Thermodynamics of formation of coffinite, USiO4 [electronic resource].
- Washington, D.C. : United States. Dept. of Energy, 2015.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
- Physical Description:
- pages 6,551-6,555 : digital, PDF file
- Additional Creators:
- Los Alamos National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
- Restrictions on Access:
- Free-to-read Unrestricted online access
- Coffinite, USiO4, is an important U(IV) mineral, but its thermodynamic properties are not well-constrained. In this work, two different coffinite samples were synthesized under hydrothermal conditions and purified from a mixture of products. The enthalpy of formation was obtained by high temperature oxide melt solution calorimetry. Coffinite is energetically metastable with respect to a mixture of UO2 (uraninite) and SiO2 (quartz) by 25.6 ± 3.9 kJ/mol. Its standard enthalpy of formation from the elements at 25 °C is -1,970.0 ± 4.2 kJ/mol. Decomposition of the two samples was characterized by X-ray diffraction and by thermogravimetry and differential scanning calorimetry coupled with mass spectrometric analysis of evolved gases. Coffinite slowly decomposes to U3O8 and SiO2 starting around 450 °C in air and thus has poor thermal stability in the ambient environment. The energetic metastability explains why coffinite cannot be synthesized directly from uraninite and quartz but can be made by low temperature precipitation in aqueous and hydrothermal environments. These thermochemical constraints are in accord with observations of the occurrence of coffinite in nature and are relevant to spent nuclear fuel corrosion.
- Report Numbers:
- E 1.99:la-ur--15-22412
- Other Subject(s):
- Published through SciTech Connect.
Proceedings of the National Academy of Sciences of the United States of America 112 21 ISSN 0027-8424 AM
Guo, Xiaofeng; Szenknect, Stéphanie; Mesbah, Adel; Labs, Sabrina; Clavier, Nicolas; Poinssot, Christophe; Ushakov, Sergey; Curtius, Hildegard; Bosbach, Dirk; Ewing, Rodney; Burns, Peter; Dacheux, Nicolas; Navrotsky, Alexandra.
- Funding Information:
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