Vanadium

VANADIUM, a metallic chemical element belonging to a family which also includes columbium (q.v.) and tantalum (q.v.). Although one of the rarer elements, vanadium (symbol V, atomic number 23, atomic weight 51), is fairly widely distributed, and since its application in the production of special steels (q.v.), several of its minerals have been extensively exploited.

Occurrence.

Patronite, native vanadium sulphide, which is an important source of the metal, occurs in Peru associated with iron pyrites in coal deposits. Carnotite, potassium uranyl vanadate, K20,2UO2,V205,3H20, is found in Colorado and Utah and is extensively worked for vanadium, radium and uranium. Vanadinite [Pb {3Pb3(VO4)2} ]C12, isomorphous with pyromor phite and mimetite, occurs as deep red crystals in Arizona, New Mexico, South East Africa and Northern Rhodesia. Other vanadium minerals are descloizite, a lead zinc vanadate found in New Mexico and Arizona, and roscoelite, a micaceous mineral in which aluminium is partially replaced by vanadium; the latter occurs in Colorado and is an important source of the metal. Mottramite, a basic vanadate of lead and copper, is found in Cheshire. In addition to these minerals in which it is a major constituent, vanadium occurs in numerous rocks and deposits. Many iron ores such as the minette of Lorraine and the German and Swedish iron ores contain as much as 0.3 to 0.7% of vanadium pentoxide.

A new metal was first observed in vanadinite by M. Del Rio (i8oi). Subsequently N. G. Sefstr5m (183o) isolated its corn pounds from the slag of Taberg iron and having noticed the beautiful colours which they displayed in solution, he called the new metal vanadium, in allusion to Vanadis, a name sometimes given to Freya, the Scandinavian goddess of beauty. F. Wohler (183o) showed that vanadium was identical with Del Rio's erythronium and a more extended study of the metal and its compounds was made by J. J. Berzelius (1831). In 1868 H. E. Roscoe proved that the supposed vanadium obtained by the earlier investigators was chiefly the nitride or oxide of the element and by a brilliant application of the principle of isomorphism, he showed that vanadium was a member, together with phosphorus and arsenic, of Group V. of the periodic classification.

Extraction of Vanadium Oxide from its Minerals.—Pat

ronite is roasted and fused with sodium carbonate, the sodium vanadate thus formed is extracted with water, and the addition of ammonium chloride then precipitates ammonium vanadate. On ignition this salt leaves vanadium pentoxide. The vanadium when dissolved as vanadate may also be precipitated as calcium or ferrous vanadate. The native vanadates, carnotite, mottramite, etc., are extracted with concentrated hydrochloric acid; the acid extract and washings are evaporated with ammonium chloride, when ammonium metavanadate separates. (For further details of separation consult special treatises indicated in the bibli ography.) Metallic Vanadium.—The metal was first obtained by Roscoe on passing hydrogen over the heated dichloride. It is also prepared by reducing the p'entoxide with "mischmetall," a mixture of the rare-earth metals. It has been prepared by the aluminium reduction method from vanadium trioxide and by the electroly sis of sodium vanadate in hydrochloric acid.

Vanadium is a silvery white metal with specific gravity 5.5 to 5.89; its melting point is 1,71o° C. The fusibility is diminished by the presence of vanadium carbide or oxide. Vanadium is stable in air and is unacted on by bromine water, aqueous alkalis, hydrochloric acid or cold sulphuric acid. It is dissolved by hydro fluoric acid or hot sulphur acid to green solutions. Molten potash or potassium nitrate attacks the metal forming potassium vana date. Its alloy with aluminium containing up to io% of vanadium is malleable. Cuprovanadium is an alloy employed in copper castings and bronzes.

Ferrovanadium.

The greater part—about 90%—of the vanadium extracted is used in form of ferrovanadium alloys con taining 25 to 30% of vanadium. Such alloys are produced by the "thermite" process on iron vanadate, by the reduction of this compound with carbon in the electric furnace, or by electrolysis of vanadium pentoxide dissolved either in fused ferrosilicon or in a molten mixture of iron fluoride and calcium carbide. When vanadium is added to steel it effects the removal of oxygen and nitrogen carrying these into the slag, and the portion which remains in the metal increases the tensile strength, toughness and elastic limit of the steel. These improvements are effected by comparatively small amounts ranging from 0.05 to 0.5%.