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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

XPS post-mortem analysis of plasma-facing units extracted from WEST after the C3 (2018) and C4 (2019) campaigns

Four monoblocks coming from one ITER-like plasma-facing unit from the Q3B sector of the lower divertor, named as monoblock (MB)3, MB9, MB20, and MB30, were exposed to the deuterium and helium plasma mixture during the C3 (2018) and C4 (2019) campaigns of the Tungsten Environment in Steady-state Tokamak (WEST), followed by a detailed ex-situ X-ray photoelectron spectroscopy investigation. The surface and in-depth chemistry of the tungsten monoblocks indicated the formation of a re-deposited mixture in the deposition-dominated area of the divertor, thicker than 218 and 172 nm for MB3 and MB9, respectively. The redeposition layer was dominated by a mixture of boron carbides accompanied by tungsten carbides in MB3, while in MB9, the redeposition layer was dominated by tungsten borides. The remaining two monoblocks, MB20 and MB30, were collected from the erosion region and showed similar chemical behavior with a blended mixture of oxidized and metallic tungsten followed by boron carbides within a 50 nm depth range. Boron fixation in the layers is an expected consequence of the boronizations used during the operation, but the chemical status of redeposited elements was characterized for the first time in this work.

Marin, Alexandru [Pennsylvania State University]↗
DOE OSTI2011

(110) Orientation growth of magnetic metal nanowires with face-centered cubic structure using template synthesis technique

A template-assisted assembly technique has been used to synthesize magnetic metal nanowire arrays. Fe, Co, Ni nanowires are fabricated using direct-current electrodeposition in the pores of anodic alumina membranes. The morphology and the crystal structure of the samples are characterized by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. The results indicate that Fe, Co, and Ni nanowires all have face-centered cubic (FCC) structure and a preferred orientation along the [110] direction. The ability to prepare well-defined orientation growth of magnetic metal nanowires with FCC structure opens up new opportunities for both fundamental studies and nanodevice applications. - Research Highlights: {yields} Fe, Co, and Ni nanowires are fabricated in the AAM templates by electrodeposition. {yields} Well-defined orientation growth of the nanowires with FCC structure were investigated. {yields} The electrodeposition parameters affect the crystal structure and growth orientation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The microstructure and formation mechanism of face-centered cubic Ti in commercial pure Ti foils during tensile deformation at room temperature

Highlights: • Two variants of fcc-Ti appear in ultra-thin commercial pure Ti foils during tension. • The appearance of obvious yield point may be attributed to the formation of fcc-Ti. • The orientation relationship between fcc-Ti phase and hcp-Ti matrix is determined. • The characteristics of dislocation structure in fcc-Ti are identified. • A model for the formation of fcc-Ti is proposed. - Abstract: Two variants of face-centered cubic (fcc) Ti phase appear in ultra-thin commercial pure Ti foils with hexagonal closed packed (hcp) structure during tensile deformation at room temperature. The orientation relationship between fcc-Ti phase and hcp-Ti matrix is determined as <0001>{sub HCP} // <001>{sub FCC}, <11 2-bar 0>{sub HCP} // <1 1-bar 0>{sub FCC} and <01 1-bar 0>{sub HCP} // <110> {sub FCC}. The fcc-Ti phase with a habit plane of {01 1-bar 0}{sub HCP} usually nucleates at grain boundary and grows along the direction of <11> } } }2 }&<; }0 2-bar 0 </>{sub HCP}. The thickness of fcc-Ti phase with a shape of thin plate ranges from 10 nm to 200 nm. Dislocations, steps and stacking faults with a space of 0.58 nm can be seen in fcc-Ti. The formation of a five-layer fcc-Ti can be accomplished by the formation of stacking faults and gliding of 1/6[11 2-bar 0] Shockley partial dislocations on the prismatic plane of hcp-Ti. The 1/3[11 2-bar 0] dislocations in hcp-matrix can cross the fcc-Ti phase because the Burgers vector of these dislocations is coincidence with 1/2[110] dislocations in the fcc-Ti.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Face-centered titanium induced by ultrasonic surface rolling process in Ti-6Al-4V alloy and its tensile behavior

Highlights: • A gradient nanostructure of fcc-Ti is formed from a depth of 440 μm to top surface. • The influence factor of hcp to fcc phase transformation is demonstrated. • The fcc phase induced by USRP decreases the yield strength of Ti-6Al-4V alloy. • The fcc phase improves combining good strength and ductility. - Abstract: The phase transformation of face-centered cubic (fcc) titanium (Ti), transformed from hexagonal close-packed (hcp) Ti, in Ti-6Al-4V alloy subjected to ultrasonic surface rolling process (USRP) and the tensile behavior were investigated. A gradient nanostructure of fcc-Ti was formed from the depth of 440 μm to the top surface. The stress concentration at the phase interface of α phase and β phase promoted hcp to fcc phase transformation in low strain and strain rate region (adjacent to the substrate) while the extremely high strain and strain rate induced this phase transformation in the surface to sub-surface regions. USRP increased the tensile strength of Ti-6Al-4V alloy slightly but decreased the yield strength dramatically, and kept a good combination strength and ductility of Ti-6Al-4V alloy mainly due to the formation of the gradient nanostructure surface layer and hcp to fcc phase transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A tutorial on the micro-trench technique for incident ion angle, material erosion, and impurity deposition measurements at plasma-facing surfaces

The micro-trench method is a new technique to measure polar and azimuthal incident ion angles, material erosion, and impurity deposition at plasma-facing surfaces, and has been applied in the DIII-D divertor. This article gives a tutorial of the micro-trench technique consisting of six steps: (1) micro-trench fabrication, (2) pre-exposure measurement of the fabricated micro-trench geometry, (3) tracer material deposition, (4) plasma exposure, (5) post-exposure observation of the tracer material, and (6) post-exposure measurement of the micro-trench geometry. Two criteria need to be satisfied to apply the micro-trench method successfully: (i) uniform impurity deposition on the micro-trench floor, and (ii) erosion dominated by the physical sputtering induced by the impinging ions. Furthermore, when those two criteria are satisfied, post-exposure analysis of the impurity deposition patterns on the micro-trench floor may be used to determine the polar and azimuthal incident ion directions (mean values of the ion angle directions), erosion rate, and impurity deposition rate during plasma exposure without computational interpretation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Liquid surfaces for fusion plasma facing components—A critical review. Part I: Physics and PSI

This review of the potential of robust plasma facing components (PFCs) with liquid surfaces for applications in future D/T fusion device summarizes the critical issues for liquid surfaces and research being done worldwide in confinement facilities, and supporting R&D in plasma surface interactions. In the paper are a set of questions and related criteria by which we will judge the progress and readiness of liquid surface PFCs. Part-II (separate paper) will cover R&D on the technology-oriented aspects of liquid surfaces including the liquid surfaces as integrated first walls in tritium breeding blankets, tritium retention and recovery, and safety.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Effect of boronization on plasma-facing graphite surfaces and its correlation with the plasma behavior in NSTX-U

Boronization is a Plasma Facing Component (PFC) conditioning technique widely used in tokamak machines. The National Spherical Torus Experiment-Upgrade (NSTX-U) applied this conditioning, using a plasma glow with a deuterated Trimethyl-boron (d-TMB) and He mixture. The use of boronization during the campaign improved the plasma performance, allowing longer plasma discharges and H-mode access. The chemical state of an ATJ graphite sample, used as a proxy for the NSTX-U PFCs, was monitored in-situ using the Materials Analysis Particle Probe (MAPP) diagnostic and X-ray Photoelectron Spectroscopy (XPS). The XPS data showed a progressive rise (from < 5% to 23%) in the oxygen concentration of the boronized ATJ sample as the D+ fluence increased. Filterscopes were used to measure the light emitted by oxygen impurities in the plasma near the surface of the PFC. An increase in the registered magnitude of the OII line, normalized to the Dγ intensity, was observed as the concentration of O on the ATJ surface increased. The plasma performance was found to be strongly correlated to oxygen impurity concentrations at the plasma edge and on the PFC surface, as measured by the discharge length and access to the H-mode regime. In this work, we present a quantitative analysis of the evolution of the chemistry of the ATJ surface, and the oxygen presence in the plasma-material interface, and report relevant plasma parameters observed during the same period of time.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Survey of tungsten gross erosion from main plasma facing components in WEST during a L-mode high fluence campaign

An initial high fluence campaign was performed in WEST, in 2023, on the newly installed actively cooled tungsten divertor composed of ITER-grade monoblocks. The campaign consisted in the repetition of a 60 s long Deuterium L-mode pulse in attached divertor conditions, cumulating over 10000s of plasma exposure. A maximum deuterium fluence of approximately 5⋅1⁢026 m−2 was reached in the outer strike point region, representative of a few high performance ITER pulses. Gross tungsten erosion inferred from visible spectroscopy shows that the most eroded plasma facing component is the inner divertor target with rates ten times larger than on the outer divertor target. The outer midplane tungsten bumpers, located a few centimeters from the plasma, show gross erosion rates two times lower than at the outer divertor. We conclude that the outer midplane bumpers have a negligible contribution to the long range tungsten migration and deposition onto the lower divertor. The cumulated gross erosion rate on the inner divertor translates in an effective gross erosion thickness of about 20μ⁢m, while it is about 2μ⁢m for the outer divertor. Strikingly, these orderings coincide with the thickness of deposits found locally on the divertor: the exposed surfaces of high field side monoblocks are covered with several tens of μ⁢m tungsten deposits, while on the lower field side, few μ⁢m thin tungsten deposits are only found on the magnetically shadowed parts of monoblocks. The strong impact of those deposits on WEST operation, namely perturbation of surface temperature measurement with infra-red thermography, and the emission of flakes causing radiative perturbation of the confined plasma, calls for anticipating similar issues in ITER. In particular, the start of research operation shall consider the definition of a divertor erosion budget in order to anticipate the formation of deleterious deposits.

Fedorczak, N.↗
DOE OSTI2018

Mechanical properties of high-entropy alloys with emphasis on face-centered cubic alloys

HHigh-entropy alloys (HEAs), also known as multi-principal element alloys or multi-component alloys, have been the subject of numerous investigations since they were first described in 2004. The earliest HEA was the equiatomic CrMnFeCoNi “Cantor” alloy, but HEAs now encompass a broad class of metallic and ceramic systems. The concept of utilizing the high entropy of mixing to develop stable multi-element alloys may not be scientifically correct but has produced extraordinary mechanical properties in specific HEAs, mainly CrCoNi-based alloys, associated with their continuous work-hardening rate that is sustained to large plastic strains (~0.5) and at low temperatures. This, in combination with the high frictional forces on dislocations and a propensity for twinning, leads to outstandingly high fracture toughness values (exceeding 200 MPa·m 1/2 ) and resistance to shear-band formation under dynamic loading. The critical shear strain for the onset of adiabatic shear band formation is ~7 for the Cantor alloy, much higher than that for conventional alloys, suggesting superior ballistic properties. The slower diffusion rates resulting from the multi-element environment contribute to the excellent intermediate-temperature performance. We review the principal mechanical properties of these alloys with emphasis on the face-centered cubic systems, such as the CrCoNi-based alloys. Their favorable mechanical properties and ease of processing by conventional means suggest extensive utilization in many future structural applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Auto-ignition study of FACE gasoline and its surrogates at advanced IC engine conditions

Robust surrogate formulation for gasoline fuels is challenging, especially in mimicking auto-ignition behavior observed under advanced combustion strategies including boosted spark-ignition and advanced compression ignition. This work experimentally quantifies the auto-ignition behavior of bi- and multi-component surrogates formulated to represent a mid-octane (Anti-Knock Index 91.5), full boiling-range, research grade gasoline (Fuels for Advanced Combustion Engines, FACE-F). A twin-piston rapid compression machine is used to achieve temperature and pressure conditions representative of in-cylinder engine operation. Changes in low- and intermediate-temperature behavior, including first-stage and main ignition times, are quantified for the surrogates and compared to the gasoline. This study identifies significant discrepancies in the first-stage ignition behavior, the influence of pressure for the bi- to ternary blends, and highlights that better agreement is achieved with multi-component surrogates, particularly at lower temperature regimes. A recently-updated detailed kinetic model for gasoline surrogates is also used to simulate the measurements. Finally, sensitivity analysis is employed to interpret the kinetic pathways responsible for reactivity trends in each gasoline surrogate.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Single crystal plastic behavior of a single-phase, face-center-cubic-structured, equiatomic FeNiCrCo alloy

To understand the fundamental deformation mechanisms of compositionally complex alloys, single crystals of a multi-component equiatomic FeNiCoCr alloy with face-centered cubic (FCC) structure were grown for mechanical studies. Similarly to typical FCC pure metals, slip trace analyses indicate that dislocation slips take place on (1 1 1) planes along [11¯0] directions. The critical resolved shear stress (CRSS) obeys the Schmid law at both 77 and 293 K, and tension–compression asymmetry is not observed. Although this material slips in a normal FCC manner both at 293 and 77 K, compared to typical FCC metals the CRSS’s strong temperature dependence is abnormal.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Facile Synthesis of Ru-Based Octahedral Nanocages with Ultrathin Walls in a Face-Centered Cubic Structure

Noble-metal nanocages with ultrathin (less than 2 nm) walls and well-defined facets have received great interest owing to their remarkable utilization efficiency of atoms and facet-dependent catalytic activities toward various reactions. Here, we report the synthesis of Ru-based octahedral nanocages covered by {111} facets, together with ultrathin walls in a face-centered cubic (fcc) structure rather than the hexagonal close-packed (hcp) of bulk Ru. The involvement of slow injection for the Ru(III) precursor, the introduction of KBr, and the use of elevated temperature were all instrumental to the formation of Pd@Ru core–shell octahedra with a conformal, uniform shell and a smooth surface. The {111} facets were well preserved during the selective removal of the Pd cores via wet etching, even when the Ru walls were only five atomic layers in thickness. Through in situ XRD, we demonstrated that the fcc structure of the Ru nanocages was stable up to 300 °C. We also used first-principles, self-consistent density functional theory calculations to study the adsorption and dissociation of N2 as a means to predict the catalytic performance toward ammonia synthesis. Our results suggested that the small proportions of Pd atoms left behind in the walls during etching could play a key role in stabilizing the adsorption of N2 as well as in reducing the activation energy barrier to N2 dissociation.

Zhao, Ming↗
DOE OSTI2020

Perspectives on Cobalt Supply through 2030 in the Face of Changing Demand

Lithium-ion battery demand, particularly for electric vehicles, is projected to increase by over 300% throughout the next decade. With these expected increases in demand, cobalt (Co)-dependent technologies face the risk of significant impact from supply concentration and mining limitations in the short term. In this study, increased extraction and secondary recovery form the basis of modeling scenarios that examine implications on Co supply to 2030. Demand for Co is estimated to range from 235 to 430 ktonnes in 2030. This upper bound on Co demand in 2030 corresponds to 280% of world refinery capacity in 2016. Supply from scheduled and unscheduled production as well as secondary production is estimated to range from 320 to 460 ktonnes. Our analysis suggests the following: (1) Co price will remain relatively stable in the short term, given that this range suggests even a supply surplus, (2) future Co supply will become more diversified geographically and mined more as a byproduct of nickel (Ni) over this period, and (3) for this demand to be met, attention should be paid to sustained investments in refined supply of Co and secondary recovery.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Surface Segregation of Liquid Metal Plasma-Facing Component Alloys: A ReaxFF Investigation

Engineering liquid metal alloys offers a transformative pathway for plasma-facing components by enabling chemically tailored surfaces that can simultaneously optimize plasma-material interactions, reduce divertor heat flux, and enhance core plasma confinement, thereby advancing the commercial viability of nuclear fusion power plants. This study, employing an atomistic simulation approach, provides direct evidence that incorporating nonmetal surface-active agents (such as O and H, or their combination) enables strong surface segregation. This capability makes tin−aluminum (Sn−Al) and tin−lithium (Sn−Li) alloys, with suitable compositions, good candidates for PFC applications. Specifically, the presence of low-Z solutes (Li, Al) leads to preferential surface enrichment, which imparts low-Z sputtering characteristics, while the Sn solvent maintains thermophysical stability. To systematically examine this behavior, we developed a ReaxFF force field spanning the full Sn/Al/Li/O/H chemistry, validated it against formation energies and elastic constants, and applied it in reactive molecular dynamics simulations at fusion-relevant temperatures. We also introduced an overlapbased segregation index that captures interfacial compositional separation directly from atomistic density distributions. Here, this metric reveals a clear hierarchy of segregation regimes and provides a unified view across all systems studied. Together, these findings establish a mechanistic link between nonmetal chemistry and interfacial structure, providing a predictive framework for designing self-adaptive, low-sputtering liquid metal alloys for fusion applications.

Alloys↗
DOE OSTI2020

Household Materials Selection for Homemade Cloth Face Coverings and Their Filtration Efficiency Enhancement with Triboelectric Charging

The COVID-19 pandemic is currently causing a severe disruption and shortage in the global supply chain of necessary personal protective equipment (e.g., N95 respirators). The U.S. CDC has recommended use of household cloth by the general public to make cloth face coverings as a method of source control. We evaluated the filtration properties of natural and synthetic materials using a modified procedure for N95 respirator approval. Common fabrics of cotton, polyester, nylon, and silk had filtration efficiency of 5–25%, polypropylene spunbond had filtration efficiency 6–10%, and paper-based products had filtration efficiency of 10–20%. An advantage of polypropylene spunbond is that it can be simply triboelectrically charged to enhance the filtration efficiency (from 6 to >10%) without any increase in pressure (stable overnight and in humid environments). Using the filtration quality factor, fabric microstructure, and charging ability, we are able to provide an assessment of suggested fabric materials for homemade facial coverings.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis of Ru Icosahedral Nanocages with a Face-Centered-Cubic Structure and Evaluation of Their Catalytic Properties

Owing to the presence of {111} facets, twin boundaries, and strain fields on the surface, noble-metal nanocrystals with an icosahedral shape have been reported with stellar performance toward an array of catalytic reactions. Here, we report the successful synthesis of Ru icosahedral nanocages with a face-centered cubic (fcc) structure by conformally coating Pd icosahedral seeds with ultrathin Ru shells, followed by selective removal of the Pd cores via chemical etching. We discovered that the presence of bromide ions was critical to the layer-by-layer deposition of Ru atoms. According to in situ XRD, the fcc structure in the Ru nanocages could be retained up to 300 °C before it was transformed into the conventional hexagonal close-packed (hcp) structure. Additionally, the icosahedral shape of the Ru nanocages could be largely preserved up to 300 °C. The Ru icosahedral nanocages with twin boundaries on the surface exhibited greatly enhanced activities toward both the reduction of 4-nitrophenol and decomposition of hydrazine than their cubic and octahedral counterparts. When benchmarked against the parental Pd@Ru core–shell nanocrystals, all the Ru nanocages displayed superior catalytic activities. First-principles density functional theory calculations also suggest that the fcc-Ru icosahedral nanocages containing residual Pd atoms are more promising than the conventional hcp-Ru solid nanoparticles in catalyzing nitrogen reduction for ammonia synthesis. With the subsurface impurities of Pd, the twin boundary regions of the icosahedral nanocages are able to stabilize the N 2 dissociation transition state, reducing the overall reaction barrier and promoting the competition with the N 2 desorption process.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Crystal structure of the MOP flippase MurJ in an inward-facing conformation

Peptidoglycan (PG) protects bacteria from osmotic lysis, and its biogenesis is a key antibiotic target. A central step in PG biosynthesis is flipping of the lipid-linked PG precursor lipid II across the cytoplasmic membrane for subsequent incorporation into PG. MurJ, part of the multidrug/oligosaccharidyl-lipid/polysaccharide (MOP) transporter superfamily, was recently shown to carry out this process. However, understanding of how MurJ flips lipid II, and of how MOP transporters operate in general, remains limited due to a lack of structural information. Here we present a crystal structure of MurJ from Thermosipho africanus in an inward-facing conformation at 2.0-Å resolution. We report a hydrophobic groove is formed by two C-terminal transmembrane helices, which leads into a large central cavity that is mostly cationic. Our studies not only provide the first structural glimpse of MurJ but also suggest that alternating access is important for MurJ function, which may be applicable to other MOP superfamily transporters.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Theoretical Model of Helium Bubble Growth and Density in Plasma-Facing Metals

We present a theoretically-motivated model of helium bubble density as a function of volume for high-pressure helium bubbles in plasma-facing tungsten. The model is a good match to the empirical correlation we published previously [Hammond et al., Acta Mater. 144, 561–578 (2018)] for small bubbles, but the current model uses no adjustable parameters. The model is likely applicable to significantly larger bubbles than the ones examined here, and its assumptions can be extended trivially to other metals and gases. We expect the model to be broadly applicable and useful in coarse-grained models of gas transport in metals.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗