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An Overview of Recent Standard and Accelerated Molecular Dynamics Simulations of Helium Behavior in Tungsten
Open AccessCommunication

Investigating Helium Bubble Nucleation and Growth through Simultaneous In-Situ Cryogenic, Ion Implantation, and Environmental Transmission Electron Microscopy

1
Sandia National Laboratories, Albuquerque, NM 87185, USA
2
Nuclear Science and Engineering, Oregon State University, Corvallis, OR 97331, USA
3
School of Computing and Engineering, University of Huddersfield, Huddersfield HD1 3DH, UK
4
Sandia National Laboratories, Livermore, CA 94551, USA
*
Author to whom correspondence should be addressed.
Materials 2019, 12(16), 2618; https://doi.org/10.3390/ma12162618
Received: 2 July 2019 / Revised: 30 July 2019 / Accepted: 13 August 2019 / Published: 16 August 2019
(This article belongs to the Special Issue Radiation Damage in Materials: Helium Effects)
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Abstract

Palladium can readily dissociate molecular hydrogen at its surface, and rapidly accept it onto the octahedral sites of its face-centered cubic crystal structure. This can include radioactive tritium. As tritium β-decays with a half-life of 12.3 years, He-3 is generated in the metal lattice, causing significant degradation of the material. Helium bubble evolution at high concentrations can result in blister formation or exfoliation and must therefore be well understood to predict the longevity of materials that absorb tritium. A hydrogen over-pressure must be applied to palladium hydride to prevent hydrogen from desorbing from the metal, making it difficult to study tritium in palladium by methods that involve vacuum, such as electron microscopy. Recent improvements in in-situ ion implantation Transmission Electron Microscopy (TEM) allow for the direct observation of He bubble nucleation and growth in materials. In this work, we present results from preliminary experiments using the new ion implantation Environmental TEM (ETEM) at the University of Huddersfield to observe He bubble nucleation and growth, in-situ, in palladium at cryogenic temperatures in a hydrogen environment. After the initial nucleation phase, bubble diameter remained constant throughout the implantation, but bubble density increased with implantation time. β-phase palladium hydride was not observed to form during the experiments, likely indicating that the cryogenic implantation temperature played a dominating role in the bubble nucleation and growth behavior. View Full-Text
Keywords: in-situ; helium implantation; environmental transmission electron microscopy; palladium tritide in-situ; helium implantation; environmental transmission electron microscopy; palladium tritide
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Taylor, C.A.; Briggs, S.; Greaves, G.; Monterrosa, A.; Aradi, E.; Sugar, J.D.; Robinson, D.B.; Hattar, K.; Hinks, J.A. Investigating Helium Bubble Nucleation and Growth through Simultaneous In-Situ Cryogenic, Ion Implantation, and Environmental Transmission Electron Microscopy. Materials 2019, 12, 2618.

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