38 Search Results

Land-atmosphere interactions play a critical role in the evolution and formation of low-level clouds. The different states of coupling between low-level clouds and the surface are uncertain, primarily over continental regions, where complex thermodynamics complicates their investigation. This study uses observations from the Atmospheric Radiation Measurement User Facility to explore cloud-surface coupling and perform a climatological analysis of this interaction in five countries across three continents. The results reveal consistent coupling thresholds and average percentages across the five sites, with coupled clouds accounting for 66% of the cases and decoupled clouds for 34%. Thermodynamic and dynamic evaluations show distinct differencesmore » between coupled and decoupled clouds. Coupled clouds are characterized by humid environments, in which vertical motions connect the surface and lower atmosphere to the cloud base, conditions that favor the formation of boundary layer clouds. Decoupled clouds prefer to occur in a drier and colder environment with vertical motions inside the boundary layer being detached from the cloud base, under which boundary layer clouds are hard to form. Coupled clouds peak during warmer hours and seasons, and vice versa for decoupled clouds. This study underscores the complexity of cloud-land-surface interactions and paves the way for further investigations into cloud formation and evolution under different atmospheric environments.« less

The quality of structural bonding in practical applications depends on various factors arising from materials, pre-processing conditions, and manufacturing. Understanding how these factors influence bonding performance and determining their relative importance are of significant interest. Thus, this study evaluates the effects of microstructural features and material properties on the structural strength of adhesively-bonded metal joints at the submillimeter scale, utilizing a combination of Finite Element Modeling (FEM) and Machine Learning (ML) with Gradient Boosting Regression (GBR). The microstructural features include adhesive thickness, internal voids within the adhesive, adherend-adhesive interfacial voids, void size and volume fraction, and surface roughness. The materialmore » properties include the constitutive behavior of the adhesive, as well as the adherend-adhesive interfacial strength and fracture energy. The changes in structural strength and morphologies of the bonded metal structures with respect to different microstructural features and material properties were clarified by FEM. By further leveraging ML-GBR, the sequence of importance of these factors affecting bonding performance across various scenarios was summarized. This work provides valuable insights into the development of improved structural bonding for adhesive joints in industries such as automotive , aerospace, and beyond.« less

In contrast to the traditional perspective that thermal fluctuations are insignificant in surface dynamics, here we report their influence on surface reaction dynamics. Using real-time low-energy electron microscopy imaging of NiAl(100) under both vacuum and O₂ atmospheres, we demonstrate that transient temperature variations substantially alter the direction of atom diffusion between the surface and bulk, leading to markedly different oxidation outcomes. During heating, substantial outward diffusion of atoms from the bulk to the surface results in step growth. Conversely, cooling induces considerable inward diffusion of adatoms, producing a distinct oxide morphology. In both scenarios, initially formed oxide islands impede localmore » atomic step mobility, thereby increasing step length due to mass transfer between the surface and bulk, with atomic steps acting as adatom sinks during heating and sources during cooling. Furthermore, we show that this pinning effect on atomic step mobility can be mitigated by applying persistent temperature fluctuations. As a result, understanding these nuances is vital for accurately predicting and dynamically manipulating the performance of active materials in various chemical processes under transient thermal conditions.« less

Additive manufacturing (AM) technologies have developed rapidly in recent years, creating new opportunities and challenges for the nuclear industry; however, adoption requires that their corrosion performance be evaluated. Here, we discuss known reactor-specific corrosion issues for multiple reactor types and engineering concerns such as regulations and standards. A review of corrosion studies conducted on select AM alloys informs a discussion on key bulk and surface factors likely to impact corrosion behaviors. Recommendations to assess corrosion performance for AM materials are provided, including management of the unique nature of as-built AM surfaces and the inherent process variability that occurs for AMmore » components.« less

Sublimation and O₂ etching kinetics for a series of individual silicon (Si) nanoparticles (NPs) were studied for NP temperatures (T_NP) from 1200 to 2050 K, using a single NP mass spectrometry technique. Sublimation was significant for T_NP > 1700 K, with rates reasonably well fit to Arrhenius kinetics, but evolving, particularly during initial heating. O₂ etching efficiencies varied from NP-to-NP and with changing T_NP, but also evolved dramatically over time. For T_NP ≤ 1500 K, NPs were observed to passivate after losing 30 to 50% of the initial NP mass. At higher T_NP, etching efficiency decreased over time, but nevermore » passivated. Interestingly, bulk Si passivation has not been observed for the range of T_NP and O₂ pressures used here, and a model was developed to test the effects of several NP-specific mechanistic parameters on both the initial and time-dependent etching behavior. As a result, the optical properties of the hot NPs were also found to evolve as the NPs etched, particularly during the initial fast mass loss, and correlations between emission intensities and etching kinetics were examined.« less

Prior in-situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) studies of electrochemical CO₂ reduction catalyzed by Au, one of the most selective and active electrocatalysts to produce CO from CO₂, suggest that the reaction proceeds solely on the top sites of the Au surface. This finding is worth updating with an improved spectroelectrochemical system where in-situ IR measurements can be performed under real reaction conditions that yield high CO selectivity. Herein, we report the preparation of a Au-coated Si ATR crystal electrode with both high catalytic activity for CO₂ reduction and strong surface enhancement of IR signals validated in themore » same spectroelectrochemical cell, which allows us to probe the adsorption and desorption behavior of bridge-bonded *CO species (*CO_B). In this study we find that the Au surface restructures irreversibly to give an increased number of bridge sites for CO adsorption within the initial tens of seconds of CO₂ reduction. By studying the potential-dependent desorption kinetics of *CO_B and quantifying the steady-state surface concentration of *CO_B under reaction conditions, we further show that *CO_B are active reaction intermediates for CO₂ reduction to CO on the Au surface. At medium overpotential, as high as 38% of the reaction occurs on the bridge sites.« less

Abstract Rechargeable battery technologies have revolutionized electronics, transportation and grid energy storage. Many materials are being researched for battery applications, with layered transition metal oxides (LTMO) the dominating cathode candidate with remarkable electrochemical performance. Yet, daunting challenges persist in the quest for further battery developments targeting lower cost, longer lifespan, improved energy density and enhanced safety. This is, in part, because of the intrinsic complexity of real-world batteries, featuring sophisticated interplay among microstructural, compositional and chemical heterogeneities, which has motivated tremendous research efforts using state-of-the-art analytical techniques. In this research field, synchrotron techniques have been identified as a suite ofmore » effective methods for advanced battery characterization in a non-destructive manner with sensitivities to the lattice, electronic and morphological structures. This article provides a holistic overview of cutting-edge developments in synchrotron-based research on LTMO battery cathode materials. We discuss the complexity and evolution of LTMO’s material properties upon battery operation and review recent synchrotron-based research works that address the frontier challenges and provide novel insights in this field. Finally, we formulate a perspective on future directions of synchrotron-based battery research, involving next-generation X-ray facilities and advanced computational developments.« less

Hydrogenation reactions are involved in several processes in heterogeneous catalysis. Platinum is the best-known catalyst; however, there are limitations to its practical use. Therefore, it is necessary to explore alternative materials and transition metal carbides (TMCs) have emerged as potential candidates. We explore the possibility of using cheap TMCs as supports for a Pt monolayer, aiming to reduce the amount of the noble metal in the catalyst without a significant loss of its activity towards H₂ dissociation. Hence, analyzing H₂ dissociation from a fundamental point of view is a necessary step towards a further practical catalyst. By means of periodicmore » DFT calculations, we analyze H₂ adsorption and dissociation on Pt/β-Mo₂C and Pt/α-WC surfaces, as a function of hydrogen surface coverage (Θ_H), resembling a more realistic model of a catalyst. H₂ dissociation rates were analyzed as a function of the reaction temperature. Overall, the results show that Pt/C-WC and Pt/Mo-Mo₂C have a Pt-like behavior for H₂ dissociation at Θ_H > 1/2 ML. At a particular temperature of 298 K, Pt/C-WC and Pt/Mo-Mo2C have low energy barriers for H₂* → 2H* (0.13 and 0.11 eV, respectively), close to the value of Pt (0.06 eV). For the highest coverage, i.e. Θ_H = 1, Pt/C-WC has a lower activation energy and a higher reaction rate than Pt. Finally, the H₂ dissociation rate is higher in Pt/Mo-Mo₂C than in Pt when increasing the temperature above 298 K. Our results put Pt/C-WC and Pt/Mo-Mo₂C under the spotlight as potential catalysts for H₂ dissociation, with a similar performance to Pt, paving the way for further experimental and/or theoretical studies, addressing the capability of Pt/TMC as practical catalysts in hydrogenation reactions.« less

This work considers a unique wide tow (450k filaments) form of low-cost carbon fiber intended for non-aerospace applications. TCF is currently produced in epoxy and urethane sizing, and there is a need to understand its resulting composite properties. In this work, the interfacial adhesion of sized TCF reinforced in thermoset urethane (TSU) composites are examined through the surface, thermal and mechanical characterization techniques. Atomic force microscopy (AFM) results showed an increase in surface roughness for urethane (276%) and epoxy sized (78%) versus unsized TCF. XPS results showed 531% increase in O in epoxy sized TCF and 250% N content inmore » urethane sized TCF compared to unsized TCF. The surface energy of epoxy and urethane sized TCF is enhanced by 78% and 96%, respectively compared to unsized TCF. The storage modulus showed improvement for urethane (23%) and epoxy (21%) sized than unsized TCF-TSU composites. The flexural, interlaminar shear strength (ILSS), and impact properties of urethane sized TCF increase by 24%, 50%, and 273%, respectively, than unsized TCF. The results demonstrate that the surface and thermal properties correlate with the mechanical properties of TCF-TSU composites and sizing enhances the wettability of the composites.« less