1911 Encyclopædia Britannica/Vanadium

VANADIUM [symbol, V; atomic weight, 51.2 (O=16)], a metallic chemical element. It was first mentioned in 1801 by M. del Rio (Gilb. Ann., 1801, 71, p. 7), but subsequently thought by him to be an impure chromium. Later, it was examined by N. G. Sefstrom, who found it in the slags of the Taberg iron ores (Pogg. Ann., 1830, 21, p. 48), by J. J. Berzelius (ibid., 1831, 22, p. 1), and finally by Sir H. Roscoe (Trans. Roy. Soc, 1868-1870), who showed that the supposed vanadium obtained by previous investigators was chiefly the nitride or an oxide of the element. In his researches, Roscoe showed that the atomic weight of the metal as determined by Berzelius and the formulae given to the oxides were incorrect, and pointed out that the element falls into its natural place in group V of the periodic classification along with phosphorus and arsenic, and not in the chromium group where it had originally been placed.

In small quantities, vanadium is found widely distributed. the chief sources being vanadite, mottramite, descloizite, roscoelite, dechenite and pucherite, whilst it is also found as a constituent of various clays, iron-ores and pitchblendes. Vanadium salts may be obtained from mottramite by digesting the mineral with concentrated hydrochloric acid, the liquid being run off and the residue well washed; the acid liquid and the washings are then evaporated with ammonium chloride, when ammonium metavanadate separates. This is recrystallized and roasted to vanadium pentoxide, which is then suspended in water into which ammonia is passed, when ammonium metavanadate is again formed and may be purified by recrystallization. The pure metal may be obtained by reducing vanadium dichloride in hydrogen, the operation being exceedingly difficult (for details, see Roscoe's original papers). In a somewhat impure condition it may be obtained by the reduction of vanadium pentoxide with a mixture of the rare earth metals which are obtained by reduction of the waste oxides formed in the manufacture of thoria (Weiss and Aichel, Ann., 1904, 337, p. 380); from the oxide by Goldschmidt's thermite method (Koppel and Kaufmann, Zeit. anorg. Chem., 1905, 45, p. 352); by electrolysis in a bath of fused fluorspar containing a steel cathode and an anode composed of carbon and vanadium pentoxide (M. Gin, L'Electricien, 1903, 25, p. 5); and by the electrolysis of vanadium trioxide when heated in an evacuated glass tube (W. v. Bolton, Zeit. f. Elektrochem., 1905, n, p. 45). H. Moissan (Comptes rendus, 1896, 122, p. 1297) obtained a vanadium containing from 10 to 16% of carbon by fusing vanadic anhydride with carbon in the electric furnace. For other methods of obtaining vanadium and its compounds, see Cowper Cowles, Engin. and Mining Journ. 67, p. 744; Herrenschmidt, Comptes rendus, 1904, 139, p. 635; M. Gin, Elektrochem. Zeit., 1906, 13, p. 119; W. Prandtl and B. Bleyer, Zeit. anorg. Chem., 1909, 64, p. 217.

Vanadium is a light-coloured metal of specific gravity 5.5. It is not volatilized even when heated to redness in a current of hydrogen, and it burns readily to the pentoxide when heated in oxygen. It dissolves slowly in hydrofluoric acid and in nitric acid, the solution turning blue; it is insoluble in hydrochloric acid. When fused with caustic soda, hydrogen is liberated and a vanadate is formed. It precipitates platinum, gold and silver from solutions of their salts, and also reduces mercuric, cupric and ferric salts. It absorbs nitrogen when heated in a current of that gas, forming a nitride. Vanadium may be detected by converting it into the pentoxide, which on passing sulphuretted hydrogen through its acid solution becomes reduced to the dioxide, the solution at the same time becoming lavender blue in colour; or if zinc be used as a reducing agent, the solution becomes at first green and ultimately blue.

Five oxides of vanadium are known (cf. Nitrogen), the mono-, di- and trioxides being basic in character, the tetra- and pentoxides being acidic and also feebly basic. The monoxide, V₂O, is formed when the metal is oxidized slowly in air. In a hydrated form it is obtained by the reduction of vanadyl monochloride, VOCl, with sodium amalgam, being precipitated from the liquid by the addition of ammonia (Locke and Edwards, Zeit. anorg. Chem., 1899, 19, p. 378). The dioxide V₂O₂, is formed in the reduction of vanadyl trichloride by hydrogen (Roscoe). It is a grey powder which is insoluble in water, but dissolves in acids to give a lavender-blue solution which possesses strong reducing properties. The addition of ammonia to this solution precipitates a brown hydrated oxide. The dioxide when heated in oxygen burns, forming the pentoxide. The trioxide, V₂O₃, is formed when the pentoxide is reduced at a red heat in a current of hydrogen, or by the action of oxalic acid on ammonium metavanadate. It forms a black amorphous powder or a dark green crystalline mass, and is insoluble in water and in most acids. The tetroxide, V₂O₄, results when the pentoxide is heated with dry oxalic acid and the resulting mixture of the tri- and pentoxide is warmed in the absence of air, or when the pentoxide is reduced by sulphur dioxide. It is an amorphous or crystalline mass of indigo-blue or steel-grey colour, which is insoluble in water and is also infusible. It oxidizes slowly in moist air, and dissolves easily in acids with the formation of blue solutions. The pentoxide, V₂O₅, is obtained when ammonium metavanadate is strongly heated, on calcining the sulphide, or by the decomposition of vanadyl trichloride with water. According to Ditte (Comptes rendus, 101, p. 698) it exists in three forms: a red amorphous soluble form which results when ammonium metavanadate is heated in a closed vessel and the residue oxidized with nitric acid and again heated; a yellow amorphous insoluble form which is obtained when the vanadate is heated in a current of air at 440 C. ; and a red crystalline form which is almost insoluble in water. It is soluble in hot concentrated sulphuric acid and in concentrated hydrochloric acid. It is an energetic oxidizing agent and is consequently readily reduced when heated with various metals (zinc, magnesium, &c.), with carbon and with oxalic acid. On fusion with the caustic alkalis and alkaline carbonates it yields vanadates. It forms numerous compounds with potassium fluoride. Many complex derivatives are known, such, for example, as phosphor-vanadates, arsenio-vanadates, tungsto-vanadates, molybdo-vanadates, &c. For the use of this oxide in the electrolytic oxidation and reduction of organic compounds, see German Patents 172654 (1903) and 183022 (1905).

Many salts of oxy-acids of vanadium are known, but of the more common oxy-acids, metavanadic acid, HVO₃, and pyrovanadic acid, H₄V₂O₇, alone appear to have been isolated. Metavanadic acid is obtained in the form of yellow scales by boiling copper vanadate with an aqueous solution of sulphur dioxide. It is only very slightly soluble in water. Pyrovanadic acid is deposited as a dark brown unstable powder when an acid vanadate is decomposed by nitric acid. Of the salts of these acids, those of the ortho- and pyro-acids are the least stable, the orthovanadates being obtained on fusion of vanadium pentoxide with an alkaline carbonate. The metavanadates are usually yellowish or colourless solids. Ammonium metavanadate is obtained when the hydrated vanadium pentoxide is dissolved in excess of ammonia and the solution concentrated. It has been used in dyeing with aniline black. Tetra- and hexavanadates have also been described (see Ditte, Comptes rendus, 104, pp. 902, 1061 ; 102, p. 918; Manasse, Ann. 240, p. 23). The hypovanadates are insoluble in water, except those of the alkali metals, which are obtained by the addition of caustic alkalis to concentrated solutions of the chloride or sulphate of the tetroxide. They are brown in colour and easily oxidize. Pure hypovanadic acid has been obtained by G. Gain (Comptes rendus, 1906, 143, p. 823) by calcining ammonium metavanadate and saturating a solution of the resulting oxides with sulphur dioxide; the resulting blue solution (from which a sulphate of composition 2V₂O₄-3SO₂-10H₂O can be isolated) is then boiled with water, when sulphur dioxide is liberated and a pale red crystalline powder of hypovanadic acid, H4V2O5, is precipitated.

Vanadium dichloride, VCl₂, is a green crystalline solid obtained when the tetrachloride is reduced with hydrogen at a dull red heat. It is very deliquescent and readily soluble in water. The trichloride, VCl₃, is a deliquescent solid formed when the tetra-chloride is heated in a retort as long as chlorine is given off (Roscoe), or by heating vanadium trisulphide in a current of chlorine and fractionally distilling the resulting product at 150° C. in a current of carbon dioxide (Halberstadt, Ber., 1882, 15, p. 1619). The tetrachloride, VCl₄, is formed by the direct union of vanadium and chlorine or by the action of sulphur chloride on vanadium pentoxide (Matignon, Comptes rendus, 1904, 138, p. 631). It is a fuming liquid, which is soluble in benzene and in acetic acid; it dissolves in water to form a deep blue solution. Several oxychlorides have also been described. Vanadium carbide, VC, was prepared by H, Moissan (Comptes rendus, 1896, 122, p. 1297) by heating vanadium pentoxide and carbon for a few minutes in the electric furnace. It is a volatile compound which burns when heated in oxygen and which is unacted upon by sulphuric and hydrochloric acids.

For vanadium steels, see Iron and Steel Manufacture.