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Vanadium —(Scandinavian goddess, Vanadis), V; atomic weight 50.9415; atomic number 23; melting point 1890 ± 10°C; boiling point 3380°C; specific gravity 6.11 (18.7°C); valence 2, 3, 4, or 5.

Vanadium was first discovered by del Rio in 1801. Unfortunately, a French chemist incorrectly declared del Rio's new element was only impure chromium; del Rio thought himself to be mistaken and accepted the French chemist's statement. The element was rediscovered in 1830 by Sefstrom, who named the element in honor of the Scandinavian goddess Vanadis because of its beautiful multicolored compounds. It was isolated in nearly pure form by Roscoe, in 1867, who reduced the chloride with hydrogen.

Vanadium of 99.3 to 99.8% purity was not produced until 1927. Vanadium is found in about 65 different minerals among which are carnotite, roscoelite, vanadinite, and patronite—important sources of the metal. Vanadium is also found in phosphate rock and certain iron ores, and is present in some crude oils in the form of organic complexes. It is also found in small percentages in meteorites. Commercial production from petroleum ash holds promise as an important source of the element. High-purity ductile vanadium can be obtained by reduction of vanadium trichloride with magnesium or with magnesium-sodium mixtures. Much of the vanadium metal being produced is now made by calcium reduction of V2O5 in a pressure vessel, an adaption of a process developed by McKechnie and Seybolt.

Natural vanadium is a mixture of two isotopes, V50 (0.24%) and V51 (99.76%). V50 is slightly radioactive, having a half-life of 6 × 1015 years. Seven other unstable isotopes are recognized. Pure vanadium is a bright white metal, and is soft and ductile. It has good corrosion resistance to alkalis, sulfuric and hydrochloric acid, and salt waters, but the metal oxidizes readily above 660°C. The metal has good structural strength and a low-fission neutron cross section, making it useful in nuclear applications. Vanadium is used in producing rust-resistant, spring, and high-speed tool steels. It is an important carbide stabilizer in making steels. About 80% of the vanadium now produced is used as ferrovanadium or as a steel additive. Vanadium foil is used as a bonding agent in cladding titanium to steel.

Vanadium pentoxide is used in ceramics and as a catalyst. It is also used as a mordant in dyeing and printing fabrics and in the manufacture of aniline black. Vanadium-gallium tape has been used in producing a superconductive magnet with a field of 175,000 gauss. Vanadium and its compounds are toxic and should be handled with care. Exposure to V2O2 dust (as V) should not exceed the ceiling value of 0.05 mg/M3, and exposure to V2O2 fume (as V) should not exceed 0.1 mg/M3 (8-hr time-weighted average—40-hr week). Ductile vanadium is commercially available.

Número de vistos: 17467 Artículo añadido: 2 February 2011 Último artículo modificado: 11 February 2011 © Copyright 2010-2021 Volver arriba
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