Stanley Siegel

The uranium-oxygen system: U3O8UO3

Abstract Preparative methods for five crystalline modifications and an amorphous form of uranium trioxide are described. Some properties of the UO 3 phases are discussed, including the density, crystal structure, heat of solution, thermal stability and infra-red spectrum. Data on the UO 2·9 phase are also given.

The low temperature oxidation of UO2 and U4O9

The low temperature oxidation of UO2 to U3O7 is shown to be a diffusion-controlled diphasic reaction. Two tetragonal phases of U3O7 have been identified: α-U3O7, with a = 5·46 A, c = 5·40 A and β-U3O7 with a = 5·38 A, c = 5·55 A. Annealing experiments with β-U3O7 show the existence of a third tetragonal phase with a composition approximately UO2·3, which is stable to 500°C. Its parameters are a = 5·41 A, c = 5·49 A. The oxidation of U4O9 is also controlled by diffusion of oxygen through a second phase, UO2·3 which is in turn converted to β-U3O7. Evidence is given to show that the oxidized surface layer which forms on UO2 at 25°C is amorphous UO3.

The uranium trioxide-water system☆

The uranium trioxide-water system has been investigated in detail. The compounds prepared are UO3. 2H2O, UO3. 0·8H2O, α,β and γ UO2(OH)2 and U3O8(OH)2. The deuterated forms of these phases were also studied. Each of the compounds was characterized by X-ray diffraction, i.r., Raman and thermoanalytical methods.

The uranium-oxygen system at high pressure☆

Abstract Phase relationships existing in the uranium-oxygen system at temperatures to 1600°C and pressures to 60 kb are reported. The compounds identified in the system include UO 2 , U 4 O 9 , U 16 O 37 , U 8 O 19 , U 2 O 5 and UO 3 . Properties of new phases have been studied by X-ray diffraction, thermal and i.r. analysis. Temperature and pressure stability ranges for three crystal forms of U 2 O 5 are outlined. The crystal symmetry of α-U 2 O 5 is unknown, β-U 2 O 5 is hexagonal and γ-U 2 O 5 is monoclinic. Marked changes in the relative stability of uranium oxides are shown to occur at high pressure, and are correlated with the respective oxide structure types.

Structural studies on Li4UO5 and Na4UO5

Abstract A complete crystal structure determination of Li4UO5 and Na4UO5, based on X-ray and neutron diffraction data, is given. The compounds are body-centered tetragonal, space group I4/m-C4h5, with two molecules in the unit cell. The cell parameters are a = 6·736, c = 4·457 A for Li4UO5 and a = 7·576, c = 4·641 A for Na4UO5. The infrared spectra of these compounds are shown to be in accord with the structures.

The crystal structure of beta-platinum dioxide

Abstract β-PtO 2 crystallizes as the orthorhombic CaCl 2 -type structure with a = 4·488(3) A , b = 4·533(3) A , and c = 3·138(2) A . The oxygen coordinates are found to be: x = 0·281 and y = 0·348. This leads to two long PtO bonds of 2·02 A, four short bonds of 1·98 A, and a mininum oxygen-oxygen approach of 2·40 A. The Pt(IV) radius is 0·63 A. A comparison of the PtO 2 structure with the rutile form of TiO 2 is presented.

The synthesis of UO2·37 at high pressure

Abstract Experiments at high pressure have established the existence of the compound UO2·37±0·02. Its crystal symmetry is monoclinic and the cell parameters are a = 5·37 8 , b = 5·55 9 , c = 5·37 8 A and β = 90·29°. The compound has been prepared from mixtures of UO2 and U3O8 at 30–40 kbars and 500–1400°C. The measured density of UO2·37 is 11·34 g/cm3. The i.r. spectrum is shown to resemble that of UO2 rather than U3O8.

Preparation and properties of Cr2UO6

Abstract Cr2UO6 has been prepared hydrothermally by the reaction of uranium trioxide with a chromium(III) nitrate solution at 325–425°C. The crystal symmetry is hexagonal, space group D 3d 1 -P 3 1m , with a = 4·988[1] and c = 4·620[1] A . The i.r. spectrum is shown to be in accord with predictions of factor group analysis. Thermal analysis indicates that Cr2UO6 is stable in air to 950°C.

Bond strength-bond length relationships for some metal-oxygen bonds☆

Abstract Examination of crystal structure data for uranyl salts has led to the development of the relation D = D(1) − K( 1−1 s )) where D is the bond length for bond strength s, D(1) is the bond length corresponding to unit bond strength, and K is a constant which can be obtained from bond length data. The expression is analogous to the Pauling logarithmic relationship D = D(1) − 2 k log s. It can be shown, however, that a more general form of the bond length-bond strength expression is D = A + K s . This equation has been applied to U+6O, BO, V+5O, and Mo+6O bonds. The range of application is limited, however, to s-values near unity and greater. A similar expression D = A′ + K′ s can be used to obtain D-s information for ionic bonds. For these cases, bond distances and bond strengths are also limited to a restricted range of values. The quantities A, A′, K s and K′ s appear to be radii with the s-dependent terms representing perhaps a polarization quality. The statement that these may be radii is not proven, but is implied because of numerical similarity to known radii values. An empirical method is suggested for computing all bond strengths over the extended range of bond distances.

On the Feasibility of the CaSO4-CaS Reaction for Regeneration of Sulfated Dolomite or Limestone in Sulfur Dioxide Pollution-Control Processes

Possible regeneration mechanisms for sulfated dolomite or limestone are presented. Preliminary test results are encouraging, however, the actual reaction mechanism has not yet been established. It may involve gas-solid interactions as intermediate steps, with the overall process represented by the solid-solid reaction: 3CaSO/sub 4/ + CaS yields 4CaO + 4SO/sub 2/. (ND)