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A new thallium(I) uranate(VI) of composition Tl4UO5 was isolated and characterised by X-ray, i. r. and chemical analyses. The compound dissociated into thallium(I) oxide and Tl2UO4 on heating to 230°C and its subsequent thermal behaviour depended on the volatilisation and oxidation characteristics of the thallium(I) oxide released. Darstellung und Charakterisierung eines neuen Thallium(I)- uranates, Tl4UO5 Ein neues Thallium(I)-uranat(VI), Tl4UO5, wurde dargestellt und durch Rontgen-, IR- und chemische Analyse charakterisiert. Beim Erhitzen auf 230°C dissoziiert die Verbindung in Tl2O und Tl2UO4, und das weitere thermische Verhalten ist gekennzeichnet von der Fluchtigkeit und Oxydationscharakteristik des freigesetzten Tl2O.

The enthalpy of reaction of cesium uranate (Cs 2 UO 4 ) with approximately 1 mol dm −3 HCl was determined by solution calorimetry to be −(43337 ± 65) cal th mol −1 . Combination of this result with measured enthalpies of solution of CsCl(c) in HCl(aq) and of UO 2 Cl 2 (c) in an aqueous mixture of CsCl + HCl, together with auxiliary thermochemical data from the literature, gave a value of −(453.46 ± 0.85) kcal th mol −1 for the standard enthalpy of formation, ΔH f o (Cs 2 UO 4 , c, 298.15 K).

Energy transfer between tungstate and uranate groups in oxides with perovskite structure is reported. The critical distance for this process is about 25 Å. Evidence is given for energy transfer between tungstate groups. In this case the critical distance is estimated to be about 8 Å.

The CsUO system was investigated by means of X-ray analysis, thermal analysis and phase studies. Eight cesium uranate phases, in which uranium is hexavalent, were found. Their thermal stability in air was investigated and the formation of new phases is described. X-ray powder data of all phases are given.

The reaction of UO2 in molten alkaline nitrate has been studied by X-ray diffraction. Generally if sodium nitrate is present, up to 60 mol.%, 30 mol.% and 5 mol.% for sodium-lithium, sodium-potassium and sodium-cesium nitrate mixtures respectively, a solid solution is formed, which can be represented by the general formula Na2−xMexU2O7. Maximum solubilities have been determined. X-ray powder diffraction patterns for sodium diuranate, lithium mono- and diuranate are also given.

The dehydrogenation of ethylbenzene to styrene and of cumene to α-methylstyrene has been investigated in a fixed bed reactor over bismuth uranate Bi2UO6 and uranium oxide as catalysts, at temperatures from 420 to 520 °C. Selectivities of 97% at a conversion of 38% for styrene and of 96% at a conversion of 66% for α-methylstyrene have been obtained in this study. Under reaction conditions Bi2UO6 loses 67 wt% of its oxygen and metallic bismuth is formed. Uranium oxide is reduced to UO2. The reaction pattern on both catalysts changes during the reduction. This investigation is mainly concerned with the performance of the reduced catalysts. A kinetic model, which takes into account the chemisorption of the saturated reactants and of the unsaturated reaction products, has been used to interpret the experimental data. Energies of activation are 34 kcal mol-1 for the ethylbenzene dehydrogenation and 27 kcal mol-1 for the cumene dehydrogenation. By-products formed from ethylbenzene are benzene and toluene, while cumene produces benzene, toluene, ethylbenzene and styrene.

When the activator ions in a phosphor have a charge different from that of any ions in the host lattice, it is generally agreed that charge compensation must take place. A new theory of luminescent centres is proposed in which the compensation of charge, by lattice vacancies or by activator ions, is localized in the vicinity of the activator ions. This theory is primarily applicable to ionic crystals, and specific configurations of lowest energy can be deduced. These configurations are described in detail for alkaline-earth oxide, uranate and fluoride phosphors. and the vibrations of these centres are discussed. A number of original phosphors of theoretical interest, including CaO. Bi, Li; CaO. U, Li; CaO. U, Sm; and the uranates, are described and spectra are shown. Finally, necessary modifications of the present theories of sensitized luminescence and multiple-band emission are considered.

The kinetics of the reduction of bismuth uranate by toluene have been studied in micro-pulse and micro-flow reactors and in a thermobalance, at toluene mole fractions between 0.003 and 0.122 and temperatures between 455 and 527 °C. During the reduction the Bi2UO6 is converted into metallic bismuth and UO2. In the overall reaction rate both the chemical reaction rate at the surface and the rate of oxygen diffusion through the lattice of the solid play a role. A kinetic model comprising these two steps is derived. It appears that Bi2UO6 contains two types of lattice oxygen, viz, approximately 2% of a nonselective oxygen with D = 3 × 10−22 m2 sec−1 and a diffusion energy of activation E = 26 kcal mole−1, and a more selective oxygen with D = 3 × 10−20 m2 sec−1 and E = 63 kcal mole−1 (at 470 °C). Some evidence is found for bismuth uranate having a shear structure, the small amount of nonselective oxygen occupying positions in the shear planes.

“Hydrolytic” uranic acid, the mother substance from which uranates can be really prepared as well as formally deduced, is prepared from uranyl solutions using alkalization by means of an anion exchange resin in OH-form. The product is identified as the so-called uranium trioxide dihydrate, α-UO3 · 2 H2O. Its behaviour as an actual acid is verified by preparing uranates in neutralization reaction. Its formula is proposed. Hydrolytisch gebildete Uran(VI)-Saure, von der Uranate sowohl formal abgeleitet als auch in der Tat hergestellt werden konnen, wird aus Uranylsalzlosungen mit Hilfe eines Anionenaustauschers in OH-Form erhalten und als sogenanntes Uran(VI)-oxid-Dihydrat, α-UO3 · 2 H2O, identifiziert. Sie wird als [UO2(OH)2UO2](OH)2(H2O)2 (UO2 · 2 H2O) formuliert.

A single crystal X-ray structure determination shows that in [(C2H5)4N]4[U(NCS)8] the eight N-bonded ligands are disposed at the vertices of a cube. Within experimental accuracy no deviations from regular cubical 8-coordination are found.

The composition and structure of the ammonium uranates have been investigated by i.r. spectrophotometry and thermal analysis. Ammonia is present in all uranates as the NH+4 ion. In an aqueous environment incorporation of ammonia into the solid occurs by a cation exchange mechanism, and ammonium uranates can therefore be regarded as cation-exchanged modifications of the parent UO3.2H2O (i.e. UO2(OH)2.H2O). The asymmetric stretching frequency of the uranyl ion decreases with increasing NH+4 content. This decrease is continuous and no band splitting is observed, indicating that the ammonium uranate system is homogeneous and continuous.

An oxidative reaction is described by which toluene is converted into benzene. The reaction is catalyzed by bismuth uranate. Selectivities up to 70% are obtained if toluene vapour reacts with the catalyst without gaseous oxygen being present; the catalyst becomes partially reduced, but can easily be reoxidized afterwards with air. Biphenyl and benzaldehyde have been identified as by-products.

Cubic magnesium uranate, Mg y U 1− y O 2+ x , was prepared by the reaction of the mixtures of MgUO 4 , MgU 3 O 10 and/or UO 2 in a stream of helium. The cubic region and the values of x and y in Mg y U 1− y O 2+ x were studied under various reaction conditions. Density measurements of this compound gave a strong support to a substitutional structure. The variation of lattice constant with composition was observed to follow a linear equation, a 0 = 5·4704−0·1170x−0·5677 y . Equilibrium oxygen pressure was found to increase with magnesium concentration. The results were discussed by modifying the equation to express partial molar entropy of oxygen given by Aronson and Clayton to valence control type Mg y U 1− y O 2+ x .

The structural problems in cubic magnesium uranate, MgyU1−yO2+χ, were studied. From the measurements of density variation with oxygen concentration, the oxygen non-stoichiometry in this compound was assigned to the interstitial oxygen and to the metal vacancy formation. The observed X-ray intensity of Bragg peak was found to decrease far more rapidly with y in MgyU1−yO2+χ in dilute range than expected from the simple theoretical model for substitutional solid solution. This discrepancy may be interpreted by the large distortion of uranium ions around a magnesium impurity ion. The B value of thermal vibrations was observed by X-ray measurements to be 0·2 ∼ 0·3 A2 over the y range from 0 to 0·24. A measure of static distortion, δa, was obtained by the integral breadth method. The variation of δa with y was discussed in connection with the decrease of peak intensity.

When brought into contact with various bismuth uranates in a stream of an inert gas at 400-500 °C, toluene is oxidized to benzene, CO2 and H2O. The best benzene yields are obtained using the compound Bi2UO6 with a high specific surface area. A fixed percentage of the oxygen atoms present in this compound gives rise to a rapid total combustion of the toluene. After the consumption of these atoms, toluene is converted into benzene with a selectivity up to 70%. During this process bismuth uranate can lose 60% of its oxygen atoms, corresponding to zero-valent bismuth and tetravalent uranium. The original activity is completely restored by oxidation with molecular oxygen. This opens the possibility of demethylating toluene by passing air and toluene alternately over bismuth uranate. The kinetics of the reaction between toluene and bismuth uranate, investigated in micropulse and microflow systems and in a thermobalance, are complicated. The surface reaction appears to be first order in toluene with an energy of activation of 30 kcal mole-1 at 480 °C, but the transport rate of oxygen from the bulk of the Bi2UO6 matrix to the surface also plays a role. The selective reaction is likely to occur via a benzoate-like intermediate. The reoxidation of reduced bismuth uranate with air is very fast, and even proceeds at 100 °C.

The solid state preparation, thermal and hydrolytic characteristics of thallium(I)—uranates(VI) are described. The phases identified were Tl2UO4, Tl2U2O7 and a range of solid solution (Tl2O. 2,33 UO3Tl2O. 6 UO3). The thallium uranates are isostructural with the corresponding potassium uranates. Tl2U2O7 is the stable phase formed from the other uranates on hydrolytic treatment. The thallium uranates lose thallium(I) oxide on heating to temperatures above 750°C and the order of thermal stability is Tl2U6O19∼Tl2U3O10∼Tl2U2O7»Tl2UO4. Thallium(I)-uranate(VI) Die Darstellung (durch Festkorperreaktion), die thermischen und die hydrolytischen Eigenschaften der Thallium(I)-uranate(VI) werden beschrieben. Als Phasen wurden identifiziert: Tl2UO4, Tl2U2O7 und ein Gebiet fester Losungen (Tl2O. 2,33 UO3Tl2O. 6 UO3). Die Thalliumuranate haben gleiche Strukturen wie die entsprechenden Kaliumuranate. Tl2U2O7 ist die stabile Phase, die sich auch bei der Hydrolyse anderer Uranate bildet. Beim Erhitzen der Uranate uber 750°C verfluchtigt sich Tl2O; die Reihenfolge der thermischen Stabilitat ist: Tl2U6O19∼Tl2U3O10∼Tl2U2O7»Tl2UO4.

The enthalpy of reaction of α-sodium uranate (Na2UO4) with approximately 0.1 M HCl has been determined to be -(41935 ± 176) calth mol−1. Combination of this result with measured enthalpies of solution of NaCl in HCl(aq) and of UO2Cl2 in an aqueous mixture of NaCl and HCl, together with auxiliary data from the literature, yielded Δ H f ° ( α − N a 2 U O 4 , c , 2 9 8 . 1 5 K ) = - ( 4 4 5 . 5 6 ± 0.8 5 ) k c a l t h m o l - 1 .

Ockerfarbenes Li3UO4, zartgrunes Li7UO6 und hellbraunes Na3UO4 als offenbar basenreichste Verbindung im System Na2O—U2O5 wurden auf thermischem Wege nach verschiedenen Methoden dargestellt. Die Eigenschaften der Verbindungen werden beschrieben. Bei der Reduktion von Li2UO4 und Na2UO4 im H2-Strom, ebenso bei der Umsetzung von UO2 mit Li2O bzw. Na2O wurden ebenfalls Uranate(V) erhalten. Alkaliuranate(IV) scheinen nicht stabil zu sein. Li7UO6 ist mit anderen Verbindungen des Formeltyps Li7AVO6 isotyp (A Sb, Bi, Nb, Ta, Ru, Os); sein Pulverdiagramm zeigt eine uberraschende, sehr weitgehende Ahnlichkeit mit Diagrammen des Verbindungstyps Li8AIVO6 (A Sn, Pb, Zr, Hf, Ir, Pt). The coloured uranates(V) Li3UO4, Li7UO6, and Na3UO4 (the latter one being probably the most basic compound in the system Na2OU2O5) have been thermally prepared Their properties are described. Li7UO6 is isotypic with other compounds having the general formula Li7AVO6 (A Sb, Bi, Nb, Ta, Ru, Os); its powder diagram is very similar with those of Li8AIVO6 compounds (A Sn, Pb, Zr, Hf, Ir, Pt). Further uranates(V) have been obtained from UO2, Li2O and Na2O, respectively, and by reduction of Li2UO4 and Na2UO4 by means of H2. Alkali uranates(IV) seem to be unstable.

The hydrates, UO 3 ·2H 2 O, UO 3 ·0·8H 2 O and UO 3 ·0·5H 2 O described by Dawson et al. (1) were shown to react with the organic base, urea, to form urea uranate H 2 UO 4 ·2CO(NH 2 ) 2 . The formation of this salt provides evidence that these “hydrates” constitute a series of acids whose relationship may be expressed as follows: (pyrouranic acid). Attempts to characterize the “hydrate” UO 3 ·0·8H 2 O were unsuccessful; instead the presence of a mixture of H 2 UO 4 and H 2 U 2 O 7 was indicated.

Pred i spe r sa l of nuclear fuel as a resul t of oxidation of uranium dioxide to uranyl uranate (mixed u r anous u r an i c oxide, U30 a) opens the way for more advantageous use of the advantages of fluidized-bed f luorinators [1-5]. This accounts for the search for an opt imum-design fluidized-bed reac tor and basic pa r ame te r s of a p rocess involving oxidative breakdown of pelletized nuclear fuel for power reac tor fuel elements. The charac ter i s t ics of the uranium dioxide employed in the work are listed in Table 1, The inert packing employed in the fluidized-bed fluorinator was aluminum oxide 100 # mesh and 500 t~ mesh.

Magnesium uranate was prepared by standard solid-state synthetic techniques. Decomposition pressures were measured between 1000° and 137OOC. At oxygen contents less than MgUO3.5 a solid solution of fluorite structure was found. Above MgUO3.75 the orthorhombic magnesium uranate phase was observed. The two phases were in equilibrium in air at 126OOC. The heat of solution of O2 in the fluorite phase was 45 kcal mole−1 and the heat of the reaction MgUO3.5+ 0.12O2→ MgUO3.75 was 83.3 kcal mole−1 (O2).

A new thallium(I) uranate(VI) of composition Tl4UO5 was isolated and characterised by X-ray, i. r. and chemical analyses. The compound dissociated into thallium(I) oxide and Tl2UO4 on heating to 230°C and its subsequent thermal behaviour depended on the volatilisation and oxidation characteristics of the thallium(I) oxide released. Darstellung und Charakterisierung eines neuen Thallium(I)- uranates, Tl4UO5 Ein neues Thallium(I)-uranat(VI), Tl4UO5, wurde dargestellt und durch Rontgen-, IR- und chemische Analyse charakterisiert. Beim Erhitzen auf 230°C dissoziiert die Verbindung in Tl2O und Tl2UO4, und das weitere thermische Verhalten ist gekennzeichnet von der Fluchtigkeit und Oxydationscharakteristik des freigesetzten Tl2O.

Decay times of the green luminescence of U6+ in oxides with perovskite structure are reported. The influence of the site symmetry is found to be considerable. The temperature dependence of the decay time gives evidence for a coupling of the electronic transition with a phonon of about 200 cm−1 in the excited state. The results show the emission to originate from a parity-forbidden transition, vibronically allowed by coupling with vibrations of ungerade symmetry.

The volume of H/sub 2/ evolved on dissolving screened nonroasted U- bearing scrap, slag, and liner in HCl were determined; the values were found to indicate the degree of removal of metallic particles by screening. Digestions of nonroasted plant-pulverized scrap with HNO/sub 3/, NaNO/sub 3/, or Fe/sub 2/(SO/ sub 4/)/sub 3/ in HCl and with HNO/sub 3/ or NaNO/sub 3/ in H/su b 2/SO/sub 4/ were not so effective as digestion with NaClO/sub 3/ in HCl. Doubling the free acid content and addition of FeSO/sub 4/ improved the efficiency of the latter digestion. Removal of CaF/sub 2/ from crude (NH/sub 4/)/sub 2/ UO/sub 4/ by solution of the uranate in acetic acid, HCl, or Hsub 2SO/sub 4/ was limited by slow filtration rates. (W.L.H.)

The equilibrium oxygen pressure above nonstoichiometric CaUO/sub x/ (4> X> 3.5) was measured over various ranges of temperature and composition, and thermodynamic quantities for the solid--gas equilibrium were derived. A comparison was made between the experimental results and theoretical calculations for a nonstoichiometric oxide with anion vacancies. (auth) (auth)