Vanadium

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23 titaniumvanadiumchromium
-

V

Nb
V-TableImage.png
General
Name, Symbol, Number vanadium, V, 23
Chemical series transition metals
Group, Period, Block 5, 4, d
Appearance silver-grey metal
V,23.jpg
Atomic mass 50.9415(1) g/mol
Electron configuration [Ar] 3d3 4s2
Electrons per shell 2, 8, 11, 2
Physical properties
Phase solid
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)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2101 2289 2523 2814 3187 3679
Atomic properties
Crystal structure cubic body centered
Oxidation states 2, 3, 4, 5
(amphoteric oxide)
Electronegativity 1.63 (Pauling scale)
Ionization energies
(more)
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
Miscellaneous
Magnetic ordering  ???
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
Poisson ratio 0.37
Mohs hardness 7.0
Vickers hardness 628 MPa
Brinell hardness 628 MPa
CAS registry number 7440-62-2
Notable 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% V is stable with 28 neutrons

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.

Contents

Occurrence

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.

History

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.

Isolation

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.

Notable characteristics

Vanadium is a transition metal in period 4 of the periodic table, situated between titanium and chromium. It is also at the top of group 5 (former group 5B), above niobium and tantalum.

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.

Isotopes

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.

Compounds

  • Vanadium(V) oxide or vanadium pentoxide (V2O5): This poisonous orange solid is the most important compound of vanadium. Upon heating, it can reversibly lose oxygen to the air. It is used as a catalyst principally in the production of sulfuric acid. It is the source of vanadium for the manufacture of ferrovanadium. It can be used as a dye and color-fixer.
  • Vanadyl sulfate or vanadium(IV) sulfate oxide hydrate (VOSO4): It is a relatively controversial dietary supplement, used primarily for increasing insulin levels 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.
  • Vanadium(IV) chloride (VCl4): This soluble form of vanadium is commonly used in the laboratory. It reacts violently with water. The oxidation state V(IV), the reduced form of V(V), commonly occurs after anaerobic respiration by certain metal-reducing bacteria.

Applications

  • Approximately 80 percent of vanadium produced is used as ferrovanadium or as a steel additive. Vanadium steel alloys are used in axles, crankshafts, gears, and other products. Vanadium is also used in specialty stainless steel for surgical instruments and high-speed tools.
  • Vanadium is mixed with aluminum in titanium alloys for jet engines and high-speed airframes.
  • It is an important carbide stabilizer in the production of steels.
  • Given its low neutron cross-section for nuclear fission reactions, vanadium has applications in nuclear reactors.
  • Vanadium foil is used in cladding titanium to steel.
  • Vanadium-gallium tape is used in superconducting magnets (175,000 gauss).
  • Vanadium pentoxide is a catalyst for manufacturing sulfuric acid and maleic anhydride. It is also used in making ceramics.
  • Glass coated with vanadium dioxide (VO2) can block infrared radiation (and not visible light) at a specific temperature.
  • It is present in some electrical fuel cells and storage batteries such as vanadium redox batteries.
  • It is added to corundum to make simulated Alexandrite jewelry.
  • Vanadate electrochemical conversion coatings help protect steel against rust and corrosion.

Biological role

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.

Mineral supplement in drinking water

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.

Toxicity of vanadium compounds

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).

Precautions

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.

See also

References

  • Vanadium Los Alamos National Laboratory. Retrieved July 10, 2007.
  • Greenwood, N. N.; and A. Earnshaw. (1998). Chemistry of the Elements, 2nd ed. Burlington, MA: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654. Online version available. Retrieved July 10, 2007.
  • Cotton, F. Albert; and Geoffrey Wilkinson. (1980). Advanced Inorganic Chemistry, 4th ed. New York: Wiley. ISBN 0471027758

External links

All links retrieved July 10, 2007.

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