Vanadium oxide, black

P.Y. Zavalij, T. Chirayil, and M.S. Whittingham, Layered tetramethylammonium vanadium oxide [N(CH3)4]V307 by x-ray Rietveld refinement, Acta Cryst. C53, 879 (1997) tma - tetramethylammonium [N(CH3)4]. The material in a form of a black crystalline powder was prepared by hydrothermal treatment at 185°C of a mixture of V2O5, tmaOH, and LiOH taken in 1 2 1 molar ratio and acidified with CH3COOH to pH = 6,5. 

Vanadium(II) oxide, black, 1 106 Vanadium(V) oxychloride, 1 106 Vermilion, 1 20... 

The principal vanadium-bearing ores are generally cmshed, ground, screened, and mixed with a sodium salt, eg, NaCl or Na2C02- This mixture is roasted at ca 850°C and the oxides are converted to water-soluble sodium metavanadate, NaVO. The vanadium is extracted by leaching with water and precipitates at pH 2—3 as sodium hexavanadate, Na V O, a red cake, by the addition of sulfuric acid. This is then fused at 700°C to yield a dense black product which is sold as technical-grade vanadium pentoxide. This product contains a minimum of 86 wt % V20 and a maximum of 6—10 wt % Na20. 

Vanadium(IV) Oxide. Vanadium(IV) oxide (vanadium dioxide, VO2) is a blue-black solid, having a distorted mtile (Ti02) stmcture. It can be prepared from the reaction of V20 at the melting point with sulfur or carbonaceous reductants such as sugar or oxaUc acid. The dioxide slowly oxidizes in air. Vanadium dioxide dissolves in acids to give the stable (VO) " ions and in hot alkaUes to yield vanadate(IV) species, eg, (HV20 ) . 

Va.na.dlum(III) Oxide. Vanadium(III) oxide (vanadium sesquioxide, V2O2) is a black soHd, having the comndum (AI2O2) stmcture. It can be prepared by reduction of the pentoxide by hydrogen or carbon. Air oxidation proceeds slowly at ambient temperatures, but oxidation by chlorine at elevated temperatures to give VOCl and V20 is rapid. 

Va.na.dium (II) Oxide. Vanadium(II) oxide is a non stoichiometric material with a gray-black color, metallic luster, and metallic-type electrical conductivity. Metal—metal bonding increases as the oxygen content decreases, until an essentially metal phase containing dissolved oxygen is obtained (14). 

Minor uses of vanadium chemicals are preparation of vanadium metal from refined pentoxide or vanadium tetrachloride Hquid-phase organic oxidation reactions, eg, production of aniline black dyes for textile use and printing inks color modifiers in mercury-vapor lamps vanadyl fatty acids as driers in paints and varnish and ammonium or sodium vanadates as corrosion inhibitors in flue-gas scmbbers. 

Vanadium. It is stable in air below 250°C. After long exposition it becomes bluish grey to brownish black significant oxidation takes place at about 300°C. Vanadium reacts with hot concentrate mineral acids, especially HN03 and HF. It has good corrosion resistance towards molten low melting metals, especially alkali metals. 

Figure 7.16 Volt-equivalent diagrams for the oxidation states of vanadium at pH = 0 (red line) and pH = 14 (black line)...

Many solid substances are remarkably active in accelerating the change especial mention may be made of finely divided platinum 6 in this respect. In the presence of platinum black at a temperature of 432° C., 96 8 per cent, of the dioxide may be converted into the trioxide.7 Sugar charcoal and the oxides of iron, copper, vanadium and arsenic 8 are amongst other substances which possess catalytic power over the reaction, and although they are weaker catalysts than platinum, the final proportions of dioxide and trioxide in the equilibrium mixture are but little affected by the nature of the catalyst used.9 The present... 

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