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| Names | |
|---|---|
| IUPAC name Divanadium pentaoxide | |
| Other names Vanadium pentoxide Vanadic anhydride Divanadium pentoxide | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.013.855 |
| EC Number |
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| KEGG |
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| RTECS number |
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| UNII | |
| UN number | 2862 |
| |
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| Properties[3] | |
| V2O5 | |
| Molar mass | 181.8800 g/mol |
| Appearance | Yellow solid |
| Density | 3.35 g/cm3[1] |
| Melting point | 681 °C (1,258 °F; 954 K)[1] |
| Boiling point | 1,750 °C (3,180 °F; 2,020 K)[1] (decomposes) |
| 0.7 g/L (20 °C)[1] | |
| +128.0·10−6 cm3/mol[2] | |
| Structure[4] | |
| Orthorhombic | |
| Pmmn, No. 59 | |
a = 1151 pm,b = 355.9 pm,c = 437.1 pm | |
| Distorted trigonal bipyramidal (V) | |
| Thermochemistry[5] | |
| 127.7 J/(mol·K) | |
Std molar entropy(S⦵298) | 131.0 J/(mol·K) |
Std enthalpy of formation(ΔfH⦵298) | −1550.6 kJ/mol |
Gibbs free energy(ΔfG⦵) | −1419.5 kJ/mol |
| Hazards | |
| GHS labelling: | |
   | |
| Danger | |
| H302,H332,H335,H341,H361,H372,H411 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 10 mg/kg (rat, oral) 23 mg/kg (mouse, oral)[7] |
LCLo (lowest published) | 500 mg/m3 (cat, 23 min) 70 mg/m3 (rat, 2 hr)[7] |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | C 0.5 mg V2O5/m3 (resp) (solid)[6]
|
| Safety data sheet (SDS) | ICSC 0596 |
| Related compounds | |
Otheranions | Vanadium oxytrichloride |
Othercations | Niobium(V) oxide Tantalum(V) oxide |
| Vanadium(II) oxide Vanadium(III) oxide Vanadium(IV) oxide | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Vanadium(V) oxide (vanadia) is theinorganic compound with theformulaV2O5. Commonly known asvanadium pentoxide, it is a dark yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because of its highoxidation state, it is both anamphoteric oxide and anoxidizing agent. From the industrial perspective, it is the most important compound ofvanadium, being the principal precursor toalloys of vanadium and is a widely usedindustrial catalyst.[8]
The mineral form of this compound, shcherbinaite, is extremely rare, almost always found amongfumaroles. A mineraltrihydrate, V2O5·3H2O, is also known under the name of navajoite.
Upon heating a mixture of vanadium(V) oxide andvanadium(III) oxide,comproportionation occurs to givevanadium(IV) oxide, as a deep-blue solid:[9]
The reduction can also be effected byoxalic acid,carbon monoxide, andsulfur dioxide. Further reduction usinghydrogen or excess CO can lead to complex mixtures of oxides such as V4O7 and V5O9 before black V2O3 is reached.
V2O5 is anamphoteric oxide, and unlike mosttransition metal oxides, it is slightly watersoluble, giving a pale yellow, acidic solution. Thus V2O5 reacts with strong non-reducing acids to form solutions containing the pale yellow salts containingdioxovanadium(V) centers:
It also reacts with strongalkali to formpolyoxovanadates, which have a complex structure that depends onpH.[10] If excess aqueoussodium hydroxide is used, the product is a colourlesssalt,sodium orthovanadate, Na3VO4. If acid is slowly added to a solution of Na3VO4, the colour gradually deepens through orange to red before brown hydrated V2O5 precipitates around pH 2. These solutions contain mainly the ions HVO42− and V2O74− between pH 9 and pH 13, but below pH 9 more exotic species such as V4O124− and HV10O285− (decavanadate) predominate.
Upon treatment withthionyl chloride, it converts to the volatile liquidvanadium oxychloride, VOCl3:[11]
Hydrochloric acid andhydrobromic acid are oxidised to the correspondinghalogen, e.g.,
Vanadates orvanadyl compounds in acid solution are reduced byzinc amalgam through the colourful pathway:
The ions are all hydrated to varying degrees.
Technical grade V2O5 is produced as a black powder used for the production ofvanadium metal andferrovanadium.[10] A vanadium ore or vanadium-rich residue is treated withsodium carbonate and anammonium salt to producesodium metavanadate, NaVO3. This material is then acidified to pH 2–3 usingH2SO4 to yield a precipitate of "red cake" (seeabove). The red cake is then melted at 690 °C to produce the crude V2O5.
Vanadium(V) oxide is produced whenvanadium metal is heated with excessoxygen, but this product is contaminated with other, lower oxides. A more satisfactory laboratory preparation involves the decomposition ofammonium metavanadate at 500–550 °C:[13]
In terms of quantity, the dominant use for vanadium(V) oxide is in the production offerrovanadium (seeabove). The oxide is heated with scrapiron andferrosilicon, withlime added to form acalcium silicateslag.Aluminium may also be used, producing the iron-vanadium alloy along withalumina as a byproduct.
Another important use of vanadium(V) oxide is in the manufacture ofsulfuric acid, an important industrial chemical with an annual worldwide production of 165 million tonnes in 2001, with an approximate value of US$8 billion. Vanadium(V) oxide serves the crucial purpose ofcatalysing the mildlyexothermicoxidation of sulfur dioxide tosulfur trioxide by air in thecontact process:
The discovery of this simple reaction, for which V2O5 is the most effective catalyst, allowed sulfuric acid to become the cheap commodity chemical it is today. The reaction is performed between 400 and 620 °C; below 400 °C the V2O5 is inactive as a catalyst, and above 620 °C it begins to break down. Since it is known that V2O5 can be reduced to VO2 by SO2, one likely catalytic cycle is as follows:
followed by
It is also used as catalyst in theselective catalytic reduction (SCR) ofNOx emissions in somepower plants and diesel engines. Due to its effectiveness in converting sulfur dioxide into sulfur trioxide, and thereby sulfuric acid, special care must be taken with the operating temperatures and placement of a power plant's SCR unit when firing sulfur-containing fuels.
Maleic anhydride is produced by the V2O5-catalysed oxidation of butane with air:
Maleic anhydride is used for the production ofpolyester resins andalkyd resins.[15]
Phthalic anhydride is produced similarly by V2O5-catalysed oxidation ofortho-xylene ornaphthalene at 350–400 °C. The equation for the vanadium oxide-catalysed oxidation ofo-xylene to phthalic anhydride:
The equation for the vanadium oxide-catalysed oxidation of naphthalene to phthalic anhydride:[16]
Phthalic anhydride is a precursor toplasticisers, used for conferring pliability to polymers.
A variety of other industrial compounds are produced similarly, includingadipic acid,acrylic acid,oxalic acid, andanthraquinone.[8]
Due to its high coefficient ofthermal resistance, vanadium(V) oxide finds use as a detector material inbolometers andmicrobolometer arrays forthermal imaging. It also finds application as an ethanol sensor in ppm levels (up to 0.1 ppm).
Vanadium redox batteries are a type offlow battery used forenergy storage, including large power facilities such aswind farms.[17] Vanadium oxide is also used as a cathode inlithium-ion batteries.[18]
Vanadium(V) oxide exhibits very modest acute toxicity to humans, with anLD50 of about 470 mg/kg. The greater hazard is with inhalation of the dust, where the LD50 ranges from 4–11 mg/kg for a 14-day exposure.[8]Vanadate (VO3−
4), formed by hydrolysis of V2O5 at high pH, appears to inhibitenzymes that processphosphate (PO43−). However the mode of action remains elusive.[10][better source needed]
