Uranium structure

In many metals each atom is attached to some of its neighbors by strong bonds and to others by much weaker bonds. An extreme case is, 8-tungsten, in which there are straight strings of strongly bonded atoms. Similar strings are also present in the a-uranium structure. 

The lanthanide metals should also be investigated to higher pressures than previously applied. It is not excluded that their 4 f electrons also participate in bonding as do the 5 f s of Bk and Cf, after the dhcp, ccp and, possibly, distorted fee phases have been reached. An indication of this possibility can be seen in the recent discovery of the a-uranium structure type in praseodymium (Pr IV) . This structure type was previously observed for cerium, but was thought to be restricted to that metal which has an exceptional position among the lanthanide elements. 

Synonyms HOAt l-Hydroxy-lH-v-triazolo[4, 5-b]pyridine 7-Aza-l-hydroxybenzotriazole [1,2, 3]Triazolo[4,5-6]pyridin-3-ol 3-Hydroxy-3H-l,2, 3-triazolo[4,5-6]pyridine HATU lH-l,2,3-Triazo-lo [4,5-6]pyridinium, 1 - [bis( dimethylamino)methyl-ene]-, hexafluorophosphate 1-), 3-oxide HATU may crystallize as guanidinimum N-oxides N-form), rather than the isomeric uranium structures (0-form) depending on storage conditions N-[(di-methylamino)-lH-l,2,3-triazolo[4,5-fc]pyridine-l-yl-methylene] -N-methylmethanaminium hexafluorophosphate. PyAOP Tri-l-pyrrolidinyl(3H-... 

Allen PG, Conradson SD, Wilson MS, Gottesfeld S, Raistrick ID (1993) Real time structural electrochemistry of platinum clusters using dispersive XAFS. Mat Res Soc Symp Proc 307 (Applications of Synchrotron Radiation Techniques to Materials Science) 51-56 Allen PG, Conradson SD, Wilson MS, Gottesfeld S, Raistrick ID, Valerio J, Lovato M (1995b) Direct observation of surface oxide formation and reduction on platinum clusters by time-resolved X-ray absorption spectroscopy. J. Electroanal Chem 384 99-103 Allen PG, Shuh DK, Bucher JJ, Edelstein NM, Palmer CEA, Silva RJ, Nguyen SN, Marquez LN, Hudson EA (1996b) Determinations of uranium structures by EXAFS schoepite and other U(VT) oxide precipitates. Radiochim Acta 75 47-53... 

Allen PG, Shuh DK, Bucher JJ, Edelstein NM, Reich T, Denecke MA, Nitsche H (1996a) EXAFS determinations of uranium structures The uranyl ion complexed with tartaric, citric, and malic acids. Inorg Chem 35 784-787... 

Steel and graphite structures - Fermi Uranium structures - Allison Helium purity - Allison... 

Uranium.—Uranium structures reported are more or less equally divided between the -t-4 and -t-6 states, the former providing the more varied geometry. 

Hayton TW. Metal-Ugand multiple bonding in uranium structure and reactivity. Dalton Trans. 2010 39 1145-1158. 

Initially, the only means of obtaining elements higher than uranium was by a-particle bombardment of uranium in the cyclotron, and it was by this means that the first, exceedingly minute amounts of neptunium and plutonium were obtained. The separation of these elements from other products and from uranium was difficult methods were devised involving co-precipitation of the minute amounts of their salts on a larger amount of a precipitate with a similar crystal structure (the carrier ). The properties were studied, using quantities of the order of 10 g in volumes of... 

The preparation and structure determination of ferrocene marked the beginning of metallocene chemistry Metallocenes are organometallic compounds that bear cyclo pentadiemde ligands A large number are known even some m which uranium is the metal Metallocenes are not only stucturally interesting but many of them have useful applications as catalysts for industrial processes Zirconium based metallocenes for example are the most widely used catalysts for Ziegler-Natta polymerization of alkenes We 11 have more to say about them m Section 14 15... 

Fig. 5.8. (a) Packing of the unequally sized ions of sodium chloride to give a f.c.c. structure KCl and MgO pack in the same v/ay. (b) Packing of ions in uranium dioxide this is more complicated than in NaCi because the U and O ions are not in 1 1 ratio. 

EXAFS is a nondestructive, element-specific spectroscopic technique with application to all elements from lithium to uranium. It is employed as a direct probe of the atomic environment of an X-ray absorbing element and provides chemical bonding information. Although EXAFS is primarily used to determine the local structure of bulk solids (e.g., crystalline and amorphous materials), solid surfaces, and interfaces, its use is not limited to the solid state. As a structural tool, EXAFS complements the familiar X-ray diffraction technique, which is applicable only to crystalline solids. EXAFS provides an atomic-scale perspective about the X-ray absorbing element in terms of the numbers, types, and interatomic distances of neighboring atoms. 

CP-1 was assembled in an approximately spherical shape with the purest graphite in the center. About 6 tons of luanium metal fuel was used, in addition to approximately 40.5 tons of uranium oxide fuel. The lowest point of the reactor rested on the floor and the periphery was supported on a wooden structure. The whole pile was surrounded by a tent of mbberized balloon fabric so that neutron absorbing air could be evacuated. About 75 layers of 10.48-cm (4.125-in.) graphite bricks would have been required to complete the 790-cm diameter sphere. However, criticality was achieved at layer 56 without the need to evacuate the air, and assembly was discontinued at layer 57. The core then had an ellipsoidal cross section, with a polar radius of 209 cm and an equatorial radius of309 cm [20]. CP-1 was operated at low power (0.5 W) for several days. Fortuitously, it was found that the nuclear chain reaction could be controlled with cadmium strips which were inserted into the reactor to absorb neutrons and hence reduce the value of k to considerably less than 1. The pile was then disassembled and rebuilt at what is now the site of Argonne National Laboratory, U.S.A, with a concrete biological shield. Designated CP-2, the pile eventually reached a power level of 100 kW [22]. 

This book presents a unified treatment of the chemistry of the elements. At present 112 elements are known, though not all occur in nature of the 92 elements from hydrogen to uranium all except technetium and promethium are found on earth and technetium has been detected in some stars. To these elements a further 20 have been added by artificial nuclear syntheses in the laboratory. Why are there only 90 elements in nature Why do they have their observed abundances and why do their individual isotopes occur with the particular relative abundances observed Indeed, we must also ask to what extent these isotopic abundances commonly vary in nature, thus causing variability in atomic weights and possibly jeopardizing the classical means of determining chemical composition and structure by chemical analysis. 

Compounds with Sc, Y, lanthanoids and actinoids are of three types. Those with composition ME have the (6-coordinated) NaCl structure, whereas M3E4 (and sometimes M4E3) adopt the body-centred thorium phosphide structure (Th3P4) with 8-coordinated M, and ME2 are like ThAsi in which each Th has 9 As neighbours. Most of these compounds are metallic and those of uranium are magnetically ordered. Full details of the structures and properties of the several hundred other transition metal-Group 15 element compounds fall outside the scope of this treatment, but three particularly important structure types should be mentioned because of their widespread occurrence and relation to other structure types, namely C0AS3,... 

Systematic features in the structural chemistry of the uranium halides, oxyhalides and related transition metal and lanthanide halides, J. C. Taylor, Coord. Chem. Rev., 1976, 20,197-273 (205). 

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