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Uranium: Metals
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Uranium is a chemical element (a metal) on the periodic table. It has an atomic number of 92. It is a very heavy element, with a very large nucleus in its center. The nucleus of a certain isotope of uranium (known as uranium-235) can be easily split into two piece after absorbing a neutron, which is known as nuclear fission. This gives off a lot of energy, and is used in both nuclear reactors and nuclear weapons. Another isotope of uranium (known as uranium-238) can absorb neutrons and turn into plutonium, which is ... useful in reactors and nuclear weapons.
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Uranium metal is heavy, silvery white, malleable, ductile, and softer than steel. It is one of the densest materials known (19 g/cm3), being 1.6 times more dense than lead. Uranium metal is not as stable as triuranium octaoxide (U3O8) or uranium dioxide (UO2) because it is subject to surface oxidation. It tarnishes in air, with the oxide film preventing further oxidation of massive metal at room temperature. Water attacks uranium metal slowly at room temperature and rapidly at higher temperatures. Uranium metal powder or chips will ignite spontaneously in air at ambient temperature.
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Uranium metal reacts with water to form hydrogen gas, this reaction forms uranium dioxide and 2 to 9% uranium hydride. It is important to note that the rate of corrosion due to water is far greater than that caused by oxygen at temperatures around 100 °C. At pH values below 2 the corrosion rate at 100 °C goes down greatly, while as pH values go from 7 upwards the corrosion rate declines. Gamma irradation has little effect on the corrosion rate. M. McD. Baker, L. N. Less, S. Orman, Trans.
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Uranium exhibits three crystallographic modifications as follows: alpha --(688°C)→ beta --(776°C)→ gamma. 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.
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Uranium was discovered by Martin Heinrich Klaproth, a German chemist, in the mineral pitchblende (primarily a mix of uranium oxides) in 1789. Although Klaproth, as well as the rest of the scientific community, believed that the substance he extracted from pitchblende was pure uranium, it was actually uranium dioxide (UO2). After noticing that 'pure' uranium reacted oddly with uranium tetrachloride (UCl4), Eugène-Melchoir Péligot, a French chemist isolated pure uranium by heating uranium dioxide with potassium in a platinum crucible. Radioactivity was first discovered in 1896 when Antoine Henri Becquerel, a French physicist, detected it from a sample of uranium. Today, uranium is obtained from uranium ores such as pitchblende, uraninite (UO2), carnotite (K2(UO2)2VO4·1-3H2O) and autunite (Ca(UO2)2(PO4)2·10H2O) as well as from phosphate rock (Ca3(PO4)2), lignite (brown coal) and monazite sand ((Ce, La, Th, Nd, Y)PO4). Since there is little demand for uranium metal, uranium is usually sold in the form of sodium diuranate (Na2U2O7·6H2O)... known as yellow cake, or triuranium octoxide (U3O8).
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Uranium was discovered in 1789 in the mineral pitchblende by the German chemist Martin Heinrich Klaproth, who named it after the planet Uranus. It was first isolated in the metallic state in 1841. The radioactive properties of uranium were first demonstrated in 1896 when the French physicist Antoine Henri Becquerel produced, by the action of the fluorescent salt potassium uranyl sulfate, an image on a photographic plate covered with a light-absorbing substance. The investigations of radioactivity that followed Becquerel's experiment led to the discovery of radium and to new concepts of atomic organization. See Atom; Nuclear Energy.
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