Preparation and Characterisation of a New Thallium(I) Uranate(VI), Tl4UO5

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.     

Specific heats of ternary oxides in the Li–U(VI)–O System

Seven ternary oxides; Li₄UO₅, Li₂UO₄, Li₂₂U₁₈O₆₅, Li₂U_1.75O_6.25, Li₂U₂O₇, Li₂U₃O₁₀ and Li₂U₆O₁₉ in the system Li–U(VI)–O were prepared by solid-state reaction route and characterized by X-ray diffraction method. Specific heats of these compounds were measured by differential scanning calorimetry in the temperature range from 300 to 860 K. The specific heats show a decreasing trend with increase in UO₃(s) content in these lithium uranates. However, the specific heat per gram atom shows an increasing trend with decrease in number of oxygen atoms in the formula unit.     

Thermal decomposition of ammonium uranates precipitated from uranyl nitrate solution with ammonium hydroxide

Thermal decomposition of ammonium uranates precipitated from uranyl nitrate solutions on addition of aqueous ammonium hydroxide under various conditions has been examined by thermogravimetry (TG), differential thermal analysis (DTA), infrared spectroscopy and X-ray diffraction study. The TG curves of all precipitates show the weight-loss corresponding to the calculated value as UO₃·NH₃·H₂O. The DTA curves of the precipitates give the endotherms at about 130, 210 and 590 °C and the exotherms at 340–420 °C. As a result, it is found that ammonium uranates thermally decompose to amorphous UO₃ at about 400 °C, and transform to U₃O₈ via β-UO₃.     

Thermogravimetric study of uranium phosphates

The thermal decomposition of UO₂NH₄PO₄ · 3H₂O and UO₂HPO₄ · 4H₂O was studied in the temperature range 25–1600?C. Both compounds gave U₂O₃P₂O₇ around 900?C after a two step dehydration and an orthophosphate-pyrophosphate transformation. UO₂NH₄PO₄ · 3H₂O did not form any pure intermediates, but (UO₂)₂P₂O₇ could be prepared from UO₂HPO₄ · 4H₂O. In air, U₂O₃P₂O₇ lost phosphorus above 1250?C. In argon, (UO)₂P₂O₇ was first formed between 1000 and 1290?C and this product only lost phosphorus at still higher temperatures. (UO)₂P₂O₇ was also obtained by reduction of (UO₂)₂P₂O₇ or U₂O₃P₂O₇ at 700?C in H₂ or with carbon black in argon above 1000?C. It oxidised in air above 250?C with the formation of U₂O₃P₂O₇.     

Thermoanalytical study on the oxidation of uranium dioxides derived from uranyl nitrate,uranyl acetate and ammonium diuranate

The oxidation of UO₂ was investigated by TG, DSC and X-ray diffraction . UO₂ samples were prepared by the reduction of UO₃ at P_H2 + P_N2 = 100 + 50 mm Hg and 5°C min^?1 up to 800°C. In order to obtain six UO₂ samples with different preparative histories, UNH, UAH and ADU were used as starting materials and their thermal decomposition was carried out at 450–625°C for 0–9 h at an air flow rate of 100 ml min^?1. α-UO₃, γ-UO₃, UO₃ - 2 H₂O, and their mixtures were obtained. The reduction of UO₃ gave β-UO_2+x with different x values from 0.030 to 0.055. The oxidation carried out at P_O2 = 150 mm Hg was found to consist of oxygen uptake at room temperature. UO₂ - U₃O₇ (Step I) and U₃O₇ → U₃O₈ (Step II). TG and DSC curves of the oxidation showed two plateaus and two exothermic peaks corresponding to Steps I and II. In the case of two of the samples, the DSC peak of Step II split into two substeps, which were assumed to be due to the different reactivities of U₃O- formed from α-CO₃ and that from other types of UO₃. The increase in O/U ratio due to the oxygen uptake at room temperature changed from 0.010 to 0.042 except for a sample prepared from ADU which showed an extraordinarily large value of 0.445. TG curves showed an increase in O/U from room temperature to near 250°C for Step I and the plateau at 250–350°C where O/U was about 2.42, and showed a sharp increase in O/U above 350°C for Step II and the plateau above 100°C where O/U was 2.72–2.75. It is thought that the prepared UO₂ had a defective structure with a large interstitial volume to accommodate the excess oxygen.     

Thallates of alkali metals and monovalent thallium formed in aqueous solutions of their hydroxides

Conclusions As a result of an investigation of the heterogeneous equilibria in M₂O-Tl₂O₃-H₂O systems, where M=Tl(I), Li, Na, K, Rb, and Cs, at 25°C it was established that the components only react in systems with thallium(I) and sodium hydroxides with the formation of thallium(I) orthothallate and restricted solid solutions between thallium oxide and the orthothallate based on thallium oxide and sodium hydroxythallate Na₃Tl(OH)₆, respectively.At elevated temperatures of 150 and 200°C it was established that potassium metathallate is formed in the K₂O-Tl₂O₃-H₂O system while sodium metathallate NaTlO₂ and a hydrated thallate of the composition 4Na₂O·Tl₂O₃·(3–4)H₂O are formed in the Na₂O-Tl₂O₃-H₂O system at 150°C. The thallates Tl₃TlO₃, Na₃Tl(OH)₆, NaTlO₂, and KTlO₂ have been isolated in a pure form and identified.The amphoteric nature of thallium oxide has been proven.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1689–1693, August, 1984.     

Thermal behaviour of co-precipitated mixtures of chromium(III) and uranium(VI)

In the CrUO system, besides the phases reported earlier, a triuranate CrU₃O_10-x (x ～ 0.3) could be identified. It is unstable above 70o°C and decomposes to a mixture of CrUO₄ and U₃O₈. Under reducing atmospheres up to 1600°C, the uranium—chromium—oxygen system gives a mixture of Cr₂O₃ and UO₂. No new phase could be identified. The compound CrUO₄ is unstable under reducing conditions and decomposes to a mixture of Cr₂O₃ and UO₂.     

Thermogravimetric study of uranium phosphates

The thermal decomposition of (UO₂)₃(PO₄)₂ and U(HPO₄)₂ ·xH₂O in the temperature range 25–1600?, was investigated. (UO₂)₃(PO₄)₂ decomposed first to 1/3[U₃O₈ + 3U₂O₃P₂O₇] and then to U₃O₅P₂O₇ before a loss of phosphorus was observed above 1350?. Decomposition in air and in inert atmospheres was nearly identical. Reduction with H₂ or with carbon black in argon gave U₃O₅P₂O₇ and [UO₂ + + (UO)₂P₂O₇] before pure UO₂ was formed. U(HPO₄)₂ ·xH₂O decomposed to UP₂O₇ in argon. It oxidized partly in air before the same product was obtained. The high temperature stability of UP₂O₇ and U₃(PO₄)₄ was also investigated.     

Mechanochemistry of the 5f-element compounds

The effect of the mechanoactivation on UO₃ and U₃O₈ in agate or stainless steel vessels in air or in toluene is studied. UO₂(OH)₂ is the main product of UO₃·H₂O activation in steel vessel in air. The presence of toluene leads to strong amorphization and dispersity increase and, probably, to the formation of U₂O₅. The activation of U₃O₈ leads to its reduction to U₃O₇ which relative content in the reaction mixture depends on the mechanoactivation conditions.     

Synthesis and study of polyuranates MIIIU3O10.5·6H2O (MIII = La, Ce, Pr, Nd, Sm)

Previously unknown individual crystalline compounds M^IIIU₃O_10.5·6H₂O were obtained by the reaction of synthetic schoepite UO₃·2.25H₂O with aqueous solutions of La, Ce, Pr, Nd, and Sm nitrates in hydrothermal conditions at 200°C. Their composition and structure were determined, and the processes of dehydration and thermal decomposition were studied by the methods of chemical analysis, X-ray diffraction, IR spectroscopy, and scanning calorimetry.     

Diagramme de phases du système Tl2OMoO3

Six thallium(I) molybdates with numerous allotropic modifications have been found in the binary system Tl₂OMoO₃; Tl₄MoO₅, Tl₂Mo₂O₇, Tl₈Mo₁₀O₃₄ (three forms), and Tl₂Mo₇O₂₂ (two forms) melt incongruently; Tl₂MoO₄ and Tl₂Mo₄O₁₃ which are trimorphic melt congruently. For the most part, the compounds were characterized by their powder diagram and by their IR spectrum which allowed comparisons with alkaline molybdates.     

The Local Uranium Environment in Cesium Uranates: A Combined XPS, XAS, XRD, and Neutron Diffraction Analysis

The cesium uranates Cs₂UO₄, Cs₂U₂O₇, Cs₄U₅O₁₇ and Cs₂U₄O₁₂ were studied using X-ray Diffraction (XRD), neutron diffraction, X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) in an attempt to couple the crystallographic structure to the uranium valence state using the local uranium environment. The diffraction spectra were used for Rietveld refinement to determine the atomic positions and interatomic distances. These distances were subsequently used in Bond Valence Sum (BVS) calculations to determine the uranium valences. The XAS spectra give direct information on the local uranium environment regarding the U-O distances and the arrangement of the oxygen atoms around the central uranium. The difference between the monovalent uranates and the multivalent Cs₂U₄O₁₂ is clearly established in all spectra, as well as in the crystal structures. The different valences present can be assigned to individual uranium lattice sites, but some amount of disorder is required to balance the charges.     

Thermal decomposition of cesium hexanitratouranium(IV)

As cesium hexanitratouranium(IV), Cs₂U(NO₃)₆, has the same Cs:U stoichiometry as that of Cs₂UO₄, thermal decomposition of this nitrato complex in air and nitrogen was studied in detail as a possible alternate method of preparing pure Cs₂UO₄. The volatility of cesium nitrate, which is one of the intermediate products, changed this Cs:U ratio during thermal decomposition. Hence, only Cs₂U₂O₇ was obtained on heating the sample to 775 K or higher. A scheme for the thermal decomposition of Cs₂U(NO₃)₆ is given by combining the observed TG, XRD and IR data.     

Synthesis and study of lithium triuranate Li2U3O10 · 6H2O

Li₂U₃O₁₀ · 6H₂O crystal hydrate was synthesized by the reaction between synthetic schoepite UO₃ · 2.25H₂O and aqueous lithium nitrate solution under hydrothermal conditions at 200°C. The composition and structure of the obtained compound were established, and its dehydration and thermal decomposition were studied, by chemical analysis, X-ray diffraction, IR spectroscopy, and scanning calorimetry.     

Electronic absorption spectroscopy of alkaline earth metal uranate compounds

Summary Electronic absorption spectra have been measured by diffuse reflectance for MgUO_4–x, MgU₃O₉, CaUo)_4–x, Ca₂UO₅, Ca₃UO₆, Ca₂U₃O₁₁, CaU₂O₇, CaU₄O₁₂, SrUO₃, SrUO₄, SrUO_3.67, Sr₂U₃O₁₁, SrU₄O_12.8, Sr₂UO₅, Sr₃UO₆, BaUO₄, Ba₃UO₆, BaU₂O₇, Ba₂U₂O₇ and Ba₂U₃O₁₁.Measurements in the near i.r. region of the spectrum have identified transitions arising within the manifold of the 5f electronic levels which indicate the presence of uranium(V) in certain compounds. The portion of the spectrum between 20 000 and 30 000 cm^–1 is shown to contain charge-transfer transitions and, in certain instances, vibrational progressions which are characteristic of the symmetry of the UO₆ octahedron in the solid state structure.     

Studium der Reaktionen von TlNO3-V2O5 in Fester Phase

The solid-state reactions of TlNO₃ with V₂O₅ in the molar ratios of 6∶5 and 2∶3 were studied by DTA, DTG and TG in the temperature ranges 20–550° and 20–400°, respectively, in a nitrogen atmosphere. For the molar ratio of 6∶5, thallium pentavanadate (Tl₃V₅O₁₄) was formed as the final product of reaction at 550°. The reaction proceeds stepwise, and Tl₂V₆O₁₆ and TlVO₃ were identified as intermediates. For the molar ratio of 2∶3, impure thallium hexavanadate (Tl₂V₆O₁₆) was obtained as the final product of reaction.

     

Schwermetall-π-Komplexe. X. Synthese und Kristallstruktur von {[(1,3,5-(CH3)3C6H3)2Tl][AlCl4]}2: ein arenstabilisiertes dimeres Thallium(I)-tetrachloroaluminat

π-Complexes of Heavy Metals. X. Synthesis and Crystal Structure of {[(1,3,5-(CH₃)₃C₆H₃)₂Tl][AlCl₄]}₂: an Arene Stabilized Dimeric Thallium(I) Tetrachloroaluminate From a solution of AlCl₃ and TlCl in mesitylene, the bis(arene)thallium complex {[(1,3,5-(CH₃)₃C₆H₃)₂Tl][AlCl₄]}₂ ( 1 ) (space group P2₁/c with a = 19.575(4) Å, b = 12.436(2) Å, c = 19.415(4) Å, β = 101.69(3)° at T = ?90 ± 1°C; Z = 4) will crystallize at low temperature. This compound can be described as a dimeric thallium(I) tetrachloroaluminate with a sceleton similar to that of (TeI₄)₄, shielded by four arenes, in pairs coordinated at the thallium atoms. In the solid state the complete configuration has point group symmetry 1 (C₁). Tl? Cl distances ranging from 3.292(3) to 3.679(3) Å point out an ionic bonding situation between arene₂Tl⁺ and AlCl₄^? fragments. The strengths of the η⁶ like Tl-arene interactions are characterized by distances Tl(1)–C of 3.250 Å and 3.315 Å, and Tl(2)? C of 3.285 Å and 3.328 Å and a temperature of release of all arene molecules of 61°C, which has been determined by differential thermal analysis, to yield pure thallium(I) tetrachloroaluminate.     

Crystal structure of catena-(2-thiobarbiturato) dithallium(I)

By powder X-ray diffraction the crystal structure of catena-(2-thiobarbiturato)dithallium(I) C₄H₂N₂O₂STl₂ (C₄H₄N₂O₂S is 2-thiobarbituric acid, H₂TBA), Tl₂TBA, is determined. Crystallographic data for Tl₂TBA are as follows: a = 15.1039(3) Å, b = 12.0818(2) Å, c = 3.86455(6) Å, β = 97.203(1)°, V = 741.34(2) ų, space group P2₁/n, Z = 4. There are two non-equivalent thallium atoms in the structure. The Tl1 polyhedron is a distorted trigonal prism due to the shortened Tl-S contact (3.634 Å), and the Tl2 polyhedron is a distorted square antiprism.     

Untersuchungen zur Struktur von Thallium(I)-halogenomercuraten(II)

Investigations on the Structure of Thallium(I) Halide Mercurates(II) Tl₄HgBr₆ crystallizes tetragonal with a = 8.978, c = 8.812 Å and Z = 2 in the space group P4/mnc. Singlecrystal methods revealed isolated HgBr₆-octahedra, compressed alonged the [001] axis, with thallium atoms between them. The results have been extended to clarify the structures of the isomorphous compounds (NH₄)₄HgBr₆ (a = 9.011, c = 8.660 Å), Tl₄HgJ₆ (a = 9.529, c = 9.387 Å) and Tl₄HgCl₂Br₄ (a = 8.896, c = 8.735 Å). It was impossible to obtain Tl₄HgCl₆; all attempts resulted in the formation of Tl₁₀Hg₃Cl₁₆, which crystallizes tetragonal (a = 8.477, c = 23.699 Å).     

Crystal structure of thallium(I) 2-thiobarbiturate

The crystal and molecular structures of thallium(I) thiobarbiturate C₄H₃N₂O₂STl (C₄H₄N₂O₂S is 2-thiobarbituric acid, Н₂ТВА) have been determined. Crystallographic data for Tl(НТВА) are a = 11.2414(7) Å, b = 3.8444(3) Å, с = 14.8381(9) Å, β = 99.452(2)°, V = 649.00(7) ų, space group P2/с, Z = 4. Each of the two independent thallium ions is bonded to four oxygen and two sulfur atoms to form a distorted tetrahedron. N?H…O and C?H…S hydrogen bonds form a branched three-dimensional network. The structure is also stabilized by π?π interaction between heterocyclic НТВА^- ions. The IR spectra of Tl(НТВА) agree with X-ray powder diffraction data. The compound is also stable below 280°C, and Tl₂SO₄ is one of the thermolysis products in an oxidative medium in the region of 500?650°C.