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|Atomic Number:||90||Atomic Symbol:||Th|
|Atomic Weight:||232.0381||Electron Configuration:||2-8-18-10-2|
|Melting Point:||1656oC||Boiling Point:||3315oC|
|Description:||Silvery rare earth metal.|
History(Thor, Scandinavian god of war) Discovered by Berzelius in 1828.
- Thorium occurs in thorite and in thorianite.
- Large deposits of thorium minerals have been reported in New England and
elsewhere, but these have not yet been exploited.
- Thorium is now thought to be about three times as abundant as uranium and
about as abundant as lead or molybdenum.
- The metal is a source of nuclear power.
- There is probably more energy available for use from thorium in the minerals
of the earth's crust than from both uranium and fossil fuels.
- Any sizable demand from thorium as a nuclear fuel is still several years in
- Work has been done in developing thorium cycle converter-reactor systems.
- Several prototypes, including the HTGR (high-temperature gas-cooled reactor)
and MSRE (molten salt converter reactor experiment), have operated.
- While the HTGR reactors are efficient, they are not expected to become
important commercially for many years because of certain operating difficulties.
- Thorium is recovered commercially from the mineral monazite, which contains
from 3 to 9% ThO2 along with rare-earth minerals.
- Much of the internal heat the earth produces has been attributed to thorium
- Several methods are available for producing thorium metal; it can be
obtained by reducing thorium oxide with calcium, by electrolysis of anhydrous
thorium chloride in a fused mixture of sodium and potassium chlorides, by
calcium reduction of thorium tetrachloride mixed with anhydrous zinc chloride,
and by reduction of thorium tetrachloride with an alkali metal.
- Thorium was originally assigned a position in Group IV of the periodic
- Because of its atomic weight, valence, etc., it is now considered to be the
second member of the actinide series of elements.
- When pure, thorium is a silvery-white metal which is air-stable and reatins
its luster for several months.
- When contaminated with the oxide, thorium slowly tarnishes in air, becoming
gray and finally black.
- The physical properties of thorium are greatly influenced by the degree of
contamination with the oxide.
- The purest spcimens often contain several tenths of a percent of the oxide.
- High-purity thorium has been made.
- Pur thorium is soft, very ductile, and can be cold-rolled, swaged, and
- Thorium is dimorphic, changing at 1400C from a cubic to a body-centered
- Thorium oxide has a melting point of 3300C, which is the highest of all
- Only a few elements, such as tungsten, and a few compounds, such as tantalum
carbide, have higher melting points.
- Thorium is slowly attacked by water, but does not dissolve readily in most
common acids, except hydrochloric.
- Powdered thorium metal is often pyrophoric and should be carefully handled.
- When heated in air, thorium turnings ignite and burn brilliantly with a
- The principal use of thorium has been in the preparation of the Welsbach
mantle, used for portable gas lights.
- These mantles, consisting of thorium oxide with about 1% cerium oxide and
other ingredients, glow with a dazzling light when heated in a gas flame.
- Thorium is an important alloying element in magnesium, imparting high
strength and creep resistance at elevated temperatures.
- Because thorium has a low work-function and igh electron emission, it is
used to coat tungsten wire used in electronic equipment.
- The oxide is also used to control the grain size of tungsten used for
electric lamps; it is also used for high-temperature laboratory crucibles.
- Glasses containing thorium oxide have a high refractive index and low
- Consequently, they find application in high quality lenses for cameras and
- Thorium oxide has also found use as a catalyst in the conversion of ammonia
to nitric acid, in petroleum cracking, and in producing sulfuric acid.
- Twenty five isotopes of thorium are known with atomic masses ranging from
212 to 236.
- All are unstable.
- 232Th occurs naturally and has a half-life of 1.4 x 10^10 years.
- It is an alpha emitter.
- 232Th goes through six alpha and four beta decay steps before becoming the
stable isotope 208Pb.
- 232Th is sufficiently radioactive to expose a photographic plate in a few
- Thorium disintegrates with the production of "thoron" (220Rn), which is an
alpha emitter and presents a radiation hazard.
Costs & HandlingGood ventilation of areas where thorium is stored
or handled is therefore essential. Thorium metal (99.9%) costs about $150/oz.