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Title: Uncloaking the thermodynamics of the studtite to metastudtite shear-induced transformation

The interplay between thermodynamics and mechanical properties in the transformation of studtite, (UO 2)(O 2)(H 2O) 2·2H 2O, into metastudtite, (UO 2)(O 2)(H 2O) 2, two important corrosion phases observed on the surface of uranium dioxide exposed to water, is revealed using density functional perturbation theory. Phonon calculations within the quasi-harmonic approximation predict that the standard entropy change for the (UO 2)(O 2)(H 2O) 2·2H 2O → (UO 2)(O 2)(H 2O) 2 + 2H 2O reaction is ΔS 0 = +80 J·mol –1·K –1 for the production of water in the liquid state and +389 J·mol–1·K–1 for water vapor. Similar to bulk H 2O(l), the bulk modulus of (UO 2)(O 2)(H 2O) 2·2H 2O increases with temperature, contrasting with (UO 2)(O 2)(H 2O) 2 which features the typical Anderson–Gruneisen temperature dependence of oxide solids. Upon removal of interstitial H 2O in studtite, the most important changes in the shear modulus, the parameter limiting the mechanical stability, arise in the planes normal to chain propagation directions. Lastly, the present findings have important implications for the dehydration of other hygroscopic materials.
Authors:
 [1] ;  [2]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  2. Univ. of Nevada, Las Vegas, NV (United States)
Publication Date:
Report Number(s):
SAND-2016-5343J
Journal ID: ISSN 1932-7447; 641393
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 120; Journal Issue: 30; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; density functional theory; thermodynamics; actinides; oxides; corrosion
OSTI Identifier:
1324610