Vanadium(IV) oxide
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| Vanadium(IV) oxide | |
|---|---|
-oxide-3D-polyhedra.png/200px-Vanadium(IV)-oxide-3D-polyhedra.png) |
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| IUPAC name | Vanadium(IV) Oxide |
| Other names | Vanadium dioxide, vanadium tetroxide |
| Identifiers | |
| CAS number | [12036-21-4] |
| Properties | |
| Molecular formula | VO2, or V2O4 |
| Molar mass | 165.88 g/mol (V2O4) |
| Appearance | Black Powder |
| Density | 4.571 g/cm3 (Monoclinic), 4.653 g/cm3 (Tetragonal) |
| Melting point |
1967°C |
| Hazards | |
| Flash point | ?°C |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Vanadium(IV) oxide is the chemical compound VO2. It is formed in the contact process from V2O5, which acts as a catalyst.
Vanadium(IV) oxide is amphoteric, dissolving in non-oxidising acids to give the vanadyl ion, [VO]2+ and in alkali to give the [V4O9]2− ion, or at high pH [VO4]4−. [1]
[edit] Structure
At room temperature VO2 has a distorted rutile structure with shorter distances between pairs of V atoms indicating metal-metal bonding. [1] Above 70°C the structure changes to an undistorted rutile structure and the metal-metal bonds are broken causing an increase in electrical conductivity and magnetic susceptibility as the bonding electrons are "released".[1]
[edit] Uses
Tungsten-doped vanadium dioxide (W:VO2) with 1.9% tungsten content has been investigated for use as a "spectrally-selective" window coating to block infrared transmission and reduce the loss of building interior heat through windows. This material behaves like a semiconductor at temperatures below 29 °C, allowing more transmission, and like a conductor at higher temperatures, providing much greater reflectivity.[2][3] Varying the amount of tungsten allows regulating the phase transition temperature. However, the coating has a slight yellow-green color.[4]
Vanadium dioxide can act as an extremely fast optical shutter. The thermochromic phase transition between the transparent semiconductive and reflective conductive phase, occurring at 68 °C, can happen in times as short as a one tenth of a trillionth of a second.[5]
Vanadium dioxide, especially in its nanocrystalline form, may find use in glazing applications, extremely fast optical shutters, optical modulators, infrared modulators for missile guidance systems, cameras, data storage, and other applications.
[edit] References
- ^ a b c Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
- ^ Sol-Gel Vanadium oxide
- ^ Intelligent Window Coatings that Allow Light In but Keep Heat Out - News Item
- ^ oe magazine - Eye on Technology
- ^ Timing nature’s fastest optical shutter
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