Xenon (Xe), the largest noble gas with nonradioactive isotopes, is difficult to contain in a solid matrix. This study demonstrates the trapping of Xe single atoms within subnanometer-sized silicate nanocages (NC) supported on metal powders. The Xe gas is first ionized using a plasma. The ions then enter the NC and get trapped in the solid upon gaining an electron from the metal support. This work presents the first demonstration of room-temperature trapping of Xe atoms in a high-surface-area material using a simple ionization method. This can lead to various practical applications such as Xe separation from air, improving the efficiency and safety of nuclear reactors, aiding in nuclear nonproliferation efforts, and producing medical isotopes, among many others.

Stainless Steel 304 is being investigated for accident tolerant claddings. In this investigation, we use multi-modal characterization to evaluate oxidation under laboratory air versus 100% steam at 1200 degrees C for 2 h. Air oxidation features Fe(NiMn)O4, Fe3O4, Fe(3,0CrxO4, and Cr2O3. Steam oxidation produces a dual layer, containing Fe2O3- enriched porous outer layer and sub-surface matrix of Fe3O4/Fe(3,0CrxO4 with SiO2/Fe(3_ x)SixO4. From these findings, we postulate the oxidation mechanism. Arrangement of oxidation products in air corroborates with anticipated diffusion behavior, except Cr2O3. However, arrangement in steam deviates due to presumably intergranular interactions with H2O, resulting in the sub-surface matrix.

Radiation-induced materials degradation is a key concern in limiting the performance of nuclear materials. The formation of nanoscale void and gas bubble superlattices in metals and alloys under radiation environments can effectively mitigate radiation-induced damage, such as swelling and aid the development of next generation radiation tolerant materials. To effectively manage radiation-induced damage via superlattice formation, it is critical to understand the microstructural changes and strain induced by such superlattices. We utilize multi-reflection Bragg coherent diffraction imaging to quantify the full strain tensor induced by void superlattices in iron irradiated chromium substrate. Our approach provides a quantitative estimation of radiation-induced three-dimensional (3D) strain generated at the microscopic level and predicts the number density of defects with a high degree of sensitivity. Such quantitative evaluation of 3D strain in nuclear materials can have a major impact on predicting materials behavior in radiation environments and can revolutionize design of radiation tolerant materials.

Silicon carbide (SiC) formed through pyrolysis of preceramic polymers loaded with SiC particles has gained significant attention for applications such as coatings, composite matrix modifications, and most importantly additive manufacturing. This work presents combined synchrotron XRD, Raman spectroscopy, scanning electron microscopy, nano-indentation, and Vickers indentation of pyrolysis bonded SiC to shed light on the changes of composition and mechanical properties of these materials. Characterization was performed on samples that were heat treated ranging from the synthesis 850 °C up to 1500 °C. Pre-treatments of the powders prior to pellet synthesis, such as heat treatment and etching using a hydrofluoric acid (HF), were investigated. It is shown that the degradation of mechanical properties when exposed to higher temperatures is due to the burnout of amorphous carbon clusters remnant of the pyrolysis process of the preceramic polymer. Furthermore, prior HF etching and removal of the native oxide layer of the powders showed improved density and hardness values in the final pellets. The average Vickers hardness of the control samples were 4.59 GPa and later 3.74 GPa when exposed to 1500 °C, while the samples synthesized using powders that were etched with HF had an average hardness value of 9.37 GPa and later 6.86 GPa when exposed to 1500 °C.

Understanding the performance of cladding materials during a loss-of-coolant accident scenario is crucial developing next-generation accident tolerant nuclear fuel rod claddings. We describe a multi-modal approach combining synchrotron-based diffraction, and Raman spectroscopy with nano-scale electron microscopy techniques for investigating oxidation of Inconel 600 (A600) in steam and air environments at 1200 ? for 2 h. We report that A600 exposed to steam develops a Cr2O3-enriched surface layer while a mixed phase oxide layer containing NiFe2O4, Cr2O3, Fe3O4 and Fe((3-x))CrxO(4) is formed in air. Mechanism of oxidation for A600 in air and steam environments is discussed.

The self-assembly of defects in materials could create unique physical and chemical properties. In nuclear fuels, the formation of self-assembled fission products mitigates fission-gas-release and swelling. Here we report the formation of a solid nanocluster superlattice in molybdenum, an important constituent in metallic fuels, under krypton gas ion implantation. X-ray absorption near edge structure measurements coupled with density functional theory calculations show that the pressure of krypton nanoclusters in molybdenum is ~2 GPa and molecular dynamic simulations reveal that the krypton atoms are solid in the nanoclusters with a krypton-to-vacancy ratio of ~0.28 at 300 K.

Self-organization of defects such as fission gas bubbles in materials can lead to high inventory capacity for fission gas storage and help mitigate swelling caused by fission gases in nuclear fuel materials under radiation in nuclear reactors. Here, we report the physical mechanism of self-organization of krypton (Kr) gas bubbles in molybdenum (Mo) under ion implantation. The ion fluence and temperature-dependent formation of Kr solid bubble superlattice (SBS) in Mo were investigated by using both synchrotron-based small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Early stage self-organization of gas bubbles is observed at a fluence of 2.5 x 10(16) ions/cm(2) at temperatures of 300-400 degrees C. The bubble lattice constant increases with increasing implantation temperature from 300 to 400 degrees C. Both experiments and atomic kinetic Monte Carlo modeling indicate that the Kr solid bubbles are weakly ordered in comparison to previously studied helium (He) gas bubble superlattice (GBS) while the lattice constant are relatively smaller for Kr SBS compared to that of He GBS. The irradiation conditions suggest that spinodal decomposition, which is a form of phase separation, probably precedes gas bubble ordering in Mo. Overall, our work sheds light on the formation mechanism of noble gas superlattice toward the development of radiation-tolerant materials which are important for the design of advanced nuclear reactors.

Limited information is available on the oxidation mechanism of accident tolerant claddings (ATC) Kanthal APMT and T91 at the onset of beyond design-basis accident (BDBA) conditions. We characterized the surface of these ATC alloys after steam and air exposure at 1200 degrees C for 2 h, defining the oxidation mechanism. Thickness and composition were analyzed with microscopy, Raman spectroscopy, and synchrotron diffraction. Our results demonstrate that APMT forms a compact and homogeneous alpha-Al2O3 layer when exposed to air or steam. T91 forms a heterogeneous porous layer, containing a mixture of Cr- and Fe-based oxides, whose composition changes with the exposure environment.

Wellbore cement is subjected to a number of mechanical, thermal and chemical stress regimes over its lifetime. Therefore, next-generation wellbore cement formulations need to be evaluated in conditions relevant to these environments. In this work, we investigate the mechanism of the alteration of a novel self-healing polymer-cement composite after exposure to a CO2-rich environment by using synchrotron-based X-ray Fluorescence (XRF), X-ray absorption near edge structure (XANES), and scanning electron microscopy coupled with energy dispersive spectroscopy. Results showed that a chemical alteration of the polymer-cement follows the rim carbonation mechanism, similar to conventional cement, although carbonation takes place to a lesser extent in polymer-cements despite the higher porosity. Along with detailed mechanistic insights on carbonation in polymer-cement composite, the performance of these in CO2-rich environment is further studied using standard compressive strength analysis.

Understanding microstructural and strain evolutions induced by noble gas production in the nuclear fuel matrix or plasma-facing materials is crucial for designing next generation nuclear reactors, as they are responsible for volumetric swelling and catastrophic failure. We describe a multimodal approach combining synchrotron-based nanoscale X-ray imaging techniques with atomic-scale electron microscopy techniques for mapping chemical composition, morphology and lattice distortion in a single crystal W induced by Kr irradiation. We report that Kr-irradiated single crystal W undergoes surface deformation, forming Kr containing cavities. Furthermore, positive strain fields are observed in Kr-irradiated regions, which lead to compression of underlying W matrix.

Complex concentrated alloys represent the idea that alloys and materials need not be based on one or two principal elements. Instead, there exists an enormous and unexplored composition space, which enables the development of new materials. However, this vast composition space is difficult to efficiently investigate due to the high degree of compositional freedom and high experimental cost required to measure material properties, such as the yield strength. Integrating computational models with selected experiments is thus essential for the rapid exploration of this enormous compositional space. To validate a recently-developed solid solution strengthening model, we have investigated a family of face-centered-cubic (FCC) quaternary-based Mx(MnFeCoNi)100-x alloys (M = Al, Cu, Cr, Mo, Ti, and V). By employing the Voce hardening law and stress relaxation experiments, the solid-solution strengthening for various alloys was quantified. To accelerate the discovery process of CCAs, an approach combining strength predictions, phase stability predictions, and experiments is proposed.

Self-organization of gas bubbles causes the formation of an ordered array of nanoscale gas bubbles (a gas bubble superlattice), a highly efficient mechanism for gas storage under irradiation. The stability of helium (He) gas bubble superlattices in molybdenum (Mo) under krypton (Kr) ion irradiation and thermal annealing has been investigated. The He gas bubble superlattices gradually become disordered under Kr ion irradiation at 300 degrees C, and the order-disorder transformation process completes at 2.5 dpa. Both transmission electron microscopy (TEM) and synchrotron-based small-angle X-ray scattering (SAXS) reveal that the order-disorder transformation of He gas bubble superlattices is associated with a slight increase in the average bubble size. Phase-field modeling indicates that the inhomogeneous growth and coarsening of bubbles/voids cause the disordering of imperfect superlattices under irradiation and implies that highly ordered superlattices could potentially exhibit much stronger resistance to irradiation damage. Under thermal annealing, the He gas bubble superlattices in Mo become unstable and disordered at 1000 degrees C with the bubble size increasing from -1.1 to-1.6 nm. The finding in this research provides insights into the disordering mechanisms of defect superlattices as well as guidance for designing stable defect superlattices in harsh environments. (C) 2020 Elsevier B.V. All rights reserved.

RMD @ NSLS-II helps pave the path to a DMMSC: Developing expertise in techniques and experimental methods for DMMSC science; Improving capabilities for models to become microstructurally aware; Workforce training and development; Help refine DMMSC scientific requirements; Complementary to DMMSC XFEL science (EDXD/EXAFS)

Irradiation-induced creep is one of the key material properties considered in designing structural components for nuclear reactors. This paper presents results for in situ irradiation-induced creep of chemical vapor deposited 3C silicon carbide studied by instrumented irradiation in the Halden reactor in Norway. The specimens examined were irradiated at 300 C and up to 2.5 x 10(24) n/m(2) (E> 0.1 MeV) under uniaxial tensile stress of <5 or 100 MPa. Irradiation-induced creep strain was defined as the differential time-dependent strain between the two specimens. Based on the dimensional inspections before and after irradiation, an axial primary creep strain of 0.06% was obtained at the end of irradiation. The lattice constant precisely determined from high-energy x-ray diffraction analysis showed a lattice expansion roughly accounting for the primary irradiation creep strain. Analysis of data from this and previous studies indicates that creep strain is significantly dependent on at least one of the experimental conditions, such as loading mode, neutron spectrum/flux, and material grade. (C) 2019 Elsevier B.V. All rights reserved.

Multi-modal imaging, which visualizes changes in the structure and chemistry of the same region of interest in materials by combining various techniques, is becoming attractive to material scientists. Here, we describe a multi-modal approach to investigate intergranular (IG) corrosion of sensitized stainless steels using synchrotron-based nanoscale X-ray imaging with sensitivity to microstructure and chemical composition. Three-dimensional tomography of 304 stainless steel samples deteriorated by IG corrosion, was carried out using X-ray fluorescence and differential phase contrast imaging. These findings were further supported with surface imaging and chemical analysis using scanning electron microscopy and energy dispersive X-ray spectroscopy. The combined quantitative structural and chemical analysis indicates that chromium segregates along grain boundaries, cracking is due to IG corrosion, and Cr-enrichment occurs on the cracked surfaces. Such quantitative 3D imaging of Cr23C6 nucleation at grain boundaries and Cr enriched oxides at cracked surfaces is a powerful tool to correlate IG corrosion mechanisms at nanoscale with buried grain boundary structure and alloy composition. Such understanding of IG corrosion mechanisms is critical for both the development of predictive multiscale corrosion models, and the engineering of corrosion resistant materials. (C) The Author(s) 2019. Published by ECS.

The implantation of noble gas atoms into metals at high gas concentrations can lead to the self-organization of nanobubbles into superlattices with symmetry similar to the metal host matrix. Here, we examine the influence of implantation parameters on the formation and structure of helium gas bubble superlattices within a tungsten host matrix to uncover mechanistic insight into the formation process. The determination of the size and symmetry of the gas bubbles was performed using a combination of small angle x-ray scattering and transmission electron microscopy. The former was demonstrated to be particularly useful in determining size and structure of the gas bubble superlattice as a function of irradiation conditions. Prior to the formation of a superlattice, we observe a persistent substructure characterized by inter-bubble spacings similar to those observable when the gas bubble superlattice has formed with very large ordering parameters. As the implantation fluence increases, the inter-bubble ordering parameter decreases, indicating improved ordering, until a superlattice is formed. Multiple implantation-specific differences were observed, including a temperature-dependent superlattice parameter that increases with increasing temperature and a flux-dependent superlattice parameter that decreases with increasing flux. The trends quantified here are in excellent agreement with our recent theoretical predictions for gas bubble superlattice formation and highlight that superlattice formation is strongly dependent on the diffusion of vacancy and implanted He atoms.

Self-assembly of defects in materials can create novel physical properties with potential applications in various technological fields. Here, we studied the physical mechanism of self-assembly of helium gas bubbles in molybdenum under ion implantation and unified the formation window of gas bubble/void superlattice in terms of irradiation temperatures and helium-atomic parts per million/displacements per atom damage levels. The ion fluence and temperature-dependent formation of gas bubble superlattice in molybdenum was examined via both transmission electron microscopy and synchrotron-based small-angle x-ray scattering. The formation of gas bubble superlattice is linked with specific implantation conditions, including ion fluence and implantation temperature. The bubble lattice constant increases with increasing the implantation temperature from 150 to 450 degrees C. Once the gas bubble superlattice forms, increasing fluence has no effect on the bubble lattice constant. Both experiments and atomic kinetic Monte Carlo modeling indicate a three-stage formation process of gas bubble superlattice, from random bubbles to planar ordering and then to three-dimensional superlattices, suggesting that one-dimensional diffusion of self-interstitial atoms can cause the formation of gas bubble superlattice. Our study advances the understanding of defect self-assembly in materials in nonequilibrium states and provides an approach of managing the defect formation and transforming them from a liability into an asset in a controllable way.