| Antimony trioxide | |
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Antimony(III) oxide |
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Other names
Antimony sesquioxide |
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| Identifiers | |
| CAS number | 1309-64-4 |
| ChemSpider | 25727 |
| UNII | P217481X5E |
| KEGG | C19192 |
| RTECS number | CC5650000 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | Sb2O3 |
| Molar mass | 291.52 g/mol |
| Appearance | white solid |
| Density | 5.2 g/cm3, α-form |
| Melting point |
656 °C |
| Boiling point |
1425 °C (sublimes) |
| Solubility in water | 1.21 mg/100 mL (0 °C) 1.80 mg/100 mL (20 °C) 8.20 mg/100 mL (100 °C), with hydrolysis |
| Solubility | insoluble |
| Refractive index (nD) | 2.087 |
| Structure | |
| Crystal structure | cubic (α)<570 °C orthorhombic (β) >570 °C |
| Coordination geometry |
pyramidal |
| Dipole moment | zero |
| Hazards | |
| MSDS | External MSDS |
| EU classification | Harmful (Xn) Carc. Cat. 3 |
| R-phrases | R40 |
| S-phrases | (S2), S22, S36/37 |
| NFPA 704 |
0
2
0
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| LD50 | 7000 mg/kg, oral (rat) |
| Related compounds | |
| Other anions | Antimony trisulfide |
| Other cations | Arsenic trioxide Bismuth trioxide |
| Related compounds | Diantimony tetraoxide Antimony pentoxide |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Antimony trioxide is the inorganic compound with the formula Sb2O3. It is the most important commercial compound of antimony. It is found in nature as the minerals valentinite and senarmontite.[1] Like most polymeric oxides, Sb2O3 dissolves in aqueous solutions only with hydrolysis.
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Global production of antimony trioxide in 2005 was 120,000 tonnes, an increase from 112,600 tonnes in 2002. China produces the largest share (47 %) followed by US/Mexico (22 %), Europe (17 %), Japan (10 %) and South Africa (2 %) and other countries (2%).[2]
Antimony trioxide is mainly produced via the smelting of stibnite ore, which is oxidised to crude Sb2O3 using furnaces operating at approximately 850 to 1,000 °C. The transformation is described as follows:
Crude Sb2O3 is purified by sublimation, which allows it to be separated from the more volatile arsenic trioxide. This step is relevant because antimony ores commonly contain significant amounts of arsenic.
Antimony oxide is also obtained via antimony trichloride, which can be obtained from stibnite.
After fractional distillation to separate it from arsenic trichloride, SbCl3 can be hydrolyzed to the oxide:
Intermediates in the hydrolysis include the oxychlorides SbOCl and Sb4O5Cl2.
Although impractical for commercial purposes, Sb2O3 can be prepared by burning elemental antimony in air:
Antimony trioxide is an amphoteric oxide, dissolving in alkaline solution to give antimonites and in acid solution to given a range of polyantimonous acids. It can be readily oxidized to antimony pentoxide and related antimony(V) compounds, but it is also easily reduced to antimony, sometimes with production of stibine.
The structure of Sb2O3 depends on the temperature of the sample. Dimeric Sb4O6 is the high temperature (1560 °C) gas.[3] Sb4O6 molecules are bicyclic cages, similar to the related oxide of phosphorus(III), phosphorus trioxide.[4] The cage structure is retained in a solid that crystallizes in a cubic habit. The Sb-O distance is 197.7 pm and the O-Sb-O angle of 95.6°.[5] This form exists in nature as the mineral senarmontite.[4] Below 606 °C, the more stable form is orthorhombic, consisting of pairs -Sb-O-Sb-O- chains that are linked by oxide bridges between the Sb centers. This form exists in nature as the mineral valentinite.[4]
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The annual consumption of antimony trioxide in the United States and Europe is approximately 10,000 and 25,000 tonnes, respectively. The main application is for flame retardants in combination with halogenated materials. The combination of the halides and the antimony being key to the flame-retardant action for polymers, helping to form less flammable chars. Such flame retardants are found in electrical apparatus, textiles, leather, and coatings.[6]
Other applications:
The toxicity of Sb2O3 is topical because it is a likely byproduct of the combustion of some materials "fireproofed" with antimony compounds. The oxides of arsenic, antimony, and bismuth are comparable in their toxicity, but their volatilities differ widely. Antimony trioxide has suspected carcinogenic potential for humans.[6] Its TLV is 0.5 mg/m3, as for most antimony compounds.[7]
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