Niobic acid
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| Names | |
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IUPAC name
Niobium(V) oxide
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| Other names
Niobium pentoxide
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3D model (JSmol)
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| ECHA InfoCard | 100.013.831 |
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PubChem CID
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| Properties | |
| Nb2O5 | |
| Molar mass | 265.81 g/mol |
| Appearance | white orthogonal solid |
| Density | 4.60 g/cm3 |
| Melting point | 1,512 °C (2,754 °F; 1,785 K) |
| insoluble | |
| Solubility | soluble in HF |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Niobium pentoxide is the inorganic compound with the formula Nb2O5. 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.
It has many polymorphic forms all based largely on octahedrally coordinated niobium atoms. The polymorphs are identified with a variety of prefixes. 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. There is an uncharacterised solid hydrate, Nb2O5.nH2O, 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.
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.
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. The oxidation of niobium dioxide, NbO2 in air forms the polymorph, L-Nb2O5. Pure Nb2O5 can be prepared by hydrolysis of NbCl5:
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.
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.
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. The main method is reduction of this oxide with aluminium:
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