'Molybdenum' (
IPA: , from the
Greek meaning "
lead-like"), is a
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.
[1] It does not react with oxygen or water at room temperature. At elevated temperatures, molybdenum trioxide is formed in the reaction 2Mo + 3O
2 → 2MoO
3.
[2]
In its pure metal form, molybdenum is silvery white and very hard, 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.
7 Molybdenum burns only at temperatures above 600°C.
[3] Molybdenum has the lowest heating expansion of any commercially used metal.
13
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.
[4]
Applications
The ability of molybdenum to withstand extreme temperatures without significantly expanding or softening make it useful in applications that involve intense heat, including aircraft parts, electrical contacts, industrial motors, and filaments.
6 Molybdenum is also used in
alloys for its high
corrosion resistance and
weldability.
3[5] Most high-strength steel alloys are .25% to 8% molybdenum.
7 Despite being used in such small portions, more than 43×10
6kg of molybdenum is used as an alloying agent each year in
stainless steels,
tool steels,
cast irons, and high temperature
superalloys.
3
Because of its lower density and more stable price, molybdenum is implemented in the place of tungsten.
3 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.
[6]
Molybdenum disulphide (MoS
2) is used as a lubricant and an anti-corrosion agent. It forms strong films on metallic surfaces, and is highly resistant to both extreme temperatures and high pressure. Sodium molybdate is a bright orange pigment used with ceramics and plastics.
13 Molybdenum trioxide (MoO
3) is used as an adhesive between
enamels and metals.
9 Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.
3
History
Molybdenite (from the Greek Μόλυβδος ''molybdos'', meaning ''lead''),
[7] 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.
13 In 1754,
Bengt Qvist examined the mineral and determined that it did not contain lead.
[8]
It was not until 1778 that
Swedish chemist
Carl Wilhelm Scheele realized molybdena was neither graphite nor lead.
[9][10] 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.
13[11]
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.
13 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.
Occurrence
.PNG)
Molybdenum output in 2005
The world's largest producers of molybdenum materials are the United States, Canada, Chile, Russia, and China.
[12][13]
Though molybdenum is found in such
minerals as
wulfenite (
PbMo
O4) and
powellite (
CaMo
O4), the main commercial source of molybdenum is
molybdenite (Mo
S2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining.
7 The large mining areas in
Colorado (
Climax) and in
British Columbia yield
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.
3 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.
[14]
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 are molybdenum mines.
Biological role
The most important use of the molybdenum atom in mammals and other animals is in enzymes. In a 70 kg human body, there is approximately 9.3 mg molybdenum, comprising .00001% of the total body mass.
[12] It occurs in higher concentrations in the liver and kidneys, and in lower concentrations in the vertebrae.
3 Molybdenum is also present within human
tooth enamel and may help prevent the decaying thereof.
[16] 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.
13
The average daily intake of molybdenum is .3 mg. Daily intake above .4 mg can be toxic.
13 Molybdenum deficiency, caused by less than .05 mg/day,
13 can cause stunted growth, reduced appetite, and impaired reproduction.
[17] Sodium tungstate is a
competitive inhibitor of molybdenum. Dietary
tungsten reduces the concentration of molybdenum in tissues.
3
Though molybdenum forms compounds with various
organic molecules, including
carbohydrates and
amino acids, it is transported throughout the body as MoO
42-.
[18] Molybdenum is present in approximately 20 enzymes, including
aldehyde oxidase,
sulfite oxidase,
xanthine oxidase.
13 In some animals, the oxidation of
xanthine to
uric acid, a process of
purine catabolism, is catalyzed by
xanthine oxidase, a molybdenum-containing enzyme. The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend, and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentrations also affect
protein synthesis,
metabolism, and growth.
18
Copper-molybdenum antagonism
High amounts of molybdenum can interfere with the body's uptake of
copper, both by preventing plasma proteins from binding the copper and by increasing the amount of copper that is excreted in
urine.
Ruminants that consume high amounts of molybdenum develop symptoms including
diarrhea, stunted growth,
anaemia, and
achromotrichia. These symptoms can be alleviated by the administration of more copper into the system, both in dietary form and by injection.
[19] The condition can be aggravated by excess
sulfur.
3
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.
[20]
Molybdenum-92 and molybdenum-100 are the only naturally occurring isotopes which are not stable. Molybdenum-100 has a
half-life of approximately 1×10
19 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.
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.
[21] 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.
[22]
See also
★ .''
References
1. Properties of Molybdenum
2. Chemistry
3.
4. Dynamic Prices and Charts for Molybdenum
5. Molybdenum Statistics and Information
6. Molybdenum
7.
8. Molybdenum
9. Molybdenum
10. Versuche mit Wasserbley;Molybdaena, C. W. K. Scheele, , , svenska vetensk. Academ. Handlingar, 1779
11. Versuche mit Molybdäna, und Reduction der selben Erde, P. J. Hjelm, , , svenska vetensk. Academ. Handlingar, 1788
12.
13. Nature's Building Blocks, , John, Emsley, Oxford University Press, , 0-19-850341-5
14. American Mineralogist, Volume 87, pages 181-184, 2002
15.
16. Dental Problems and Diet
17. Guide to Healthy Minerals
18. Overview of Environment Database
19. Recent studies of the copper-molybdenum antagonism, , N. F., Suttle, Proceedings of the Nutrition Society,
20.
21. Material Safety Data Sheet - Molybdenum
22. NIOSH Documentation for ILDHs Molybdenum
External links
★
WebElements.com — Molybdenum
★
International Molybdenum Association — environmental data
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