Developing a predictive understanding of mineral-phase stability in extreme chemical conditions such as those found in nuclear waste is challenging given the unknown influence of ionizing radiation. The long-term impacts of cumulative radiation damage in the solid state and exposure to radiolysis products in solution can impact mineral precipitation, dissolution, and aggregation behavior. Here, we sought to disentangle some of these effects by examining the dissolution of gibbsite platelets in NaOH solutions using atomic force microscopy with an integrated X-ray source that was used to compare dissolution rates when particles were initially irradiated in a dry state versus irradiated in solution, both of which were compared to unirradiated controls. By tracking particle morphology changes and quantifying material lost over time, dissolution rates and particle roughness were found to be enhanced most when irradiation was carried out during dissolution in NaOH, and to a lesser but significant extent when irradiated dry prior to dissolution. The maximum observed dissolution enhancement in the former case suggests the importance of both a direct effect of absorbed dose on gibbsite stability and an indirect effect arising from surface interaction with solution radiolysis products.

Journal Article Multimodal Imaging of Light Isotope Distributions in Irradiated Materials Get access Xiao-Ying Yu, Xiao-Ying Yu Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA Corresponding author: yuxiaoying@ornl.gov Search for other works by this author on: Oxford Academic Google Scholar Jiyoung Son, Jiyoung Son Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Tanguy Terlier, Tanguy Terlier SEA, Rice University, Houston, TX, USA Search for other works by this author on: Oxford Academic Google Scholar Shawn Riechers, Shawn Riechers Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Shalini Tripathi, Shalini Tripathi Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Gary Sevigny Gary Sevigny Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 1949–1950, https://doi.org/10.1093/micmic/ozad067.1009 Published: 22 July 2023

Thermo-mechanical processing of uranium-10 wt% molybdenum (U-10Mo) alloy fuel plates with a zirconium (Zr) interlayer leads to microstructure changes at fuel/interlayer interfaces. Secondary phases formed at this interface are particularly important to interfacial bond strength, process optimization, and maintaining structural integrity of the fuel plates during irradiation. In this work, we determined the phases and phase transformation products occurring at the interface of the U-10Mo fuel and Zr interlayer when fuel plates are subjected to short and long hot isostatic pressing (HIP) cycles. Interfacial morphology, crystal structure and composition of phases formed, and relative hardness across the U-10Mo/Zr interfaces were studied using a multi-length scale, multimodal characterization approach involving electron microscopy, atom probe tomography, and atomic force microscopy. Results highlight that the extent of phase transformations, secondary phase formation, and hardness variability across interfaces can be controlled by modifying processing parameters. In addition, phases formed at U-10Mo/Zr interfaces are similar for both HIP process conditions, however, phase distribution, interface thickness, and relative hardness vary significantly. The extent of the discontinuous precipitation reaction leading to alpha-U formation is also impacted by temperature and pressure in the HIP step; greater time at elevated temperature/pressure increases extent of the DP reaction.

Journal Article Towards On-the-Fly Feedback Loops for Direct Energy Deposition Systems Get access Matthew Olszta, Matthew Olszta Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Lance Hubbard, Lance Hubbard Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Nicole Overman, Nicole Overman Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Floyd Hilty, Floyd Hilty Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Ankit Roy, Ankit Roy Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Shawn Riechers Shawn Riechers Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Page 85, https://doi.org/10.1093/micmic/ozad067.034 Published: 22 July 2023

Understanding the corrosion of spent nuclear fuel is important for the development of long-term storage solutions. However, the risk of radiation contamination presents challenges for experimental analysis. Adapted from the system for analysis at the liquid–vacuum interface (SALVI), we developed a miniaturized uranium oxide (UO2)-attached working electrode (WE) to reduce contamination risk. To protect UO2 particles in a miniatured electrochemical cell, a thin layer of Nafion was formed on the surface. Atomic force microscopy (AFM) shows a dense layer of UO2 particles and indicates their participation in electrochemical reactions. Particles remain intact on the electrode surface with slight redistribution. X-ray photoelectron spectroscopy (XPS) reveals a difference in the distribution of U(IV), U(V), and U(VI) between pristine and corroded UO2 electrodes. The presence of U(V)/U(VI) on the corroded electrode surface demonstrates that electrochemically driven UO2 oxidation can be studied using these cells. Our observations of U(V) in the micro-electrode due to the selective semi-permeability of Nafion suggest that interfacial water plays a key role, potentially simulating a water-lean scenario in fuel storage conditions. This novel approach offers analytical reproducibility, design flexibility, a small footprint, and a low irradiation dose, while separating the α-effect. This approach provides a valuable microscale electrochemical platform for spent fuel corrosion studies with minimal radiological materials and the potential for diverse configurations.

Complex dissolution and precipitation processes provide a challenge for the removal and remediation of nuclear waste.Of particular interest are aluminum bearing phases such as gibbsite and boehmite which constitute a large fraction of tank waste at legacy sites such as the Hanford Nuclear Reservation in Washington State.These minerals are formed under complex chemical and radiological conditions, far from equilibrium, which can be difficult to replicate in an experimental setting.Developing a fundamental understanding of radiation induced processes is of particular interest.The Interfacial Dynamics in Radioactive Environments and Materials (IDREAM) Energy Frontier Research Center is dedicated to the development of experimental and computational methods necessary for understanding interfacial processes in such environments to determine key factors that underpin crucial processes such as dissolution.In this work the integration of atomic force microscopy and Xray irradiation for the direct visualization of gibbsite dissolution is presented [1][2].This initial ex situ experimental work compared dissolution rates in 0.1 M NaOH by directly measuring pre/post dissolution morphology of individual gibbsite particles.A nearly two-fold increase in dissolution rate was observed when dissolution was carried out under X-ray irradiation.Surprisingly, this enhancement was present even outside the X-ray irradiation region.This suggests radiolytic products, especially longer-lived species such as peroxide, play a primary role in dissolution.Irradiation was also carried out under inert dry conditions prior to dissolution to exclude the influence of these radiolytic products.In this case the dissolution rate was nearly identical, but only at the X-ray center suggesting direct X-ray damage also plays a significant role.This approach augments bulk measurement techniques, such as ICP by allowing for the comparison of particle dissolution based on individual particle morphology/crystallinity, defects, and aggregation.This work paves the way for in situ observations of radiation induced dissolution under a wide range of experimental conditions providing a platform for better understanding these complex systems.

Introduction: This study aims to develop a microgram-scale microfluidic electrochemical cell (E-cell) for investigating the redox behavior of uranium oxide (UO 2 ). The traditional bulk electrochemical methods may require shielded facilities to investigate the hazardous materials, e.g., spent nuclear fuel, due to high radiation levels. Microfluidic E-cells offer advantages such as reduced radiation exposure, control over fluid flow rates, and high-throughput capabilities. Methods: The design of the E-cell considers electrode morphology, adhesion to a thin membrane, electrode configuration, and vacuum compatibility. Three techniques, including FIB-SEM lift-out, Au coating, and polyvinylidene fluoride (PVDF) binder, are explored for fabricating and attaching microgram quantities of UO 2 as working electrodes. The PVDF binder method proves to be the most effective, enabling the creation of a vacuum-compatible microfluidic E-cell. Results and discussion: The PVDF binder method demonstrates successful electrochemical responses and allows for real-time monitoring of UO 2 electrode behavior at the microscale. It offers chemical imaging capabilities using in situ SEM/EDS analysis. The technique provides consistent redox outcomes similar to bulk electrochemical analysis. Conclusion: The development of a microgram-scale microfluidic electrochemical cell using the PVDF binder technique enables the investigation of UO 2 redox behavior. It offers a low-risk approach with reduced radiation exposure and high-throughput capabilities. The technique provides real-time monitoring and chemical imaging capabilities, making it valuable for studying spent nuclear fuel systems and material characterization.

The presence of mineral surfaces can affect the outcome of geochemical reactions by providing alternative nucleation pathways, but not in ways that can yet be reliably quantified. In this work, the reaction of Co(II) with calcite (CaCO3) and magnesite (MgCO3) powders at room temperature was used to quantify the effects of the nature of the mineral substrate and of solution chemistry on the competitive heterogeneous growth between cobalt carbonate (CoCO3) and cobalt hydroxide (Co(OH)2). Experiments were first performed to determine the appropriate solubility product constants of CoCO3 and Co(OH)2, for which several values have been reported in the literature. X-ray photoelectron spectroscopy measurements were then performed to quantify the relative proportion of each phase in surface precipitates as a function of the nature of the substrate, initial saturation level, and pH. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were also used to characterize the morphology and composition of surface precipitates. On calcite powders, Co(OH)2 formed predominantly despite the initial solutions being more supersaturated with respect to CoCO3 than to Co(OH)2, indicating that the kinetics of heterogenous growth were faster for Co(OH)2 than for CoCO3. In contrast, magnesite powders were much more favorable to the growth of CoCO3 because of the low lattice mismatch between the two phases, which allowed for heteroepitaxial growth. However, the proportion of CoCO3 in surface precipitates decreased with increasing initial supersaturation, likely due to the resulting decrease of the free energy barrier for Co(OH)2 nucleation and the rapid kinetics of Co(OH)2 growth. Lowering pH increased the proportion of CoCO3 on both substrates. These findings highlight how the interplay between lattice mismatch, heterogeneous nucleation barriers, and rates of heterogenous growth can influence competitive heterogeneous growth and dramatically affect the outcome of geochemical reactions.

We have developed a specialized microfluidic electrochemical cell that enables in situ investigation of the electrochemical corrosion of microgram quantities of redox active solids. The advantage of downscaling is the reduction of hazards, waste, expense, and greatly expanding data collection for hazardous materials, including radioactive samples. Cyclic voltammetry was used to monitor the oxidation-reduction cycle of minute quantities of micron-size uraninite (UO2) particles, from the formation of hexavalent uranium (U(vi)), U3O7 and reduction to UO2+x. Reaction progress was also studied in situ with scanning electron microscopy. The electrochemical measurements matched those obtained at the bulk-scale and were consistent with ex situ characterization of the run products by X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and atomic force microscopy; thus, demonstrating the utility of the microfluidic approach for studying radioactive materials.

Journal Article Multimodal Imaging of the Evolving Interface of Irradiated Aluminide-coated Stainless-steel Cladding Get access Xiao-Ying Yu, Xiao-Ying Yu Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Corresponding author: xiaoying.yu@pnnl.gov; yuxiaoyingbei@gmail.com Search for other works by this author on: Oxford Academic Google Scholar Bethany Matthews, Bethany Matthews Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Shawn Riechers, Shawn Riechers Physical and Computational Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Steven R Spurgeon, Steven R Spurgeon Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Zihua Zhu, Zihua Zhu Environmental and Molecular Science Laboratory, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Gary Sevigny, Gary Sevigny Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Walter Luscher Walter Luscher Energy and Environment Directorate, Pacific Northwest National Laboratory, WA, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 996–997, https://doi.org/10.1017/S1431927622004317 Published: 01 August 2022

Studying the electrochemical behavior of nanoparticles using electron microscopy techniques is challenging due to the difficulty in fabricating the working electrode (WE) containing nanoparticles with a consistent loading of particles of interest while minimizing the background signal from the substrate. In this paper, we describe a new nanoparticle stamping method to prepare electrodes contained within a microfluidic platform that is suitable for in-operando electron microscopy [1, 2]. Microscopic and microanalysis techniques, including atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), were used to characterize the as-fabricated electrodes and electrochemical analysis was used to verify electrode performance.

Radiation driven reactions at mineral/air interfaces are important to the chemistry of the atmosphere, but experimental constraints (e.g. simultaneous irradiation, in situ observation, and environmental control) leave process understanding incomplete. Using a custom atomic force microscope equipped with an integrated X-ray source, transformation of potassium bromide surfaces to potassium nitrate by air radiolysis species was followed directly in situ at the nanoscale. Radiolysis initiates dynamic step edge dissolution, surface composition evolution, and ultimately nucleation and heteroepitaxial growth of potassium nitrate crystallites mediated by surface diffusion at rates controlled by adsorbed water. In contrast to in situ electron microscopy and synchrotron-based imaging techniques where high radiation doses are intrinsic, our approach illustrates the value of decoupling irradiation and the basis of observation.

Understanding compositional and microstructural changes in functional intermetallic coatings is of great importance for fusion energy and nuclear materials applications. Tritium (3H) and lithium (6Li, 7Li) transport within a neutron irradiated target rod employing an aluminide-coated austenitic stainless-steel cladding was investigated using state-of-the-art multimodal imaging. Specifically, a scanning electron microscope augmented with focused ion beam (SEM-FIB) was used to prepare lift-out samples of the irradiated coating for microanalysis. Scanning transmission electron microscopy (STEM) was used to acquire atomic-scale information on the coating surface microstructure, morphology, and composition. Atomic force microscopy (AFM) was used to determine lift-out dimensions nondestructively. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed the presence of carbonaceous species and unexpected lithium isotopic distributions in the irradiated tubing, suggesting light isotope mobility between internal target components during irradiation. SIMS chemical mapping of aluminide coatings at core midplane and lower core locations of the cladding shows that light isotopic (e.g., 3H, 6Li, 7Li) distributions are different in the irradiated coating. Advance correlative imaging results suggest lithium transport during the tritium production process and give new insights into the fundamental transport mechanism within the target during irradiation and non-equilibrium conditions.

Electrochemical analysis is an efficient way to study various materials. However, nanoparticles are challenging due to the difficulty in fabricating a uniform electrode containing nanoparticles. We developed novel approaches to incorporate nanoparticles as a working electrode (WE) in a three-electrode microfluidic electrochemical cell. Specifically, conductive epoxy was used as a medium for direct application of nanoparticles onto the electrode surface. Three approaches in this work were illustrated, including sequence stamping, mix stamping, and droplet stamping. Shadow masking was used to form the conductive structure in the WE surface on a thin silicon nitride (SiN) membrane. Two types of nanomaterials, namely cerium oxide (CeO2) and graphite, were chosen as representative nanoparticles. The as-fabricated electrodes with attached particles were characterized using atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Electrochemical analysis was performed to verify the feasibility of these nanoparticles as electrodes. Nanomaterials can be quickly assessed for their electrochemical properties using these new electrode fabrication methods in a microfluidic cell, offering a passport for rapid nanomaterial electrochemical analysis in the future.

We developed a new approach to attach particles onto a conductive layer as a working electrode (WE) in a microfluidic electrochemical cell with three electrodes. Nafion, an efficient proton transfer molecule, is used to form a thin protection layer to secure particle electrodes. Spin coating is used to develop a thin and even layer of Nafion membrane. The effects of Nafion (5 wt% 20 wt%) and spinning rates were evaluated using multiple sets of replicates. The electrochemical performance of various devices was demonstrated. Additionally, the electrochemical performance of the devices is used to select and optimize fabrication conditions. The results show that a higher spinning rate and a lower Nafion concentration (5 wt%) induce a better performance, using cerium oxide (CeO2) particles as a testing model. The WE surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy-focused ion beam (SEM-FIB), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and X-ray photoelectron spectroscopy (XPS). The comparison between the pristine and corroded WE surfaces shows that Nafion is redistributed after potential is applied. Our results verify that Nafion membrane offers a reliable means to secure particles onto electrodes. Furthermore, the electrochemical performance is reliable and reproducible. Thus, this approach provides a new way to study more complex and challenging particles, such as uranium oxide, in the future.

Plant growth-promoting rhizobacteria (PGPR) play a crucial role in biological control and pathogenic defense on and within plant tissues, however the mechanisms by which plants associate with PGPR to elicit such beneficial effects need further study. Here, we present time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging of Brachypodium distachyon (Brachypodium) seeds with and without exposure to two model PGPR, i.e., Gram-negative Pseudomonas fluorescens SBW25 (P.) and Gram-positive Arthrobacter chlorophenolicus A6 (A.). Delayed image extraction was used to image PGPR-treated seed sections to reveal morphological changes. ToF-SIMS spectral comparison, principal component analysis (PCA), and two-dimensional (2D) imaging show that the selected PGPR have different effects on the host seed surface, resulting in changes in chemical composition and morphology. Metabolite products and biomarkers, such as flavonoids, phenolic compounds, fatty acids, and indole-3-acetic acid (IAA), were identified on the PGPR-treated seed surfaces. These compounds have different distributions on the Brachypodium seed surface for the two PGPR, indicating that the different bacteria elicit distinct responses from the host. Our results illustrate that ToF-SIMS is an effective tool to study plant-microbe interactions and to provide insightful information with submicrometer lateral resolution of the chemical distributions associated with morphological features, potentially offering a new way to study the mechanisms underlying beneficial roles of PGPR.

Y Significant work on the aqueous nucleation and growth of pure calcium carbonate has brought to light the importance of intermediate amorphous phases. In contrast, the factors that control the composition and polymorph selection of crystalline end products in mixed-cation carbonate systems are poorly understood. In this work, in situ pair distribution function (PDF) and small-angle X-ray scattering (SAXS) analyses were performed in a mixed-flow reactor to measure the structure, composition, and transformation pathways of the solid phases that form in the Ca/ Cd carbonate system. A novel short-range-ordered amorphous phase that differed from amorphous calcium carbonate (ACC) and amorphous cadmium carbonate (ACdC) was identified from the PDF measurements. The transformation of this amorphous phase, referred to as Cd-ACC, to vaterite was inhibited relative to that of ACC even at a low CdCO3 content of approximately 2 mol %. The results were highly dependent on the level of supersaturation with respect to ACC, whereby, for a given Cd2+ concentration, Cd stabilized amorphous phases at high ACC supersaturation but not at low ACC supersaturation. This finding suggests that supersaturation is a pathway-determining quantity in mixed-cation carbonate systems. Overall, this work provides a quantitative understanding of the intermediate phase structure and stability in mixed-cation carbonate systems.