683. Some aspects of the system uranium trioxide–water

Abstract

Uranium trioxide in contact with water at about 180" gives an orthorhombic hydrate, U0,,0.8H2O, with the cell dimensions a = 10-23 & 0-01, b = 6.89 f 0.01, c = 4-28 & 0.01 A. These dimensions appear to vary slightly with deviation of the water content from 0-8 mole per uranium atom. Between 200" and 280' another phase appears, UO,,l*OH,O, also orthorhombic with cell dimensions a = 5.638 f 0.005, b = 6.273 f 0.005, c = 9-925 f 0.005 A, space-group Pbca. The hemihydrate, U0,,0.5Hz0,is stable in water above 250". A further phase, possibly due to a relatively high pH and probably triclinic, was observed when the uranium trioxide was heated in water at 230" in contact with glass.Some of the properties of these hydrates are described, together with observations on the preparation of pure anhydrous uranium trioxide from uranyl nitrate.PREVIOUS investigations on the hydrated oxides of uranium indicated that the trioxide is stable in water, up to high temperatures, and that over the range 70-300" (approx.) it forms a monohydrate.1 The system is quite complex, however, and Katz and Rabinowitz quoted the following four crystalline modifications observed by D. T. Vier : (i) a-UO,,H,O, large six-sided orthorhombic basal tablets ; (ii) B-UO,,H,O, small orthorhombic prismatic tablets with slightly larger unit cell than the a-form ; (iii) y-UO,,H,O, six-sided columnar crystals, with X-ray diffraction pattern similar to that of the a-and the @-form, but perhaps belonging to a different system : contains (0.9 mole of H20 per uranium atom; (iv) 8-UO3,H2O, triclinic, giving a complex X-ray diffraction pattern. The last form may be due to impurities.Very few details were given of the preparation and the relations between these various forms, and the present investigation was undertaken to obtain more extensive information in the range 180-320". The particular form of UO,,H,O obtained may be sensitive to the presence of traces of impurities, such as the soluble uranyl ion, and so some observations are made also on the preparation of uranium trioxide free from all contaminants down to a level of a few parts per million. EXPERIMENTALA sample (about 100 mg.) was suspended in a platinum boat on the end of a 35-cm. extension fibre from the lower end of the helix. The temperature of the sample was raised linearly at about 2"/min.

The crystal structure and anisotropic thermal expansion of β-uranyl dihydroxide, UO2(OH)2

“…The large number of strong high-angle reflexions, including four in the range 80°< 0 < 84.6 °, also contributed to the precision of this work. The lattice parameters tend to be larger than those of RCL and of Dawson, Wait, Alcock & Chilton (1956), and are more precise.…”

Thermodynamic properties of selected uranium compounds and aqueous species at 298.15 K and 1 bar and at higher temperatures; preliminary models for the origin of coffinite deposits

“…One series is represented by 3-UOo*2H20, a-U0 3 *HoO, U0 3 *0.8HoO, U0 3 *0.5H 20, and finally a 1103 polymorph that Dawson et al (1956) suggest is monoclinic. The second series (note that the series does not contain a hemihydrate phase) involves a-lK^'Z^O, 3-UOo'HoO and a simple cubic UO^ polymorph that can be oxygen diffident (with the limit about U02.88» Dawson et al).…”

“…These phases include three dihydrates (Christ and Clark, 1960), three monohydrates (e.g., Cordfunke and Debets, 1964), and a hemi hydrate (e.g., Dawson et al, 1956). Some earlier workers reported four monohydrate phases (e.g., Katz and Rabinowitch, 1951), however Cordfunke and Debets suggest that two were structurally identical and varied only in water content.…”

The deuterium location in deuterium triuranate, D2U3O10, by neutron diffraction

“…The DzU3010 was prepared using basically the method of Dawson, Wait, Alcock & Chilton (1956) in which UOa and D20 are heated in an autoclave. The UOa used was a very active form prepared by decomposing UO4.2H20.…”

“…Hydrogen triuranate, H2UaO10, was first prepared by Dawson, Wait, Alcock & Chilton (1956). The uranium and oxygen locations were determined recently by Siegel, Viste, Hoekstra & Tani (1972), in a single crystal X-ray diffraction study, using 756 independent reflexions.…”