The Formation and Structure of Tungsten Nanotendrils
Abstract not provided.
Publications
Effects of low-fluence helium plasma exposure characterized by helium ion microscopy scanning probes and in-situ ellipsometry
Abstract not provided.
Helium release from tungsten nanostructure during high-temperature annealing
Abstract not provided.
Enabling hydrogen energy infrastructure through surface passivation of structural materials
Abstract not provided.
Helium Interactions with Tungsten as a Plasma Facing Surface Material
Abstract not provided.
Application of multi-angle scattering maps to stepped surfaces
Surface Science
This study examines channeling, multiple scattering, and neutralization/re-ionization of ions scattered along the stepped Al(332) plane. Our experimental approach involves probing the surface with 1–2 keV He+ and Ne+ beams, and then systematically mapping the scattered ion fluxes over a large solid angle. This provides comprehensive ion channeling information over all directions, rather than along a few low-index azimuths, as is common practice in ion scattering spectroscopy. We first probe the surface with 2 keV He+ at near-normal incidence, and then map the backscattered particle flux (both ions and neutrals) via time of flight (TOF) spectrometry. The features contained in these maps can be correlated with axial and inter-planar channeling effects, and are reproduced well via binary collision simulations. Sensitivity to the stepped surface topography is heightened considerably for oblique ion incidence in the forward-scattering direction. In this geometry, we used 2 keV Ne+ to probe the surface and mapped the corresponding scattered fluxes of both single and multiply-charged ions. In both cases, the scattering intensity depends strongly on the precise trajectory taken along the surface, and is particularly sensitive to how extensively the incident ions interact with the step edges. We interpret the information contained in these maps by considering several mechanisms for charge transfer and double ion production. The formation of Ne++ appears to be correlated with a previously observed inelastic mechanism that occurs when the collision apsis, Rmin, is less than 0.65 Å. This contributes to an energy loss of 48 ± 8 eV for Ne+ undergoing single scattering; the Rmin threshold for this inelastic step coincides with the emergence of a distinct Ne++ peak. Using the information gained from the maps, we propose methods for extending this approach to chemisorbed layers.
Effects of helium plasmas on tungsten surfaces characterized by helium ion microscopy ion channeling and in-situ spectroscopic ellipsometry
Abstract not provided.
Role of Surface Oxidation in the Dehydrogenation of Complex Metal Hydrides
Abstract not provided.
Materials and Hydrogen Isotope Science at Sandia's California Laboratory
Abstract not provided.
Facility Update: Sandia National Laboratories / CA
Abstract not provided.
Characterization of He plasma-induced damage of tungsten surfaces using He ion microscopy ion channeling and in-situ spectroscopic ellipsometry
Abstract not provided.
Oxygen Impurity Effects on Hydrogen Assisted Fatigue and Fracture of X100 Pipeline Steel
Abstract not provided.
Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH4
Proposed for publication
Abstract not provided.
Saturation of tungsten surfaces with hydrogen: A density functional theory study complemented by low energy ion scattering and direct recoil spectroscopy data
Acta Materialia
Herein, we investigate the saturation limits of hydrogen on the (110) and (100) surfaces of tungsten via Density Functional Theory (DFT) and complement our findings with experimental measurements. We present a detailed study of the various stable configurations that hydrogen can adopt upon the surfaces at coverage ratios starting below 1.0, up to the point of their experimental coverage ratios, and beyond. We provide the many low-energy configurations that exist at all coverages along with the energy landscape they form. Our findings allow us to estimate that the saturation limit on each surface exists with one monolayer of hydrogen atoms adsorbed. In the case of (110) this corresponds to a coverage ratio of one hydrogen atom per tungsten atom, while in the case of (100) a full monolayer is present at a coverage ratio of 2.0 hydrogen atoms per tungsten atoms. Preliminary Low Energy Ion Scattering (LEIS) and Direct Recoil Spectroscopy (DRS) measurements complement this work on the W(110) surface. These results and some previously published measurements obtained on the W(100) surface confirm the findings obtained by DFT. In particular, the saturation limits on each surface, the preferred adsorption sites on both surfaces up to saturation, and the reconstruction of the bare and unsaturated (100) surface.
Materials science challenges in magnetic fusion
Abstract not provided.
Direct detection of chemisorbed hydrogen on metal hydride and structural material surfaces using low energy ion scattering
Abstract not provided.
Roles of Titanium and Oxygen at the Surface in the Dehydrogenation of Titanium-Doped Sodium Aluminum Hydride
Abstract not provided.
HyMARC (Sandia) Annual Report
The Sandia HyMARC team continued its development of new synthetic, modeling, and diagnostic tools that are providing new insights into all major classes of storage materials, ranging from relatively simple systems such as PdHx and MgH2, to exceptionally complex ones, such as the metal borohydrides, as well as materials thought to be very well-understood, such as Ti-doped NaAlH4. This unprecedented suite of capabilities, capable of probing all relevant length scales within storage materials, is already having a significant impact, as they are now being used by both Seedling projects and collaborators at other laboratories within HyMARC. We expect this impact to grow as new Seedling projects begin and through collaborations with other scientists outside HyMARC. In the coming year, Sandia efforts will focus on the highest impact problems, in coordination with the other HyMARC National Laboratory partners, to provide the foundational science necessary to accelerate the discovery of new hydrogen storage materials.
Near-surface morphology changes to helium plasma-exposed tungsten characterized with spectroscopic ellipsometry and helium ion microscopy
Abstract not provided.
Tailoring Reaction Enthalpies and Activation Energies in Complex Metal Hydrides Doped with Reactive Metal Ions
Abstract not provided.
Low energy ion scattering characterization of materials for hydrogen storage applications
Abstract not provided.
A Comparison of Near Surface Precipitation in Tungsten Alloys Due to High Flux Plasma Exposure
Abstract not provided.
High-flux plasma exposure of ultra-fine grain tungsten
International Journal of Refractory Metals and Hard Materials
In this work, we examine the response of an ultra-fine grained (UFG) tungsten material to high-flux deuterium plasma exposure. UFG tungsten has received considerable interest as a possible plasma-facing material in magnetic confinement fusion devices, in large part because of its improved resistance to neutron damage. However, optimization of the material in this manner may lead to trade-offs in other properties. We address two aspects of the problem in this work: (a) how high-flux plasmas modify the structure of the exposed surface, and (b) how hydrogen isotopes become trapped within the material. The specific UFG tungsten considered here contains 100 nm-width Ti dispersoids (1 wt%) that limit the growth of the W grains to a median size of 960 nm. Metal impurities (Fe, Cr) as well as O were identified within the dispersoids; these species were absent from the W matrix. To simulate relevant particle bombardment conditions, we exposed specimens of the W-Ti material to low energy (100 eV), high-flux (> 1022 m− 2 s− 1) deuterium plasmas in the PISCES-A facility at the University of California, San Diego. To explore different temperature-dependent trapping mechanisms, we considered a range of exposure temperatures between 200 °C and 500 °C. For comparison, we also exposed reference specimens of conventional powder metallurgy warm-rolled and ITER-grade tungsten at 300 °C. Post-mortem focused ion beam profiling and atomic force microscopy of the UFG tungsten revealed no evidence of near-surface bubbles containing high pressure D2 gas, a common surface degradation mechanism associated with plasma exposure. Thermal desorption spectrometry indicated moderately higher trapping of D in the material compared with the reference specimens, though still within the spread of values for different tungsten grades found in the literature database. For the criteria considered here, these results do not indicate any significant obstacles to the potential use of UFG tungsten as a plasma-facing material, although further experimental work is needed to assess material response to transient events and high plasma fluence.
Enabling Reversibility in Hydrogen Storage Materials
Abstract not provided.
Hydrogen Materials-Advanced Research Consortium: Sandia Efforts for Understanding Hydrogen Storage Systems
Abstract not provided.
Results 26–50 of 109