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THORIUM Basic information
History Occurance Uses Reaction Toxicity References
Product Name:THORIUM
Product Categories:Inorganics
Mol File:7440-29-1.mol
THORIUM Structure
THORIUM Chemical Properties
Melting point 1750° (Katzin, Sonnenberger); mp 1690° (Cuthbert)
Boiling point bp ~3800°
density 1.03 g/mL at 25 °C
form soft gray-white metal
Water Solubility soluble acids; insoluble H2O, alkalies [HAW93]
Safety Information
Hazard Codes T
Risk Statements 23/24/25-34
Safety Statements 26-27-28-36/37/39-45
RIDADR UN 3264 8/PG 3
HazardClass 7
PackingGroup Commercial
MSDS Information
THORIUM Usage And Synthesis
HistoryThorium is a silvery-white metal that is air-stable and retains its lustre for several months. When contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and finally black. The physical properties of thorium are greatly influenced by the degree of contamination with the oxide. Thorium oxide (ThO2), one of thorium s compounds, has many uses. Thorium was discovered by Jöns Jacob Berzelius, a Swedish chemist, in 1828. He discovered it in a sample of a mineral that was given to him by the Reverend Has Morten Thrane Esmark, who suspected that it contained an unknown substance. Esmark s mineral is now known as thorite (ThSiO4). Thorium makes up about 0.0007% of the Earth s crust and is primarily obtained from thorite, thorianite (ThO2), and monazite ((Ce, La, Th, Nd, Y)PO4).Thorium oxide (ThO2), also called thoria, has one of the highest melting points of all oxides (3300°C). When heated in air, thorium metal turnings ignite and burn brilliantly with a white light. Because of these properties, thorium has found applications in lightbulb elements, lantern mantles, arc-light lamps, welding electrodes, and heat-resistant ceramics. Glass containing thorium oxide has a high refractive index and dispersion and is used in high-quality lenses for cameras and scientific instruments.
OccuranceThorium is a naturally occurring, radioactive substance. In the environment, thorium exists in combination with other minerals, such as silica. Small amounts of thorium are present in all rocks, soil, water, plants, and animals. Soil contains an average of about 6 parts of thorium per million parts of soil. More than 99% of natural thorium exists in the form of thorium-232 and later breaks down into two parts – a small part called ‘alpha’ radiation and a large part called the decay product. The decay product is also not stable and continues to break down through a series of decay products until a stable product is formed. During these decay processes, radioactive substances are produced. These include radium and radon. These substances give off radiation, including alpha and beta particles and gamma radiation. Rocks of certain underground mines contain thorium in a more concentrated form. After these rocks are mined, thorium is usually concentrated and changed into thorium dioxide or other chemical forms. After most of the thorium is removed, the rocks are called ‘depleted’ ore or tailings. Soil commonly contains an average of around 6 ppm of thorium. Thorium is more abundant than uranium and is widely distributed in nature as an easily exploitable resource in many countries and has not been exploited fully and commercially. Thorium fuels, therefore, complement uranium fuels and ensure long-term sustainability of nuclear power. Thorium fuel cycle is an attractive way to produce long-term nuclear energy with low radiotoxicity waste. In addition, the transition to thorium could be done through the incineration of weapons-grade plutonium (WPu) or civilian plutonium.
UsesThorium has extensive societal applications: to make ceramics, gas lantern mantles, and metals used in the aerospace industry and in nuclear reactions. In India, there has always been a strong incentive for development of thorium fuels and fuel cycles because of large thorium deposits compared to the very modest uranium reserves. Thorium oxide is also used to make glass with a high index of refraction that is used to make high-quality camera lenses. Thorium oxide is used as a catalyst in the production of sulphuric acid (H2SO4), in the cracking of petroleum products, and in the conversion of ammonia (NH3) to nitric acid (HNO3). Thorium exists in nature in a single isotopic form – Th-232 – which decays very slowly (its half-life is about three times the age of the Earth). The decay chains of natural thorium and uranium give rise to minute traces of Th-228, Th-230, and Th-234, but the presence of these in mass terms is negligible. Also, ThO2 is relatively inert and does not oxidise unlike UO2, which oxidises easily to U3O8 and UO3. Hence, long-term interim storage and permanent disposal in repository of spent ThO2-based fuel are simpler without the problem of oxidation.
ReactionThorium combines with practically all nonmetallic elements except noble gases, forming binary compounds. The most stable oxidation state is +4. Heating the metal in air or oxygen forms the oxide, ThO2. Heating the metal in hydrogen at 600°C yields the dihydride ThH2. Also, higher halides of thorium are known. They are produced by heating the dihydride in hydrogen at 250°C. Thorium hydrides are pyrophoric.
Thorium combines with nitrogen at elevated temperatures to form nitrides ThN and Th2N3. Reaction with carbon at elevated temperatures forms the carbides ThC and ThC2.
Thorium reacts with all halogens forming tetrahalides. Thorium also forms inter-metallic compounds with iron, copper, aluminum, selenium, nickel, cobalt, manganese, bismuth, and many other metals at elevated temperatures.
ToxicityAll thorium isotopes are radioactive. Also all its intermediate decay products including radon-220 are radioactive and present radiation hazard. Exposure can cause cancer.
Chemical PropertiesSoft metal with bright silvery luster when freshly cut, similar to lead in hardness when pure. Can be cold-rolled, extruded, drawn, and welded. Soluble in acids; insoluble in alkalies and water. Some alloys may ignite spontaneously, the metal in massive form is not flammable.
Chemical PropertiesThorium is a silvery-white, soft, ductile metal which is a natural radioactive element.
Physical propertiesThorium is a radioactive, silvery-white metal when freshly cut. It takes a month or morefor it to tarnish in air, at which point it forms a coating of black oxide. Although it is heavy,it is also a soft and malleable actinide metal. The metal has a rather low melting point, but itsoxide has a very high melting point of about 3,300°C. Thorium reacts slowly with water butreacts more vigorously with hydrochloric acid (HCl).
Thorium’s melting point is 1,750°C, its boiling point is 4,788°C, and its density is 11.79g/cm3.
IsotopesThere are 30 radioisotopes of thorium. One isotope in particular, thorium-232,although a weak source of radiation, has such a long half-life (1.405×10+10 years, orabout 14 billion years) that it still exists in nature and is considered stable.
Origin of NameThorium was named for Thor, the Scandinavian (Norse) god of “thunder.”
OccurrenceThorium is the 37th most abundant element found on Earth, and it makes up about0.0007% of the Earth’s crust. It is mostly found in the ores of thorite, thorianite (the oxide ofthorium), and monazite sand. It is about as abundant as lead in the Earth’s crust. As a potentialfuel for nuclear reactors, thorium has more energy potential than the entire Earth’s supply ofuranium, coal, and gas combined.
CharacteristicsThorium is chemically similar to hafnium (72Hf ) and zirconium (40Zr), located just above itin group 4 (IVB). Thorium-232 is found in nature in rather large quantities and goes througha complicated decay process called the thorium decay series. This series involves both alphaand beta emissions, as follows: Th-232 →Ra-228→Ac-228→Th-228→Ra-224→Rn-220→Po-216→Po-212→Pb-212→Bi-212→Ti-208→Pb-208. Thorium-232 can also be convertedinto thorium-233 or uranium-233 by bombarding it with neutrons. This results in Th-232adding a neutron to its nucleus, thus increasing its atomic weight. It then decays into uranium-233. This makes it potentially useful as an experimental new type of fissionable materialfor use in nuclear reactors designed to produce electricity.
HistoryDiscovered by Berzelius in 1828. Thorium occurs in thorite (ThSiO4) and in thorianite (ThO2 + UO2). 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 for thorium as a nuclear fuel is still several years in the future. 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 and uranium. 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 table. 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 retains 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 specimens often contain several tenths of a percent of the oxide. High-purity thorium has been made. Pure thorium is soft, very ductile, and can be coldrolled, swaged, and drawn. Thorium is dimorphic, changing at 1400°C from a cubic to a body-centered cubic structure. Thorium oxide has a melting point of 3300°C, which is the highest of all oxides. 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 white light. 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 high 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 dispersion. Consequently, they find application in high quality lenses for cameras and scientific instruments. 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. Thorium has not found many uses due to its radioactive nature and its handling and disposal problems. Thirty isotopes of thorium are known with atomic masses ranging from 210 to 237. All are unstable. 232Th occurs naturally and has a half-life of 1.4 × 1010 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 hours. Thorium disintegrates with the production of “thoron” (220Rn), which is an alpha emitter and presents a radiation hazard. Good ventilation of areas where thorium is stored or handled is therefore essential. Thorium metal (99.8%) costs about $25/g.
UsesAs fuel in nuclear reactors, as source of fissionable 233U. In manufacture of incandescent gas-light mantles, welding electrodes, ceramics. As hardener in Mg alloys; for filament coatings in incandescent lamps and vacuum tubes; as chemical catalyst.
UsesThorium has several commercial uses. For example, thorium oxide (ThO2) has several uses,including in the Welsbach lantern mantle that glows with a bright flame when heated by agas burner. Because of the oxide’s high melting point, it is used to make high-temperaturecrucibles, as well as glass with a high index of refraction in optical instruments. It is alsoused as a catalyst in the production of sulfuric acid (H2SO4), in the cracking procedures inthe petroleum industry, and in the conversion of ammonia (NH3) into nitric acid (HNO3).Thorium is used as a “jacket” around the core of nuclear reactors, where it becomes fissionableuranium-233 that is then used for the nuclear reaction to produce energy. Additionally,it is used in photoelectric cells and X-ray tubes and as a coating on the tungsten used to makefilaments for light bulbs. It has great potential to supplant all other nonrenewable energysources (i.e., coal, gas, and atomic energy). Thorium-232 can be converted into uranium-233,a fissionable fuel available in much greater quantities than other forms of fissionable materialsused in nuclear reactors.
DefinitionMetallic element of atomic number 90, a member of the actinide series (group IIIB of periodic table), aw 232.0381, valence of 4; radioactive, no stable isotopes.
DefinitionA toxic radioactive element of the actinoid series that is a soft ductile silvery metal. It has several long-lived radioisotopes found in a variety of minerals including monazite. Thorium is used in magnesium alloys, incandescent gas mantles, and nuclear fuel elements. Symbol: Th; m.p. 1780°C; b.p. 4790°C (approx.); r.d. 11.72 (20°C); p.n. 90; r.a.m. 232.0381.
Definitionthorium: Symbol Th. A grey radioactivemetallic element belonging tothe actinoids; a.n. 90; r.a.m.232.038; r.d. 11.5–11.9 (17°C); m.p.1740–1760°C; b.p. 4780–4800°C. It occursin monazite sand in Brazil,India, and USA. The isotopes of thoriumhave mass numbers from 223to 234 inclusive; the most stable isotope,thorium–232, has a half-life of1.39 × 1010 years. It has an oxidationstate of (+4) and its chemistry resemblesthat of the other actinoids. It canbe used as a nuclear fuel for breederreactors as thorium–232 capturesslow neutrons to breed uranium–233.Thorium dioxide (thoria, ThO2) isused on gas mantles and in specialrefractories. The element was discoveredby J. J. Berzelius in 1829.
General DescriptionSilver to grayish radioactive metal. Twice as dense as lead. Radioactive materials emit ionizing radiation, detectable only using special instruments. Exposure to intense levels of radiation or prolonged exposure to low levels can be harmful. Film is also damaged by radiation.
Air & Water ReactionsPyrophoric material, spontaneously ignites in air.
Reactivity ProfileTHORIUM when heated with chlorine (or sulfur), reacts vigorously with incandescence [Mellor 7:208 1946-47]. When thorium is heated with phosphorus, they unite with incandescence [Svenska Akad. 1829 p.1].
HazardFlammable and explosive in powder form. Dusts of thorium have very low ignition points and may ignite at room temperature. Radioactive decay isotopes are dangerous when ingested.
HazardAs thorium undergoes natural radioactive decay, a number of products, including gases,are emitted. These decay products are extremely dangerous radioactive poisons if inhaled oringested.
Health HazardRadiation presents minimal risk to transport workers, emergency response personnel and the public during transportation accidents. Packaging durability increases as potential hazard of radioactive content increases. Undamaged packages are safe. Contents of damaged packages may cause higher external radiation exposure, or both external and internal radiation exposure if contents are released. Low radiation hazard when material is inside container. If material is released from package or bulk container, hazard will vary from low to moderate. Level of hazard will depend on the type and amount of radioactivity, the kind of material it is in, and/or the surfaces it is on. Some material may be released from packages during accidents of moderate severity but risks to people are not great. Released radioactive materials or contaminated objects usually will be visible if packaging fails. Some exclusive use shipments of bulk and packaged materials will not have "RADIOACTIVE" labels. Placards, markings and shipping papers provide identification. Some packages may have a "RADIOACTIVE" label and a second hazard label. The second hazard is usually greater than the radiation hazard; so follow this GUIDE as well as the response GUIDE for the second hazard class label. Some radioactive materials cannot be detected by commonly available instruments. Runoff from control of cargo fire may cause low-level pollution.
Safety ProfileSuspected carcinogen. Taken internally as Th02, it has proven to be carcinogenic due to its radioactivity. On an acute basis it has caused dermatitis. Flammable in the form of dust when exposed to heat or flame, or by chemical reaction with oxidizers. The powder may ignite spontaneously in air. Potentially hazardous reactions with chlorine, fluorine, bromine, oxygen, phosphorus, silver, sulfur, air, nitryl fluoride, peroxyformic acid.
Potential ExposureMetallic thorium is used in nuclear reactors to produce nuclear fuel; in the manufacture of incandescent mantles; as an alloying material, especially with some of the lighter metals, for example, magnesium as a reducing agent in metallurgy; for filament coatings in incandescent lamps and vacuum tubes; as a catalyst in organic synthesis; in ceramics; and in welding electrodes. Exposure may occur during production and use of thorium-containing materials, in the casting and machining of alloy parts; and from the fume produced during welding with thorium electrodes. Thorium nitrate is an oxidizer. Contact with combustibles, and reducing agents will cause violent combustion or ignition.
ShippingUN2975 Thorium metal, pyrophoric, Hazard class: 7; Labels: 7-Radioactive material, 4.2-Spontaneously combustible material. Note: UN/NA 2975 doesn’t appear in the 49 CFR Hazmat Table.
IncompatibilitiesThe powder may ignite spontaneously in air. Heating may cause violent combustion or explosion. May explosively decompose from shock, friction, or concussion. Incompatible with strong oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause violent fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides, nitryl fluoride; peroxyformic acid; silver, sulfur.
Waste DisposalRecovery and recycling is in the preferred route.
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