10026-08-1Relevant articles and documents
Synthesis and characterization of the first sandwich complex of: Trivalent thorium: A structural comparison with the uranium analogue
Parry, Julian S.,Cloke, F. Geoffrey N.,Coles, Simon J.,Hursthouse, Michael B.
, p. 6867 - 6871 (1999)
Reduction of the bulky 8-annulene thorium complex [Th{COT(TBS)2}2] (COT(TBS)2 =η-C8H6(tBuMe2Si)2-1,4) by potassium yields the anionic compound {Th[COT(TBS)2]2}K·(DME)2, which was crystallographically characterized and is the first sandwich complex of Th(III). EPR spectroscopy indicates that the molecule possesses a 6d1 ground state. A structural comparison is made with the isostructural uranium(III) complex and the thorium(IV) parent compound.
The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO4(M = Ce, U)
Strzelecki, Andrew C.,Barral, Thomas,Estevenon, Paul,Mesbah, Adel,Goncharov, Vitaliy,Baker, Jason,Bai, Jianming,Clavier, Nicolas,Szenknect, Stephanie,Migdisov, Artaches,Xu, Hongwu,Ewing, Rodney C.,Dacheux, Nicolas,Guo, Xiaofeng
, p. 718 - 735 (2021)
Orthosilicates adopt the zircon structure types (I41/amd), consisting of isolated SiO4 tetrahedra joined by A-site metal cations, such as Ce and U. They are of significant interest in the fields of geochemistry, mineralogy, nuclear waste form development, and material science. Stetindite (CeSiO4) and coffinite (USiO4) can be formed under hydrothermal conditions despite both being thermodynamically metastable. Water has been hypothesized to play a significant role in stabilizing and forming these orthosilicate phases, though little experimental evidence exists. To understand the effects of hydration or hydroxylation on these orthosilicates, in situ high-temperature synchrotron and laboratory-based X-ray diffraction was conducted from 25 to ～850 °C. Stetindite maintains its I41/amd symmetry with increasing temperature but exhibits a discontinuous expansion along the a-axis during heating, presumably due to the removal of water confined in the [001] channels, which shrink against thermal expansion along the a-axis. Additional in situ high-temperature Raman and Fourier transform infrared spectroscopy also confirmed the presence of the confined water. Coffinite was also found to expand nonlinearly up to 600 °C and then thermally decompose into a mixture of UO2 and SiO2. A combination of dehydration and dehydroxylation is proposed for explaining the thermal behavior of coffinite synthesized hydrothermally. Additionally, we investigated high-temperature structures of two coffinite-thorite solid solutions, uranothorite (UxTh1-xSiO4), which displayed complex variations in composition during heating that was attributed to the negative enthalpy of mixing. Lastly, for the first time, the coefficients of thermal expansion of CeSiO4, USiO4, U0.46Th0.54SiO4, and U0.9Th0.1SiO4 were determined to be αV = 14.49 × 10-6, 14.29 × 10-6, 17.21 × 10-6, and 17.23 × 10-6 °C-1, respectively.
OBSERVATION OF A PHASE TRANSITION IN ThBr4 AND ThCl4 SINGLE CRYSTALS BY FAR-INFRARED AND RAMAN SPECTROSCOPY STUDY.
Hubert,Delamoye,Lefrant,Lepostollec,Hussonnois
, p. 36 - 44 (1981)
At 4 K the visible and infrared absorption and emission spectra of U**4** plus in ThBr//4 and ThCl//4 single crystals are not very consistent with what is predicted by the selection rules for the room temperature structure. Thus we investigated Raman scattering in the temperature range 10-300 K to look for a structure change and obtain a better understanding of the specroscopy of U**4** plus in ThBr//4 and ThCl//4. At room temperature, the observed Raman lines have been assigned on the basis of D//4//h factor group analysis. The study of the temperature dependence of the Raman spectra permitted us to discover phase transitions of ThBr//4 and ThCl//4 at 95 and 70 K, respectively. The splitting observed for the strongest E//g symmetry modes shows a lowering of the symmetry below the transition point.
Energetics of a uranothorite (Th1-xUxSiO4) solid solution
Guo, Xiaofeng,Szenknect, Stéphanie,Mesbah, Adel,Clavier, Nicolas,Poinssot, Christophe,Wu, Di,Xu, Hongwu,Dacheux, Nicolas,Ewing, Rodney C.,Navrotsky, Alexandra
, p. 7117 - 7124 (2016)
High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO4)x-(ThSiO4)1-x, solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and high-temperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO4, and U-rich intermediate silicate phases with respect to a mixture of binary oxides. However, variations in unit cell parameters and negative excess volumes of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.
Synthesis and Characterization of Thorite Nanoparticles by Hydrothermal Method
Ghadiri,Abdollahy,Khanchi,Khalesi,Akbari
, p. 1829 - 1835 (2019)
Abstract: The synthesis of thorium silicate (thorite) was carried out to characterize the parameters affecting the process. A synthetic thorite with formula ThSiO4 was prepared by hydrothermal method with a mixture of 0.14 M thorium chloride (ThCl4) solution and sodium silicate containing 0.14 M SiO2. The effect of several experimental parameters on synthesis of thorite was investigated. The most important of these parameters were the pH of solution in hydrothermal process and volumetric ratio of SiO2 : ThCl4. The optimum pH in the hydrothermal process was 8–9, which was obtained by buffering with sodium bicarbonate. The increasing of volumetric ratio of SiO2 : ThCl4 led to gelatinization of synthetic material. The operating conditions of synthesis of thorite were determined as follows: volumetric ratio of SiO2 : ThCl4 = 0.9; pH after adding of 8 M NaOH, 8–8.5; pH after adding 0.5 M sodium bicarbonate, 8–9; temperature of heating in furnace, 250°C; time of heating in furnace, 24 h; pH after hydrothermal process, 8–9; temperature of drying in oven, 60°C; time of drying in oven, 24 h. In each batch of synthesis process, about 2.2 g or 7 mmol of thorium silicate was produced. The purity of thorite was determined 97.80%.
Synthesis of Coordinatively Unsaturated Tetravalent Actinide Complexes with η5 Coordination of Pyrrole
Batrice, Rami J.,Fridman, Natalia,Eisen, Moris S.
, p. 2998 - 3006 (2016)
The synthesis of new actinide complexes utilizing bridged α-alkyl-pyrrolyl ligands is presented. Lithiation of the ligands followed by treatment with 1 equiv of actinide tetrachloride (uranium or thorium) produces the desired complex in good yield. X-ray diffraction studies reveal unique η5:η5 coordination of the pyrrolyl moieties; when the nonsterically demanding methylated ligand is used, rapid addition of the lithiated ligand solution to the metal precursor forms a bis-ligated complex that reveals η5:η1 coordination as determined by crystallographic analysis.
The Vibrational Spectra of some Tetrachlorides in Rare Gas Matrices with particular Reference to the Molecular Shapes of ThCl4 and UCl4
Arthers, Stephen A.,Beattie, Ian R.
, p. 819 - 826 (1984)
Infrared spectra of tin, lead, hafnium, thorium, and uranium tetrachlorides isolated in inert gas matrices are reported.The results obtained for the tin, lead, and hafnium compounds follow the expected isotope patterns for a tetrahedral molecule except for the observation of additional weak features to high frequency of the all-35Cl isotopomers.By contrast for the thorium tetrachloride the observed spectrum is not characteristic of a Td molecule but can be fitted to a species with C2ν symmetry.Similar results (altough less detailed) were obtained for uranium tetrachloride.
Electrochemistry of thorium in LiCl-KCl eutectic melts
Cassayre,Serp,Soucek,Malmbeck,Rebizant,Glatz
, p. 7432 - 7437 (2007)
This work presents a study of the electrochemical properties of Th chloride ions dissolved in a molten LiCl-KCl eutectic, in a temperature range of 693-823 K. Transient electrochemical techniques such as cyclic voltammetry, chronopotentiommetry and chronoamperometry have been used in order to investigate the reduction mechanism on a tungsten electrode and the diffusion coefficient of dissolved Th ions. All techniques showed that only one valence state was stable in the melt. The reduction into Th metal was found to occur according to a one-step mechanism, through a nucleation-controlled process which requires an overpotential of several 100 mV. At 723 K, the diffusion coefficient is DTh(723 K) = 3.15 ± 0.15 × 10-5 cm2 s-1. EMF measurements indicated that, at 723 K, the standard apparent potential is EThC l4 / Th* 0 (723 K) = -2.582 V versus Cl2/Cl-, and the activity coefficient γThC l4 (723 K) = 4.6 × 10-4 on the mole fraction scale (based on a pure liquid reference state).
A Simple Access to Pure Thorium(IV) Halides (ThCl4, ThBr4, and ThI4)
Deubner, H. Lars,Rudel, Stefan Sebastian,Kraus, Florian
, p. 2005 - 2010 (2017)
In this work we present a facile, lab scale synthesis for thorium tetrahalides ThX4 (X = Cl, Br, and I). The reaction between the easily available ThO2 and AlX3 (X = Cl, Br, and I) and a subsequent in situ chemical vapor transport (CVT) leads to a product of high purity, which is obtained in the form of crystals or large aggregates of crystals. Their identity and purity was evidenced by X-ray powder diffraction and IR spectroscopy. The usage of ThO2 avoids, unlike earlier syntheses, the utilization of scarcely available thorium metal or of other reactants, such as CCl4, which leads to impurities. Furthermore, the reaction tolerates even less pure ThO2.
Incorporation of Thorium in the Zircon Structure Type through the Th1-xErx(SiO4)1-x(PO4)x Thorite-Xenotime Solid Solution
Mesbah, Adel,Clavier, Nicolas,Lozano-Rodriguez, M. Janeth,Szenknect, Stephanie,Dacheux, Nicolas
, p. 11273 - 11282 (2016)
Pure powdered compounds with a general formula Th1-xErx(SiO4)1-x(PO4)x belonging to the zircon-xenotime family were successfully synthesized under hydrothermal conditions (250 °C, 7 days) as recently reported for the preparation of coffinite. Therefore, a thorough, combined PXRD, EDX, EXAFS, Raman, and FTIR analysis showed the formation of a solid solution in agreement with Vegard's law. Moreover, the examination of the local structure shows that the Th-O distances remain close to those found in ThSiO4, whereas the Er-O distances show a significant decrease from 2.38(14) to 2.34(7) ? when increasing the erbium content from x = 0.2 to x = 1. The variation of the local structure also affects the PO43- groups that are surely distorted in the structure.
