Niobium dioxide

Niobium dioxide
IUPAC name niobium(IV) oxide, niobium dioxide
Other names niobium(IV) oxide, columbium dioxide
Identifiers
CAS number	12034-59-2
Properties
Molecular formula	NbO2
Molar mass	124.91 g/mol
Appearance	bluish black
Melting point	1915 °C [1]
Structure
Crystal structure	Tetragonal, tI96
Space group	I41/a, No. 88
Y dioxide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Niobium dioxide, is the chemical compound with the formula NbO₂. It is a bluish black non-stoichiometric solid with a composition range of NbO_1.94-NbO_2.09^[1] It can be prepared by reacting Nb₂O₅ with H₂ at 800-1350 °C.^[1] An alternative method is reaction of Nb₂O₅ with Nb powder at 1100 °C.^[2]

The room temperature form NbO₂ has a tetragonal, rutile-like structure with short Nb-Nb distances indicating Nb-Nb bonding.^[3] High temp form also has a rutile-like structure with short Nb-Nb distances.^[4] Two high pressure phases have been reported one with a rutile-like structure, again with short Nb-Nb distances, and a higher pressure with baddeleyite-related structure.^[5]

NbO₂ is insoluble in water and is a powerful reducing agent, reducing carbon dioxide to carbon and sulfur dioxide to sulfur.^[1] In an industrial process for the production of niobium metal[1], NbO₂ is produced as an intermediate, by the hydrogen reduction of Nb₂O₅.^[6] The NbO₂ is subsequently reacted with magnesium vapour to produce niobium metal.^[7]

References

1. ^ ^{a b c d} C. K. Gupta, A. K. Suri, S Gupta, K Gupta (1994), Extractive Metallurgy of Niobium, CRC Press, ISBN 0849360714
2. ^ Pradyot Patnaik (2002), Handbook of Inorganic Chemicals,McGraw-Hill Professional, ISBN 0070494398
3. ^ Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
4. ^ Bolzan, A; Fong, Celesta; Kennedy, Brendan J.; Howard, Christopher J. (1994). "A Powder Neutron Diffraction Study of Semiconducting and Metallic Niobium Dioxide". Journal of Solid State Chemistry 113: 9. doi:10.1006/jssc.1994.1334. 
5. ^ Haines, J.; Léger, J. M.; Pereira, A. S. (1999). "High-pressure structural phase transitions in semiconducting niobium dioxide". Physical Review B 59 (21): 13650. doi:10.1103/PhysRevB.59.13650. 
6. ^ Patent EP1524252 , Sintered bodies based on niobium suboxide, Schnitter C, Wötting G
7. ^ Method for producing tantallum/niobium metal powders by the reduction of their oxides by gaseous magnesium, US patent 6171363 (2001), Shekhter L.N., Tripp T.B., Lanin L.L. (H. C. Starck, Inc.)