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Uranates
A uranate is a ternary oxide involving the element uranium in one of the oxidation states 4, 5 or 6. A typical chemical formula is MxUyOz, where M represents a cation. The uranium atom in uranates(VI) has two short collinear U–O bonds and either four or six more next nearest oxygen atoms. The structures are infinite lattice structures with the uranium atoms linked by bridging oxygen atoms. Uranium oxides are the foundation of the nuclear fuel cycle ("ammonium diuranate" and "sodium diuranate" are intermediates in the production of uranium oxide nuclear fuels) and their long-term geological disposal requires a thorough understanding of their chemical reactivity, phase transitions, and physical and chemical properties. Synthesis A method of general applicability involves combining two oxides in a high temperature reaction. For example, :Na2O + UO3 → Na2UO4 Another method is the thermal decomposition of a complex, such as an acetate complex. For example, microcrystalline bariu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium Trioxide
Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph is amorphous UO3. Production and use There are three methods to generate uranium trioxide. As noted below, two are used industrially in the reprocessing of nuclear fuel and uranium enrichment. # U3O8 can be oxidized at 500 °C with oxygen. Note that above 750 °C even in 5 atm O2 UO3 decomposes into U3O8. # Uranyl nitrate, UO2(NO3)2·6H2O can be heated to yield UO3. This occurs during the reprocessing of nuclear fuel. Fuel rods are dissolved in HNO3 to separate uranyl nitrate from plutonium and the fission products (the PUREX method). The pure uranyl nitrate is converted to solid UO3 by heating at 400 °C. After reduction with hydrogen (with other inert gas present) to uranium dioxide, the uranium can be used in new MOX fuel rod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ammonium Diuranate
Ammonium diuranate or (ADU) ((NH4)2U2O7), is one of the intermediate chemical forms of uranium produced during yellowcake production. The name "yellowcake" originally given to this bright yellow salt, now applies to mixtures of uranium oxides which are actually hardly ever yellow. It also is an intermediate in mixed-oxide ( MOX) fuel fabrication. Although it is usually called "ammonium diuranate" as though it has a "diuranate" ion , this is not necessarily the case. It can also be called diammonium diuranium heptaoxide. The structure was theorized to be similar to that of uranium trioxide dihydrate. Recent literature has shown that the structure more closely resembles the mineral metaschoepite, the partially dehydrated form of schoepite. It is precipitated by adding aqueous ammonium hydroxide after uranium extraction by tertiary amines in kerosene. This precipitate is then thickened and centrifuged before being calcined to uranium oxide. Canadian practice favours the production o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Diuranate
Sodium diuranate, also known as the yellow oxide of uranium, is an inorganic chemical compound with the chemical formula . It is a sodium salt of a diuranate anion. It forms a hexahydrate . Sodium diuranate is commonly referred to by the initials SDU. Along with ammonium diuranate it was a component in early yellowcakes. The ratio of the two compounds is determined by process conditions; however, yellowcake is now largely a mix of uranium oxides. Preparation In the classical procedure for extracting uranium, pitchblende is broken up and mixed with sulfuric and nitric acids. The uranium dissolves to form uranyl sulfate and sodium carbonate is added to precipitate impurities. If the uranium in the ore is in the tetravalent oxidation state, an oxidiser is added to oxidise it to the hexavalent oxidation state, and sodium hydroxide is then added to make the uranium precipitate as sodium diuranate. The alkaline process of milling uranium ores involves precipitating sodium uran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Symmetry
In chemistry, molecular symmetry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain many of a molecule's chemical property, chemical properties, such as whether or not it has a molecular dipole moment, dipole moment, as well as its allowed spectroscopy, spectroscopic transitions. To do this it is necessary to use group theory. This involves classifying the states of the molecule using the irreducible representations from the character table of the symmetry group of the molecule. Symmetry is useful in the study of molecular orbitals, with applications to the Hückel method, to ligand field theory, and to the Woodward–Hoffmann rules. Many university level textbooks on physical chemistry, quantum chemistry, spectroscopy and inorganic chemistry discuss symmetry. Another framework on a larger scale is the use of crystal sy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium Glass Collection
Uranium is a chemical element; it has symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactively decays, usually by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes, making them useful for dating the age of the Earth. The most common isotopes in natural uranium are uranium-238 (which has 146 neutrons and accounts for over 99% of uranium on Earth) and uranium-235 (which has 143 neutrons). Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead and slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite. Many contemporary u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
