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Title: Time-dependent local and average structural evolution of δ-phase 239Pu-Ga alloys

Abstract

Here, plutonium metal is a very unusual element, exhibiting six allotropes at ambient pressure, between room temperature and its melting point, a complicated phase diagram, and a complex electronic structure. Many phases of plutonium metal are unstable with changes in temperature, pressure, chemical additions, or time. This strongly affects structure and properties, and becomes of high importance, particularly when considering effects on structural integrity over long periods of time [1]. This paper presents a time-dependent neutron total scattering study of the local and average structure of naturally aging δ-phase 239Pu-Ga alloys, together with preliminary results on neutron tomography characterization.

Authors:
 [1];  [2];  [2];  [3];  [1];  [1];  [1];  [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); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of California, Berkeley, CA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1324570
Report Number(s):
LA-UR-16-22439
Journal ID: ISSN 2059-8521; applab
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
MRS Advances
Additional Journal Information:
Journal Name: MRS Advances; Journal ID: ISSN 2059-8521
Publisher:
Materials Research Society (MRS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Smith, Alice I., Page, Katharine L., Siewenie, Joan E., Losko, Adrian S., Vogel, Sven C., Gourdon, Olivier A., Richmond, Scott, Saleh, Tarik A., Ramos, Michael, and Schwartz, Daniel S. Time-dependent local and average structural evolution of δ-phase 239Pu-Ga alloys. United States: N. p., 2016. Web. doi:10.1557/adv.2016.541.
Smith, Alice I., Page, Katharine L., Siewenie, Joan E., Losko, Adrian S., Vogel, Sven C., Gourdon, Olivier A., Richmond, Scott, Saleh, Tarik A., Ramos, Michael, & Schwartz, Daniel S. Time-dependent local and average structural evolution of δ-phase 239Pu-Ga alloys. United States. doi:10.1557/adv.2016.541.
Smith, Alice I., Page, Katharine L., Siewenie, Joan E., Losko, Adrian S., Vogel, Sven C., Gourdon, Olivier A., Richmond, Scott, Saleh, Tarik A., Ramos, Michael, and Schwartz, Daniel S. Fri . "Time-dependent local and average structural evolution of δ-phase 239Pu-Ga alloys". United States. doi:10.1557/adv.2016.541. https://www.osti.gov/servlets/purl/1324570.
@article{osti_1324570,
title = {Time-dependent local and average structural evolution of δ-phase 239Pu-Ga alloys},
author = {Smith, Alice I. and Page, Katharine L. and Siewenie, Joan E. and Losko, Adrian S. and Vogel, Sven C. and Gourdon, Olivier A. and Richmond, Scott and Saleh, Tarik A. and Ramos, Michael and Schwartz, Daniel S.},
abstractNote = {Here, plutonium metal is a very unusual element, exhibiting six allotropes at ambient pressure, between room temperature and its melting point, a complicated phase diagram, and a complex electronic structure. Many phases of plutonium metal are unstable with changes in temperature, pressure, chemical additions, or time. This strongly affects structure and properties, and becomes of high importance, particularly when considering effects on structural integrity over long periods of time [1]. This paper presents a time-dependent neutron total scattering study of the local and average structure of naturally aging δ-phase239Pu-Ga alloys, together with preliminary results on neutron tomography characterization.},
doi = {10.1557/adv.2016.541},
journal = {MRS Advances},
number = ,
volume = ,
place = {United States},
year = {Fri Aug 05 00:00:00 EDT 2016},
month = {Fri Aug 05 00:00:00 EDT 2016}
}

Journal Article:
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  • [Full Text] Plutonium metal is a highly unusual element, exhibiting six allotropes at ambient pressure, from room temperature to its melting point. Many phases of plutonium metal are unstable with temperature, pressure, chemical additions, and time. This strongly affects structure and properties, and becomes of high importance, particularly when considering effects on structural integrity over long time periods. The fcc δ-phase deserves additional attention, not only in the context of understanding the electronic structure of Pu, but also as one of the few high-symmetry actinide phases that can be stabilized down to ambient pressure and room temperature by alloying itmore » with trivalent elements. We will present results on recent work on aging of Pu-2at.%Ga and Pu-7at.%Ga alloys« less
  • Because diffraction measurements are sensitive only to the long range average arrangement of the atoms in the coherent portion of a crystal, complementary local structure measurements are required for a complete understanding of the structure of a complex material. This is particularly an issue in solid solutions where even random distributions of a solute will result in nanometer-scale fluctuations in the local composition. The structure will be further complicated if collective and cooperative phenomena organize the solute distribution via longer range interactions between non-bonded solute sites. If the solute affects the phase stability then the question is raised of whethermore » the atoms in domains with local compositions outside the limits of the bulk phase will rearrange into the structure stable for that composition and temperature or if the resulting stress would prevent such a local phase transition. If the former, then phase separated, heterogeneous structures at or below the diffraction limit will form. This nanometerscale competition between the phase transition and the epitaxial mismatch – exacerbated by the added strain if the transition involves a volume change – raises the potential for the formation of novel structures that do not occur in bulk material, e.g., fcc Fe. This coupling over multiple scales between inhomogeneity ordering, elastic forces, phase competition, and texture in the form of coexisting structures is a hallmark of martensites, a class of complex materials that includes δ-stabilized PuGa and that often exhibit correlated atomic and electronic properties. The enigmatic and extreme nature of Pu is consistent with its exhibiting unusual structural behavior of this type, including nanoscale heterogeneity in δ-stabilized PuGa and its enhanced homogeneity on aging that has been suggested based on earlier X-ray Absorption Fine Structure (XAFS) spectroscopy and x-ray pair distribution function (pdf) measurements. Measurements on a defined set of laboratory-prepared materials now corroborate and better describe this heterogeneity while additional aged samples demonstrate the role of heterogeneity in aging processes in Pu.« less
  • We study the time evolution (aging) of the elastic moduli of an eight-year-old polycrystalline δ- Pu 2.0 at % Ga alloy (δ-Pu:Ga ) from 295K to nearly 500K in real time using Resonant Ultrasound Spectroscopy (RUS). After 8 years of aging at 295K, the bulk and shear moduli increase at a normalized rate of 0.2%/year and 0.6%/year respectively. As the temperature is raised, two time dependences are observed, an exponential one of about a week, followed by a linear one (constant rate). The linear rate is thermally activated with an activation energy of 0.33+0.06 eV. Above 420K a qualitative changemore » in the time evolution is observed; the bulk modulus decreases with time while the shear modulus continues to stiffen. No change is observed as the α-β transition temperature is crossed as would be expected if a decomposition of δ-Pu:Ga to α-Pu and Pu 3Ga occurred over the temperature range studied. Our results indicate that the main mechanism of aging is creation of defects that are partially annealed starting at T = 420 K.« less