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Amorphous Uranium(VI) Oxide
Amorphous uranium(VI) oxide (''am''-U2O7) is an orange diuranyl compound, most commonly obtained from the thermal decomposition of uranyl peroxide tetrahydrate at temperatures between 150 and 500 °C. It exists at room temperature as a powder. ''Am''-U2O7 does not comprise a regular, long-range atomic structure, as demonstrated by its characteristic diffuse scattering pattern obtained by X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles .... As a result, the molecular structure of this material is little understood, although experimental and computational attempts to elucidate a local atomic environment have yielded some success.S. Odoh, J. Shamblin, C. Colla, S. Hickam, H. Lobeck, R. Lopez, T. Olds, J. Szymanowski, G. Sigmon, J. Neuefeind, W. Casey, M. Lang, L. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranyl Peroxide
Uranyl peroxide or uranium peroxide hydrate (UO4·nH2O) is a pale-yellow, soluble peroxide of uranium. It is found to be present at one stage of the enriched uranium fuel cycle and in yellowcake prepared via the ''in situ'' leaching and resin ion exchange system. This compound, also expressed as UO3·(H2O2)·(H2O), is very similar to uranium trioxide hydrate UO3·''n''H2O. The dissolution behaviour of both compounds are very sensitive to the hydration state (n can vary between 0 and 4). One main characteristic of uranium peroxide is that it consists of small needles with an average AMAD of about 1.1 μm. The uranyl minerals studtite, UO4·4H2O, and metastudtite, UO4·2H2O, are the only minerals discovered to date found to contain peroxide. The product is a light yellow powder. Synthesis In general, uranyl peroxide can be obtained from a solution of uranium (VI) by adding a peroxide, usually hydrogen peroxide solution. The dihydrate is obtained from a boiling solution of uran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triuranium Octoxide
Triuranium octoxide (U3O8) is a compound of uranium. It is present as an olive green to black, odorless solid. It is one of the more popular forms of yellowcake and is shipped between mills and refineries in this form. U3O8 has potential long-term stability in a geologic environment. In the presence of oxygen (O2), uranium dioxide (UO2) is oxidized to U3O8, whereas uranium trioxide (UO3) loses oxygen at temperatures above 500 °C and is reduced to U3O8. The compound can be produced by any one of three primary chemical conversion processes, involving either uranium tetrafluoride (UF4) or uranyl fluoride (UO2F2) as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U3O8 is one of the most kinetically and thermodynamically stable forms of uranium. Its particle density is 8.3 g cm−3. Triuranium octoxide is converted to uranium hexafluoride for the purpose of uranium enrichment. Solid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium
Uranium is a chemical element with the 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 is weakly radioactive because all isotopes of uranium are unstable; the half-lives of its naturally occurring isotopes range between 159,200 years and 4.5 billion years. 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. In nature, uranium is found as uranium-238 (99. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 (called a passivation layer) that protects the foil from further corrosion.Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. . Stoichiometry (the measurable relationship between reactants and chemical equations of a equation or reaction) Oxides are extraordinarily diverse in terms of stoichiometries and in terms of the structures of each stoichiometry. Most elements form oxides of more than one stoichiometry. A well known example is carbon monoxide and carbon dioxide.Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray Diffraction
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their crystallographic disorder, and various other information. Since many materials can form crystals—such as salts, metals, minerals, semiconductors, as well as various inorganic, organic, and biological molecules—X-ray crystallography has been fundamental in the development of many scientific fields. In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences among various mat ... [...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, γ-UO3, is a yellow-orange powder. 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 n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Density Functional Theory
Density-functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body systems, in particular atoms, molecules, and the condensed phases. Using this theory, the properties of a many-electron system can be determined by using functionals, i.e. functions of another function. In the case of DFT, these are functionals of the spatially dependent electron density. DFT is among the most popular and versatile methods available in condensed-matter physics, computational physics, and computational chemistry. DFT has been very popular for calculations in solid-state physics since the 1970s. However, DFT was not considered accurate enough for calculations in quantum chemistry until the 1990s, when the approximations used in the theory were greatly refined to better model the exchange and correlation interactions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranyl
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . It has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen. Four or more ligands may be bound to the uranyl ion in an equatorial plane around the uranium atom. The uranyl ion forms many complexes, particularly with ligands that have oxygen donor atoms. Complexes of the uranyl ion are important in the extraction of uranium from its ores and in nuclear fuel reprocessing. Structure and bonding The uranyl ion is linear and symmetrical, with both U–O bond lengths of about 180 pm. The bond lengths are indicative of the presence of multiple bonding between the uranium and oxygen atoms. Since uranium(VI) has the electronic configuration of the preceding noble gas, radon, the electrons used in forming the U–O bonds are supplied by the oxygen atoms. The electrons are donated into empty atomic orbitals on the uranium atom. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peroxide
In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen peroxide (), colloquially known simply as "peroxide". It is marketed as solutions in water at various concentrations. Many organic peroxides are known as well. In addition to hydrogen peroxide, some other major classes of peroxides are: * Peroxy acids, the peroxy derivatives of many familiar acids, examples being peroxymonosulfuric acid and peracetic acid, and their salts, one example of which is potassium peroxydisulfate. * Main group peroxides, compounds with the linkage (E = main group element). * Metal peroxides, examples being barium peroxide (), sodium peroxide () and zinc peroxide Zinc peroxide (ZnO2) appears as a bright yellow powder at room temperature. It was historically used as a surgical antiseptic. More recently zinc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schoepite
Schoepite, empirical formula (UO2)8O2(OH)12•12(H2O) is a rare alteration product of uraninite in hydrothermal uranium deposits. It may also form directly from ianthinite. The mineral presents as a transparent to translucent yellow, lemon yellow, brownish yellow, or amber orthorhombic tabular crystals. Although over 20 other crystal forms have been noted; rarely in microcrystalline aggregates. When exposed to air schoepite converts over a short time to the metaschoepite form (UO3 • H2O, ) within a few months of being exposed to ambient air. The hardness is 2.5, density is 4.8 g/cm3, and it streaks yellow. It was first described from specimens from Shinkolobwe mine in Belgian Congo in 1923, several additional localities are known. Schoepite was named to honor Alfred Schoep (1881–1966), Professor of Mineralogy at the University of Ghent, Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
