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Material Information Thorium
Th
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General Description:
Thorium was discovered in 1829 by J.J. Berzelius in Stockholm.
Thorium is a dark grey, radioactive metal of which the principal source is the ore, monazite, a complex phosphate of thorium, uranium, cerium and lanthanides. The metal is soft and ductile and is extracted by precipitation as the hydroxide, along with cerium and uranium; separation is achieved by further extraction with tributyl phosphate from an acid solution. The metal is made by calcium reduction of the oxide or fluoride, and pure thorium can be obtained by decomposing ThI4 on a hot filament (the Van Arkel process).
Thorium is used as an alternative reactor fuel to uranium, thorium being converted readily into uranium in the reactor. Thorium is extremely efficient as an energy source, the earthly reserves of thorium containing more energy than all other fossil fuel sources combined.
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Atomic Properties
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| Atomic number | 90 |
| Atomic radius - Goldschmidt ( nm ) | 0.180 |
| Atomic weight ( amu ) | 232.0381 |
| Crystal structure | Face centred cubic |
| Electronic structure | Rn 6d2 7s2 |
| Ionization potential | No. | eV |
| | 1 | 6.95 |
| | 2 | 11.5 |
| | 3 | 20.0 |
| | 4 | 28.8 |
| Natural isotope distribution | Mass No. | % |
| | 232 | 100 |
| Photo-electric work function ( eV ) | 3.5 |
| Thermal neutron absorption cross-section ( Barns ) | 7.4 |
| Valences shown | 2, 3, 4 |
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Electrical Properties
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| Temperature coefficient @0-100C ( K-1 ) | 0.0040 |
| Electrical resistivity @20C ( µOhmcm ) | 14.0 |
| Superconductivity critical temperature ( K ) | 1.38 |
| Thermal emf against Pt (cold 0C - hot 100C) ( mV ) | -0.13 |
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Mechanical Properties
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| Material condition | Soft | Hard | Polycrystalline |
| Bulk modulus ( GPa ) | | | 54 |
| Hardness - Vickers | 38 | 70 |
| Izod toughness ( J m-1 ) | 41 | | 6 |
| Poisson's ratio | | | 0.26 |
| Tensile modulus ( GPa ) | | | 78.3 |
| Tensile strength ( MPa ) | 115 | 305 |
| Yield strength ( MPa ) | 48 | 295 |
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Physical Properties
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| Boiling point ( C ) | 4790 |
| Density @20C ( g cm-3 ) | 11.72 |
| Melting point ( C ) | 1750 |
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Thermal Properties
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| Coefficient of thermal expansion @0-100C ( x10-6 K-1 ) | 11.2 |
| Latent heat of evaporation ( J g-1 ) | 2202 |
| Latent heat of fusion ( J g-1 ) | 82.8 |
| Specific heat @25C ( J K-1 kg-1 ) | 113 |
| Thermal conductivity @0-100C ( W m-1 K-1 ) | 54 |
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