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Title: Formation of solid thorium monoxide at near-ambient conditions as observed by neutron reflectometry and interpreted by screened hybrid functional calculations

Oxidation of a ~1000 Å sputter-deposited thorium thin film at 150 °C in 100 ppm of flowing oxygen in argon produces the long-sought solid form of thorium monoxide. Changes in the scattering length density (SLD) distribution in the film over the 700-min experiment measured by in-situ, dynamic neutron reflectometry (NR) shows the densities, compositions and thickness of the various thorium oxides layers formed. Screened, hybrid density-functional theory calculations of potential thorium oxides aid interpretation, providing atomic-level picture and energetics for understanding oxygen migration. NR provided evidence of the formation of substoichiometric thorium oxide, ThO y (y < 1) at the interface between the unreacted thorium metal and its dioxide overcoat which grows inward, consuming the thorium at a rate of 2.1 Å/min while y increases until reaching 1:1 oxygen-to-thorium. Its presence indicates that kinetically-favored solid-phase ThO can be preferentially generated as a majority phase under the thermodynamically-favored ThO 2 top layer at conditions close to ambient.
Authors:
 [1] ; ORCiD logo [2] ;  [3] ;  [1] ;  [1] ;  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering
  3. Brigham Young Univ., Provo, UT (United States). Dept. of Physics and Astronomy
Publication Date:
Report Number(s):
LA-UR-14-24055
Journal ID: ISSN 0022-3115
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Volume: 487; Journal Issue: C; Journal ID: ISSN 0022-3115
Publisher:
Elsevier
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Thorium monoxide; Thorium dioxide; Neutron reflectometry; Nuclear fuel; Thin film; Oxidation; DFT
OSTI Identifier:
1469519
Alternate Identifier(s):
OSTI ID: 1396882

He, Heming, Majewski, Jaroslaw, Allred, David D., Wang, Peng, Wen, Xiaodong, and Rector, Kirk D.. Formation of solid thorium monoxide at near-ambient conditions as observed by neutron reflectometry and interpreted by screened hybrid functional calculations. United States: N. p., Web. doi:10.1016/j.jnucmat.2016.12.046.
He, Heming, Majewski, Jaroslaw, Allred, David D., Wang, Peng, Wen, Xiaodong, & Rector, Kirk D.. Formation of solid thorium monoxide at near-ambient conditions as observed by neutron reflectometry and interpreted by screened hybrid functional calculations. United States. doi:10.1016/j.jnucmat.2016.12.046.
He, Heming, Majewski, Jaroslaw, Allred, David D., Wang, Peng, Wen, Xiaodong, and Rector, Kirk D.. 2017. "Formation of solid thorium monoxide at near-ambient conditions as observed by neutron reflectometry and interpreted by screened hybrid functional calculations". United States. doi:10.1016/j.jnucmat.2016.12.046. https://www.osti.gov/servlets/purl/1469519.
@article{osti_1469519,
title = {Formation of solid thorium monoxide at near-ambient conditions as observed by neutron reflectometry and interpreted by screened hybrid functional calculations},
author = {He, Heming and Majewski, Jaroslaw and Allred, David D. and Wang, Peng and Wen, Xiaodong and Rector, Kirk D.},
abstractNote = {Oxidation of a ~1000 Å sputter-deposited thorium thin film at 150 °C in 100 ppm of flowing oxygen in argon produces the long-sought solid form of thorium monoxide. Changes in the scattering length density (SLD) distribution in the film over the 700-min experiment measured by in-situ, dynamic neutron reflectometry (NR) shows the densities, compositions and thickness of the various thorium oxides layers formed. Screened, hybrid density-functional theory calculations of potential thorium oxides aid interpretation, providing atomic-level picture and energetics for understanding oxygen migration. NR provided evidence of the formation of substoichiometric thorium oxide, ThOy (y < 1) at the interface between the unreacted thorium metal and its dioxide overcoat which grows inward, consuming the thorium at a rate of 2.1 Å/min while y increases until reaching 1:1 oxygen-to-thorium. Its presence indicates that kinetically-favored solid-phase ThO can be preferentially generated as a majority phase under the thermodynamically-favored ThO2 top layer at conditions close to ambient.},
doi = {10.1016/j.jnucmat.2016.12.046},
journal = {Journal of Nuclear Materials},
number = C,
volume = 487,
place = {United States},
year = {2017},
month = {2}
}