Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DECOUPLING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Understanding the Influence of Receptive Field and Network Complexity in Neural Network-Guided TEM Image Analysis

Abstract Trained neural networks are promising tools to analyze the ever-increasing amount of scientific image data, but it is unclear how to best customize these networks for the unique features in transmission electron micrographs. Here, we systematically examine how neural network architecture choices affect how neural networks segment, or pixel-wise separate, crystalline nanoparticles from amorphous background in transmission electron microscopy (TEM) images. We focus on decoupling the influence of receptive field, or the area of the input image that contributes to the output decision, from network complexity, which dictates the number of trainable parameters. For low-resolution TEM images which rely on amplitude contrast to distinguish nanoparticles from background, we find that the receptive field does not significantly influence segmentation performance. On the other hand, for high-resolution TEM images which rely on both amplitude and phase-contrast changes to identify nanoparticles, receptive field is an important parameter for increased performance, especially in images with minimal amplitude contrast. Rather than depending on atom or nanoparticle size, the ideal receptive field seems to be inversely correlated to the degree of nanoparticle contrast in the image. Our results provide insight and guidance as to how to adapt neural networks for applications with TEM datasets.

42 ENGINEERING↗
DOE OSTI2018

Equilibria and Rate Phenomena from Atomistic to Mesoscale: Simulation Studies of Magnetite

Batteries are complex devices composed of multiple components that operate far from equilibrium and may operate under extreme stress and varying loads. Research of isolated battery components are valuable to the fundamental understanding of the physical processes occurring within each constituent element. When the components are integrated into a full device and operated under realistic conditions, it can be difficult to decouple the physical processes that occur across multiple interfaces and multiple length scales. Thus, the physical processes studied in isolated components may change in a full battery setup or may be irrelevant to performance. Simulation studies on many length scales play a key role in the analysis of experiments and in the elucidation of the relevant physical processes impacting performance. In this Account, we aim to highlight the use of modeling on multiple length scales to identify rate limiting phenomena in lithium-ion batteries. To illustrate the utility of modeling, we examine lithium-ion batteries with nanostructured magnetite, Fe 3 O 4 , as the positive electrode active material against a solid Li 0 negative electrode. Due to continuous operation away from equilibrium, batteries exhibit highly nonideal behavior, and a model that aims to reproduce behavior under realistic operating conditions must be able to capture the physics occurring on the length scales relevant to the performance of the system. It is our experience that limiting behavior in lithium-ion batteries can be observed on the atomic scale and up through the electrode scale and thus, predictive models must be capable of integrating and communicating physics across multiple length scales. Magnetite is studied as an electrode material for lithium-ion batteries, but it is found to suffer from slow solid-state transport of lithium, slow reaction kinetics, and poor cycling. Magnetite (Fe 3 O 4 ) is a material capable of undergoing multiple electron transfers (MET), and can accept up to eight lithium per formula unit (Li 8 Fe 3 O 4 ). Magnetite, (Fe 8a 3+ )[Fe 3+ Fe 2+ ] 16d O 4,32e 2– , has a close-packed inverse spinel structure and undergoes intercalation, structural rearrangement, and conversion reactions upon full lithiation. To overcome solid-state transport resistances, magnetite can be nanostructured to decrease Li + diffusion lengths, and this has been shown to increase capacity. Additionally, unique architectures incorporating both carbon and Fe 3 O 4 have shown to alleviate transport and cycling issues in the material. Here, we solely address traditional composite electrodes, in which Fe 3 O 4 is synthesized as nanoparticles and combined with additives to fabricate the electrode. In the case of nanoparticulate magnetite, it has been found that the electrode fabrication process results in the formation of micrometer-sized agglomerates of the Fe 3 O 4 nanoparticles, introducing a secondary structural motif. The agglomerates may form in one or more fabrication processes, and their elimination may not be straightforward or warranted. Here, we highlight the impact of these secondary formations on the performance of the Fe 3 O 4 lithium-ion battery. We illustrate how simulations can be used to design experiments, prioritize research efforts, and predict performance.

25 ENERGY STORAGE↗
DOE OSTI2019

Anisotropic Vapor-Deposited Glasses: Hybrid Organic Solids

CONSPECTUS: The term "organic solids" encompasses both crystals and glasses. Organic crystals are commonly grown for purification and structure determination and are being extensively explored for applications in organic electronics including field effect transistors. The ability to control the packing of one molecule relative to its neighbors is of critical importance for most uses of organic crystals. Often, anisotropic packing is also highly desirable as it enhances charge transport and optimizes light absorption/emission. When compared to crystals, the local packing in organic glasses is highly disordered and often isotropic. Glasses, however, offer two key advantages with respect to crystals. First, glasses typically lack grain boundaries and thus exhibit better macroscopic homogeneity. Second, glass composition can often be varied over a wide range while maintaining homogeneity. Besides electronic materials, many modern plastics used in a wide range of technologies are organic glasses, and the glassy state is being increasingly utilized to deliver pharmaceuticals because of higher bioavailability. In this article, we introduce vapor-deposited organic glasses as hybrid materials that combine some of the useful features of crystals and traditional liquid-cooled glasses. Physical vapor deposition produces glasses by directly condensing molecules from the gas phase onto a temperature-controlled substrate and allows film thickness to be controlled with nanometer precision. Just as liquid-cooled glasses, vapor-deposited glasses have smooth surfaces and lack grain boundaries. These attributes are critical for applications such as organic light emitting diodes (OLEDs), in which vapor-deposited glasses of organic semiconductors form the active layers. In common with crystals, vapor-deposited glasses can exhibit anisotropic packing, and the extent of anisotropy can be comparable to that of the typical organic crystal. For vapor-deposited glasses, in contrast to crystals, anisotropic packing can generally be controlled as a continuous variable. Deposition conditions can be chosen to produce glasses with significant molecular orientation (molecules "standing up" or "lying down" relative to the substrate), and pr-stacking can be directed along different directions relative to the substrate. Over the last five years, we have gained a fundamental understanding of the mechanism that controls the anisotropy of vapor-deposited glasses and learned how to control many aspects of anisotropic packing. Two key elements that enable such control are the high mobility present at the surface of an organic glass and the tendency of the surface to promote anisotropic packing of molecules. In contrast to traditional epitaxial growth, for vapor-deposited glasses, the free surface (not the substrate) acts as a template that controls the structure of a growing film. Lastly, the structure of any given layer is decoupled from those beneath it, thereby providing considerable freedom in producing layered glassy structures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Insights into the Morphology and Kinetics of Growth of Silver Metal–Organic Nanotubes

The kinetics of the formation of novel porous metal organic nanotubes, [Ag2(4,4 -(1,4-(xylene)diyl)bis- (1,2,4-triazole) (NO3)2] NMP, was investigated by means of ex-situ time-resolved small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). The SAXS results were modeled using the Gualtieri model, which decouples the nucleation and growth processes giving additional insight into the crystal formation mechanism. The results show that the semirigid 4,4 -(1,4-(xylene)diyl)bis(1,2,4-triazole) ligand (L) binds with silver ions, adopting a seesaw geometry to form a polydisperse isotropic framework immediately after mixing the ligands and metal ions. In addition, the SEM imaging demonstrates that the microcrystals grow anisotropically, with nucleation along the edge of the 3D aggregate. These combined data demonstrate that the growth of this MONT occurs in two steps: a rapid formation of an isotropic porous structure immediately after mixing the reactant, which then develops anisotropically as the aggregates of nanorods grow in a preferred direction. The anisotropic growth of the crystal is autocatalytic and determined by the rate of nucleation of new growth sites on the crystals. Moreover, the results of this analysis elucidate, for the rst time, the exact order of the competing processes that occur in the synthesis of these MONTs, showing that their anisotropic growth occurs on the initial 3D aggregate and appears to be directed by the interplay between the surface energies that exist during the MONT formation process. This insight is crucial to the use of crystal engineering to guide the crystal formation processes in MONTs to targeted structures, properties, and applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Tuning Perovskites’ Hydration-Induced Chemical Expansion with Octahedral Tilt Angles

Hydration-induced strains in proton-conducting oxides compromise chemo-mechanical stability when these materials are applied in protonic ceramic electrochemical cells. Here, to develop design principles for zero-strain materials, we systematically studied the hydration coefficients of chemical expansion (CCEs) in perovskite (Sr, Ba)(Ce, Zr, Y)O 3–x solid solutions with in situ dilatometry and thermogravimetric analysis in the range of 430–630 °C. By including and decoupling a wide range of tolerance factors and lattice parameters, we were able to identify a minimum in hydration CCEs (0–0.02) at intermediate tolerance factor values (t ≈ 0.95). Conversely, despite expectations of lower CCEs in larger unit cells, no general trend in CCE versus lattice parameter was found, and opposite trends could be seen for Sr(Ce, Zr, Y)O 3–x versus Ba(Ce, Zr, Y)O 3–x separately. In situ neutron diffraction (ND) enabled atomistic insight. Upon decreasing t, chemical strain anisotropy increased, but this trend did not match the U-shaped dependence of macroscopic CCEs on t. Instead, perovskites with intermediate t, hosting intermediate octahedral tilt angles in the nominally dry state, underwent the largest change in the B–O–B angles during hydration. Accommodating hydration through decreasing B–O–B angles is beneficial because it does not result in large lattice parameter changes. We propose an intermediate tolerance factor as a simple structural descriptor to enable near-zero hydration strains in proton-conducting perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Orbital-Selective Instabilities and Spin Fluctuations at the Verge of Superconductivity in Interlayer-Expanded Iron Selenide

Understanding electron correlation-driven instabilities and their coupling to structural phases is essential for deciphering multiorbital pairing in unconventional superconductors. We investigate Li x (C 5 H 5 N) y Fe 2 Se 2 (x ∼ 0.6; y ∼ 0.7−0.9), a tetragonal β-FeSe intercalate with a superconducting transition temperature (T c = 39 K) closely tied to an expanded Fe-layer spacing (∼11.4 Å). High-resolution synchrotron Xray diffraction and core-level absorption spectroscopy reveal subtle lattice distortions on cooling without a symmetry-breaking transition. Instead, the material exhibits negative thermal expansion (NTE) in the two-dimensional Fe network below T S ∼ 70 K, and stiffening of local Se−Fe−Se bond dynamics near T c . The spatially incoherent rearrangement of FeSe 4 tetrahedra and the site-local fluctuations, signal reduced electron correlations compared to those of parent β-FeSe (T c = 8 K). Complementary X-ray emission spectroscopy, a fast local probe of Fe 3d valence states, detects persistent local Fe spin moments below T S , unlike quenching in related systems. These findings indicate that decoupling of Fe planes leads to an electronically driven lattice instability. The latter emerges as NTE induced from weak, orbital-selective localization of in-plane Fe 3d states rather than conventional transverse vibrations. Governed by Hund’s coupling, this selectivity permits coexistence of local spin fluctuations with itinerant d-electrons critical for enhancing T c . These results suggest that intercalation-driven d-orbital differentiation moderates electron correlations, providing a pathway to optimize the superconductivity in low-dimensional quantum materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Expanding Configurational Complexity through Dipole Dilution in Pseudohalide Argyrodite Ion Conductors

The advantageous properties of (pseudo)halide argyrodite ion conductors of the formula Li 6 PS 5 X (X = Cl – , Br – , I – , CN – ) have motivated extensive studies of their structure-transport relationships, particularly as they pertain to the role of atomic site disorder. The argyrodite structure can accommodate additional configurational complexity to promote ion transport via extended three-anion site mixing and the potential for orientational disorder of molecular anions. In this work, we explore a ternary anion system including the cyanide anion, expanding site disorder and introducing dipolar orientations as an additional degree of freedom. We prepared the series Li 6 PS 5 (CN) 1–x Br x , in which the dipolar cyanide anions are systematically diluted with bromide. We find that anion disorder, as determined by synchrotron and neutron diffraction and quantified by configurational entropy (S config ), is correlated with lowered activation barriers and increased lithium ion conductivity. We propose that S config describes the electrostatic heterogeneity of the Li environments, flattening the energetic landscape for ion transport. While anion substitution strongly impacts the activation barrier for transport, the temperature-independent Arrhenius prefactor does not follow the same trend. Through heat-capacity measurements of attempt frequency and deconvolution of terms within the prefactor, we rationalize the apparent decoupling of activation energy and prefactor to strong cyanide-lithium interactions that increase the entropy of migration. Together, these results expand the structure–property relationships in the argyrodite family to encompass multiple facets of disorder and the subsequent impact on lithium ion transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Revealing the Charge Transport Mechanism in Polymerized Ionic Liquids: Insight from High Pressure Conductivity Studies

Polymerized ionic liquids (polyILs), composed mostly of organic ions covalently bonded to the polymer backbone and free counterions, are considered as an ideal electrolytes for various electrochemical devices, including fuel cells, supercapacitors and batteries. Despite large structural diversity of these systems, all of them reveal a universal but poorly understood feature - a charge transport faster than the segmental dynamics. Here, to address this issue, we have studied three novel polymer electrolyte membrane for fuel cells as well as four single-ion conductors including highly conductive siloxane-based polyIL. Our ambient and high pressure studies revealed fundamental differences in the conducting properties of the examined systems. Finally, we demonstrate that the proposed methodology is a powerful tool to identify the charge transport mechanism in polyILs in general and thereby contribute to unraveling the microscopic nature of the decoupling phenomenon in these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Reaction Heterogeneity in LiNi 0.8 Co 0.15 Al 0.05 O 2 Induced by Surface Layer

Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air, through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact vs an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a “two-phase” reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.

Grenier, Antonin↗
DOE OSTI2018

Engineering Two-Phase and Three-Phase Microstructures from Water-Based Dispersions of Nanoparticles for Eco-Friendly Polymer Solar Cell Applications

Nanoparticle organic photovoltaics, a subfield of organic photovoltaics (OPV), has attracted increasing interest in recent years due to the eco-friendly fabrication of solar modules afforded by colloidal ink technology. Importantly, using this approach it is now possible to engineer the microstructure of the light absorbing/charge generating layer of organic photovoltaics; decoupling film morphology from film deposition. In this study, single-component nanoparticles of poly(3-hexylthiophene) (P3HT) and phenyl-C 61 butyric acid methyl ester (PC 61 BM) were synthesized and used to generate a two-phase microstructure with control over domain size prior to film deposition. Scanning transmission X-ray microscopy (STXM) and electron microscopy were used to characterize the thin film morphology. Uniquely, the measured microstructure was a direct input for a nanoscopic kinetic Monte Carlo (KMC) model allowing us to assess exciton transport properties that are experimentally inaccessible in these single-component particles. Photoluminescence, UV-vis spectroscopy measurements, and KMC results of the nanoparticle thin films enabled the calculation of an experimental exciton dissociation efficiency (η ED ) of 37% for the two-phase microstructure. The glass transition temperature (T g ) of the materials was characterized with dynamic mechanical thermal analysis (DMTA) and thermal annealing led to an increase in ηED to 64% due to an increase in donor-acceptor interfaces in the thin film from both sintering of neighboring opposite-type particles in addition to the generation of a third mixed phase from diffusion of PC 61 BM into amorphous P3HT domains. Finally, this study demonstrates the higher level of control over donor-acceptor film morphology enabled by customizing nanoparticulate colloidal inks, where the optimal three-phase film morphology for an OPV photoactive layer can be designed and engineered.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Single-Atom Alloy Catalysis

Single-Atom Alloys (SAAs) play an increasingly significant role in the field of single-site catalysis and are typically composed of catalytically active elements atomically dispersed in more inert, but more catalytically selective host metals. SAAs have been shown to catalyze a range of industrially important reactions in thermal, photo- and electro-catalysis studies. Due to the unique geometry of SAAs, the location of the transition state and the binding site of reaction intermediates are often decoupled, which can enable both facile dissociation of reactants and weak binding of intermediates, two key factors for efficient and selective catalysis. Often, this results in deviations from transition metal scaling relationships that limit conventional catalysts. SAAs also offer reduced susceptibility to CO poisoning, cost savings from reduced precious metal usage, opportunities for bifunctional mechanisms via spillover, and higher resistance to deactivation by coking that plagues many industrial catalysts. In this review, we begin by introducing SAAs and describe how model systems and real catalysts can be prepared and characterized. Finally, we then review all available SAA literature on a per reaction basis before concluding with a description of the general properties of this new class of heterogeneous catalysts and presenting opportunities for future research and development.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Sequential Dosing Strategies for Controlling Selectivity and Plasma-Phase Contributions in Plasma Catalysis

Plasma-assisted catalysis has advanced in recent years, particularly for transforming stable reactants at atmospheric pressure and ambient temperature. However, achieving a deeper understanding of the many plasma and catalytic contributions remains a significant goal, as improving product yield and selectivity in plasma catalysis depends on proper catalyst selection, which is often challenging due to the complex interplay between plasma-phase and plasma-surface reactions. A sequential methodology has emerged as a means to decouple the catalyst activity from plasma-phase reactions. In this approach, nonthermal plasma is used in one step to activate and/or convert a gas phase or surface bound reactant, while in a second step, the catalyst directs product formation under steady-state or temperature-programmed conditions. This review examines studies using this technique for reactions involving N 2 , CO 2 , and SO 2 , offering insights into reaction mechanisms and catalyst behavior/selection for these transformations. These systematic studies provide a framework that can be applied to other plasma-assisted reactions. We also highlight remaining questions, propose directions for future studies, and discuss the potential of applying this methodology to other reaction systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Results of an Ocean Trial of the Symbiotic Machine for Ocean uRanium Extraction

Amidoxime-based adsorbents have become highly promising for seawater uranium extraction. However, current deployment schemes are stand-alone, intermittent operation systems that have significant practical and economic challenges. This paper presents two 1/10th scale prototypes of a Symbiotic Machine for Ocean uRanium Extraction (SMORE) which pairs with an existing offshore structure. This pairing reduces mooring and deployment costs while enabling continuous, autonomous uranium extraction. Utilizing a shell enclosure to decouple the mechanical and chemical requirements of the adsorbent, one design concept prototyped continuously moves the shells through the water while the other keeps them stationary. Water flow in the shells on each prototype was determined using the measurement of radium adsorbed by MnO 2 impregnated acrylic fibers. The results from a nine-week ocean trial show that while movement of the shells through the water may not have an effect on uranium adsorption by the fibers encased, it could help reduce biofouling if above a certain threshold speed (resulting in increased uptake), while also allowing for the incorporation of design elements to further mitigate biofouling such as bristle brushes and UV lamps. The trace metal uptake by the AI8 adsorbents in this trial also varied greatly from previous marine deployments, suggesting that uranium uptake may depend greatly upon the seawater concentrations of other elements such as vanadium and copper. Lastly, the results from this study will be used to inform future work on the seawater uranium production cost from a full-scale SMORE system.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Measuring Nitrous Oxide Mass Transfer into Non-Aqueous CO2BOL CO2 Capture Solvents

This paper investigates CO2 absorption behavior in CO2BOL solvents by decoupling the physical and chemical effects using N2O as a non-reactive mimic. Absorption measurements were performed using a wetted-wall contactor. Testing was performed using a “first generation” CO2 binding organic liquid (CO2BOL), comprised of an independent base and alcohol. Measurements were made with N2O at a lean (0.06 mol CO2/mol BOL) and rich (0.26 mol CO2/mol BOL) loading, each at three temperatures (35, 45 and 55 °C). Liquid-film mass transfer coefficients (kg') were calculated by subtracting the gas film resistance – determined from a correlation from literature – from the overall mass transfer measurement. The resulting kg' values for N2O in CO2BOLs were found to be higher than that of 5 M aqueous MEA under comparable conditions, which is supported by published measurements of Henry’s coefficients for N2O in various solvents. These results suggest that the physical solubility contribution for CO2 absorption in CO2BOLs is greater than that of aqueous amines, an effect that may pertain to other non-aqueous solvents.

Whyatt, Greg A.↗
DOE OSTI2018

Effects of Protective Shell Enclosures on Uranium Adsorbing Polymers

Here, this study aims to evaluate the impact of shell enclosures on the uranium uptake of amidoxime-based polymeric adsorbents they contain. Researchers have observed that the tensile strength of the adsorbent’s polyethylene backbone is degraded after γ-irradiation to induce grafting of the amidoxime ligand. A two-part system was developed to decouple the mechanical and chemical requirements of the adsorbent by encapsulating them in a hard, permeable shell. The water flow in six shell designs and an unenclosed adsorbent for control in a recirculating flume was analyzed via a novel method developed using the measurement of radium extracted onto MnO 2 impregnated acrylic fibers. Although the water flow was found to vary with enclosure design, orien- tation to the flow, and placement within the flume, little to no difference was observed in the uranium adsorption rate between all enclosures. The results of this study will be used to design a large-scale ocean deployment of a uranium harvesting system.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗