Molybdenum



42 technetium
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General
Number molybdenum, Mo, 42
transition metals
Block d
Appearance gray metallic
(2)  g·mol−1
Kr] 4d5 5s1
shell 2, 8, 18, 13, 1
Physical properties
Phase solid
r.t.) 10.28  g·cm−3
Liquid m.p. 9.33  g·cm−3
F)
F)
kJ·mol−1
kJ·mol−1
Heat capacity (25 °C) 24.06  J·mol−1·K−1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 2742 2994 3312 3707 4212 4879
Atomic properties
Crystal structure cubic body centered
acidic oxide)
Electronegativity 2.16 (Pauling scale)
more) 1st:  684.3  kJ·mol−1
2nd:  1560  kJ·mol−1
3rd:  2618  kJ·mol−1
Atomic radius 145  pm
Atomic radius (calc.) 190  pm
Covalent radius 145  pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 °C) 53.4 n Ω·m
Thermal conductivity (300 K) 138  W·m−1·K−1
Thermal expansion (25 °C) 4.8  µm·m−1·K−1
r.t.) 5400  m·s−1
Young's modulus 329  GPa
Shear modulus 126  GPa
Bulk modulus 230  GPa
Poisson ratio 0.31
Mohs hardness 5.5
Vickers hardness 1530  MPa
Brinell hardness 1500  MPa
CAS registry number 7439-98-7
Selected isotopes
Main article: Isotopes of molybdenum
iso NA half-life DM DE (MeV) DP
92Mo 14.84% Mo is neutrons
93Mo syn 4×103 y ε - 93Nb
94Mo 9.25% Mo is neutrons
95Mo 15.92% Mo is neutrons
96Mo 16.68% Mo is neutrons
97Mo 9.55% Mo is neutrons
98Mo 24.13% Mo is neutrons
99Mo syn 65.94 h β- 0.436, 1.214 99Tc
γ 0.74, 0.36,
0.14 		-
100Mo 9.63% 7.8×1018 y β-β- 3.04 100Ru
References

Molybdenum (Carl Wilhelm Scheele and first isolated in 1781 by Peter Jacob Hjelm.

Characteristics

Molybdenum is a electronegativity of 1.8 on the Pauling scale and an atomic mass of 95.9 g/mole.[2] It does not react with oxygen or water at room temperature. At elevated temperatures, molybdenum trioxide is formed in the reaction 2Mo + 3O2 → 2MoO3.[3]

In its pure metal form, molybdenum is silvery white and very hard, though it is somewhat more tungsten have higher melting points.[4] Molybdenum burns only at temperatures above 600°C.[5] It also has the lowest heating expansion of any commercially used metal.[6]

Molybdenum has a value of approximately $65,000 per tonne as of 4 May 2007. It maintained a price at or near $10,000 per tonne from 1997 through 2002, and reached a high of $103,000 per tonne in June 2005.[7]

Isotopes

Main article: Isotopes of molybdenum

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.[8]

Molybdenum-92 and molybdenum-100 are the only naturally-occurring isotopes that are not stable. Molybdenum-100 has a 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.[8]

Occurrence

  The world's largest producers of molybdenum materials are the United States, Canada, Chile, Russia, and China.[9][6]

Though molybdenum is found in such molybdenite while the Chuquicamata mines in northern Chile produce molybdenum as a byproduct of copper mining. The Knaben mine in southern Norway was opened in 1885, making it the first molybdenum mine. It remained open until 1973.

Molybdenum is the 42nd-most-abundant element in the universe, and the 25th-most-abundant element in Earth's oceans, with an average of 10.8 mt/km³.[5] The Russian Luna 24 mission discovered a single molybdenum-bearing grain (1 × 0.6 µm) in a pyroxene fragment taken from Mare Crisium on the Moon.[10]

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

See also: category:Molybdenum compounds


Biological role

The most important use of the molybdenum atom in mammals and other animals is in enzymes (see below). In a 70 kg human body, there is approximately 9.3 mg molybdenum, comprising .00001% of the total body mass.[11] It occurs in higher concentrations in the liver and kidneys, and in lower concentrations in the vertebrae.[5] Molybdenum is also present within human tooth enamel and may help prevent the decaying thereof.[12] 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.[6]

The average daily intake of molybdenum is .3 mg. Daily intake above .4 mg can be toxic.[6] Molybdenum deficiency, caused by less than .05 mg/day,[6] can cause stunted growth, reduced appetite, and impaired reproduction.[13] Sodium tungstate is a tungsten reduces the concentration of molybdenum in tissues.[5]

Though molybdenum forms compounds with various metabolism, and growth.[14]

Copper-molybdenum antagonism

High amounts of molybdenum can interfere with the body's uptake of sulfur.[5]

Applications

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 aircraft parts, electrical contacts, industrial motors, and filaments.[16][6] Molybdenum is also used in superalloys.[5]

Because of its lower density and more stable price, molybdenum is implemented in the place of tungsten.[5] Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2623 °C, molybdenum rapidly oxidizes at temperatures above 760 °C, making it better-suited for use in vacuum environments.[16]

Molybdenum trioxide (MoO3) is used as an adhesive between enamels and metals.[19] Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.[5]

Also used in NO, NO2, NOx analyzers in power plants for pollution controls. At 350 °C the element acts as a catalyst for NO2/NOx to form only NO molecules for consistent readings by infrared light.

History

Molybdenite (from the Greek Μόλυβδος molybdos, meaning lead),[4] 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 lead ore.[6] In 1754, Bengt Qvist examined the mineral and determined that it did not contain lead.[20]

It was not until 1778 that Swedish chemist linseed oil in 1781.[6][22] 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 manueverability, and, despite being thinner, better protection.[6] The high demand of molybdenum in World War I and World War II and the step decrease after the wars had a great influence on prices and production of molybdenum.

Precautions

Molybdenum dusts and fumes, as can be generated by mining or metalworking, are not toxic. There are no long-term effects associated with exposure to molybdenum; however, prolonged exposure can cause irritation to the eyes and skin. The direct inhalation or ingestion of molybdenum should also be avoided.[23] 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.[24]

See also

Crow T. Robot (made of molybdenum)

References

  1. ^ Molybdenum: molybdenum(I) fluoride compound data. OpenMOPAC.net. Retrieved on 2007-12-10.
  2. ^ Properties of Molybdenum. Integral Scientist Periodic Table. Qivx, Inc. (2003). Retrieved on 2007-06-10.
  3. ^ Winter, Mark. Chemistry. Molybdenum. The University of Sheffield. Retrieved on 2007-06-10.
  4. ^ a b c d Lide, David R., ed. (1994), , , vol. 4, Chemical Rubber Publishing Company, pp. 18, 0-8493-0474-1
  5. ^ a b c d e f g h i Considine, Glenn D., ed. (2005), , , New York: Wylie-Interscience, pp. 1038-1040, 0-471-61525-0
  6. ^ a b c d e f g h i j Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press, 262-266. 0-19-850341-5. 
  7. ^ Dynamic Prices and Charts for Molybdenum. InfoMine Inc. (2007). Retrieved on 2007-05-07.
  8. ^ a b Lide, David R., ed. (2006), , vol. 11, CRC, pp. 87-88, 0-8493-0487-3
  9. ^ Lide, David R., ed. (2006), , vol. 4, Chemical Rubber Publishing Company, pp. 22-23, 0-8493-0487-3
  10. ^ American Mineralogist, Volume 87, pages 181-184, 2002. Retrieved on 2007-04-09.
  11. ^ Lide, David R., ed. (2006), , vol. 7, Chemical Rubber Publishing Company, pp. 18, 0-8493-0487-3
  12. ^ Ismail, Mumtaz. Dental Problems and Diet. Health and Nutrition. Bawarchi. Retrieved on 2007-05-19.
  13. ^ Guide to Healthy Minerals. Cherokee Naturals. Retrieved on 2007-05-17.
  14. ^ a b Mitchell, Phillip C. H. (2003). Overview of Environment Database. International Molybdenum Association. Retrieved on 2007-05-05.
  15. ^ Suttle, N. F. (December 1974). "Recent studies of the copper-molybdenum antagonism". Proceedings of the Nutrition Society 33 (3): 299-305. CABI Publishing. doi:10.1079/PNS19740053. Retrieved on 2007-05-11.
  16. ^ a b Molybdenum. AZoM.com Pty. Limited (2007). Retrieved on 2007-05-06.
  17. ^ Molybdenum Statistics and Information. U.S. Geological Survey (2007-05-10). Retrieved on 2007-05-10.
  18. ^ International Molybdenum Association, www.moly.imoa.info
  19. ^ a b Gagnon, Steve. Molybdenum. Jefferson Science Associates, LLC. Retrieved on 2007-05-06.
  20. ^ Van der Krogt, Peter (2006-01-10). Molybdenum. Elementymology & Elements Multidict. Retrieved on 2007-05-20.
  21. ^ C. W. K. Scheele (1779). "Versuche mit Wasserbley;Molybdaena". svenska vetensk. Academ. Handlingar 40: 238.
  22. ^ P. J. Hjelm (1788). "Versuche mit Molybdäna, und Reduction der selben Erde". svenska vetensk. Academ. Handlingar 49: 268.
  23. ^ Material Safety Data Sheet - Molybdenum. The REMBAR Company, Inc. (2000-09-19). Retrieved on 2007-05-13.
  24. ^ NIOSH Documentation for ILDHs Molybdenum. National Institute for Occupational Safety and Health (1996-08-16). Retrieved on 2007-05-31.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Molybdenum". A list of authors is available in Wikipedia.