Niobium pentoxide

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Niobium pentoxide
IUPAC name Niobium(V) oxide
Other names Niobium pentoxide
Identifiers
CAS number [1313-96-8]
Properties
Molecular formula Nb2O5
Molar mass 265.81
Appearance white solid
Density 4.47
Melting point

1380 °C

Solubility in water insoluble
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Niobium pentoxide, is the chemical compound with the formula Nb2O5. It is used mainly in the production of capacitors, lithium niobate, and optical glass.[1].
It has many polymorphic forms all based largely on octahedrally coordinated niobium atoms.[2] The polymorphs are identified with a variety of prefixes.[2] The form most commonly encountered is monoclinic H-Nb2O5 which has a complex structure, with a unit cell containing 28 niobium atoms and 70 oxygen, where 27 of the niobium atoms are octahedrally coordinated and one tetrahedrally.[3] There is an un-characterised solid hydrate Nb2O5.nH2O, so-called niobic acid which can be prepared by hydrolysis of a basic solution of niobium pentachloride or Nb2O5 dissolved in HF.[4]
Thin films of Nb2O5 form the dielectric layers in solid electrolyte capacitors and these layers can be grown electrolytically on sintered bodies containing niobium monoxide.[5]

Contents

[edit] Preparation

Nb2O5 forms when niobium metal is oxidised in air.[6]
The oxidation of niobium dioxide, NbO2 in air forms the polymorph, L-Nb2O5.[7] Pure Nb2O5 can be prepared by hydrolysis of NbCl5:[8]

2NbCl5 + 5H2O → Nb2O5 + 10HCl

A method of production via sol-gel techniques has been reported hydrolysing niobium alkoxides in the presence of acetic acid, followed by calcination of the gels to produce the polymorphic form, T-Nb2O5.[9]

[edit] Reactions

Generally Nb2O5 is considered to be very insoluble and unreactive, it is attacked by concentrated HF and will dissolve in fused alkali.[4][10] Reduction with carbon forms the basis of the two stage Balke process for producing niobium:[11][12]

Nb2O5 + 7C → 2NbC + 5CO heated under vacuum at 1800°C
5NbC + Nb2O5 → 7Nb + 5CO

High temperature reduction with H2 gives NbO2:[10]

Nb2O5 + H2 → 2NbO2 + H2O

Nb2O5 reacts with CCl4 to give the oxychloride:[6]

2Nb2O5 + 3CCl4 → 4NbOCl3 + 3CO2

and reacts with carbon and bromine to give the oxybromide:

Nb2O5 + 3Br2 + 3C → 2NbOBr3 + 3CO

Reacting Nb2O5 with aqueous NaOH at 200 °C gives crystalline sodium niobate, NaNbO3 whereas the reaction with KOH gives soluble hexaniobates.[13] Single crystals of lithium niobate, LiNbO3 can be prepared by reaction of molten lithium carbonate and Nb2O5.[14]

[edit] Uses

Niobium pentoxide is used mainly in the production of capacitors, lithium niobate, and optical glass.[1]

[edit] External links

[edit] References

  1. ^ a b Francois Cardarelli (2008) Materials Handbook Springer London ISBN 978-1-84628-668-1
  2. ^ a b Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  3. ^ The crystal structure of the high temperature form of niobium pentoxide B. M. Gatehouse and A. D. Wadsley Acta Cryst. (1964). 17, 1545-1554 doi:10.1107/S0365110X6400384X
  4. ^ a b D.A. Bayot and M.M. Devillers, Precursors routes for the preparation of Nb based multimetallic oxides in Progress in Solid State Chemistry Research, Arte M. Newman, Ronald W. Buckley, (2007),Nova Publishers, ISBN 1600213138
  5. ^ Katsuhiro Yoshida, Noriko Kuge (NEC Corporation), Sintered bodies based on niobium suboxide US patent 6215652, 2001
  6. ^ a b Pradyot Patnaik, (2002), Handbook of Inorganic Chemicals McGraw-Hill Professional ISBN 0070494398
  7. ^ Electrical properties of NbO2 and Nb2O5 at elevated temperature in air and flowing argon, G. C. Vezzoli Phys. Rev. B 26, 3954 - 3957 (1982)doi:10.1103/PhysRevB.26.3954
  8. ^ Process for the manufacture of niobium pentoxide or tantalum pentoxide, Kern, Therwil, Jacob, Hooper (CIBA Switzerland), US Patent number: 3133788, (1964)
  9. ^ Sol-gel route to niobium pentoxide, P Griesmar, G Papin, C Sanchez, J Livage - Chem. Mater.; 1991; 3(2); 335-339 doi:10.1021/cm00014a026
  10. ^ a b Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 
  11. ^ Alan E. Comyns (1999) Encyclopedic Dictionary of Named Processes in Chemical Technology CRC Press, ISBN 0849312051
  12. ^ U.S. Environmental Protection Agency, Development Document for Effluent Limitations, Guidelines and Standards for the Nonferrous Metals Manufacturing Point Source Category, Volume VIII, Office of Water Regulations and Standards, May 1989
  13. ^ Studies on the hydrothermal synthesis of niobium oxides, I.C. M. S. Santos, L. H. Loureiro, M. F. P. Silva and Ana M. V. Cavaleiro, Polyhedron, 21, 20, (2002), 2009-2015, doi:10.1016/S0277-5387(02)01136-1
  14. ^ US Patent 5482001 - Process for producing lithium niobate single crystal,1996, Katoono T., Tominaga H.,