10026-08-1Relevant articles and documents
Raymond, David P.,Duffield, John R.,Williams, David R.
, p. 309 - 314 (1987)
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.
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.
Moissan, H.,Hoenigschmid, O.
, (1906)
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.
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).
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.