Thorium dioxide
Thorium dioxide (ThO2), also called thorium(IV) oxide, is a crystalline solid, often white or yellow in colour. Also known as thoria, it is mainly a by-product of lanthanide and uranium production. Thorianite is the name of the mineralogical form of thorium dioxide. It is moderately rare and crystallizes in an isometric system. The melting point of thorium oxide is 3300 °C – the highest of all known oxides. Only a few elements (including tungsten and carbon) and a few compounds (including tantalum carbide) have higher melting points. All thorium compounds, including the dioxide, are radioactive because there are no stable isotopes of thorium.
| Names | |
|---|---|
| IUPAC names
Thorium dioxide Thorium(IV) oxide | |
| Other names
Thoria Thorium anhydride | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.013.842 |
| EC Number |
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| 141638 | |
PubChem CID |
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| UNII | |
| UN number | 2910 2909 |
CompTox Dashboard (EPA) |
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| Properties | |
| ThO2 | |
| Molar mass | 264.037 g/mol |
| Appearance | white solid |
| Odor | odorless |
| Density | 10.0 g/cm3 |
| Melting point | 3,350 °C (6,060 °F; 3,620 K) |
| Boiling point | 4,400 °C (7,950 °F; 4,670 K) |
| insoluble | |
| Solubility | insoluble in alkali slightly soluble in acid |
| −16.0·10−6 cm3/mol | |
Refractive index (nD) |
2.200 (thorianite) |
| Structure | |
| Fluorite (cubic), cF12 | |
| Fm3m, No. 225 | |
a = 559.74(6) pm | |
| Tetrahedral (O2−); cubic (ThIV) | |
| Thermochemistry | |
Std molar entropy (S⦵298) |
65.2(2) J K−1 mol−1 |
Std enthalpy of formation (ΔfH⦵298) |
−1226(4) kJ/mol |
| Hazards | |
| GHS labelling: | |
| Danger | |
| H301, H311, H331, H350, H373 | |
| P203, P260, P261, P264, P270, P271, P280, P301+P316, P302+P352, P304+P340, P316, P318, P319, P321, P330, P361+P364, P403+P233, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
400 mg/kg |
| Related compounds | |
Other anions |
Thorium(IV) sulfide |
Other cations |
Hafnium(IV) oxide Cerium(IV) oxide |
Related compounds |
Protactinium(IV) oxide Uranium(IV) oxide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |
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