properties
[ Ar ] 3 d 3 4 s 2
23 V
General
Name , symbol , atomic number Vanadium, V, 23
Element category Transition metals
Group , period , block 5 , 4 , d
Appearance steel gray metallic, shimmering bluish
CAS number 7440-62-2
EC number 231-171-1
ECHA InfoCard 100.028.337
Mass fraction of the earth's envelope 0.041%
Atomic
Atomic mass 50.9415 (1) and
Atomic radius (calculated) 135 (171) pm
Covalent radius 153 pm
Electron configuration [ Ar ] 3 d 3 4 s 2
1. Ionization energy 6th.746 187 (21) eV 650.91 kJ / mol
2. Ionization energy 14th.634 (7) eV1 412 kJ / mol
3. Ionization energy 29.3111 (25) eV2 828.09 kJ / mol
4. Ionization energy 46.709 (5) eV4 506.7 kJ / mol
5. Ionization energy 65.28165 (17) eV6 298.72 kJ / mol
Physically
Physical state firmly
Crystal structure body-centered cubic
density 6.11 g / cm 3 (20 ° C )
Mohs hardness 7.0
magnetism paramagnetic ( Χ m = 3.8 10 −4 )
Melting point 2183 K (1910 ° C)
boiling point 3680 K (3407 ° C)
Molar volume 8.32 · 10 −6 m 3 · mol −1
Heat of evaporation 444 kJ / mol
Heat of fusion 21.5 kJ mol −1
Speed ​​of sound 4560 m s −1 at 293.15 K.
Specific heat capacity 489 J kg −1 K −1
Electric conductivity 5 · 10 6 A · V −1 · m −1
Thermal conductivity 31 W m −1 K −1
Chemically
Oxidation states +5 , +4, + 3, + 2
Electronegativity 1.63 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
48 V {syn.} 15.9735 d ε 4.012 48 Ti
49 V {syn.} 330 d ε 0.602 49 Ti
50 V 0.25% 1.5 · 10 17 a ε 2.208 50 Ti
β - 1.037 50 Cr
51 V 99.75  % Stable
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
50 V ? 6th 0+2.67065 10 7 0.05571 019.977
51 V ? 7/2 0+7.04551 · 10 7 0.3836 052.702
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 .

Vanadium , also outdated vanadium , is a chemical element with the symbol V and the atomic number 23. It is a steel-gray, bluish shimmering transition metal that is very soft in its pure state . In the periodic table, the metal, together with the heavier niobium , tantalum and dubnium, forms the 5th  IUPAC group or vanadium group . Most of the vanadium is used as so-called ferrovanadium in steel production. The addition of vanadium to chrome - vanadium steels increases the toughness and thus increases the resistance of the steel.

The element has different biological meanings and is essential for many living things . So it plays a role in the control of enzymes of phosphorylation and is used by bacteria to nitrogen fixation used. On the other hand, it or its compounds are suspected of causing chromosome aberrations as a mutagenic clastogen and thus acting as a poison and carcinogen .

The best-known compound of vanadium is vanadium (V) oxide , which is used as a catalyst for the production of sulfuric acid .

## history

Andrés Manuel del Río

The later vanadium was discovered for the first time in 1801 by the Spanish mineralogist Andrés Manuel del Río in a Mexican lead ore, later vanadinite . He called the new element Panchromium first because of the multicolored nature of the compounds , later Erythronium , because the salts turned red when acidified. However, del Rio revoked the discovery a short time later, when first Alexander von Humboldt and later the French chemist HV Collett-Desotils claimed that the new element was contaminated chromium because of its similarity to chromium compounds .

The rediscovery of the element succeeded in 1830 by the Swedish chemist Nils Gabriel Sefström . He examined iron from the Swedish iron ore mine Taberg by dissolving it in hydrochloric acid . In the process, he discovered, among other known substances, an unknown element that resembled chromium in some properties and uranium in others , but was not one of these elements after further research. He named the new element after Vanadis , an epithet of the Nordic deity Freyja . A short time later, Friedrich Wöhler , who had already dealt with the task at Berzelius, provided evidence of the identity of vanadium with erythronium.

Metallic vanadium was first in 1867 by Henry Enfield Roscoe by reduction of vanadium (II) chloride with hydrogen produced. John Wesley Marden and Malcolm Rich were able to obtain 99.7% pure vanadium for the first time in 1925 by reducing vanadium (V) oxide with calcium.

Vanadium was first used in 1903 when the first vanadium-containing steel was produced in England . The element's increased use in the steel industry began in 1905 when Henry Ford started using vanadium steels in the construction of automobiles .

## Occurrence

Vanadium is a common element on earth, its share in the continental crust is about 120  ppm . Zirconium , chlorine and chromium have a similar abundance of elements . The element is mainly found bound in various minerals . Despite the abundance of vanadium, deposits with high concentrations of the element are rare, and many vanadium minerals are not common. Compared to the earth's crust, the content in seawater is significantly lower, it is around 1.3 μg / l.

The most important vanadium minerals include, in particular, vanadates such as vanadinite [Pb 5 (VO 4 ) 3 Cl], Descloizit Pb (Zn, Cu) [OH | VO 4 ] and carnotite [K 2 (UO 2 ) 2 (VO 4 ) 2 · 3H 2 O], as well as the vanadium sulfide Patrónit VS 4 . Most of the vanadium is found in traces in other minerals, especially iron ores such as magnetite . The vanadium content of titanium magnetite ores is usually between 0.3 and 0.8%, but can reach up to 1.7% in some South African ores.

Animals and plants contain vanadium, so humans contain about 0.3 mg / kg of the element. This is mostly located in cell nuclei or mitochondria . Some living things, especially some species of sea ​​squirt and the fly agaric , are able to enrich vanadium. The vanadium content in sea squirts is up to 10 7 times higher than in the surrounding sea water. Due to the vanadium content of living beings, coal and crude oil that arise from them also contain vanadium. The content is up to 0.1%. Particularly high levels of vanadium are found in petroleum from Venezuela and Canada.

In 2015, a total of 79,400 tons of vanadium ore were mined (calculated as vanadium metal). The most important producing countries are South Africa , China and Russia . With known reserves totaling 15 million tons (as of 2015), a delivery bottleneck for vanadium is not expected in the foreseeable future.

## Vanadium as a mineral

Vanadium has been recognized as a mineral by the International Mineralogical Association (IMA) since 2012 . It was first discovered by Mikhail Ostrooumov as a resublimation product in the high-temperature fumaroles of the Mexican volcano Colima . Potassium vanadium sulfide Colimait (K 3 VS 4 ) and the vanadium oxide Shcherbinait (V 5+ 2 O 5 ) , which were also discovered there for the first time, appeared as accompanying minerals .

The first description was published by Ostrooumov and Yuri Taran in 2015, initially in the Macla. Revista de la Sociedad Española de Mineralogía and 2016 in Mineralogical Magazine .

Besides its type locality at the volcano Colima vanadium was dignified yet only at a unspecified Hibonit -Fundstätte in Argentina's Sierra de los Comechingones be discovered. Another find in the Rhovan opencast vanadium mine near Rustenburg in the South African province of Northwest has not yet been confirmed.

According to the systematics of minerals according to Strunz (9th edition) , vanadium is classified under system no. 1.AF.05 (elements - metals and intermetallic compounds - iron-chromium family - iron group).

## Extraction and presentation

Vanadium 99.95%, electron beam melted and macro-etched
Vanadium 99.9%, dendritically grown crystal, produced by vacuum sublimation
Vanadium, produced by the Van Arkel de Boer process; left oxidized in air

Vanadium is represented in several steps. First of all, vanadium (V) oxide must be obtained from various starting materials . This can then be reduced to elementary metal and cleaned if necessary.

Possible starting materials from which vanadium can be extracted are vanadium ores such as carnotite or patronite, vanadium-containing titanium-magnetite ores and petroleum . Vanadium ores were important for production in the past, but no longer play an important role and have mainly been replaced by titanium-magnetite ores.

The actual vanadium extraction takes place by reducing the vanadium (V) oxide with other metals. Aluminum , calcium , ferrosilicon or carbon can be used as reducing agents ; with the latter, however, carbides are formed in the reaction , which are difficult to separate from the metal.

${\ displaystyle \ mathrm {V_ {2} O_ {5} +5 \ Ca \ longrightarrow 2 \ V + 5 \ CaO}}$
Reduction with calcium

In order to obtain pure vanadium, expensive calcium or aluminum is used as a reducing agent, since the cheaper ferrosilicon cannot achieve high purity. While pure vanadium is obtained directly with calcium, a vanadium-aluminum alloy is initially formed with aluminum, from which pure vanadium is obtained by sublimation in a vacuum .

A large part of the vanadium is not used as a pure metal, but in the form of the iron-vanadium alloy ferrovanadium , which contains at least 50% vanadium. In order to produce this, it is not necessary to extract the pure vanadium beforehand. Instead, the vanadium and iron-containing slag is reduced to ferrovanadium with ferro-silicon and lime . This alloy is sufficient for most technical applications.

The purest vanadium can be produced either electrochemically or according to the Van-Arkel-de-Boer method . For this purpose, the pure vanadium is melted together with iodine in an empty glass ampoule. The vanadium (III) iodide formed in the heated ampoule decomposes on a hot tungsten wire to form highly pure vanadium and iodine.

${\ displaystyle \ mathrm {2 \ V + 3 \ I_ {2} \ rightleftharpoons 2 \ VI_ {3}}}$
Reaction in the Van Arkel de Boer process

## properties

### Physical Properties

Crystal structure of vanadium, a  = 302.4 pm

Vanadium is a non-magnetic, tough, malleable and clearly steel-blue heavy metal with a density of 6.11 g / cm 3 . Pure vanadium is relatively soft, but becomes harder when other elements are added and then has high mechanical strength. In most of its properties it is similar to its neighbor in the periodic table, titanium . The melting point of pure vanadium is 1910 ° C, but this is significantly increased by impurities such as carbon . With a carbon content of 10% it is around 2700 ° C. Vanadium crystallizes like chromium or niobium in a body-centered cubic crystal structure with the space group Im 3 m (space group no. 229) and the lattice parameter a = 302.4 pm as well as two formula units per unit cell .

Below a critical temperature of 5.13 K vanadium becomes a superconductor . Just like pure vanadium, alloys of vanadium with gallium , niobium and zirconium are superconducting. At temperatures below 5.13 K, vanadium, like the vanadium group metals niobium and tantalum , shows in tiny lumps of up to 200 atoms a hitherto unexplained, spontaneous electrical polarization that is otherwise only exhibited by non-metallic substances .

### Chemical properties

Vanadium is a base metal and is able to react with many non-metals . In the air it remains shiny metallic for weeks. When viewed over longer periods of time, clearly visible green rust is perceived. If vanadium is to be preserved, it must be kept under argon. In the heat it is attacked by oxygen and oxidized to vanadium (V) oxide . While carbon and nitrogen only react with vanadium when it is incandescent , the reaction with fluorine and chlorine takes place in the cold.

Compared with acids and bases is vanadium usually stable at room temperature because of a thin passivating oxide layer; In this state it is only attacked by hydrofluoric acid and strongly oxidizing acids such as hot nitric acid , concentrated sulfuric acid and aqua regia .

Up to a temperature of 500 ° C is vanadium capable of hydrogen to absorb . The metal becomes brittle and can be easily powdered. The hydrogen can be removed at 700 ° C in a vacuum.

## Isotopes

A total of 27 isotopes and a further 6 core isomers are known of vanadium . Of these, two occur naturally. These are the isotopes 50 V with a natural frequency of 0.25% and 51 V with a frequency of 99.75%. 50 V is weakly radioactive , with a half-life of 1.5 · 10 17 years it decays 83% with electron capture to 50 Ti, 17% with β - decay to 50 Cr. Both cores can be used for investigations with NMR spectroscopy .

The most stable artificial isotopes are 48 V with a half-life of 16 days and 49 V with a half-life of 330 days. These are used as tracers . All other isotopes and core isomers are very unstable and disintegrate in minutes or seconds.

## use

Only a small percentage of pure vanadium is used as a cladding material for nuclear fuels due to its small neutron capture cross- section . However, more resistant vanadium alloys can also be used. Over 90% of production is used in a variety of alloys , mostly with the metals iron, titanium, nickel, chromium, aluminum or manganese. Only a small part is used in compounds, mostly as vanadium (V) oxide.

With 85% of the vanadium produced, by far the largest part is consumed in the steel industry . Since this does not require high purities, ferrovanadium is used as a raw material. Even in small quantities, vanadium increases the strength and toughness of steels and thus their wear resistance significantly. This is caused by the formation of hard vanadium carbide . Depending on the application, different amounts of vanadium are added; structural steels and tool steels contain only small amounts (0.2 to 0.5%) of vanadium, high-speed steel up to 5%. Vanadium-containing steels are mainly used for tools and springs that are subject to mechanical stress. Steels that contain cobalt in addition to iron and vanadium are magnetic.

Titanium alloys, which contain vanadium and mostly aluminum, are particularly stable and heat-resistant and are used in aircraft construction for load-bearing parts and turbine blades of aircraft engines.

Vanadium compounds can be used for electrochemical energy storage in redox flow cells , see Vanadium redox accumulator . In this application, the vanadium salts are used in acidic aqueous solutions that can be stored in tanks.

## proof

A preliminary test is provided by the phosphorus salt bead , in which vanadium appears characteristic green in the reduction flame. The oxidation flame is pale yellow and therefore too unspecific.

Qualitative evidence for vanadium is based on the formation of peroxovanadium ions. To do this, an acidic solution containing vanadium in the +5 oxidation state is mixed with a little hydrogen peroxide . The reddish-brown [V (O 2 )] 3+ cation is formed. This reacts with larger amounts of hydrogen peroxide to form the pale yellow peroxovanadic acid H 3 [VO 2 (O 2 ) 2 ].

Vanadium can be quantitatively determined by titration . For this purpose, a vanadium - containing sulfuric acid solution is oxidized with potassium permanganate to pentavalent vanadium and then back-titrated with an iron (II) sulfate solution and diphenylamine as an indicator . A reduction of existing pentavalent vanadium with iron (II) sulfate to the tetravalent oxidation state and subsequent potentiometric titration with potassium permanganate solution is also possible.

In modern analytics , vanadium can be detected using several methods. These are, for example, atomic absorption spectrometry at 318.5 nm and spectrophotometry with N-benzoyl-N-phenylhydroxylamine as the color reagent at 546 nm.

## Biological importance

Sea squirts contain high levels of vanadium

Vanadium compounds have various biological meanings. It is characteristic of vanadium that it occurs both anionically as vanadate and cationically as VO 2 + , VO 2+ or V 3+ . Vanadates are very similar to phosphates and accordingly have similar effects. Since vanadate binds more strongly to suitable enzymes than phosphate, it is able to block and thus control enzymes of phosphorylation . This concerns, for example, the sodium-potassium-ATPase , which controls the transport of sodium and potassium into cells. This blockage can be quickly removed with desferrioxamine B , which forms a stable complex with vanadate. Vanadium also affects glucose uptake. It is able to stimulate glycolysis in the liver and inhibit the competitive process of gluconeogenesis . This leads to a lowering of the glucose level in the blood. It is therefore being investigated whether vanadium compounds are suitable for the treatment of type 2 diabetes mellitus . However, no clear results have yet been found. Vanadium also stimulates the oxidation of phospholipids and suppresses the synthesis of cholesterol by inhibiting squalene synthase , a microsomal enzyme system in the liver. Consequently, a deficiency causes increased levels of cholesterol and triglycerides in the blood plasma .

Vanadium plays a role in photosynthesis in plants . It is able to catalyze the reaction to form 5-aminolevulinic acid without enzyme. This is an important precursor to the formation of chlorophyll .

In some organisms there are vanadium-containing enzymes, so some types of bacteria have vanadium-containing nitrogenases for nitrogen fixation . These are, for example, species of the genus Azotobacter and the cyanobacterium Anabaena variabilis . However, these nitrogenases are not as efficient as the more common molybdenum nitrogenases and are therefore only activated when there is a molybdenum deficiency. Other vanadium-containing enzymes can be found in brown algae and lichens . These have vanadium-containing haloperoxidases with which they build up organochlorine, bromine or iodine-organic compounds.

The function of vanadium, which is present in large quantities in sea squirts as the metalloprotein vanabine , is not yet known. It was originally assumed that the vanadium, similar to the hemoglobin, serves as an oxygen transporter; however, this has been found to be wrong.

## Hazards

Like other metal dusts, vanadium dust is flammable. Vanadium and its inorganic compounds have been shown to be carcinogenic in animal experiments . They are therefore classified in carcinogen category 2. If vanadium dust is inhaled by workers in metal smelting for a long time, it can lead to so-called vanadism . This recognized occupational disease can manifest itself in irritation of the mucous membranes , green-black discoloration of the tongue and chronic bronchial, lung and intestinal diseases.

Vanadium can be present in compounds in various oxidation states . Often levels are +5, +4, +3 and +2, more rarely are +1, 0, −1 and −3. The most important and most stable oxidation states are +5 and +4.

### Aqueous solution

Vanadium can easily be converted into different oxidation states in aqueous solution. Since the different vanadium ions have characteristic colors, color changes occur.

In acidic solution pentavalent vanadium forms colorless VO 2 + ions, which upon reduction to blue first tetravalent VO 2+ are ions. The trivalent level with V 3+ ions is green, the lowest level that can be achieved in aqueous solution, the divalent V 2+ ion is gray-violet.

### Oxygen compounds

The most important and most stable vanadium-oxygen compound is vanadium (V) oxide V 2 O 5 . This orange-colored compound is used in large quantities as a catalyst for the production of sulfuric acid. There it acts as an oxygen carrier and is reduced to another vanadium oxide, vanadium (IV) oxide VO 2 during the reaction . Further known vanadium oxides are vanadium (III) oxide V 2 O 3 and vanadium (II) oxide VO.

### Halogen compounds

Vanadium forms a large number of compounds with the halogens fluorine , chlorine , bromine and iodine . In the oxidation states +4, +3 and +2 there are compounds with all halogens, only with iodine only compounds in the stages +2 and +3 are known. Of these halides, however, only the chlorides vanadium (IV) chloride and vanadium (III) chloride are technically relevant. Among other things, they serve as a catalyst for the production of ethylene-propylene-diene rubber .

### Vanadium oxide chlorides

Vanadium also forms mixed salts with oxygen and chlorine, the so-called vanadium oxide chlorides . Vanadium (III) oxychloride, VOCl, is a yellow-brown, water-soluble powder. The vanadium (IV) oxychloride, VOCl 2 , used in photography and as a textile stain consists of green, hygroscopic crystal tablets which dissolve in water with a blue color. Finally, vanadium (V) oxychloride, VOCl 3 , is a yellow liquid that is very easily hydrolyzed by water . VOCl 3 is used as a catalyst component in low-pressure ethylene polymerization .

### More vanadium compounds

In organic vanadium compounds, vanadium reaches its lowest oxidation states 0, −I and −III. The metallocenes , the so-called vanadocenes , are particularly important here. These are used as catalysts for the polymerization of alkynes .

Vanadium carbide VC is used in powder form for plasma spraying and plasma powder build-up welding . Furthermore, vanadium carbide is added to hard metals in order to reduce grain growth .

## literature

Commons : Vanadium  album with pictures, videos and audio files
Wiktionary: Vanadium  - explanations of meanings, word origins, synonyms, translations

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