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#1 2025-09-23 15:40:31

Jai Ganesh
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Registered: 2005-06-28
Posts: 52,105

Thorium

Thorium

Gist

Thorium (Th, atomic number 90) is a weakly radioactive, naturally occurring metallic element with a high melting point, used in industries like ceramics and welding. It is also a fertile material, meaning it can be converted into a usable nuclear fuel, uranium-233, making it a potential resource for nuclear power. Thorium is found in rocks, soil, and water, with major deposits in India.

Thorium's primary use is as a potential nuclear fuel, where it can be converted into fissile uranium-233 for energy generation in certain reactor types. Historically and currently, it is used in manufacturing and industrial applications, such as strengthening magnesium alloys, coating tungsten wire, manufacturing camera and telescope lenses, and in heat-resistant ceramics and welding rods. Other uses include applications in radiometric dating and in some scientific instruments like sun lamps and photoelectric cells.

Summary

Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.

All known thorium isotopes are unstable. The most stable isotope, 232Th, has a half-life of 14.0 billion years, or about the age of the universe; it decays very slowly via alpha decay, starting a decay chain named the thorium series that ends at stable 208Pb. On Earth, thorium and uranium are the only elements with no stable or nearly-stable isotopes that still occur naturally in large quantities as primordial elements. Thorium is estimated to be over three times as abundant as uranium in the Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare-earth elements.

Thorium was discovered in 1828 by the Swedish chemist Jöns Jacob Berzelius during his analysis of a new mineral found by Morten Thrane Esmark on Lovoya near Brevik in the Langesund fjord. He named it after Thor, the Norse god of thunder and war. Its first applications were developed in the late 19th century. Thorium's radioactivity was widely acknowledged during the first decades of the 20th century. In the second half of the 20th century, thorium was replaced in many uses due to concerns about its radioactive properties.

Thorium is still used as an alloying element in TIG welding electrodes but is slowly being replaced in the field with different compositions. It was also material in high-end optics and scientific instrumentation, used in some broadcast vacuum tubes, and as the light source in gas mantles, but these uses have become marginal. It has been suggested as a replacement for uranium as nuclear fuel in nuclear reactors, and several thorium reactors have been built. Thorium is also used in strengthening magnesium, coating tungsten wire in electrical and welding equipment, controlling the grain size of tungsten in electric lamps, high-temperature crucibles, and glasses including camera and scientific instrument lenses. Other uses for thorium include heat-resistant ceramics, aircraft engines, and in light bulbs. Ocean science has used 231Pa/230Th isotope ratios to understand the ancient ocean.

Details

Thorium (Th) is a radioactive chemical element of the actinoid series of the periodic table, atomic number 90; it is a useful nuclear reactor fuel. Thorium was discovered (1828) by Swedish chemist Jöns Jacob Berzelius. It is silvery white but turns gray or black on exposure to air. It is about half as abundant as lead and is three times more abundant than uranium in Earth’s crust. Thorium is commercially recovered from the mineral monazite and occurs also in other minerals such as thorite and thorianite. Thorium metal has been produced in commercial quantities by reduction of the tetrafluoride (ThF4) and dioxide (ThO2) and by electrolysis of the tetrachloride (ThCl4). The element was named for the Norse god Thor.

The metal may be extruded, rolled, forged, swaged, and spun, but drawing is difficult because of thorium’s low tensile strength. This and other physical properties such as melting and boiling points are greatly affected by small amounts of certain impurities, such as carbon and thorium dioxide. Thorium is added to magnesium and magnesium alloys to improve their high-temperature strength. It has been used in commercial photoelectric cells for measuring ultraviolet light of wavelengths ranging from 2000 to 3750 angstroms. Added to glass, thorium yields glasses with a high refractive index, useful for specialized optical applications. It was formerly in great demand as a component of mantles for gas and kerosene lamps and has been used in the manufacture of tungsten filaments for lightbulbs and vacuum tubes.

The radioactivity of thorium was found independently (1898) by German chemist Gerhard Carl Schmidt and by French physicist Marie Curie. Natural thorium is a mixture of radioactive isotopes, predominantly the very long-lived thorium-232 (1.40 × {10}^{10}-year half-life), the parent of the thorium radioactive decay series. Other isotopes occur naturally in the uranium and actinium decay series, and thorium is present in all uranium ores. Thorium-232 is useful in breeder reactors because on capturing slow-moving neutrons it decays into fissionable uranium-233. Synthetic isotopes have been prepared; thorium-229 (7,880-year half-life), formed in the decay chain originating in the synthetic actinoid element neptunium, serves as a tracer for ordinary thorium (thorium-232).

Thorium exhibits an oxidation state of +4 in almost all of its compounds. The Th4+ ion forms many complex ions. The dioxide (ThO2), a very refractory substance, has many industrial applications; thorium nitrate has been available as a commercial salt.

Element Properties

atomic number  :  90
atomic weight  :  232.038
melting point  :  about 1,700 °C (3,100 °F)
boiling point  :  about 4,000 °C (7,200 °F)
specific gravity  :  about 11.66 (17 °C)
oxidation state  :  +4.

Additional Information

Appearance

A weakly radioactive, silvery metal.

Uses

Thorium is an important alloying agent in magnesium, as it imparts greater strength and creep resistance at high temperatures. Thorium oxide is used as an industrial catalyst.

Thorium can be used as a source of nuclear power. It is about three times as abundant as uranium and about as abundant as lead, and there is probably more energy available from thorium than from both uranium and fossil fuels. India and China are in the process of developing nuclear power plants with thorium reactors, but this is still a very new technology.

Thorium dioxide was formerly added to glass during manufacture to increase the refractive index, producing thoriated glass for use in high-quality camera lenses.

Biological role

Thorium has no known biological role. It is toxic due to its radioactivity.

Natural abundance

Thorium is found as the minerals thorite, uranothorite and thorianite. It is also found in monazite, which is the most important commercial source. Several methods are used to produce the metal, such as reducing thorium oxide with calcium or electrolysis of the fluoride.

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