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DOE OSTI2024

Silicon x-ray backlighter improvement by targets with spike-like microstructures

In order to accurately probe high energy density matter states, it is vital to create powerful x-ray backlighters. One approach to create such x-ray sources is based on the usage of short-pulse, high-energy lasers, which greatly benefits from an optimization of the laser target coupling. Here, the spectral and temporal x-ray emission profiles of structured silicon targets with micron-sized spikes on the front surface are studied at laser intensities of 10 17 W cm -2 . The laser pulse length is varied between 1 and 20 ps with an energy of up to 1 kJ. The structured targets show an up to 13× enhancement of silicon He α emission compared to flat foils with a well-defined, sharp emission pulse profile. Furthermore, the performance of the microstructured targets is compared to targets with a CH shield as well as foils irradiated with a UV prepulse.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Two-dimensional glass transition–like behavior of Janus particle–laden interface

Abstract Understanding the interactive behavior of Janus particles (JPs) is a growing field of research. The enhancement in binding energy, in comparison to homogenous particles, and the dual characteristic of JPs open up new possibilities for novel applications. In many such applications, interfacial materials become subjected to flows that produce dilational and shear stresses. Therefore, it is important to understand the impact that the Janus character brings to interfaces. In this work, we study the microstructure of two-dimensional (2D) JP monolayers formed at the air–water interface and examine the shear viscoelasticity with an interface rheometer that was adapted for in situ surface pressure control via a Langmuir trough. We extend concepts from bulk rheology to data obtained from interfacial rheology as a tool to understand and predict the monolayer’s viscoelastic behavior. Finally, by calculating the time relaxation spectrum from the measured 2D dynamic moduli, we conclude that a phenomenon similar to glass transition is taking place by analogy.

42 ENGINEERING↗

DOE OSTI2023

Carbonation dynamics of hydrated alite revealed by electron microscopy

CO 2 sequestration in concrete is crucial to relieve the environmental burden, while the carbonation mechanisms remain unclear. Here, we explored the carbonation dynamics of alite hydrates through electron microscopy. We discovered that calcite is the main phase of carbonate crystals throughout the entire carbonation period in the alite system. Further, the shape evolution of calcite crystals was captured: spindle carbonates initially formed on C-S-H substrate and then transformed into rhombohedrons; Intermediate states such as polyhedral particles and layered rhomboids were also observed. Based on our quantitative calculations, the growth rate of calcite particles was determined approximately 0.2 μm/day, which may be affected by the relative concentration between calcium ions and CO 2 source. A direct relation between the microstructure and mechanical properties of calcite was uncovered using atomic force microscopy. Furthermore, we found that the morphology development of calcite crystals during carbonation may be explained by the surface energy variation of different facets. This work suggests a unique approach to track carbonation kinetics and provides new opportunities to unveil underlying carbonation mechanisms at the nanoscale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Radiation Tolerance of Nanoporous Gadolinium Titanate

Defect sinks play a crucial role in reducing radiation-induced damage accumulation, but their effectiveness varies. This study directly compares the efficacy of grain boundaries and pores (free surfaces) in gadolinium titanate (Gd 2 Ti 2 O 7 ) using in situ ion irradiation transmission electron microscopy (TEM). A unique sample configuration is developed, where each of the three distinct regions, each containing only one primary sink of interest, is in the same TEM lamella for simultaneous irradiation. Regular assessments of crystallinity in each region via nanobeam electron diffraction show that, at both room temperature and 600°C, free surface (pore) defect sinks are more effective than grain boundaries in capturing radiation-induced defects and delaying the onset of amorphization. These findings have significant implications for further microstructural engineering and the design of radiation-resistant microstructures.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Computational Modeling of Heterogeneity of Stress, Charge, and Cyclic Damage in Composite Electrodes of Li-Ion Batteries

Charge heterogeneity is a prevalent feature in many electrochemical systems. In a commercial cathode of Li-ion batteries, the composite is hierarchically structured across multiple length scales including the sub-micron single-crystal primary-particle domains up to the macroscopic particle ensembles. The redox kinetics of charge transfer and mass transport strongly couples with mechanical stresses. This interplay catalyzes substantial heterogeneity in the charge (re)distribution, stresses, and mechanical damage in the composite electrode during charging and discharging. We assess the heterogeneous electrochemistry and mechanics in a LiNi x Mn y Co z O 2 (NMC) cathode using a fully coupled electro-chemo-mechanics model at the cell level. A microstructure-resolved model is constructed based on the synchrotron X-ray tomography data. We calculate the stress field in the composite and then quantitatively evaluate the kinetics of surface charge transfer and Li transport biased by mechanical stresses. We further model the cyclic behavior of the cell. The repetitive deformation of the active particles and the weakening of the interfacial strength cause gradual increase of the interfacial debonding. The mechanical damage impedes electron transfer, incurs more charge heterogeneity, and results in the capacity degradation in batteries over cycles.

25 ENERGY STORAGE↗

DOE OSTI2024

Microstructural characterization and equibiaxial flexural strength of CeO 2 and Ti-doped CeO 2

In this study, the synthesis of CeO 2 and titanium dioxide (TiO 2 ) doped CeO 2 (TDC) monoliths are investigated, and their fracture strength is assessed using an equibiaxial flexure testing technique at room temperature. Pellets were synthesized using conventional powder processing and sintering methods to produce the desired characteristics. The TiO 2 dopant concentration was optimized at 0.1 wt % TiO 2 to obtain dense, solid-solution pellets with an enhanced grain microstructure. A ball-on-ring fixture was used to obtain the TRS and Weibull parameters of over 30 pellets for CeO 2 and 0.1 wt % TDC to compare fracture behavior. The TRS of CeO 2 pellets ranged from 88 to 160 MPa and the TRS of 0.1 wt % TDC pellets ranged from 102 to 171 MPa, both being consistent with published values. Weibull parameters, such as characteristic strength and Weibull modulus, were extracted as 129 MPa and 8.5 for CeO 2 and 150 MPa and 9.3 for 0.1 wt % TDC, respectively. Although Hertzian contact damage was observed on compressive surfaces, failure initiation occurred on the tensile surfaces of both types of samples. Fracture surface analysis for CeO 2 indicated a predominantly intergranular fracture while 0.1 wt % TDC had a predominantly transgranular fracture mode. Finally, the TRS of 0.1 wt % TDC resulted in increased Weibull parameters when compared to CeO 2 , indicating sample chemistry and microstructure impact mechanical behavior for these samples.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Formation of Bimetallic Nanoparticles via Exsolution Using a Reducible Metal Oxide Capping Layer

Bimetallic nanoparticles are promising catalysts that can improve performance in heterogeneous catalysis and solid-state electrochemistry. Exsolution is a useful method for forming such nanoparticles; however, it is limited by the elements present within the host oxide lattice. Here, in this work, we develop and demonstrate a strategy to form bimetallic particles from La 0.5 Sr 0.5 Ti 0.94 Ni 0.06 O 3 (LSTN) exsolution and using a reducible SnO 2 capping layer, expanding the range of elements available for bimetallic nanoparticle formation. Using this capping layer strategy, we formed nickel–tin (Ni 0 –Sn 0 ) bimetallic nanoparticles via exsolution. We used in situ near-ambient pressure X-ray photoelectron spectroscopy to monitor surface chemical changes during exsolution, showing that first, SnO 2 volatilized. This SnO 2 loss exposed the perovskite surface of LSTN to reducing conditions, which induced Ni exsolution, and compounded with SnO 2 reduction led to the formation of bimetallic Ni 0 –Sn 0 particles. To evaluate the associated microstructural evolution, we measured grazing incidence small-angle X-ray scattering (GISAXS), which confirmed the loss of the SnO 2 capping layer, and scattering simulations suggested the formation of bimetallic particles. We confirmed the bimetallic nanoparticle composition and morphology by Auger spectroscopy and scanning transmission electron microscopy. The resulting bimetallic nanoparticles were smaller and more thermally stable than the monometallic Ni counterparts on LSTN. This capping layer and exsolution approach allow synthesizing multimetallic nanoparticles and can be applied to other reducible metal oxides and perovskite hosts, broadening the compositional space for advanced catalytic materials.

36 MATERIALS SCIENCE↗

DOE OSTI2024

X-ray linear dichroic tomography of crystallographic and topological defects

Abstract The functionality of materials is determined by their composition 1–4 and microstructure, that is, the distribution and orientation of crystalline grains, grain boundaries and the defects within them 5,6 . Until now, characterization techniques that map the distribution of grains, their orientation and the presence of defects have been limited to surface investigations, to spatial resolutions of a few hundred nanometres or to systems of thickness around 100 nm, thus requiring destructive sample preparation for measurements and preventing the study of system-representative volumes or the investigation of materials under operational conditions 7–15 . Here we present X-ray linear dichroic orientation tomography (XL-DOT), a quantitative, non-invasive technique that allows for an intragranular and intergranular characterization of extended polycrystalline and non-crystalline 16 materials in three dimensions. We present the detailed characterization of a polycrystalline sample of vanadium pentoxide (V 2 O 5 ), a key catalyst in the production of sulfuric acid 17 . We determine the nanoscale composition, microstructure and crystal orientation throughout the polycrystalline sample with 73 nm spatial resolution. We identify and characterize grains, as well as twist, tilt and twin grain boundaries. We further observe the creation and annihilation of topological defects promoted by the presence of volume crystallographic defects. The non-destructive and spectroscopic nature of our method opens the door to operando combined chemical and microstructural investigations 11,18 of functional materials, including energy, mechanical and quantum materials.

Science & Technology - Other Topics↗

DOE OSTI2021

Oxidation and Associated Pore Structure Modification During Experimental Alteration of Granite

Weathering plays a crucial role in a number of environmental processes, and the microstructure and evolution of multi-scale pore space is a critically important factor in the weathering of geological formations. In igneous rocks the infiltration of meteoric water into initially relatively dry material can cause the rock to begin to disaggregate, increasing porosity and surface area, and allowing further disaggregation and weathering to occur. These processes, in turn, allow biota to colonize the rock, further enhancing the weathering rate. In some igneous rocks this may be driven by oxidation of primary minerals. One such mineral, biotite, has been repeatedly mentioned as a cause of cracking during oxidation. However, the scale-dependence of the processes by which this occurs are poorly understood. We cannot, therefore, accurately extrapolate laboratory reaction rates to the field in predictive numerical models. In order to better understand the effects of oxidation and test the hypothesis that fracture and disaggregation are initiated by swelling of oxidizing biotites, we reacted granite cores in a selenic acid-rich aqueous solution at 200°C for up to 438 days. Elevated temperatures and selenic acid were used to provide relatively fast reaction rates and highly oxidizing conditions in sealed reaction vessels. These experiments were analyzed using a combination of imaging, X-ray diffraction, Mössbauer spectroscopy, and small- and ultra-small angle neutron scattering to interrogate porosity and microfracture formation. The experimental results show little observable biotite swelling, but significant transport and growth of iron oxides and/or clays along grain boundaries throughout the sample. Significant increases in porosity were also observed at the sample rim, likely associated with feldspar alteration. Fractures and transport were observed throughout the core, suggesting that stresses due to crystallization pressures caused by the growing iron phases may be the initiating factors in granite weathering, possibly followed by biotite swelling after sufficient permeability is achieved.

Anovitz, Lawrence M.↗

DOE OSTI2022

An algorithm for physics informed scan path optimization in additive manufacturing

Site specific microstructure control is a critical research area within the field of additive manufacturing due to its potential to revolutionize part performance. One way to achieve site specific microstructure control is through control of the solidification conditions via the construction of intricate scan paths; however, the search space for such a problem is large. Previous attempts only considered the solidification conditions at the top surface while also requiring either lots of manual-fine tuning or large amounts of computational resources. This paper introduces a general method for scan path optimization which considers the solidification conditions in the bulk of the material without an increase in computational expense. This method consists of three core components:1. A heat transfer model for simulating the temperature field at a given time.2. A surrogate model which takes scan pattern information and temperature data and predicts the solidification conditions of the bulk as well as the meltpool depths for a spot melt.3. A decision algorithm to decide which spot melt should be printed next based on the outputs of the surrogate model.Each of these components can be changed without changing the overall method. Within this work, this method is applied in the creation of an algorithm containing a semi-analytic heat transfer model to simulate the temperature field, a fully convolutional neural network (FCNN) as the surrogate model, and a greedy decision algorithm. The resulting algorithm produced complex scan patterns which gave strong results for simulated microstructure control.

36 MATERIALS SCIENCE↗

DOE OSTI2025

A Review of the Influence of Processing Parameters on ODS Steels Produced via Additive Manufacturing Techniques

Abstract This paper reviews current observations regarding processing conditions for oxide dispersion-strengthened steels consolidated through additive manufacturing techniques. Variations in ODS steels observed across process parameters include changes in grain size, grain texture, oxide size, density of oxides, porosity, melt pool characteristics, and mechanical properties. These properties were then compared across techniques to understand which techniques and processing conditions lead to the highest strength, ductility, and oxide density. Current literature suggests that a mix of grain types, in the form of either morphology or phase, can significantly increase the strength of printed ODS steels. Meanwhile, the most ductile samples, regardless of consolidation technique or matrix material, were made from feedstock with oxide additions located on the powder surface. Reported grain and oxide sizes were plotted against the ratio of laser power to scan speed, volumetric energy density, and normalized enthalpy. No strong correlation between these values and microstructural features was observed. The plots that were made suggest that a larger data set, more in-depth representative equations, and more defined material properties as a function of specific feedstock used are necessary to determine a value that can be correlated to the printed ODS steel microstructure.

deJong, Matthew↗

DOE OSTI2021

Pressure and thermal annealing effects on the photoconversion efficiency of polymer solar cells

This paper presents the results of experimental and theoretical studies of the effects of pressure and thermal annealing on the photo-conversion efficiencies (PCEs) of polymer solar cells with active layers that consist of a mixture of poly(3-hexylthiophene-2,5-diyl) and fullerene derivative (6,6)-phenyl-C 61 -butyric acid methyl ester. The PCEs of the solar cells increased from ~2.3% (for the unannealed devices) to ~3.7% for devices annealed at ~150 °C. A further increase in thermal annealing temperatures (beyond 150 °C) resulted in lower PCEs. Further improvements in the PCEs (from ~3.7% to ~5.4%) were observed with pressure application between 0 and 8 MPa. However, a decrease in PCEs was observed for pressure application beyond 8 MPa. The improved performance associated with thermal annealing is attributed to changes in the active layer microstructure and texture, which also enhance the optical absorption, mobility, and lifetime of the optically excited charge carriers. The beneficial effects of applied pressure are attributed to the decreased interfacial surface contacts that are associated with pressure application. The implications of the results are then discussed for the design and fabrication of organic solar cells with improved PCEs.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Leveraging Additive Manufacturing to Fabricate High Temperature Alloys With Co-Designed Mechanical Properties and Environmental Resistance

A paradigm shift in the traditional sequential design approaches is critically essential to create application-specific hierarchical and multifunctional materials with superior long-term performance for next-generation energy technologies involving extreme environments. In the current work, we aim to leverage the flexibility and geometric/compositional complexity offered by additive manufacturing to demonstrate this new approach by codesigning a compositionally graded Ni-based alloy for molten salts\sCO 2 heat exchangers to enable mitigation of environmental degradation of surfaces exposed to molten halide salts, while simultaneously suppressing the consequent deterioration in mechanical stability. Further, thermokinetic modeling describing the underlying physics of thermally- and environmentally induced spatiotemporal compositional and microstructural evolution will be employed to predict the parameter space of material deposition processes and precisely identify the required composition gradient. Preliminary corrosion and mechanical testing of the dual material demonstrated the potential of the material to replace existing solid solution strengthened materials for this application.

36 MATERIALS SCIENCE↗

DOE OSTI2021

A Constitutive Structural Parameter for the Work Hardening Behavior of Additively Manufactured Ti-6Al-4V

The mechanical behavior of Ti-6Al-4V produced by additive manufacturing processes is assessed based on a formulation developed from the Kocks-Mecking relationship. A constitutive parameter derived for the microstructure is characteristic of the work hardening behavior determined by the plastic strain between the proportional limit and the strength at the instability point. The varied plasticity behavior associated with surface and build direction effects can be evaluated with this approach as presented for the case of Ti-6Al-4V under uniaxial tension.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Characterization of the degradation of gamma-irradiated elastomers using Raman spectroscopy

This report presents key findings from Raman spectroscopic analysis of gamma-irradiated rubber samples extracted from a laminated lead-damped rubber (LDR) seismic isolation device. The samples were exposed to gamma radiation from a 60Co source in a Foss Therapy Services gamma irradiator, reaching absorbed doses up to 1600 kGy. A distinct threshold near 400 kGy was identified, beyond which significant spectral changes were observed. Two Raman peaks - at approximately 425 cm-1 and 2440 cm-1 - were tracked as a function of dose using Gaussian fitting. The 425 cm-1 peak, attributed to sulfur–sulfur (S–S) bond stretching (resulting from vulcanization of the rubber), exhibited a dose-dependent upshift, indicating radiation-induced crosslinking within the sulfur-based polymer network. Conversely, the 2440 cm-1 peak, likely associated with vibrational modes of additives or impurities, showed a downward shift with increasing dose, suggesting chain scission and degradation of non-rubber constituents. These results provide first-of-a-kind insights into the microstructural evolution of elastomers under high-dose gamma irradiation and establish a preliminary dose threshold for significant degradation. Future work will incorporate multi-modal characterization—including Fourier Transform Infrared (FTIR) spectroscopy, scanning electrom microscopy (SEM) of the rubber surface morphology, thermogravimetric analysis (TGA) to determine changes in thermal stability, and mechanical testing—to correlate molecular-level changes with macroscopic performance of these elastomers as damping media in seismic isolation devices. These findings are expected to provide regulatory guidance and design criteria for qualifying low-damping rubber seismic isolators in advanced nuclear reactor applications.

36 - MATERIALS SCIENCE↗

DOE OSTI2020

Single-Step Shear-Based Deformation Processing of Electrical Conductor Wires

Commercial electrical conductor wires are currently produced from aluminum alloys by multi-step deformation processing involving rolling and drawing. These processes typically require 10 to 20 steps of deformation, since the plastic strain or reduction that can be imposed in a single step is limited by material workability and process mechanics. Here, we demonstrate a fundamentally different, single-step approach to produce flat wire aluminum products using machining-based deformation that also ensures adequate material workability in the formed product. Two process routes are proposed: (1) chip formation by free-machining (FM), with a post-machining, light drawing reduction (<20%) to achieve desired finish and (2) constrained chip formation by large strain extrusion machining (LSEM). Using commercially pure aluminum conductor alloys (Al 1100 and EC1350) as representative material systems, we demonstrate key features of the machining-based processing, including (a) single-step processing to achieve flat wire geometries, (b) surface finish (Ra = 0.2 to 1.0 μm) comparable to that of commercial wire products made by drawing/rolling, (c) deformation control independent of wire size, and (d) hardness increases of 50–150% over that of annealed wires, while retaining high electrical conductivity (>56% IACS). Here, the wire microstructure, which can also be varied via the large-strain deformation parameters, is correlated with mechanical and electrical properties. Implications for commercial manufacture of flat wire products are discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Fabrication of Polymer Membrane-Suspended Microstructures on Printed Circuit Boards

When microelectromechanical systems are manufactured in high densities, the necessary routing layer structures can become complex and thus expensive if executed in silicon technology. If, additionally, the microstructures are also to be fabricated suspended on membranes, complex thinning processes become necessary to form these often rather fragile membranes. Here, a novel fabrication concept is demonstrated that allows for the fabrication of membrane-suspended microstructures using standard microfabrication techniques directly integrated with printed circuit boards (PCB) by laminating polyimide (PI) films over cavities in the PCB. This results in cost-effective routing layer fabrication and direct compatibility with common electronic component standards such as SMT (surface-mount technology) and THT (through-hole technology). To illustrate the capabilities of the fabrication process, we fabricated an array of membrane suspended microheaters. Individual platinum microheater elements are suspended on PI membranes that are 25 μm thick and 500 μm in diameter. The fabricated PCB carries a 10x10 array of suspended microheaters on an area of 26,mm x 26,mm. Here, the characterization of the microheater array shows that a yield of 86% functional microheaters was achieved. An individual microheater shows an almost linear heating characteristic at least up to 200°C demonstrating the viability of the technique for creating functional membrane-suspended microstructures on a PCB. [2021-0226]

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Chemical durability and surface alteration of lanthanide zirconates (A 2 Zr 2 O 7 : A = La-Yb)

Chemical durability of lanthanide zirconates (A 2 Zr 2 O 7 ) (A = La-Yb) under near-field environments is important for evaluating their application as potential nuclear waste forms. In this work, A 2 Zr 2 O 7 (A = La-Yb) are synthesized by spark plasma sintering with controlled microstructure and their chemical durability are evaluated in a nitric acid solution (pH = 1). Scanning transmission electron microscopy analysis reveals an amorphous passivation film either enriched with Zr or lanthanide. The complex chemistry of the passivation films can be correlated with a transition in corrosion mechanisms from a preferential release of lanthanide in La 2 Zr 2 O 7 to a preferential release of Zr in Er 2 Zr 2 O 7 and Yb 2 Zr 2 O 7 . These results suggest a dominant mechanism of incongruent dissolution and surface reorganization for the formation of passivation films. Strong correlations are identified between the leaching rates and cation ionic size, ionic potential, electronegativity differences between A-site cation and Zr, and bonding valence sum of oxygen, suggesting important impacts of structural and bonding characteristics in controlling chemical durability of lanthanide zirconates.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗