Niobium pentoxide: Difference between revisions

| verifiedrevid = 309945041

| ImageSize = 250px

| IUPACName = Niobium(V) oxide

| OtherNames = Niobium pentoxide

| Section1 = {{Chembox Identifiers

| CASNo_Ref = {{cascite}}

| PubChem =

| SMILES =

| Section2 = {{Chembox Properties

| Formula = Nb₂O₅

| MolarMass = 265.81 g/mol

| Appearance = white [[orthogonal]] solid

| Density = 4.60 g/cm<sup>3<sup>

| MeltingPt = 1512 °C

| BoilingPt =

| Solubility = insoluble

| SolubleOther = soluble in [[hydrofluoric acid|HF]]

'''Niobium pentoxide''' is the [[inorganic compound]] with the [[chemical formula|formula]] [[Niobium|Nb]]₂[[oxide|O]]₅. It is a colourless insoluble solid that is fairly unreactive. It is the main precursor to all materials made of niobium, the dominant application being alloys, but other specialized applications include capacitors, [[lithium niobate]], and optical glasses.<ref name = "Cardarelli">Francois Cardarelli (2008) ''Materials Handbook'' Springer London ISBN 978-1-84628-668-1</ref>

It has many polymorphic forms all based largely on octahedrally coordinated niobium atoms.<ref name = "Wells"> Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications ISBN 0-19-855370-6 </ref> The polymorphs are identified with a variety of prefixes.<ref name = "Wells"/> The form most commonly encountered is monoclinic H-[[Niobium|Nb]]₂[[oxide|O]]₅ 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.<ref>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}}</ref> There is an uncharacterised solid hydrate, Nb₂O₅.''n''H₂O, the so-called '''niobic acid''' (previously called '''columbic acid'''), which can be prepared by hydrolysis of a basic solution of niobium pentachloride or Nb₂O₅ dissolved in HF.<ref name = "Bayot">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</ref>

==Production==

Nb₂O₅ is prepared by hydrolysis of alkali-metal niobates and alkoxides and the fluorides using base. Such ostensibly simple procedures afford hydrated oxides that are calcined.

===Other routes===

Given that Nb₂O₅ is the most common and robust compound of niobium, many methods, both practical and esoteric, exist for its formation. The oxide for example, arises when niobium metal is oxidised in air.<ref name = "Greenwood"/> The oxidation of niobium dioxide, NbO₂ in air forms the polymorph, L-Nb₂O₅.<ref>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}}</ref> Pure Nb₂O₅ can be prepared by hydrolysis of [[niobium pentachloride|NbCl₅]]:<ref>Process for the manufacture of niobium pentoxide or tantalum pentoxide, Kern, Therwil, Jacob, Hooper (CIBA Switzerland), US Patent number: 3133788, (1964)</ref>

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.<ref>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}}</ref>

Nano-sized niobium pentoxide particles have been synthesised by LiH reduction of NbCl₅, followed by aerial oxidation as part of a synthesis of nano structured niobates.

Nb₂O₅ is attacked by HF and dissolves in fused alkali.<ref name = "Bayot"/><ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref>

The conversion of Nb₂O₅ is the main route for the industrial production of niobium metal. In the 1980s, about 15,000,000 kg of Nb₂O₅ were consumed annually for reduction to the metal.<ref name=Ullmann>Joachim Eckert, Hermann C. Starck "Niobium and Niobium Compounds" Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. {{DOI|10.1002/14356007.a17_251}}</ref> The main method is reduction of this oxide with [[aluminium]]:

An alternative but less practiced route involves carbothermal reduction, which proceeds via reduction with carbon and forms the basis of the two stage Balke process:<ref>Alan E. Comyns (1999) ''Encyclopedic Dictionary of Named Processes in Chemical Technology'' CRC Press, ISBN 0849312051</ref><ref>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</ref>

:Nb₂O₅ + 7 C → 2 NbC + 5 CO (heated under vacuum at 1800°C)

Many methods are known for conversion of Nb₂O₅ to the halides. The main problem is incomplete reaction to give the oxyhalides. In the laboratory, the conversion can be effected with thionyl chloride:<ref>D. Brown "Niobium(V) Chloride and Hexachloroniobates(V)" Inorganic Syntheses, 1957 Volume 9, pp. 88–92.{{DOI|10.1002/9780470132401.ch24}}</ref>

Treating Nb₂O₅ with aqueous [[sodium hydroxide|NaOH]] at 200 °C can give crystalline sodium niobate, NaNbO₃ whereas the reaction with [[potassium hydroxide|KOH]] may yield soluble Lindqvist-type hexaniobates, {{chem|Nb|6|O|19|8-}}.<ref>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}}</ref> [[Lithium niobate]]s such as LiNbO₃ and Li3NbO₄ can be prepared by reaction [[lithium carbonate]] and Nb₂O₅.<ref>US Patent 5482001 - Process for producing lithium niobate single crystal,1996, Katoono T., Tominaga H.,</ref><ref name=Li3NbO4/>

:Nb₂O₅ + H₂ → 2 NbO₂ + H₂O

Niobium monooxide arises from a comproportionation using an arc-furnace:<ref>T. B. Reed, E. R. Pollard "Niobium Monoxide" Inorganic Syntheses, 1995 Volume 30, pp. 108–110, 2007. {{DOI|10.1002/9780470132616.ch22}}</ref>

:Nb₂O₅ + 3Nb → 5 NbO

The burgundy-coloured niobium(III) oxide, one of the first superconducting oxides, can be prepared again by an comproportionation:<ref name=Li3NbO4>Margret J. Geselbracht, Angelica M. Stacy, "Lithium Niobium Oxide: LiNbo2 and Superconducting Li_XNbO₂" Inorganic Syntheses 1995, Volume 30, Pages: 222–226.{{DOI|10.1002/9780470132616.ch42}}</ref>

Niobium pentoxide is used mainly in the production of niobium metal,<ref name=Ullmann/> but specialized applications exist for [[lithium niobate]] and as a component of optical glass.<ref name = "Cardarelli"/>

*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.Katsuhiro Yoshida, Noriko Kuge (NEC Corporation), Sintered bodies based on niobium suboxide US patent 6215652, 2001.

{{reflist|2}}

[[Category:Niobium compounds]]

[[Category:Oxides]]

[[de:Niob(V)-oxid]]

[[it:Ossido di niobio]]

[[pl:Tlenek niobu(V)]]

[[pt:Óxido de nióbio (V)]]

[[fi:Niobiumpentoksidi]]

[[zh:五氧化二铌]]