Uranium oxidation numbers

Preparation of Uranium Metal. Uranium is a highly electropositive element, and extremely difficult to reduce. As such, elemental uranium caimot be prepared by reduction with hydrogen. Instead, uranium metal must be prepared using a number of rather forcing conditions. Uranium metal can be prepared by reduction of uranium oxides (UO2 [1344-59-8] or UO [1344-58-7] with strongly electropositive elements (Ca, Mg, Na), reduction of uranium halides (UCl [10025-93-1], UCl [10026-10-5] UF [10049-14-6] with electropositive metals (Li, Na, Mg, Ca, Ba), electro deposition from molten... 

Determine the oxidation number of uranium in each of the known compounds UOj, U3Oe, U2Os, U02, UO, K2U04, Mg-UjO,. 

Unsaturated, hydrocarbons, 342 Uranium compounds, 223 electron configuration, 415 oxidation number, 414 preparation, 35 Uranium hexafluoride, 35 Uranus, data on, 444 Urea, 434... 

The crystal structures of a number of diphosphine disulphides (121) and (122) show a remarkable constancy in the bond lengths. Two types of molecule are observed in the crystal of the tetramethyl compound (121, X = Y = Me). The crystal structure of triphenylphosphine oxide (P—C 176 pm, P—O 164 pm) varies little from that observed in the uranium oxide complexes, and does not confirm P—O bond lengthening in complexes, as indicated by vp=.o (see Section 3C). 

Here, the main features of the valence band results for Th02 and UO2 will be illustrated. Since a large number of publications exists in this field (especially for uranium oxides), reference will be made only to a few selected investigations, chosen for the purpose of highlighting those aspects of the oxide bond discussed previously. A very comprehensive review of these results can be found (and references therein electronic and spectroscopic properties in Refs. 109-111). Figure 21 shows the photoemission spectrum of Th02 and UO2 up to Et = 45 eV The valence band region extends to about 10 eV. The marked difference is the appearance in UO2 of a sharp and intense peak at Et =... 

In the 1960s, a number of binary oxides, including molybdenum, tellurium, and antimony, were found to be active for the reactions and some of them were actually used in commercial reactors. Typical commercial catalysts are Fe-Sb-O by Nitto Chemical Ind. Co. (62 -64) and U-Sb-O by SOHIO (65-67), and the former is still industrially used for the ammoxidation of propylene after repeated improvements. Several investigations were reported for the iron-antimony (68-72) and antimony-uranium oxide catalysts (73-75), but more investigations were directed at the bismuth molybdate catalysts. The accumulated investigations for these simple binary oxide catalysts are summarized in the preceding reviews (5-8). 

Tile element uranium also exhibits a formal oxidation number of (II) in a few solid compounds, semimetallic in nature, such as UO and US. No simple uranium ions of oxidation state (II) are known in solution. 

Of all the elements, fluorine is the most reactive and the most electronegative (a measure of tendency to acquire electrons). In its chemically combined form, it always has an oxidation number of -1. Fluorine has numerous industrial uses, such as the manufacture of UF6, a gas used to enrich uranium in its fissionable isotope, uranium-235. Fluorine is used to manufacture uranium hexafluoride, SF6, a dielectric material contained in some electrical and electronic apparatus. A number of organic compounds contain fluorine, particularly the chlorofluorocarbons used as refrigerants and organofluorine polymers, such as DuPont s Teflon. 

Although there are a number of reported methods for preparing uranium hexachloride, most of them can be grouped under two types.(1) Uranium hexachloride can be prepared by further chlorination of lower uranium chlorides. This type includes those preparations in which a uranium oxide is the starting material, since a lower uranium chloride is normally formed as an intermediate in these chlorination reactions. (2) Uranium hexachloride is formed in the thermal decomposition of uranium pentachloride. Neither method yields uranium hexachloride in a very pure form. Uranium/chlorine ratios of 1 5.8 to 5.9 are normally the best encountered. 

There are a number of structurally interesting mixed-ligand uranyl hydroxides. For example, the basic compound of composition Zn(U02)2S04(00)4 1.5020, has a structure based on chains of 1102(011)302 pentagonal bipyramids containing tridentate bridging OH groups. Species of this type have also been studied in solution, but the complexity of the system has precluded structural characterization. There are many hydrated binary and ternary uranium oxides, such as the uraninites, that contain uranyl hydroxide complexes within their structure. 

The activity of a specimen is measured by comparing the number of impulses which it produces per minute in a Geiger counter with that produced by a substance of known specific activity, say uranium oxide, in the same position in the same counting equipment. 

Electron microscope examination by Burlein and Mastel (61) has shown the diameter of the track of a fission fragment in uranium oxide to measure 150 A. This dimension corresponds nearly to that of the micrograins of the microporous solids which were used. Consequently, the temperature of the surface of a certain number of micrograins that are in direct contact with the gaseous reactants may be raised to a very high value (more than 1000°C.) at this temperature kinetic and thermodynamic considerations applicable at the over-all macroscopic temperature cease to be valid. 

Uranium oxides Interpretation of observations for the dissociations of uranium oxides (and hydroxides) are complicated by the large number of phases and solid solutions mentioned in the literature. Karkahnavala and Phadnis [76] conclude that the thermal stabilities of the following phases increase with symmetry. The same sequence is shown by the enthalpies, rates and values of for these reactions, decomposition temperatures are shown in brackets ... 

Chicago Pile Number One, the first man-made nuclear reactor, under construction at the University of Chicago, November 1942. Lower layer holds uranium oxide pseudospheres, unfinished dead layer overlying. Note hammer in foreground for scale. 

In an attempt to determine how the actual number of resonance neutrons inside the furnace relative to those outside varied with temperature, caused by the different temperature-dependence of absorption by the carbon and other materials, two types of check experiments were made. At each temperature several bombardments were made of the cyclotron monitor, the 10-cm monitor, and the hot-dish monitor, but with no uranium present, leaving a hole in the graphite where its uranium oxide sphere was otherwise placed. These experiments were not very accurate, but they show that for a given bombardment of the furnace the number of neutrons absorbed by a hot iodine or Ga sample inside the hot furnace is the same within 8 percent as when the furnace is cold. 

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