vanadium

A bright white, soft, ductile metallic element found in several minerals, notably vanadinite and carnotite, having good structural strength and used in rust-resistant high-speed tools, as a carbon stabilizer in some steels, as a titanium-steel bonding agent, and as a catalyst. Atomic number 23; atomic weight 50.942; melting point 1,890°C; boiling point 3,000°C; specific gravity 6.11; valence 2, 3, 4, 5.

[From Old Norse Vanadīs, the goddess Freya.]

A chemical element, V, with atomic number 23. Natural deposits contain two isotopes, ⁵⁰V (0.24%), which is weakly radioactive, and ⁵¹V (99.76%). Commercially important as an oxidation catalyst, vanadium also is used in the production of alloy steel and ceramics and as a colorizing agent. Studies have demonstrated the biological occurrence of vanadium, especially in marine species; in mammals, vanadium has a pronounced effect on heart muscle contraction and renal function. See also Periodic table; Transition elements.

Very pure vanadium is difficult to prepare because the metal is highly reactive at temperatures above the melting point of its oxide (663°C or 1225°F) from which it is produced. Vanadium is a bright white metal that is soft and ductile. It has a melting point of 1890°C (3434°F), a boiling point of 3380°C (6116°F), and a density of 6.11 g/cm³ (3.53 oz/in.³) at 18.7°C (65.7°F). The thermal and electrical conductivity of vanadium is superior to that of titanium.

At room temperature, the metal is resistant to corrosion by oxygen, salt water, alkalies, and nonoxidizing acids, the exception being hydrogen fluoride (HF). Vanadium cannot withstand the oxidizing conditions presented by nitric acid or aqua regia. At elevated temperatures it will combine with most nonmetals to form oxides, nitrides, carbides, arsenides, and other such compounds.

The physical properties of vanadium are very sensitive to interstitial impurities. The strength varies from 30,000 lb/in.² (200 megapascals) in the purest form to 80,000 lb/in.² (550 MPa) in the commercial grade. The melting point is markedly altered by small impurities; vanadium containing 10% carbon has a melting point of 2700°C (4892°F).

Vanadium has a low fission neutron cross section. This property combined with the metal's excellent retention of strength at elevated temperatures has made its use in atomic energy applications attractive.

Carbon and alloy steels consume more than half the vanadium produced in the United States. Many plate, structural, bar, and pipe steels contain vanadium to enhance strength and toughness. The basis for the unique properties of these carbon alloy steels is the formation of vanadium carbide. These carbides are extremely hard and wear-resistant; they do not coalesce readily, but maintain a state of fine dispersion. Many large steel forgings contain vanadium in the range 0.05–0.15%; here vanadium acts as a grain refiner, and also improves the mechanical properties of the forgings. Tool steels are another large class of vanadium-containing steels; vanadium ensures the retention of hardness and cutting ability at the elevated temperatures generated by the rapid cutting of metals.

The production of ferrovanadium, an iron alloy, is very important since the primary commercial use of vanadium is in steel. Ferrovanadium is produced by aluminum or silicon reduction of V₂O₅ in the presence of iron in an electric arc furnace. The commonly practiced aluminum reduction is exothermic, so that little additional heat from the arc is required. Silicon processing requires a two-stage reduction to achieve efficient operation. See also Ferroalloy; Steel manufacture.

Vanadium compounds, especially V₂O₅ and NH₄VO₃, are excellent oxidation catalysts in the chemical industry. Processes that employ such catalysts include the manufacture of polyamides, such as nylon; sulfuric acid production by the contact process; phthalic and maleic anhydride syntheses; and various oxidations of organic compounds such as the conversion of anthracene to anthraquinone, ethanol to acetaldehyde, and sugar to oxalic acid. Vanadium pentoxide is used as a mordant in dyeing and printing fabrics and in producing aniline black for the dye industry. Vanadium compounds are used in the ceramics industry for glazes and enamels. A wide range of colors can be obtained with combinations of vanadium oxide, zirconia, silica, lead, tin, zinc, cadmium, and selenium. See also Ceramics; Dyeing; Mordant.

Vanadium has long been recognized as an essential element in biological systems; however, the role of the metal often is obscure. Tunicates accumulate vanadium to levels 1 million times greater than the surrounding seawater. This vanadium was once thought to act as an oxygen carrier but now is believed to be an oxidation catalyst that repairs damage to the polymeric, protective tunic of these animals. The first vanadium-dependent enzyme, vanadium bromoperoxidase, was isolated from brown, red, and green marine algae (for example, Ascophyllum nodosum); this enzyme catalyzes the bromination of a variety of organic molecules by using hydrogen peroxide and bromide. This activity may be the source of many important brominated compounds that potentially may be used as antifungal and antineoplastic agents. See also Enzyme.

A variety of physiological effects in mammalian systems have been reported, the most significant being in cardiovascular and renal function. Vanadate causes constriction of veins in the kidney and can alter the retention and excretion of sodium and chloride ions. Cardiac effects of vanadium are species-specific, with observed increases (rabbit and rat) and decreases (guinea pig and cat) in heart muscle contractility. Because vanadate is a potent inhibitor of Na,K-ATPase in the laboratory, it has been suggested that this is the site of the metal's action. However, the physiology of vanadate is probably more complicated, since vanadium behaves as a hormone mimic by elevating intracellular calcium ion (Ca²⁺) levels in a process that is poorly understood. See also Bioinorganic chemistry.

A mineral known to be essential; it activates a number of enzymes. Sufficiently widespread for human dietary deficiency to be unknown, and there are no estimates of requirements.

An essential trace element which has several metabolic functions. Deficiency causes sterility in certain animals. However, there is as yet no record of deficiency symptoms in humans so no recommended intakes have been established. Dietary sources of vanadium include wholegrain breads, cereals, nuts, shellfish, and liver.

Description

Named after the Scandinavian goddess of youth and beauty, vanadium is a trace element that has gained attention in recent years as a possible aid in controlling diabetes. While such macrominerals as calcium, magnesium, and potassium have become household names because they make up over 98% of the body's mineral content, certain trace minerals are also considered essential in very tiny amounts to maintain health and ensure proper functioning of the body. They usually act as coenzymes, working as a team with proteins to facilitate important chemical reactions. Even without taking vanadium supplements, people have about 20–25 micrograms (mcg) of the mineral in their bodies, which is derived from an average balanced diet. Despite the fact that vanadium has been studied for over 40 years, it is still not known for certain if the mineral is critical for optimal health. Whether taking extra amounts of vanadium is therapeutic or harmful is even more controversial. Like chromium, another trace mineral, vanadium has become the focus of study as a possible aid in lowering blood sugar levels in people with diabetes. Vanadium has also been touted as a potential treatment for osteoporosis. Some athletes and weight lifters take it to build muscle or improve performance.

Studies in animals suggest that vanadium may be necessary for the formation of bones, teeth, and cartilage. The mineral may also play a role in growth and reproduction as well as affect the processing of cholesterol and insulin in the body. In one animal study, goat kids whose mothers received a diet deficient in vanadium showed skeletal damage; they died within days of their birth. In studies of mice, vanadium has been shown to lower blood sugar and levels of low-density lipoprotein (LDL) cholesterol and triglyceride. It is not certain, however, that such study results as these confirm the nutritional importance of the mineral for human beings. The effects of a vanadium-free diet have not been studied in people. Even if vanadium supplements prove to be effective for certain purposes, such as helping to control diabetes, animal studies suggest that the high dosages of vanadium necessary to produce results may be harmful. High dosages are often necessary because vanadium is not well absorbed by the body. As of 2000, a significant amount of research is still required to determine if vanadium can in fact produce significant health benefits safely and effectively. The proper dosage of the mineral supplement has also yet to be determined.

General Use

Vanadium has been investigated most often as a possible aid in controlling diabetes. Studies in animals with type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes indicate that vanadium can help to improve blood sugar levels. Studies using human subjects have produced encouraging if preliminary results. Vanadium is used by some athletes and weight lifters to build muscle despite the fact that it does not appear to be effective for this purpose. Moreover, the potential usefulness of vanadium in treating osteoporosis is considered highly speculative. All of the human studies discussed below were conducted in small numbers of people for short periods of time and involved relatively high dosages of the mineral.

Diabetes

Several studies conducted in people suggest that vanadium may help to control blood sugar levels in diabetics. The mineral appears to work by mimicking the effects of insulin or by increasing the body's sensitivity to the hormone. This mechanism could allow diabetics to effectively control their blood sugar while using lower dosages of insulin medication. In a placebo-controlled study published in 1996 in the medical journal Metabolism, eight people with type 2 diabetes received vanadium for one month. Researchers found that vanadium was moderately successful in lowering blood sugar levels and had few side effects. Six of the eight patients taking vanadium during the study experienced gastrointestinal side effects during the first week of treatment, but these disappeared with continued use. In another small study of vanadium involving people with type 2 diabetes, published in the Journal of Clinical Investigation in 1995, researchers from the Albert Einstein College of Medicine reported that three weeks of treatment with the mineral improved the body's sensitivity to insulin. The effects of vanadium in lowering blood sugar levels persisted for up to two weeks after the drug was discontinued. A study published in the journal Diabetes in 1996, which involved seven people with type 2 diabetes as well as six nondiabetics, reported that vanadium improved insulin sensitivity in the diabetic subjects. Interestingly, the mineral did not improve sensitivity in the subjects who did not have the disease.

Sports Medicine

The use of vanadium by body builders appears to stem from a misunderstanding of the mineral's effects. Because insulin is a hormone that plays a role in increasing muscle mass, some weight lifters have taken vanadium in high dosages because they believe it will act like insulin and make them stronger. The problem is that vanadium does not appear to mimic insulin or increase its efficiency in healthy people, only in diabetics. For people considering vanadium as an aid in strengthening muscles, the scientific evidence is not very convincing. In one double-blind, placebo-controlled study published in the International Journal of Sport Nutrition in 1996, high dosages of vanadium were given to a few dozen weight trainers for 12 weeks. The bench press and leg extension weight-training exercises were used to measure results. Researchers found that there was no difference in body composition between those who took vanadium and those in the placebo group. Vanadium appeared to slightly enhance performance during the leg extension aspect of the study, but this advantage can be explained by other factors and cannot be attributed to the mineral itself with any certainty.

Osteoporosis

It is important not to confuse vanadium with calcium. Calcium is considered an essential building block of bone, and calcium supplements are often an important part of a bone-strengthening program in women with osteoporosis. Studies in mice indicating that vanadium is also deposited in bone have led to suggestions that the mineral may be effective as a potential treatment for osteoporosis. It is known, however, that minerals can be added to bones without actually making them stronger. There is no evidence that taking vanadium supplements can increase bone density in humans.

Preparations

The estimated dosage of vanadium, which is available as an over-the-counter dietary supplement, generally ranges from 10–30 mcg a day. It is important to remember, however, that safe and effective dosages for the mineral have not yet been established. Some practitioners of complementary medicine, such as Dr. Robert Atkins, have recommended dosages as high as 25–50 mg (milligrams, not micrograms) daily for people with diabetes. The long-term health risks associated with taking dosages in this range are unknown.

Even without taking supplements, most adults get anywhere between 10–60 mcg of vanadium through a normal diet. Some authorities believe it is safer for people to avoid vanadium supplements altogether and increase their intake of foods known to contain the mineral. These include meat, seafood, whole grains, vegetable oil, canned fruit juices, soy products, and such vegetables as green beans, corn, carrots, and cabbage. Alcoholic beverages such as wine and beer also contain vanadium. Over-dosing on the vanadium contained in food is not considered a significant risk because the mineral is present only in very small amounts in plants and animals.

Precautions

It is important not to exceed the recommended intake of vanadium without medical supervision. Studies conducted in rats suggest that high dosages of vanadium can be harmful. This results from the fact that the mineral tends to build up in the body, reaching dangerously high levels when taken in excess. The reader should keep in mind that high dosages of vanadium have not yet been proven to have significant health benefits. The long-term health risks associated with taking vanadium supplements (in any dosage) are unknown.

Side Effects

When taken in recommended dosages, vanadium has not been associated with any significant or bothersome side effects. At high dosages, vanadium has been known to cause stomach cramping and diarrhea as well as a green tongue.

Interactions

No drugs are known to interact adversely with vanadium. Smokers may absorb less of the mineral.

Resources

Books

Atkins, Robert C. Dr. Atkins' Vita-Nutrient Solution. New York: Simon & Schuster, 1998.

Miller, Lucinda G., and Wallace J. Murray. Herbal Medicinals: A Clinician's Guide. New York: Pharmaceutical Products Press, 1998.

Sifton, David W. PDR Family Guide to Natural Medicines and Healing Therapies. New York: Three Rivers Press, 1999.

Organizations

Herb Research Foundation. 1007 Pearl Street, Suite 200. Boulder, CO 80302.

National Diabetes Information Clearinghouse. 1 Information Way. Bethesda, MD 20892-3560.

Other

Discovery Health. http://www.discoveryhealth.com.

National Institute of Diabetes and Digestive and Kidney Diseases. http://www.niddk.nih.gov.

[Article by: Greg Annussek]

For more information on vanadium, visit Britannica.com.

A chemical element, atomic number 23, atomic weight 50.942, symbol V. Its salts have been used in treating various diseases.

• v. poisoning — in humans poisoning is usually by inhalation causing respiratory irritation and pneumonia. In livestock poisoning is by ingestion of contaminated pasture and manifested by diarrhea, incoordination and oliguria.

titanium ← vanadium → chromium - ↑ V ↓ Nb 23V Periodic table
Appearance
blue-silver-grey metal
General properties
Name, symbol, number	vanadium, V, 23
Element category	transition metal
Group, period, block	5, 4, d
Standard atomic weight	50.9415(1) g·mol−1
Electron configuration	[Ar] 3d3 4s2
Electrons per shell	2, 8, 11, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	6.0 g·cm−3
Liquid density at m.p.	5.5 g·cm−3
Melting point	2183 K, 1910 °C, 3470 °F
Boiling point	3680 K, 3407 °C, 6165 °F
Heat of fusion	21.5 kJ·mol−1
Heat of vaporization	459 kJ·mol−1
Specific heat capacity	(25 °C) 24.89 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k at T/K 2101 2289 2523 2814 3187 3679
Atomic properties
Oxidation states	5, 4, 3, 2, 1, -1 (amphoteric oxide)
Electronegativity	1.63 (Pauling scale)
Ionization energies (more)	1st: 650.9 kJ·mol−1
	2nd: 1414 kJ·mol−1
	3rd: 2830 kJ·mol−1
Atomic radius	134 pm
Covalent radius	153±8 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 197 nΩ·m
Thermal conductivity	(300 K) 30.7 W·m−1·K−1
Thermal expansion	(25 °C) 8.4 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 4560 m/s
Young's modulus	128 GPa
Shear modulus	47 GPa
Bulk modulus	160 GPa
Poisson ratio	0.37
Mohs hardness	6.7
CAS registry number	7440-62-2
Most stable isotopes
Main article: Isotopes of vanadium
iso NA half-life DM DE (MeV) DP 48V syn 15.9735 d ε+β+ 4.0123 48Ti 49V syn 330 d ε 0.6019 49Ti 50V 0.25% 1.5×1017y ε 2.2083 50Ti β− 1.0369 50Cr 51V 99.75% 51V is stable with 28 neutrons
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Vanadium (pronounced /vəˈneɪdiəm/, və-NAY-dee-əm) is the chemical element with the symbol V and atomic number 23. It is a soft, silvery grey, ductile transition metal. The formation of an oxide layer stabilizes the metal against oxidation. Andrés Manuel del Río discovered vanadium in 1801 by analyzing the mineral vanadinite, and named it erythronium. Four years later, however, he was convinced by other scientists that erythronium was identical to chromium. The element was rediscovered in 1831 by Nils Gabriel Sefström, who named it vanadium after the Norse goddess of beauty and fertility, Vanadis (Freya). Both names were attributed to the wide range of colors found in vanadium compounds.

The element occurs naturally in about 65 different minerals and in fossil fuel deposits. It is produced in China and Russia from steel smelter slag; other countries produce it either from the flue dust of heavy oil, or as a byproduct of uranium mining. It is mainly used to produce specialty steel alloys such as high speed tool steels. The compound vanadium pentoxide is used as a catalyst for the production of sulfuric acid. Vanadium is found in many organisms, and is used by some life forms as an active center of enzymes.

Contents 1 History 2 Characteristics 2.1 Isotopes 2.2 Chemistry and compounds 2.2.1 Oxy and oxo compounds 2.2.2 Halide compounds 2.2.3 Coordination compounds 2.2.4 Organometallic compounds 3 Occurrence 4 Production 5 Applications 5.1 Alloys 5.2 Other uses 6 Biological role 7 Safety 8 References 9 External links

History

Vanadium was originally discovered by Andrés Manuel del Río, a Spanish-born Mexican mineralogist, in 1801. Del Río extracted the element from a sample of Mexican "brown lead" ore, later named vanadinite. He found that its salts exhibit a wide variety of colors, and as a result he named the element panchromium (Greek: all colors). Later, Del Río renamed the element erythronium as most of its salts turned red upon heating. In 1805, the French chemist Hippolyte Victor Collet-Descotils, backed by del Río's friend, Baron Alexander von Humboldt, incorrectly declared that del Río's new element was only an impure sample of chromium. Del Río accepted the Collet-Descotils' statement, and retracted his claim.^[1]

In 1831, the Swedish chemist, Nils Gabriel Sefström, rediscovered the element in a new oxide he found while working with iron ores. Later that same year, Friedrich Wöhler confirmed del Río's earlier work.^[2] Sefström chose a name beginning with V, which had not been assigned to any element yet. He called the element vanadium after Vanadis (another name for Freya, the Norse goddess of beauty and fertility), because of the many beautifully colored chemical compounds it produces.^[2] In 1831, the geologist George William Featherstonhaugh suggested that vanadium should be renamed "rionium" after del Río, but this suggestion was not followed.^[3]

1910 Model T

The isolation of vanadium metal proved difficult. In 1831, Berzelius reported the production of the metal, but Henry Enfield Roscoe showed that Berzelius had in fact produced the nitride, vanadium nitride (VN). Roscoe eventually produced the metal in 1867 by reduction of vanadium(III) chloride, VCl₃, with hydrogen.^[4] In 1927, pure vanadium was produced by reducing vanadium pentoxide with calcium.^[5] The first large scale industrial use of vanadium in steels was found in the chassis of the Ford Model T, inspired by French race cars. Vanadium steel allowed for reduced weight while simultaneously increasing tensile strength.^[6]

Characteristics

Vanadium is a soft, ductile, silver-grey metal. It has good resistance to corrosion and it is stable against alkalis, sulfuric and hydrochloric acids.^[7] It is oxidized in air at about 933 K (660 °C, 1220 °F), although an oxide layer forms even at room temperature.

Isotopes

Main article: Isotopes of vanadium

Naturally occurring vanadium is composed of one stable isotope ⁵¹V and one radioactive isotope ⁵⁰V. The latter has a half-life of 1.5×10¹⁷ years and a natural abundance 0.25%. ⁵¹V has a nuclear spin of 7/2 which is useful for NMR spectroscopy.^[8] A number of 24 artificial radioisotopes have been characterized, ranging in mass number from 40 to 65. The most stable of these isotopes are ⁴⁹V with a half-life of 330 days, and ⁴⁸V with a half-life of 15.9735 days. All of the remaining radioactive isotopes have half-lives shorter than an hour, most of which are below 10 seconds. At least 4 isotopes have metastable excited states.^[8] Electron capture is the main decay mode for isotopes lighter than the ⁵¹V. For the heavier ones, the most common mode is beta decay. The electron capture reactions lead to the formation of element 22 (titanium) isotopes, while for beta decay, it leads to element 24 (chromium) isotopes.

Chemistry and compounds

See also: Category:Vanadium compounds

Vanadium(V) oxide is a catalyst in the Contact process for producing sulfuric acid

The chemistry of vanadium is noteworthy for the accessibility of four adjacent oxidation states. The common oxidation states of vanadium are +2 (lilac), +3 (green), +4 (blue) and +5 (yellow). Vanadium(II) compounds are reducing agents, and vanadium(V) compounds are oxidizing agents. Vanadium(IV) compounds often exist as vanadyl derivatives which contain the VO²⁺ center.^[7]

Metavanadate chains

Ammonium vanadate(V) (NH₄VO₃) can be successively reduced with elemental zinc to obtain the different colors of vanadium in these four oxidation states. Lower oxidation states occur in compounds such as V(CO)₆, [V(CO)₆]⁻ and substituted derivatives.^[7]

The vanadium redox battery utilizes these oxidation states; conversions of these oxidation states is illustrated by the reduction of a strongly acidic solution of a vanadium(V) compound with zinc dust. The initial yellow color characteristic of the vanadate ion, VO3−4, is replaced by the blue color of [VO(H₂O)₅]²⁺, followed by the green color of [V(H₂O)₆]³⁺ and then violet, due to [V(H₂O)₆]²⁺.^[7]

The most commercially important compound is vanadium pentoxide, which is used as a catalyst for the production of sulfuric acid.^[7] This compound oxidizes sulfur dioxide (SO₂) to the trioxide (SO₃). In this redox reaction, sulfur is oxidized from +4 to +6, and vanadium is reduced from +5 to +3:

V₂O₅ + 2 SO₂ → V₂O₃ + 2 SO₃

The catalyst is regenerated by oxidation with air:

V₂O₃ + O₂ → V₂O₅

Oxy and oxo compounds

The Pourbaix diagram for vanadium in water.^[9]

The oxyanion chemistry of vanadium(V) is complex. The vanadate ion, VO3−4, is present in dilute solutions at high pH. On acidification, HVO2−4 and H₂VO−4 are formed, analogous to HPO2−4 and H₂PO−4. The acid dissociation constants for the vanadium and phosphorus series are remarkably similar. In more concentrated solutions many polyvanadates are formed. Chains, rings and clusters involving tetrahedral vanadium, analogous to the polyphosphates, are known. In addition, clusters such as the decavanadates V₁₀O4−28 and HV₁₀O3−28, which predominate at pH 4-6, are formed in which compound is octahedral about vanadium.^[7]

The correspondence between vanadate and phosphate chemistry can be attributed to the similarity in size and charge of phosphorus(V) and vanadium(V). Orthovanadate VO3−4 is used in protein crystallography^[10] to study the biochemistry of phosphate.^[11]

Halide compounds

Several halides are known for oxidation states +2, +3 and +4. VCl₄ is the most important commercially. This liquid is mainly used as a catalyst for polymerization of dienes.

Coordination compounds

A ball-and-stick model of VO(acac)₂

Vanadium's early position in the transition metal series lead to three rather unusual features of the coordination chemistry of vanadium. Firstly, metallic vanadium has the electronic configuration [Ar]4s²3d³, so compounds of vanadium are relatively electron-poor. Consequently, most binary compounds are Lewis acids (electron pair acceptors); examples are all the halides forming octahedral adducts with the formula VX_nL_6−n (X = halide; L = other ligand). Secondly, the vanadium ion is rather large and can achieve coordination numbers higher than 6, as is the case in [V(CN)₇]⁴⁻. Thirdly, the vanadyl ion, VO²⁺, is featured in many complexes of vanadium(IV) such as vanadyl acetylacetonate (V(=O)(acac)₂). In this complex, the vanadium is 5-coordinate, square pyramidal, meaning that a sixth ligand, such as pyridine, may be attached, though the association constant of this process is small. Many 5-coordinate vanadyl complexes have a trigonal bypyramidal geometry, such as VOCl₂(NMe₃)₂.^[12]

Organometallic compounds

Main article: Organovanadium chemistry

Organometallic chemistry of vanadium is well developed, but organometallic compounds are of minor commercial significance. Vanadocene dichloride is a versatile starting reagent and even finds minor applications in organic chemistry.^[13] Vanadium carbonyl, V(CO)₆, is a rare example of a metal carbonyl containing an unpaired electron, but which exists without dimerization. The addition of an electron yields V(CO)−6 (isoelectronic with Cr(CO)₆), which may be further reduced with sodium in liquid ammonia to yield V(CO)3−6 (isoelectronic with Fe(CO)₅).^[14][15]

Occurrence

See also: Category:Vanadate minerals

Vanadinite

Metallic vanadium is not found in nature, but is known to exist in about 65 different minerals. Economically significant examples include patronite (VS₄),^[16] vanadinite (Pb₅(VO₄)₃Cl), and carnotite (K₂(UO₂)₂(VO₄)₂·3H₂O). Much of the world's vanadium production is sourced from vanadium-bearing magnetite found in ultramafic gabbro bodies. Vanadium is mined mostly in South Africa, north-western China, and eastern Russia. In 2007 these three countries mined more than 95 % of the 58,600 tonnes of produced vanadium.^[17]

Vanadium is also present in bauxite and in fossil fuel deposits such as crude oil, coal, oil shale and tar sands. In crude oil, concentrations up to 1200 ppm have been reported. When such oil products are burned, the traces of vanadium may initiate corrosion in motors and boilers.^[18] An estimated 110,000 tonnes of vanadium per year are released into the atmosphere by burning fossil fuels.^[19] Vanadium has also been detected spectroscopically in light from the Sun and some other stars.^[20]

Production

Ferrovanadium chunks

Most vanadium is used as ferrovanadium as an additive to improve steels. Ferrovanadium is produced directly by reducing a mixture of vanadium oxide, iron oxides and iron in an electric furnace. Vanadium-bearing magnetite iron ore is the main source for the production of vanadium.^[21] The vanadium ends up in pig iron produced from vanadium bearing magnetite. During steel production, oxygen is blown into the pig iron, oxidizing the carbon and most of the other impurities, forming slag. Depending on the used ore, the slag contains up to 25% of vanadium.^[21]

Vanadium metal is obtained via a multistep process that begins with the roasting of crushed ore with NaCl or Na₂CO₃ at about 850 °C to give sodium metavanadate (NaVO₃). An aqueous extract of this solid is acidified to give "red cake", a polyvanadate salt, which is reduced with calcium metal. As an alternative for small scale production, vanadium pentoxide is reduced with hydrogen or magnesium. Many other methods are also in use, in all of which vanadium is produced as a byproduct of other processes.^[21] Purification of vanadium is possible by the crystal bar process developed by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925. It involves the formation of the metal iodide, in this example vanadium(III) iodide, and the subsequent decomposition to yield pure metal.^[22]

2 V + 3 I₂ 2 VI₃

Applications

Tool made from vanadium steel

Vanadium

Alloys

Approximately 85% of vanadium produced is used as ferrovanadium or as a steel additive.^[21] The considerable increase of strength in steel containing small amounts of vanadium was discovered in the beginning of the 20th century,^[23] and from that time vanadium steel was used for applications in axles, bicycle frames, crankshafts, gears, and other critical components. Vanadium forms stable nitrides and carbides, resulting in a significant increase in the strength of the steel. There are two groups of vanadium containing steel alloy groups. Vanadium high-carbon steel alloys containing 0.15 to 0.25 percent vanadium and high speed tool steels (HSS) with a vanadium content ranges from 1 % to 5 %. For high speed tool steels, a hardness above HRC 60 can be achieved. HSS steel is used in surgical instruments and tools.^[24]

Vanadium stabilizes the beta form of titanium and increases the strength and temperature stability of titanium. Mixed with aluminium in titanium alloys it is used in jet engines and high-speed airframes. One of the common alloys is Titanium 6AL-4V, a titanium alloy with 6% aluminium and 4% vanadium.^[25]

Other uses

Vanadium is compatible with iron and titanium, therefore vanadium foil is used in cladding titanium to steel.^[26] The moderate thermal neutron-capture cross-section and the short half-life of the isotopes produced by neutron capture makes vanadium a suitable material for the inner structure of a fusion reactor.^[27][28] Several vanadium alloys show superconducting behaviour. The first A15 phase superconductor was a vanadium compound, V₃Si, which was discovered in 1952.^[29] Vanadium-gallium tape is used in superconducting magnets (17.5 teslas or 175,000 gauss). The structure of the superconducting A15 phase of V₃Ga is similar to that of the more common Nb₃Sn and Nb₃Ti.^[30]

The most common oxide of vanadium Vanadium pentoxide, V₂O₅, is used as a catalyst in manufacturing sulfuric acid by the contact process^[31] and as an oxidizer in maleic anhydride production.^[32] Vanadium pentoxide is also used in making ceramics.^[33] Another oxide of vanadium, vanadium dioxide VO₂, is used in the production of glass coatings, which blocks infrared radiation (and not visible light) at a specific temperature.^[34] Vanadium oxide can be used to induce color centers in corundum to create simulated alexandrite jewelry, although alexandrite in nature is a chrysoberyl.^[35] The possibility to use vanadium redox couples in both half-cells, thereby eliminating the problem of cross contamination by diffusion of ions across the membrane is the advantage of vanadium redox rechargeable batteries.^[36] Vanadate can be used for protecting steel against rust and corrosion by electrochemical conversion coating.^[37] Lithium vanadium oxide has been proposed for use as a high energy density anode for lithium ion batteries, at 745 Wh/l when paired with a lithium cobalt oxide cathode.^[38] It has been proposed by some researchers that a small amount, 40 to 270 ppm, of vanadium in Wootz steel and Damascus steel, significantly improves the strength of the material, although it is unclear what the source of the vanadium was.^[39]

Biological role

Ascidiacea contain vanadium.

Amanita muscaria contains amavadin.

Vanadium plays a very limited role in biology. A vanadium-containing nitrogenase is used by some nitrogen-fixing micro-organisms. Vanadium is essential to ascidians or sea squirts in vanadium chromagen proteins. The concentration of vanadium in their blood is more than 100 times higher than the concentration of vanadium in the seawater around them. Rats and chickens are also known to require vanadium in very small amounts and deficiencies result in reduced growth and impaired reproduction.^[40] Vanadium is a relatively controversial dietary supplement, primarily for increasing insulin sensitivity^[41] and body-building. Whether it works for the latter purpose has not been proven, and there is some evidence that athletes who take it are merely experiencing a placebo effect.^[42] Vanadyl sulfate may improve glucose control in people with type 2 diabetes.^{[43][44][45][46][47]}. In addition, decavanadate and oxovanadates are species that potentially have many biological activities and that have been successfully used as tools in the comprehension of several biochemical processes.^[48]

Ten percent of the blood cell pigment of the sea cucumber is vanadium. Just as the horseshoe crab has blue blood due to copper in hemocyanin, and land animals have red blood from the iron in hemoglobin, the blood of the sea cucumber is yellow because of the vanadium in the vanabin pigment.^[49] Nonetheless, there is no evidence that vanabins carry oxygen, in contrast to hemoglobin and hemocyanin.^[50] Several species of macrofungi, namely Amanita muscaria and related species, accumulate vanadium (up to 500 mg/kg in dry weight). Vanadium is present in the coordination complex, amavadin,^[51] in fungal fruit-bodies. However, the biological importance of the accumulation process is unknown.^[52][53]

Safety

All vanadium compounds should be considered to be toxic. Tetravalent VOSO₄ has been reported to be over 5 times more toxic than trivalent V₂O₃.^[54] The Occupational Safety and Health Administration (OSHA) has set an exposure limit of 0.05 mg/m³ for vanadium pentoxide dust and 0.1 mg/m³ for vanadium pentoxide fumes in workplace air for an 8-hour workday, 40-hour work week.^[55] The National Institute for Occupational Safety and Health (NIOSH) has recommended that 35 mg/m³ of vanadium be considered immediately dangerous to life and health. This is the exposure level of a chemical that is likely to cause permanent health problems or death.^[55]

Vanadium compounds are poorly absorbed through the gastrointestinal system. Inhalation exposures to vanadium and vanadium compounds result primarily in adverse effects on the respiratory system.^[56][57][58] Quantitative data are, however, insufficient to derive a subchronic or chronic inhalation reference dose. Other effects have been reported after oral or inhalation exposures on blood parameters,^[59][60] on liver,^[61] on neurological development in rats,^[62] and other organs.^[63]

There is little evidence that vanadium or vanadium compounds are reproductive toxins or teratogens. Vanadium pentoxide was reported to be carcinogenic in male rats and male and female mice by inhalation in an NTP study,^[64] although the interpretation of the results has recently been disputed.^[65] Vanadium has not been classified as to carcinogenicity by the U.S. EPA.^[66]

Vanadium traces in diesel fuels present a corrosion hazard; it is the main fuel component influencing high temperature corrosion. During combustion, it oxidizes and reacts with sodium and sulfur, yielding vanadate compounds with melting points down to 530 °C, which attack the passivation layer on steel, rendering it susceptible to corrosion. The solid vanadium compounds also cause abrasion of engine components.

References

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v • d • e   Vanadium compounds VBr3 · VC · V(CO)6 · VCl2 · VCl3 · VCl4 · VF3 · VF4 · VI3 · VN · VO · VO2 · VOCl3 · VOF3 · V2O3 · V2O5 · V2(SO4)3

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