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7440-61-1

Name URANIUM
CAS 7440-61-1
EINECS(EC#) 231-170-6
Molecular Formula U
MDL Number MFCD00049688
Molecular Weight 238.03
MOL File 7440-61-1.mol

Chemical Properties

Description
Uranium is a silver-white, lustrous, heavy, mildly radioactive metal. Its appearance will change upon exposure to air or water, as oxidation occurs. Its colour darkens through brass, from brown to charcoal grey. Powders, fines, chips, or turnings oxidise rapidly, yielding a dull or flat dark grey or brown colour. Uranium is almost as hard as steel and much denser than lead. Natural uranium is used to make fuel for nuclear power plants; depleted uranium is the leftover product. Some alloys will oxidise more slowly, retaining the silver-white and then brassy colour. No odour is found. Uranium is used as an abundant source of concentrated energy. Uranium occurs in most rocks in concentrations of 2–4 parts per million and is as common in the Earth’s crust as tin, tungsten, and molybdenum. Uranium occurs in seawater and can be recovered from the oceans.
Uranium is a naturally occurring radioactive element. Natural uranium is a mixture of three isotopes: 234U, 235U, and 238U. The most common isotope is 238U; it makes up about 99% of natural uranium by mass. Depleted uranium is a mixture of the same three uranium isotopes except that it has very little 234U and 235U. It is less radioactive than natural uranium. The high density of uranium means that it also finds uses in the keels of yachts and as counterweights for aircraft control surfaces, as well as for radiation shielding. Uranium metal is known to react dangerously with carbon tetrachloride, chlorine, fluorine, nitric acid, nitric oxide, selenium, sulphur, and water (in finely divided form). On decomposition with fire, it produces uranium metal fume and/or oxide. Radioactive progenies (daughters), thorium-234, protactinium-234, and protactinium-234m (metastable), are produced by natural radioactive decay; they are the source of the majority of the penetrating radiation. These isotopes can be concentrated in situations where the metal is melted, condensed, or dissolved, potentially elevating the observed external dose rate. Many industries involved in mining, milling, and processing of uranium can also release it into the environment. Inactive uranium industries may continue to release uranium into the environment.
Appearance Dense, silvery solid. Strongly electropositive, ductile and malleable, poor conductor of electricity. Forms solid solutions (for nuclear reactors) with molybdenum, niobium, titanium, and zirconium. The metal reacts with nearly all nonmetals. It is attacke
Melting point  314-316°C (dec.)
Boiling point  4160.06°C (estimate)
density  1.01 g/mL at 25 °C
storage temp.  Refrigerator
solubility  Aqueous Base (Slightly)
form  silvery-white orthorhombic crystals
color  Pale Brown
History Yellow-colored glass, containing more than 1% uranium oxide and dating back to 79 A.D., has been found near Naples, Italy. Klaproth recognized an unknown element in pitchblende and attempted to isolate the metal in 1789. The metal apparently was first isolated in 1841 by Peligot, who reduced the anhydrous chloride with potassium. Uranium is not as rare as it was once thought. It is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, davidite, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. Large deposits of uranium ore occur in Utah, Colorado, New Mexico, Canada, and elsewhere. Uranium can be made by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, aluminum, or carbon at high temperatures. The metal can also be produced by electrolysis of KUF5 or UF4, dissolved in a molten mixture of CaCl2 and NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament. Uranium exhibits three crystallographic modifications as follows: α--688℃--→β--776℃--→γ Uranium is a heavy, silvery-white metal that is pyrophoric when finely divided. It is a little softer than steel, and is attacked by cold water in a finely divided state. It is malleable, ductile, and slightly paramagnetic. In air, the metal becomes coated with a layer of oxide. Acids dissolve the metal, but it is unaffected by alkalis. Uranium has twenty-three isotopes, one of which is an isomer and all of which are radioactive. Naturally occurring uranium contains 99.2745% by weight 238U, 0.720% 235U, and 0.0055% 234U. Studies show that the percentage weight of 235U in natural uranium varies by as much as 0.1%, depending on the source. The U.S.D.O.E. has adopted the value of 0.711 as being their “official” percentage of 235U in natural uranium. Natural uranium is sufficiently radioactive to expose a photographic plate in an hour or so. Much of the internal heat of the Earth is thought to be attributable to the presence of uranium and thorium. 238U, with a half-life of 4.46 × 109 years, has been used to estimate the age of igneous rocks. The origin of uranium, the highest member of the naturally occurring elements — except perhaps for traces of neptunium or plutonium — is not clearly understood, although it has been thought that uranium might be a decay product of elements of higher atomic weight, which may have once been present on Earth or elsewhere in the universe. These original elements may have been formed as a result of a primordial “creation,” known as “the big bang,” in a supernova, or in some other stellar processes. The fact that recent studies show that most trans-uranic elements are extremely rare with very short half-lives indicates that it may be necessary to find some alternative explanation for the very large quantities of radioactive uranium we find on Earth. Studies of meteorites from other parts of the solar system show a relatively low radioactive content, compared to terrestrial rocks. Uranium is of great importance as a nuclear fuel. U can be converted into fissionable plutonium by the following reactions: 238U(n,γ)→239U--β--→239Np--β--→239Pu
This nuclear conversion can be brought about in “breeder” reactors where it is possible to produce more new fissionable material than the fissionable material used in maintaining the chain reaction. 235U is of even greater importance, for it is the key to the utilization of uranium. 235U, while occurring in natural uranium to the extent of only 0.72%, is so fissionable with slow neutrons that a self-sustaining fission chain reaction can be made to occur in a reactor constructed from natural uranium and a suitable moderator, such as heavy water or graphite, alone. 235U can be concentrated by gaseous diffusion and other physical processes, if desired, and used directly as a nuclear fuel, instead of natural uranium, or used as an explosive. Natural uranium, slightly enriched with 235U by a small percentage, is used to fuel nuclear power reactors for the generation of electricity. Natural thorium can be irradiated with neutrons as follows to produce the important isotope 233U. 232Th(n,γ)→233Th--β--→233Pa--β--→233U While thorium itself is not fissionable, 233U is, and in this way may be used as a nuclear fuel. One pound of completely fissioned uranium has the fuel value of over 1500 tons of coal. The uses of nuclear fuels to generate electrical power, to make isotopes for peaceful purposes, and to make explosives are well known. The estimated world-wide production of the 437 nuclear power reactors in operation in 1998 amounted to about 352,000 megawatt hours. In 1998 the U.S. had about 107 commercial reactors with an output of about 100,000 megawatt-hours. Some nuclear-powered electric generating plants have recently been closed because of safety concerns. There are also serious problems with nuclear waste disposal that have not been completely resolved. Uranium in the U.S. is controlled by the U.S. Nuclear Regulatory Commission, under the Department of Energy. Uses are being found for the large quantities of “depleted” uranium now available, where uranium-235 has been lowered to about 0.2%. Depleted uranium has been used for inertial guidance devices, gyrocompasses, counterweights for aircraft control surfaces, ballast for missile reentry vehicles, and as a shielding material for tanks, etc. Concerns, however, have been raised over its low radioactive properties. Uranium metal is used for X-ray targets for production of high-energy X-rays. The nitrate has been used as photographic toner, and the acetate is used in analytical chemistry. Crystals of uranium nitrate are triboluminescent. Uranium salts have also been used for producing yellow “vase-line” glass and glazes. Uranium and its compounds are highly toxic, both from a chemical and radiological standpoint. Finely divided uranium metal, being pyrophoric, presents a fire hazard. The maximum permissible total body burden of natural uranium (based on radiotoxicity) is 0.2 μCi for soluble compounds. Recently, the natural presence of uranium and thorium in many soils has become of concern to homeowners because of the generation of radon and its daughters (see under Radon). Uranium metal is available commercially at a cost of about $6/g (99.7%) in air-tight glass under argon.
Uses
Uranium is a white radioactive metallic element found in pitchblende ore, also known as uraninite. Uranyl chloride and uranyl nitrate are two uranium compounds used in photography.
EPA Substance Registry System Uranium (7440-61-1)

Safety Data

Hazard Codes  T+
Risk Statements 
Safety Statements 
RIDADR  UN 3264 8/PG 3
WGK Germany  3
HazardClass  7
PackingGroup  Commercial
HS Code  28441000
Safety Profile
A highly toxic element on an acute basis. The permissible levels for soluble compounds are based on chemical toxicity, whereas the permissible body level for insoluble compounds is based on radiotoxicity. The high chemical toxicity of uranium and its salts is largely shown in kidney damage, which may not be reversible. Acute arterial lesions may occur after acute exposures. The most soluble uranium compounds are UF6, UO2(NO3)2, U02Cl2, UO2F2, and uranyl acetates, sulfates, and carbonates. Some moderately soluble compounds are UF4, UO2, UO4, (NH4)2 U2O7, UO3, and uranyl nitrates. The rapid passage of soluble uranium compounds through the body tends to allow relatively large amounts to be absorbed. Soluble uranium compounds may be absorbed through the skin. The least soluble compounds are high-F2ed UO2, U3O8, and uranium hydrides and carbides. The high toxicity effect of insoluble compounds is largely due to lung irradation by inhaled particles. This material is transferred from the lungs of animals quite slowly. A very dangerous fire hazard in the form of a solid or dust when exposed to heat or flame. It can react violently with air, Cl2, F2, HNO3, NOx Se, S, water, NH3, BrF3, trichloroethylene, nitryl fluoride. During storage it may form a pyrophoric surface due to effects of air and moisture. Depleted uranium (the 238U by-product of the uranium enrichment process, with relatively low radioactivity) is used in armor-piercing shells, ship or aircraft ballast, and counterbalances. Uranium is also used in making colored ceramic glazes.
Hazardous Substances Data 7440-61-1(Hazardous Substances Data)
Toxicity
Three isotopes (234U, 235U, 238U) exist, and a large number of uranium salts are known. They present both toxic and radiological hazards. The most important use of uranium is in the nuclear energy industry, but uranium compounds are also used in ceramics, as catalysts and in certain alloys. Entry into the body can occur during a variety of processes involved with the mining, processing or use of uranium and its compounds, and is probably largely by inhalation of dusts, fumes, etc. or by ingestion. Acute uranium toxicity is primarily nephrotoxicity. About 50% of plasma uranium is bound, as the uranyl ion, to bicarbonate (HCO23 ), which is filtered by the glomerulus. As a result of acidification in the proximal tubule, the bicarbonate complex dissociates followed by reabsorption of the HCO23 ; the released UO21 then becomes attached to the membrane of the proximal tubule cells. Loss of cell function follows, as evidenced by increased concentration of glucose, amino acids, and proteins in the urine. 2,3-Mercapto-1-propanol (British Anti-Lewisite, BAL) is ineffective as a therapeutic agent for uranium poisoning; CaEDTA is recommended. Chronic uranium toxicity appears to be radiation related, the effects being similar to those of ionizing radiation. In humans, cancer of the lung, bone, and lymphatic system are all known to occur.
IDLA 10 mg U/m3

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