum has several common oxidation states, +2 +3 +4 +5 and +6. The highest oxidation state is common in the molybdenum(VI) oxide MoO3 while the normal sulfur compound is molybdenum disulfide MoS2. The broad range of oxidation states shows up in the chlorides of molybdenum: Like chromium and some other transition metals molybdenum is able to form quadruple bonds

Biological role

The most important use of the molybdenum atom in living organisms is as a metal hetero-atom at the active site in certain enzymes. In nitrogen fixation in certain bacteria, the nitrogenase enzyme which is involved in the terminal step of reducing molecular nitrogen, usually contains molybdenum in the active site (though replacement of Mo with iron or vanadium is known).
In March 2008, researchers reported that they had found strong evidence for the hypothesis that a scarcity of molybdenum in the earth's early oceans was a limiting factor in the further evolution of eukaryotic life (which includes all plants and animals) as eukaryotes cannot fix nitrogen and must acquire it from prokaryotic bacteria. http://www.eurekalert.org/pub_releases/2008-03/asu-ito032508.php http://www.eurekalert.org/pub_releases/2008-03/nu-sut032508.php The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. Oxygen dissolved in seawater is the primary mechanism for dissolving molybdenum from minerals on the sea bottom.
Though molybdenum forms compounds with various organic molecules, including carbohydrates and amino acids, it is transported throughout the human body as MoO42-. Molybdenum is present in approximately 20 enzymes in animals, including aldehyde oxidase, sulfite oxidase, xanthine oxidase. It occurs in higher concentrations in the liver and kidneys, and in lower concentrations in the vertebrae. Pork, lamb, and beef liver each have approximately 1.5 parts molybdenum per million. Other significant dietary sources include green beans, eggs, sunflower seeds, wheat flour, lentils, and cereal grain. Molybdenum deficiency is not usually seen in healthy people. Sodium tungstate is a competitive inhibitor of molybdenum. Dietary tungsten reduces the concentration of molybdenum in tissues. The condition can be aggravated by excess sulfur. Most high-strength steel alloys are .25% to 8% molybdenum.
Molybdenum 99 is used as a parent radioisotope to the radioisotope Technetium 99, which is used in many medical procedures
Molybdenum disulfide (MoS2) is used as a lubricant and an agent. It forms strong films on metallic surfaces, and is highly resistant to both extreme temperatures and high pressure, and for this reason, it is a common additive to engine motor oil; in case of a catastrophic failure, the thin layer of molybdenum prevents metal-on-metal contact. Lead molybdate co-precipitated with lead chromate and lead sulfate is a bright-orange pigment used with ceramics and plastics. Molybdenum trioxide (MoO3) is used as an adhesive between enamels and metals. the principal ore from which molybdenum is now extracted, was previously known as molybdena. Molybdena was confused with and often implemented as though it were graphite. Even when the two ores were distinguishable, molybdena was thought to be a lead ore.
It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized 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 using carbon and linseed oil in 1781. For a long time there was no industrial use for molybdenum. The French Schneider Electrics company produced the first steel molybdenum alloy armor plates in 1894. Until World War I most other armor factories also used molybdenum alloys. In World War I, some British tanks were protected by 75 mm manganese plating, but this proved to be ineffective. The manganese plates were then replaced with 25 mm molybdenum plating. These allowed for higher speed, greater maneuverability, and, despite being thinner, better protection. OSHA regulations specify the maximum permissible molybdenum exposure in an 8-hour day to be 5 mg/m³. Chronic exposure to 60 to 600 mg Mo/m³ can cause symptoms including fatigue, headaches, and joint pains.

Supply and demand

Although current molybdenum production meets demand, refiners, or roasters, are expected to run into a shortfall between 2009 and 2015, depending on demand.
A roaster processes the moly into a fine powder, pellets, or other forms. Total world moly roaster capacity is currently 320 million pounds per year, barely enough to meet demand. There is not much excess roasting capacity, and no one is actively permitting for the production of any new roasters in the United States. Global roaster capacity also looks limited, and a future roaster shortage is predicted. The data above are based on the assumption that mines will be able to increase output.
Western demand is projected to increase by around 3 percent annually, while China and the CIS demand is projected to increase by around 10 percent annually, increasing overall global demand by around 4.5 percent annually. Increasing demand can be attributed to two main factors. Hydroprocessing catalysts are becoming essential for crude oil. The other contributing factor is the increase in nuclear reactor construction. There are 48 nuclear reactors to be built by 2013, and approximately 100 are to be built by 2020. The International Molybdenum Association (IMOA) says that an average reactor contains about 520,000 feet of stainless steel alloy. Some larger reactors contain over 1 million feet of stainless steel alloy. Unless moly mine production picks up at a rapid pace, shortfalls of the metal are expected to arrive around 2009.

References

External links

molybdenum in Afrikaans: Molibdeen
molybdenum in Arabic: موليبدنوم
molybdenum in Azerbaijani: Molibden
molybdenum in Bengali: মলিবডেনাম
molybdenum in Belarusian: Малібдэн
molybdenum in Bosnian: Molibden
molybdenum in Bulgarian: Молибден
molybdenum in Catalan: Molibdè
molybdenum in Chuvash: Молибден
molybdenum in Czech: Molybden
molybdenum in Corsican: Molibdenu
molybdenum in Danish: Molybdæn
molybdenum in German: Molybdän
molybdenum in Estonian: Molübdeen
molybdenum in Modern Greek (1453-): Μολυβδαίνιο
molybdenum in Spanish: Molibdeno
molybdenum in Esperanto: Molibdeno
molybdenum in Basque: Molibdeno
molybdenum in Persian: مولیبدن
molybdenum in French: Molybdène
molybdenum in Friulian: Molibden
molybdenum in Manx: Molybdenum
molybdenum in Korean: 몰리브데넘
molybdenum in Armenian: Մոլիբդեն
molybdenum in Hindi: मोलिब्डेनम
molybdenum in Croatian: Molibden
molybdenum in Ido: Molibdeno
molybdenum in Indonesian: Molibdenum
molybdenum in Icelandic: Mólýbden
molybdenum in Italian: Molibdeno
molybdenum in Hebrew: מוליבדן
molybdenum in Javanese: Molibden
molybdenum in Swahili (macrolanguage): Molibdeni
molybdenum in Kurdish: Molîbdên
molybdenum in Latin: Molybdenum
molybdenum in Latvian: Molibdēns
molybdenum in Luxembourgish: Molybdän
molybdenum in Lithuanian: Molibdenas
molybdenum in Lojban: mlibdena
molybdenum in Hungarian: Molibdén
molybdenum in Malayalam: മൊളിബ്ഡിനം
molybdenum in Marathi: मॉलिब्डेनम
molybdenum in Dutch: Molybdeen
molybdenum in Japanese: モリブデン
molybdenum in Norwegian: Molybden
molybdenum in Norwegian Nynorsk: Molybden
molybdenum in Occitan (post 1500): Molibdèn
molybdenum in Uzbek: Molibden
molybdenum in Polish: Molibden
molybdenum in Portuguese: Molibdênio
molybdenum in Romanian: Molibden
molybdenum in Russian: Молибден
molybdenum in Sicilian: Molibdenu
molybdenum in Simple English: Molybdenum
molybdenum in Slovak: Molybdén
molybdenum in Slovenian: Molibden
molybdenum in Serbian: Молибден
molybdenum in Serbo-Croatian: Molibden
molybdenum in Finnish: Molybdeeni
molybdenum in Swedish: Molybden
molybdenum in Tamil: மாலிப்டினம்
molybdenum in Thai: โมลิบดีนัม
molybdenum in Vietnamese: Mô lip đen
molybdenum in Turkish: Molibden
molybdenum in Ukrainian: Молібден
molybdenum in Chinese: 钼
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