Thorium dioxide
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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.[4] 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.[6] All thorium compounds, including the dioxide, are radioactive because there are no stable isotopes of thorium.
Names | |
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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[1] |
Appearance | white solid[1] |
Odor | odorless |
Density | 10.0 g/cm3[1] |
Melting point | 3,350 °C (6,060 °F; 3,620 K)[1] |
Boiling point | 4,400 °C (7,950 °F; 4,670 K)[1] |
insoluble[1] | |
Solubility | insoluble in alkali slightly soluble in acid[1] |
−16.0·10−6 cm3/mol[2] | |
Refractive index (nD) |
2.200 (thorianite)[3] |
Structure | |
Fluorite (cubic), cF12 | |
Fm3m, No. 225 | |
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:[5] | |
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).
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