|Name, Symbol, Number||vanadium, V, 23|
|Chemical series||transition metals|
|Group, Period, Block||5, 4, d|
|Atomic mass||50.9415(1) g/mol|
|Electron configuration||[Ar] 3d3 4s2|
|Electrons per shell||2, 8, 11, 2|
|Density (near r.t.)||6.0 g/cm³|
|Liquid density at m.p.||5.5 g/cm³|
|Melting point||2183 K
(1910 °C, 3470 °F)
|Boiling point||3680 K
(3407 °C, 6165 °F)
|Heat of fusion||21.5 kJ/mol|
|Heat of vaporization||459 kJ/mol|
|Heat capacity||(25 °C) 24.89 J/(mol·K)|
|Crystal structure||cubic body centered|
|Oxidation states||2, 3, 4, 5
|Electronegativity||1.63 (Pauling scale)|
|1st: 650.9 kJ/mol|
|2nd: 1414 kJ/mol|
|3rd: 2830 kJ/mol|
|Atomic radius||135 pm|
|Atomic radius (calc.)||171 pm|
|Covalent radius||125 pm|
|Electrical resistivity||(20 °C) 197 nΩ·m|
|Thermal conductivity||(300 K) 30.7 W/(m·K)|
|Thermal expansion||(25 °C) 8.4 µm/(m·K)|
|Speed of sound (thin rod)||(20 °C) 4560 m/s|
|Speed of sound (thin rod)||(r.t.) 128 m/s|
|Shear modulus||47 GPa|
|Bulk modulus||160 GPa|
|Vickers hardness||628 MPa|
|Brinell hardness||628 MPa|
|CAS registry number||7440-62-2|
Vanadium (chemical symbol V, atomic number 23) is a rare, silver-gray metal. It is found combined in several minerals and is one of the 26 elements that commonly occur in living things. It is used mainly in various alloys. For instance, it is an additive in specialty stainless steel for surgical instruments and high-speed tools. It is mixed with aluminum in titanium alloys for jet engines and high-speed airframes. In addition, it is present in vanadium redox batteries, and it is added to corundum to make simulated Alexandrite jewelry. Vanadium-gallium tape is used in superconducting magnets, and vanadium pentoxide is a catalyst for manufacturing sulfuric acid and other products.
Vanadium is never found as a free element in nature, but it occurs in about 65 different minerals. Among them are patronite (VS4), vanadinite (Pb5(VO4)3Cl), and carnotite (K2(UO2)2(VO4)2.3H2O). It is also present in bauxite and carbon-containing deposits such as crude oil, coal, oil shale, and tar sands. It has also been detected spectroscopically in light from the Sun and some other stars.
Vanadium was originally discovered by Andrés Manuel del Río, a Spanish mineralogist in Mexico City, in 1803. Using a mineral called "brown lead" (now named vanadinite), he prepared several salts. Their colors reminded him of chromium salts, so he named the element "panchromium." He later renamed it "erythronium" (meaning "red") because most of the salts turned red when heated. French chemist Hippolyte Victor Collet-Descotils incorrectly declared that del Rio's new element was only impure chromium. Del Rio thought himself to be mistaken and accepted the French chemist's statement, which was backed by del Rio's friend, Baron Alexander von Humboldt.
In 1831, Nils Gabriel Sefström of Sweden rediscovered vanadium in a new oxide he found while working with some iron ores. Later that same year, Friedrich Wöhler confirmed del Rio's earlier work. Later, George William Featherstonhaugh, one of the first U.S. geologists, suggested the element be named "rionium" after Del Rio, but that never happened.
Metallic vanadium was isolated by Henry Enfield Roscoe in 1867, by reducing vanadium(III) chloride (VCl3) with hydrogen. The name vanadium comes from Vanadis, a goddess in Scandinavian mythology, because the element has beautiful, multicolored chemical compounds.
Commercially, metallic vanadium is usually recovered in sufficient quantities as a byproduct of other processes. Production of samples in the laboratory is therefore not normally required.
Industrial production involves the heating of vanadium ore or residues from other processes with sodium chloride (NaCl) or sodium carbonate (Na2CO3) at about 850 °C, to give sodium vanadate (NaVO3). This product is dissolved in water and acidified to give a red solid, which in turn is melted to generate a crude form of vanadium pentoxide (V2O5). Reduction of the pentoxide with calcium gives pure vanadium. An alternative suitable for small-scale production is the reduction of vanadium pentachloride (VCl5) with hydrogen or magnesium. Various other methods are also employed.
Industrially, most vanadium is used as an additive to improve steels. Rather than proceed from pure vanadium metal, it is often sufficient to react the vanadium pentoxide with crude iron. This process produces ferrovanadium, which is suitable for further work.
Soft and ductile, vanadium is resistant to corrosion by alkalis, sulfuric acid, and hydrochloric acid. It oxidizes readily at a temperature of about 933 Kelvin (K). It has good structural strength and a low neutron cross-section for nuclear fission reactions, making it useful for nuclear applications. Although a metal, its oxides have acidic properties, similar to the oxides of chromium and manganese.
Common oxidation states of vanadium include +2, +3, +4 and +5. In a popular experiment, when ammonium vanadate (NH4VO3) is reduced with zinc metal, colored products with these four oxidation states are obtained. A +1 oxidation state is rarely seen.
Naturally occurring vanadium is composed of one stable isotope, 51V, and one radioactive isotope, 50V, with a half-life of 1.5×1017 years. Many artificial radioisotopes have been characterized, with mass numbers ranging from 40 to 65. The most stable of these is 49V, with a half-life of 330 days, followed by 48V, with a half-life of 15.9735 days. All the remaining radioactive isotopes have half-lives shorter than an hour, the majority of them being less than 10 seconds.
In biological systems, vanadium is an essential component of some enzymes, particularly the vanadium nitrogenase used by some nitrogen-fixing microorganisms. Vanadium is also needed by ascidians or sea squirts in vanadium chromagen proteins. The concentration of vanadium in their blood is more than one hundred times higher than that in the surrounding seawater. Rats and chickens are also known to require vanadium in very small amounts and deficiencies result in reduced growth and impaired reproduction.
Administration of oxovanadium compounds has been shown to alleviate diabetes mellitus symptoms in certain animal models and humans. Much like the chromium effect on sugar metabolism, the mechanism of this effect is unknown.
In Japan, vanadium pentoxide (V2O5) is marketed as mineral health supplement present in drinking water taken mainly from the slopes of Mount Fuji. The water's vanadium pentoxide content ranges from about 80 to 130 μg/liter. It is marketed as being effective against diabetes, eczema, and obesity, but there is no mention of its toxicity.
The toxicity of vanadium depends on its physicochemical state—particularly, its valence state and solubility. Pentavalent VOSO4 has been reported to be more than five times as toxic as trivalent V2O3 (Roschin 1967). Vanadium compounds are poorly absorbed through the gastrointestinal system. Inhalation exposures to vanadium and vanadium compounds result primarily in adverse effects to the respiratory system (Sax 1984; ATSDR 1990). Quantitative data are, however, insufficient to derive a subchronic or chronic inhalation.
There is little evidence that vanadium or vanadium compounds are reproductive toxins or teratogens. There is also no evidence that any vanadium compound is carcinogenic, but very few adequate studies are available for evaluation. Vanadium has not been classified regarding carcinogenicity by the U.S. Environmental Protection Agency (EPA) (1991a).
Powdered metallic vanadium is a fire hazard, and unless known otherwise, all vanadium compounds should be considered highly toxic. Generally, the higher the oxidation state of vanadium, the more toxic the compound is. The most dangerous one is vanadium pentoxide.
The U.S. Occupational Safety and Health Administration (OSHA) has set an exposure limit of 0.05 milligrams per cubic meter (mg/m3) for vanadium pentoxide dust and 0.1 mg/m3 for vanadium pentoxide fumes in workplace air, for an eight-hour workday, 40-hour work week. 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 corresponds to the exposure level that is likely to cause permanent health problems or death.
All links retrieved January 14, 2016.
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