molybdenum

properties
[ Kr ] 4 d 5 5 s 1 42 Mon Periodic table
General
Name , symbol , atomic number	Molybdenum, Mo, 42
Element category	Transition metals
Group , period , block	6 , 5 , d
Appearance	gray metallic
CAS number	7439-98-7
EC number	231-107-2
ECHA InfoCard	100.028.279
Mass fraction of the earth's envelope	14 ppm
Atomic
Atomic mass	95.95 (1) and
Atomic radius (calculated)	145 (190) pm
Covalent radius	154 pm
Electron configuration	[ Kr ] 4 d 5 5 s 1
1. Ionization energy	7th.09243 (4) eV ≈ 684.32 kJ / mol
2. Ionization energy	16.16 (12) eV ≈ 1 559 kJ / mol
3. Ionization energy	27.13 (12) eV ≈ 2 618 kJ / mol
4. Ionization energy	40.33 (6) eV ≈ 3 891 kJ / mol
5. Ionization energy	54.417 (19) eV ≈ 5 250 kJ / mol
Physically
Physical state	firmly
Crystal structure	body-centered cubic
density	10.28 g / cm 3 (20 ° C )
Mohs hardness	5.5
magnetism	paramagnetic ( Χ m = 1.2 · 10 −4 )
Melting point	2896 K (2623 ° C)
boiling point	4885 K (4612 ° C)
Molar volume	9.38 10 −6 m 3 mol −1
Heat of evaporation	617 kJ / mol
Heat of fusion	36 kJ mol −1
Speed ​​of sound	6190 m · s −1
Electric conductivity	18.2 · 10 6 A · V −1 · m −1
Thermal conductivity	139 W m −1 K −1
Chemically
Oxidation states	2, 3, 4, 5, 6
Normal potential	−0.152 V (MoO 2 + 4e - + 4 H + → Mo + 2 H 2 O)
Electronegativity	2.16 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP 92 Mon 14.84% Stable 93 months {syn.} 4000 a ε 0.405 93 Nb 94 months 9.25% Stable 95 mo 15.92% Stable 96 months 16.68% Stable 97 months 9.55% Stable 98 Mon 24.13% Stable 99 mo {syn.} 65.94 h β - 1.357 99 Tc 100 months 9.63% 7.3 x 10 18 a β - β - 3.034 100 Ru
For other isotopes see list of isotopes
NMR properties
Spin quantum number I γ in rad · T −1 · s −1 E r  ( 1 H) f L at B = 4.7 T in MHz 95 mo 5/2 −1.751 · 10 7 0.0005 6.52 97 months 5/2 −1.788 10 7 0.0003 6.65
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Molybdenum [ molʏpˈdɛːn ] ( Greek Μόλυβδος mólybdos for lead) is a chemical element with the element symbol Mo and the atomic number 42. It is one of the transition metals , in the periodic table it is in the 5th period and the 6th subgroup (group 6) or Chromium group .

history

Molybdenum, which is usually found in deposits as molybdenum luster (molybdenum disulfide), has long been confused with lead luster or graphite . In 1778 Carl Wilhelm Scheele succeeded in producing the white molybdenum (VI) oxide MoO ₃ (also called molybdenum trioxide or water lead earth) from molybdenum luster by treatment with nitric acid . In 1781 Peter Jacob Hjelm reduced the oxide to elemental molybdenum with coal . Because of its difficult machinability (pure molybdenum can be plastically deformed, but even contamination with 1 ppm oxygen or nitrogen makes molybdenum extremely brittle), molybdenum was ignored for a long time. At the end of the 19th century, employees of the French company Schneider & Co. noticed the useful properties of molybdenum in steel alloys in the manufacture of armor plates. In the two world wars, the demand for the metal was great, after the Second World War, prices fell dramatically. Below the Alpeiner Scharte in the Valsertal in Tyrol, where the most important molybdenum concentration in the Eastern Alps is located, a mine was built at great expense during the Second World War without molybdenum ever being extracted. The only Western European mine was operated in Knaben , Norway until 1973 .

Occurrence

Molybdenum mostly occurs as molybdenite (molybdenum luster, MoS ₂ ). There is also wulfenite (yellow lead ore, PbMoO ₄ ) and powellite Ca (Mo, W) O ₄ . The co- product molybdenite, which arises from copper mining, is mainly used for smelting . The MoS ₂ concentrate as it leaves the mines in the direction of the “roaster” contains around 50–60% molybdenum. Large deposits are found in the United States , Chile , China , Canada, and Peru .

Molybdenum in dignified , i.e. elemental form, could only be detected in four samples so far (status: 2011): on earth in a rock sample from the Korjakskaja Sopka volcano on the Russian peninsula of Kamchatka and in three rock samples from the moon from the Apollonius highlands ( Luna 20 ), the Mare Crisium (Luna 24) and the Mare Fecunditatis (Luna 16). However, since the discoveries were published without examination by the IMA / CNMNC , the status of molybdenum as a mineral has not yet been confirmed, even if it has the mineral system no. 1.AC.05 (based on the 9th edition of Strunz's mineral systematics ).

Extraction, presentation and price

Most of the molybdenum is obtained as a by-product in copper production and only approx. 30% directly from molybdenum ores. All ores are mainly processed into ammonium heptamolybdate . This is accomplished by calcining at about 400 ° C in molybdenum trioxide MoO ₃ transferred. The latter is reduced to pure molybdenum powder in two stages using hydrogen . The first stage leads to the metastable brown-violet molybdenum dioxide MoO ₂ at 500–600 ° C , the second stage leads to pure metal powder at around 1100 ° C. Molybdenum is compressed into compact metal in the HIP process , by remelting in an arc furnace under argon as a protective gas or in an electron beam furnace . Single crystals are produced using the zone melting process. Molybdenum recovery from scrap is almost 100% as there are no oxidation losses.

${\displaystyle \mathrm {(NH_{4})_{6}Mo_{7}O_{24}\longrightarrow 7\ MoO_{3}+6\ NH_{3}+3\ H_{2}O} }$

${\displaystyle \mathrm {MoO_{3}+H_{2}\longrightarrow MoO_{2}+H_{2}O} }$

${\displaystyle \mathrm {MoO_{2}+2\ H_{2}\longrightarrow Mo+2\ H_{2}O} }$

World production in 2007 was 211,000 tons (2006 179,000 tons). In 2007 the USA - as the largest producer - produced 62,000 tons, China 60,000 tons and Chile 45,000 tons. In 2013 the total amount of molybdenum produced was 258,000 tons; The main producers were China (101,000 t), the USA (60,700 t), Chile (38,700 t) and Peru (18,100 t). The USGS gives the prices for molybdenum USD 34.83 per kg in 2010 and USD 22.85 per kg for 2013. The London Metal Exchange listed molybdenum at around USD 25 / kg during 2018.

properties

Molybdenum, crystalline fragment

Molybdenum is a 5th period transition metal. The high-strength, tough and hard metal has a silvery white sheen. It has the highest melting point of all elements of the 5th period . Like the heavy homologue tungsten, it is not attacked by non-oxidizing acids (including hydrofluoric acid ) . That is why molybdenum is used in large quantities for the production of acid-resistant stainless steels and nickel materials. Oxidizing acids such as hot concentrated sulfuric acid , nitric acid or aqua regia lead to high removal rates. Molybdenum is just as unstable in oxidizing alkali melts.

use

The polyhedral structures of [Mo ₆ O ₁₉ ] ²⁻  (a) and [Mo ₇ O ₂₄ ] ⁶⁻  (b)

In small additions it is used to harden and prevent tempering embrittlement of steel . More than two thirds of the molybdenum produced is used to produce metal alloys such as ferro-molybdenum. The shortage of tungsten in the First World War led to the increased use of molybdenum for the production of high-strength materials. To this day, molybdenum is an alloying element used to increase strength, corrosion and heat resistance. High-performance materials containing molybdenum such as Hastelloy ^® , Incoloy ^® or Nicrofer ^® have made many technical processes possible or economically viable in the first place.

Because of its high temperature resistance, molybdenum is used to manufacture parts for extreme applications, such as in aerospace or metallurgy technology. In oil processing it is used as a catalyst to remove sulfur.

Due to its layer structure, molybdenum disulfide is an ideal lubricant, even at elevated temperatures. It can be used as a solid such as graphite, but also suspended in conventional lubricating oils.

Molybdenum can also be found in electronic components. In TFTs (thin-film transistors) it serves as a conductive metal layer and it is also used as a metallic return conductor in thin-film solar cells.

Molybdenum foils serve as gas-tight current conduction in quartz glass , u. a. on halogen incandescent lamps and high pressure gas discharge lamps .

Molybdenum wires can also be used in the same lamp types if instead of quartz glass a glass (usually aluminosilicate glass ) is used that has a thermal expansion adapted to molybdenum and is therefore suitable for a glass-metal connection .

Molybdates are used to impregnate fabrics to make them flame retardant.

Molybdenum is also used in X-ray diagnostics as a target material in the anode. X-ray tubes with molybdenum anode are used because of the lower energy of the characteristic X-ray radiation ( at 17.4 keV and at 19.6 keV compared to 58 / 59.3 keV and 67.0 / 67.2 / 69.1 keV of tungsten ) Molybdenum v. a. used in the examination of the female breast ( mammography ). ${\displaystyle K_{\alpha }}$ ${\displaystyle K_{\beta }}$

In nuclear medicine , split molybdenum is used in technetium-99m generators . The relatively long-lived ⁹⁹ Mo (HWZ 66 h) breaks down within the RNG into ^{99 m} Tc ( Technetium , HWZ 6 h). In this way, this important technetium isotope can be obtained directly on site for research purposes.

physiology

Bacteria molybdenum cofactor bis (molybdopterin guanine dinucleotide) molybdenum

As a trace element , molybdenum is essential for almost all living organisms, as it is an essential component of the active center of a large number of enzymes such as nitrogenase , nitrate reductase and sulfite oxidase . Living beings use enzymes containing molybdenum and the like. a. for purine decomposition and uric acid formation. The bioavailable , i.e. H. the form of molybdenum absorbed by organisms is the molybdate ion MoO ₄ ²⁻ . This is incorporated into the corresponding enzymes in several steps as molybdenum cofactors . There the Mo atom can switch between the oxidation numbers + IV, + V and + VI, and thus catalyze one-electron redox reactions.

Molybdenum is essential for plants. A lack of molybdenum can make a soil sterile, which explains why fertilization with ammonium heptamolybdate increases the yield on such soils. The molybdenum concentration in plants and animals is a few ppm . Molybdenum is a very important trace element, especially for legumes . The bacteria living in symbiosis with legumes ( nodule bacteria ) are able to bind atmospheric nitrogen with an enzyme containing molybdenum ( nitrogenase ). You need molybdenum for two processes: fixation of molecular nitrogen and nitrate reduction.

Molybdenum is also essential for human nutrition. The DGE estimate for adolescents and adults assumes 50 to 100 µg molybdenum as an appropriate daily intake. A molybdenum deficiency does not occur with a normal diet and is therefore extremely rare. If high intakes (10–15 mg / day) are achieved - for example through molybdenum-rich soils, gout-like symptoms, joint pain and enlarged liver occur.

However, the molybdenum cofactor deficiency only occurs as a hereditary disease ; one of the enzymes that catalyze the biosynthesis of the molybdenum cofactors is mutated .

links

Molybdenum forms numerous compounds in oxidation states 2 to 6. The best known are the molybdates derived from molybdenum (VI) oxide , such as various ammonium molybdates . Molybdenum (IV) oxide is produced by reducing molybdenum (VI) oxide. Peroxomolybdates can be produced from molybdate solutions and hydrogen peroxide and are very reactive. Molybdenum blue is a name for different molybdenum oxide hydroxides.

With chlorine, molybdenum forms several chlorides in oxidation states 2 to 5. MoCl _{5 is} obtained by heating molybdenum powder in a stream of chlorine, MoCl ₄ by reducing MoCl ₅ . Molybdenum (VI) fluoride is preferably formed with fluorine . In addition, a number of oxide fluorides, such as MoOF ₄ , and oxofluoromolybdates, such as K ₂ [MoOF ₅ ], are known.

Several molybdenum sulphides are formed with sulfur : Among them molybdenum (IV) sulphide and molybdenum (VI) sulphide , from which thiomolybdates can be derived, such as ammonium tetrathiomolybdate (VI) (NH ₄ ) ₂ [MoS ₄ ].

Complex compounds with cyanides are, for example, octacyanomolybdate (IV), such as K ₄ [Mo (CN) ₈ ]. Thiocyanates form hexathiocyanomolybdate (III) complexes such as (NH ₄ ) ₃ [Mo (SCN) ₆ ]. Molybdenum also forms different carbonyl complexes , such as B. [Mo (CO) ₅ ] ²⁻ with the oxidation state −2, and carbonyls with zero-valent molybdenum, such as molybdenum hexacarbonyl .

safety instructions

Molybdenum dust and compounds such as molybdenum (VI) oxide and water-soluble molybdates exhibit slight toxicity when inhaled or ingested orally.

Tests suggest that molybdenum, in contrast to many other heavy metals, is relatively less toxic. Acute poisoning is unlikely because of the quantities required. In the area of ​​molybdenum mining and production, higher molybdenum exposures could occur. So far, however, no cases of illness have become known.

Although natural molybdenum contains 9.63% of the radioactive isotope ¹⁰⁰ Mo, no special safety precautions for radiation protection are normally required. Shielding can usually be dispensed with in practical use as well. The radiation is very weak because of the long half-life and can only be measured with great effort.

proof

A qualitative proof of hexavalent molybdenum is possible through the formation of heteropoly acids with phosphate . If phosphoric acid is added to a solution containing molybdate containing sulfuric acid , crystalline molybdenum yellow precipitates . When the mild reducing agent ascorbic acid is added, the solution turns a strong blue (formation of molybdenum blue ). With lower concentrations of molybdate there is no precipitation, only a change in color of the solution.

${\displaystyle \mathrm {H_{2}PO_{4}^{-}+12\ MoO_{4}^{2-}+22\ H_{3}O^{+}+3\ NH_{4}^{+}\longrightarrow (NH_{4})_{3}[P(Mo_{3}O_{10})_{4}](gelb)+34\ H_{2}O} }$

These reactions are also used for the photometric determination of molybdate or phosphate in the trace range. Alternatively, molybdenum can be determined using atomic spectrometry . In polarography , hexavalent molybdenum in sulfuric acid with a concentration of 0.5 mol / l gives two levels at −0.29 and −0.84 V (versus SCE ). These are due to the reduction to Mo (V) or Mo (III).

Web links

Wiktionary: Molybdenum  - explanations of meanings, word origins, synonyms, translations

Commons : Molybdenum  - Collection of images, videos, and audio files

Wikibooks: Internship Inorganic Chemistry / Molybdenum  - Learning and teaching materials

• International Molybdenum Association - English language site with lots of information and links

Individual evidence

1. ^ Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. ↑ The values ​​for the properties (info box) are taken from www.webelements.com (molybdenum) , unless otherwise stated .
3. ↑ CIAAW, Standard Atomic Weights Revised 2013 .
4. ↑ ^{a b c d e} Entry on molybdenum in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 11, 2020.
5. ↑ ^{a b c d e} Entry on molybdenum at WebElements, https://www.webelements.com , accessed on June 11, 2020.
6. ^ NN Greenwood, A. Earnshaw: Chemistry of the elements. 1st edition. 1988, ISBN 3-527-26169-9 , p. 1291.
7. ↑ Robert C. Weast (Ed.): CRC Handbook of Chemistry and Physics . CRC (Chemical Rubber Publishing Company), Boca Raton 1990, ISBN 0-8493-0470-9 , pp. E-129 to E-145. Values ​​there are based on g / mol and given in cgs units. The value specified here is the SI value calculated from it, without a unit of measure.
8. ↑ ^{a b} Yiming Zhang, Julian RG Evans, Shoufeng Yang: Corrected Values ​​for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks. In: Journal of Chemical & Engineering Data . 56, 2011, pp. 328-337, doi: 10.1021 / je1011086 .
9. ↑ ^{a b} Entry on molybdenum in the GESTIS substance database of the IFA , accessed on April 26, 2017(JavaScript required) .
10. ↑ SAGEN.at - The mine under the Alpeiner Scharte - Molybdenum mining. Retrieved March 7, 2017 . 
11. ↑ Mindat - Molybdenum (English).
12. ↑ IMA / CNMNC List of Mineral Names - Molybdenum (English, PDF 1.8 MB, p. 191: Status (N) = published without approval by the CNMNC).
13. ↑ Lucien F. Trueb: The chemical elements. A journey through the periodic table. S. Hirzel Verlag, Stuttgart / Leipzig 1996, ISBN 3-7776-0674-X .
14. ↑ ^{a b} Statistics at the United States Geological Society (Molybdenum) (PDF; 60 kB).
15. ↑ MINERAL COMMODITY SUMMARIES 2015. (PDF 2.3 MB, pp. 106–107) USGS , accessed on October 14, 2015 (English).  
16. ↑ lme.com - Historical price graph for Molybdenum. Retrieved July 7, 2018 . 
17. ^ G. Schwarz, RR Mendel, MW Ribbe: Molybdenum cofactors, enzymes and pathways . In: Nature . tape 460 , no. 7257 , 2009, p. 839-847 , PMID 19675644 .
18. ↑ DA-CH : Reference values ​​for nutrient intake, 2000.
19. ↑ Jochen Reiss, Rita Hahnewald: Molybdenum cofactor deficiency: Mutations in GPHN, MOCS1, and MOCS2. In: Human Mutation . 32, 2011, pp. 10-18, doi: 10.1002 / humu.21390 .
20. ↑ Heinrich Remy : Textbook of Inorganic Chemistry. Volume II, Akademische Verlagsgesellschaft Geest & Portig, Leipzig 1961, pp. 200–208.