Thermodynamics of formation of coffinite, USiO4 [electronic resource].

Published:: 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

Access Online

www.osti.gov

Availability

Finding items...

Restrictions on Access:

Free-to-read Unrestricted online access

Summary:

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
la-ur--15-22412

Subject(s):

Other Subject(s):

Note:

Published through SciTech Connect.
05/26/2015.
"la-ur--15-22412"
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:

AC52-06NA25396

View MARC record | catkey: 23777179