Feb 6 2003
Background
Thorium was discovered in 1829 by J.J. Berzelius in Stockholm.
Occurrence and Extraction
Thorium (Th) is a dark grey, radioactive metal of which the principal source is the ore, monazite, a complex phosphate of thorium, uranium, cerium and lanthanides. Thorium 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. Thorium 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).
Applications
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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Thorium contains more energy than the majority of fossil fuels sources. Image Credit: SutterStock/P.V.R.Murty
Key Properties
The key properties of Thorium are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
90 |
| Atomic radius - Goldschmidt ( nm ) |
0.180 |
| Atomic weight ( amu ) |
232.0381 |
| Crystal structure |
Face centred cubic |
| Electronic structure |
Rn 6d2 7s2 |
| Photo-electric work function ( eV ) |
3.5 |
| Thermal neutron absorption cross-section ( Barns ) |
7.4 |
| Valences shown |
2, 3, 4 |
| Ionisation Potential |
No. |
eV |
| |
1 |
6.95 |
| |
2 |
11.5 |
| |
3 |
20.0 |
| |
4 |
28.8 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
232 |
100 |
| Electrical Properties |
| Electrical resistivity @ 20 °C ( µOhm.cm ) |
14.0 |
| Temperature coefficient @ 0-100 °C ( K-1 ) |
0.0040 |
| Superconductivity critical temperature ( K ) |
1.38 |
| Thermal emf against Pt (cold 0 °C - hot 100 °C) ( mV ) |
-0.13 |
| Mechanical Properties |
| 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 |
|
| Physical Properties |
| Boiling point ( °C ) |
4790 |
| Density @ 20 °C ( g.cm-3 ) |
11.5 |
| Melting point ( °C ) |
1750 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( 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 @ 25 °C ( J.K-1.kg-1 ) |
113 |
| Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) |
54 |
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