Analysis of the dynamic behavior of flooded porous electrodes.
Steady state and transient analysis of flooded isothermal porous electrodes without bulk flow of electrolyte
ELECTROLYTE METABOLISM↗
SEARCH · Engineering Papers
Results for “Bulk behavior”
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.
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Emergent solvation phenomena in non-aqueous electrolytes with multiple anions
As the search for new battery chemistries with higher capacities and more stable supply chains expands, requiring increasingly complex electrolytes with multiple solvents and anions, it is becoming clear that understanding and controlling the working cation solvation structure is key to enabling improved stability and reversibility. In this work, we discover an emergent solvation behavior in multivalent electrolytes containing multiple anions, where bis(trifluoromethane sulfonyl) imide (TFSI⁻) anions that are fully dissociated in isolation form contact ion pairs with Zn 2+ when combined with more strongly coordinating halides. This coordination modifies the electrochemical response, activating additional redox species as the halide association strength weakens (i.e., Cl⁻ > Br⁻ > I⁻) and systematically lowering overpotentials for metal deposition. This work suggests a completely new framework for electrolyte design in which anion chemistry can be used to tune both the bulk speciation and the interfacial solvation structure, enabling profound changes to the electrochemical behavior of the system.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Developing Machine Learning Interatomic Potential for Fe-Cr-Ni Alloys
Accurate prediction of creep and fatigue behavior of stainless steel at elevated temperatures in hydrogen environment requires fundamental understanding of alloy-hydrogen interaction at cross-scale including bulk lattice and key defects such as vacancies, grain boundaries, surfaces, stacking faults, dislocations, and precipitates. This project aims to predict creep behavior of 347H stainless steel with H using machine learning interatomic potentials based on first-principles density functional theory simulations. The Moment Tensor Potentials platform is adopted for this work since it demonstrates a fine balance between model accuracy and computational efficiency. The potential is well trained based on large amount of high-fidelity density functional theory calculations. The validation is carried out by comparing various important properties including short range order, coefficient of thermal expansion, elastic properties, stacking fault energy, grain boundary energy, and surface energy. This work lays the foundation for reliable atomistic simulation of high temperature hydrogen attack of stainless steel.
density functional theory (DFT)↗
Investigating instabilities in magnetized low-pressure capacitively coupled RF plasma using particle-in-cell (PIC) simulations
The effect of a uniform magnetic field on particle transport in low-pressure radio frequency (RF) capacitively coupled plasma (CCP) has been studied using a particle-in-cell model. Three distinct regimes of plasma behavior can be identified as a function of the magnetic field. In the first regime at low magnetic fields, asymmetric plasma profiles are observed within the CCP chamber due to the effect of $\overrightarrow{E}$ × $\overrightarrow{B}$ drift. As the magnetic field increases, instabilities develop and form self-organized spoke-shaped structures that are distinctly seen within the bulk plasma closer to the sheath. In this second regime, the spoke-shaped coherent structures rotate inside the plasma chamber in the -$\overrightarrow{E}$ × $\overrightarrow{B}$ direction, where $\overrightarrow{E}$ × $\overrightarrow{B}$ are the DC electric and magnetic field vectors, respectively, and the DC electric field exists in the sheath and pre-sheath regions. The spoke rotation frequency is in the megahertz range. As the magnetic field strength increases further, the rotating coherent spokes continue to exist near the sheath. The coherent structures are, however, accompanied by new small-scale incoherent structures originating and moving within the bulk plasma region away from the sheath. This is the third regime of plasma behavior. The threshold values of the magnetic field between these regimes were found not to vary with changing plasma reactor geometry (e.g., area ratio between ground and powered electrodes) or the use of an external capacitor between the RF-powered electrode and the RF source. The threshold values of the magnetic field between these regimes shift toward higher values with increasing gas pressure. Analysis of the results indicates that the rotating structures are due to the lower hybrid instability driven by density gradients and electron-neutral collisions. This paper provides guidance on the upper limit of the magnetic field for instability-free operation in low-pressure CCP-based semiconductor deposition and etch systems that use the external magnetic field for plasma uniformity control.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
A theoretical investigation of the effect of Ga alloying on thermodynamic stability, electronic-structure, and oxidation resistance of Ti 2 AlC MAX phase
We present a systematic investigation of thermodynamic stability, phase-reaction, and chemical activity of Al containing disordered Ti 2 (Al-Ga)C MAX phases using machine-learning driven high-throughput framework to understand the oxidation resistance behavior with increasing temperature and exposure to static oxygen. The A-site (at Al) disordering of Ti 2 AlC with Ga shows significant change in the chemical activity of Al with increasing temperature and exposure to static oxygen, which is expected to enable surface segregation of Al, thereby, the formation of Al 2 O 3 and improved oxidation resistance. We performed in-depth convex hull analysis of ternary Ti-Al-C, Ti-Ga-C, and Ti-Al-Ga-C based MAX phase, and provide detailed contribution arising from electronic, chemical and vibrational entropies. The thermodynamic analysis shows change in the Gibbs formation enthalpy (ΔG form ) at higher temperatures, which implies an interplay of temperature-dependent enthalpy and entropic contributions in oxidation resistance Ga doped Ti 2 AlC MAX phases. A detailed electronic structure and chemical bonding analysis using crystal orbital Hamilton population method reveal the origin of change in phases stability and in oxidation resistance in disorder Ti2(Al 1-x Ga x )C MAX phases. Our electronic structure analysis correlate well with the change in oxidation resistance of Ga doped MAX phases. We believe our study provides a useful guideline to understand to role of alloying on electronic, thermodynamic, and oxidation related mechanisms of bulk MAX phases, which can work as a precursor to understand oxidation behavior of twodimensional MAX phases, i.e., MXenes (transition metal carbides, carbonitrides and nitrides).
36 MATERIALS SCIENCE↗
Corrosion Resistance of 309L Stainless Steel Claddings on Carbon Steel Produced with Wire-Fed Directed Energy Deposition
Additive manufacturing (AM) tools are capable of applying overlay austenitic stainless steel (SS) claddings to carbon steel components. The benefits of this approach over arc welding include a smaller heat-affected zone, residual stress reduction, and material savings. In particular, wire-directed energy deposition is a suitable technique because of its low material cost and high rate of production compared to other AM methods. However, metallurgical variations in composition, phase fraction, and microsegregation can potentially influence the corrosion behavior of such claddings. In this work, 309L SS is clad on carbon steel substrates and electrochemical methods are used to measure their general and pitting corrosion resistance in simulated marine environments (3.5 wt% NaCl solutions). Two-layer claddings are fabricated with four laser powers to understand the effects of bulk chemical composition, austenite/δ-ferrite phase fractions, and individual phase compositions on corrosion behavior. The two-layer claddings are compared to a single-layer cladding, wrought 304 SS, and the carbon steel substrate for a comprehensive assessment of corrosion performance. The two-layer claddings are remarkably resistant to general corrosion in the 3.5 wt% NaCl environment because of their high Cr content (21.6 wt% to 23.3 wt% Cr). The single-layer cladding exhibits localized corrosion at unmixed Fe-rich peninsulas that originate at the dissimilar metal boundary and protrude into the first cladding layer. All two-layer claddings possess higher pitting corrosion resistance than wrought 304 SS, demonstrating their effectiveness as a corrosion-resistant barrier. Here, the pitting corrosion resistance is superior for claddings made with lower laser powers, due to low dilution and greater δ-ferrite contents.
36 MATERIALS SCIENCE↗
Anomalous stability of non-van der Waals bonded B4C nanosheets through surface reconstruction
Boron carbide (B4C) has been well studied both theoretically and experimentally in its bulk form due to its exceptional hardness and use as a high-temperature thermoelectric. However, the properties of its two-dimensional nanosheets are not well established. In this paper, using van der Waals-corrected density-functional theory simulations, we show that bulk B4C can be cleaved along different directions to form B4C nanosheets with low formation energies. We find that there is minimal dependence of formation energies on cleavage planes and surface terminations, even though the bulk is not van der Waals layered. This anomalous stability of B4C nanosheets is found to be a result of surface reconstructions that are unique to B-rich systems. While the density of states of the bulk B4C indicate that it is a semiconductor, the B4C nanosheets are found to be predominantly metallic. We attribute this metallic behavior to a redistribution of charges on the surface bonds of the films. The Seebeck coefficients of the B4C films remain comparable to those of the bulk and are nearly constant as a function of temperature. Our results provide guidance for experimental synthesis efforts and future application of B4C nanosheets in nanoelectronic and thermoelectric applications.
Physics↗
Magnetic structure and exchange interactions in the layered semiconductor CrPS 4
Compounds with two-dimensional (2D) layers of magnetic ions weakly connected by van der Waals bonding offer routes to enhance quantum behavior, stimulating both fundamental and applied interest. CrPS 4 is one such magnetic van der Waals material, however, it has undergone only limited investigation. Here we present a comprehensive series of neutron scattering measurements to determine the magnetic structure and exchange interactions. The observed magnetic excitations allow a high degree of constraint on the model parameters not normally associated with measurements on a powder sample. The results demonstrate the 2D nature of the magnetic interactions, while also revealing the importance of interactions along 1D chains within the layers. The subtle role of competing interactions is observed, which manifest in a nontrivial magnetic transition and a tunable magnetic structure in a small applied magnetic field through a spin-flop transition. Our results on the bulk compound provide insights that can be applied to an understanding of the behavior of reduced layer CrPS 4 .
36 MATERIALS SCIENCE↗
Multiscale modeling-enabled design of multifunctional composites
This study aims to create a comprehensive model that considers multiple scales and physics for predicting the electromechanical behavior of fiber-reinforced composites enhanced with barium titanate (BaTiO3). In our earlier work, we have demonstrated that depositing BaTiO3 microparticles of 200-nm-diameter, on fiber surfaces during fiber-reinforced composite fabrication enhances mechanical strength, passive self-sensing, and energy harvesting properties. The key is to carefully control the microparticle concentration to prevent agglomeration. Since the particles are micron-sized, understanding how agglomeration affects the composites' electromechanical properties is crucial for guiding such multifunctional materials’ design. This study introduces a micromechanics-based approach to explore the impact of microparticle dispersion on the bulk composites' electromechanical properties. Insights gained from this investigation are applied in experiments, enabling accurate predictions of mechanical and self-sensing responses in BaTiO3-enhanced fiber-reinforced composites. Micro-level findings from this computational approach can be integrated into larger continuum models to comprehensively capture the electromechanical behavior of the composite structures at bulk scale. The proposed model is validated by comparing predictions with experimental results, accounting for the nonlinear mechanical and electromechanical behaviors of constituent materials. Consequently, this computational model serves as a digital platform for efficiently designing multifunctional composites.
Gupta, Sumit↗
Anion Exchange Ionomers: Impact of Chemistry on Thin-Film Properties
Ionomer thin-films (i.e., 20–100 nm) on supports serve as model systems to understand ionomer-catalyst interfacial behavior as well as the confinement-driven deviation in properties from bulk membranes. While ionomer thin-films have been examined for proton exchange ionomers, the thin-film properties of anion exchange ionomers (AEIs) remain largely unexplored. More importantly, delineating the convoluted impact of chemistry and confinement on thin-film morphology and hydration is of interest to advancing the field on functional ionic interfaces. In this work, these aspects are studied by using AEIs of different backbones (perfluorinated, aliphatic, and aromatic) and side chains (various lengths, and single versus dual functional groups). Quartz-crystal microbalance and spectroscopic ellipsometry are used to analyze density and coupled with calculated free volume fraction of thin-films to provide insights on their gas transport properties. AEI side-chain's chemical character plays a key role in how confinement modulates hydration (in thin-film versus bulk). Overall, the results elucidate the effects of backbone, side-chain chemistry versus anion/cation type in the confinement-driven changes in thin-film morphology and swelling. This study also provides new insights for tuning AEI transport functionalities at interfaces via chemistry, which can benefit the design and development of electrode-ionomers for alkaline membrane-based energy systems.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Understanding Recombination Pathways of CdSeTe/CdTe Devices Using Temperature Dependence of Fill Factor
Understanding the temperature dependence of photovoltaic parameters is critical for identifying performance limiting mechanisms in CdTe-based solar cells. In this study, we investigate the temperature dependence of fill factor (FF(T)) in CdSeTe/CdTe solar cells using a combination of experimental current density-voltage (JV) measurements and numerical simulations. The measured FF(T) exhibits a nonlinear response with temperature, peaking at moderate temperature values (10–30°C). Through numerical modeling, we reveal that this peaking behavior in FF(T) arises when the dominant recombination mechanism transitions from bulk to interface with increasing temperature. This transition is primarily driven by low hole mobility (0.6–1.2 cm2/V·s), while electron mobility, interface recombination velocities, and carrier lifetime also contribute to the effect. Our findings demonstrate that FF(T) analysis is a promising diagnostic tool for distinguishing recombination pathways and guiding the optimization of thin-film CdTe solar cells under real-world conditions.
CdTe photovoltaics↗
Probing Dopant Redistribution, Phase Propagation, and Local Chemical Changes in the Synthesis of Layered Oxide Battery Cathodes
Achieving the targeted control of layered oxide properties calls for more fundamental studies to mechanistically probe their evolution during their synthesis. Herein, dopant distribution, phase propagation, and local chemical changes as well as their interplay in multielement-doped LiNiO 2 materials are investigated using spectroscopic, imaging, and scattering techniques. It is shown that dopants undergo dynamic redistribution in the Ni(OH) 2 host lattice at the early stage of calcination (below 300 °C). Such redistribution behavior exhibits strong dopant-dependent characteristics, allowing for targeted surface and bulk doping control. The Ni oxidation process exhibits depth-dependent characteristics and the most rapid Ni oxidation takes place between 300 and 700 °C. Using Ni oxidation state as the proxy for the phase transformation, the buildup of heterogenous phase propagation in the early stage of calcination is shown, especially along the radial direction of secondary particles. Furthermore, the radial heterogenous phase distribution gradually decreases upon completing the calcination. However, a high degree of mosaic-like heterogeneity may still be present in the final product, departing from the perfect layered oxide. Overall, the present study offers fundamental insights into manipulating multiscale materials properties during calcination for obtaining stable, high-energy layered oxide cathodes.
36 MATERIALS SCIENCE↗
Fluorinated polythiophenes with ester side chains for boosting the V OC and efficiency in non-fullerene polymer solar cells
As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approximates the 19 % threshold, wide bandgap (WBG) polythiophenes (PTs) have gained increasing attention due to their simple chemical structures and ease of synthesis, making them promising candidates for large-scale production. However, the benchmark polymer poly(3-hexylthiophene) (P3HT) is limited by its high-lying HOMO energy level, which restricts the open-circuit voltage (V OC ) in solar cells. Here, in this study, we introduce a novel series of PT derivatives (PDC8-T, PDC8-3T, PDC16-3T, and PDC16-3T-2F) featuring ester side chains designed to fine-tune electronic properties through a streamlined three-step synthesis. Additionally, we incorporated a π-spacer to reduce steric hindrance and elongated alkyl side chains to improve solubility and processability. Compared to P3HT, these PT derivatives demonstrate a significant reduction in HOMO energy levels, lowering by approximately 0.3–0.4 eV. Among them, PDC16-3T-2F—with fluorine atom substitution—achieves the lowest HOMO energy level, induces a coplanar molecular conformation, and enhances polymer aggregation behavior. We evaluated these PT derivatives in inverted non-fullerene bulk-heterojunction (NFA BHJ) OPVs. The PDC8-3T device showed a relatively low PCE of 0.69 %, with a V OC of 0.76 V, a short-circuit current density (J SC ) of 3.32 mA/cm 2 , and a fill factor (FF) of 27.3 %. In contrast, the PDC16-3T-2F device achieved an impressive PCE of 7.21 %, with a V OC of 0.85 V, a J SC of 14.60 mA/cm 2 , and an FF of 58.4 %. This remarkable improvement is attributed to the fluorine substitution, which not only enhances molecular orientation but also downshifts the HOMO energy level and further boosts the V OC . Hence, these molecular design strategies have led to a fibrillar bicontinuous interpenetrating network with optimal nanoscale phase separation within the active layer.
14 SOLAR ENERGY↗
Effects of the Grazing Incidence Geometry on X-ray Photon Correlation Spectroscopy Measurements
X-ray photon correlation spectroscopy (XPCS) is a versatile tool to measure dynamics on the nanometer to micrometer scale in bulk samples. XPCS has also been applied in grazing incidence (GI) geometry to examine the dynamics of surface layers. However, considering GI scattering experiments more universally, the GI geometry leads to a superposition of signals due to reflection and refraction effects, also known from the distorted-wave Born approximation (DWBA). In this paper, the impact of these reflection and refraction effects on the correlation analysis is determined experimentally by measuring grazing incidence transmission XPCS (GT-XPCS) and grazing incidence XPCS (GI-XPCS) simultaneously for a thin film sample, showing non-equilibrium dynamics. Here the results of the GI and GT geometry comparisons are combined within the framework of the standardly applied, simplified DWBA. These calculations allow identifying the main contributions of the detected signal from the leading scattering terms along the out-of-plane direction q z , which dominate the measured intensity pattern on the detector. In combination with the calculation of the non-linear effect of refraction in GTSAXS and GISAXS, it is possible to identify experimental conditions that can be chosen to run experiments and data analysis as close as possible to transmission XPCS and to explain which limitations for data interpretations are observed. Consequently, the beam exposure can be significantly reduced by using GI geometry only. Calculations of experimental settings prior to experiments are detailed to determine suitable q z regions for a variety of material systems measured in bulk-sensitive GI-XPCS experiments, allowing us to determine the scaling behavior of typical decay times as a function of q that is comparable to the scaling behavior obtained in distortion-free GT-XPCS or transmission XPCS experiments.
36 MATERIALS SCIENCE↗
Fluctuation dynamics near the QCD critical point
The evolution of nonhydrodynamic slow processes near the QCD critical point is explored with the novel hydro+ framework, which extends the conventional hydrodynamic description by coupling it to additional explicitly evolving slow modes describing long wavelength fluctuations. Here, their slow relaxation is controlled by critical behavior of the correlation length and is independent from gradients of matter density and pressure that control the evolution of the hydrodynamic quantities. In this exploratory study, we follow the evolution of the slow modes on top of a simplified QCD matter background, allowing us to clearly distinguish and study, both separately and in combination, the main effects controlling the dynamics of critical slow modes. In particular, we show how the evolution of the slow modes depends on their wave number, the expansion of and advection by the fluid background, and the behavior of the correlation length. Nonequilibrium contributions from the slow modes to bulk matter properties that affect the bulk dynamics (entropy, pressure, temperature, and chemical potential) are discussed and found to be small.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Evaluating the Effects of Nitrogen Doping and Oxygen Doping on SRF Cavity Performance
Superconducting radiofrequency (SRF) cavities are resonators with extremely low surface resistance that enable accelerating cavities to have extremely high quality factors (Q₀). High Q₀ decreases the capital required to keep the accelerators cold by reducing power loss. The performance of SRF cavities is largely governed by the surface composition of the first §I{100}{nm} of the cavity surface. Impurities such as oxygen and nitrogen have been observed to yield high Q₀, but their precise roles are still being studied. Here, we compare the performance of cavities doped with nitrogen and oxygen in terms of surface composition and heating behavior with field. A simulation of the diffusion of oxygen into the bulk of the cavity was built using COMSOL Multiphysics software. Simulated results were compared to the actual surface composition of the cavities as determined from secondary ion mass spectrometry analysis. Understanding how these impurities affects performance allows us to have further insight into the underlying mechanisms that enable these surface treatments to yield high Q₀.
43 PARTICLE ACCELERATORS↗
(U) PRAD0697 & PRAD0698: Complex Loading of CeO₂ Powder
Cerium(IV) oxide (CeO₂) powder is shock compressed using the Precision High Energy-density Liner Implosion eXperiment (PHELIX) platform. Experimental results are compared against several modeling approaches. Compaction behavior is best captured with a P-∝ model, which calculates CeO₂ powder bulk densities within 80-99% of experimental values but overpredicts densi cation at the cylindrical target's outer radius and center by up to 20%. Preliminary calculations suggest that accuracy could be increased with the inclusion of a coupled strength model. Several common computational modeling approaches for the shock compression response of granular materials and the magnetohydrodynamic (MHD) force upon the impactor/liner in pulsed power compression experiments are investigated and analyzed for their validity. The Bi-linear Ramp, P-∝ PACXP, and P-∝ Menikoff-Kober continuum compaction models are calibrated to planar impact Hugoniot data for CeO₂ powder and used to predict the powder's shock compaction response under non-planar shock wave compression. MHD calculations of the PHELIX pulsed power driver are performed using an idealized resistor-inductor-capacitor (RLC) circuit calibrated to previous experiments. All simulations are performed using the LANL code FLAG. Two validation experiments are computationally designed using the calibrated compaction and circuit models, executed using the PHELIX platform on CeO₂ targets with initial porous densities of 3.95 and 4.03 g/cm³, measured with proton radiography, and analyzed against the model predictions. The two P-∝ models more accurately describe CeO₂ powder densi cation than the Bi-linear Ramp model. However, the two P-∝ models overpredict bulk density of the shock compressed CeO₂ powder by up to 20% when the appropriate impact velocities are applied. MHD calculations for both validation experiments underpredict liner impact velocities by 4-11% when using the idealized RLC circuit model calibrated to previous experiments. Compensating underpredictions of impact velocity and overpredictions of powder densication lead to a false accuracy in pre-shot calculations compared to experimental data. To improve correlation between simulations and experiments, the following improvements are suggested: 1. A coupled strength model for CeO₂ powder that updates strength as a function of porosity and applied stress. 2. An improved MHD circuit model that more accurately captures the PHELIX machine.
36 MATERIALS SCIENCE↗
The magnetic effects of brecciation and shock in meteorites. II - The ureilites and evidence for strong nebular magnetic fields. III - The achondrites
Magnetic studies were conducted on samples of the ureilitic meteorites Goalpara, Havero, Novo Urei, and Kenna. Measurements included bulk magnetic susceptibility, natural remanent magnetization (NRM), saturation remanence, and the demagnetization behavior of NRM and saturation remanence. An approximate 'fossil' magnetic field intensity was determined by analysis of coercivity spectra of NRM and saturation remanence after reheating. It was found that the magnetic susceptibility of ureilites increased with severity of shock, and the NRM intensity decreases while its coercivity spectrum generally hardens with increasing shock. Goalpara and Kenna are distinguished by unexpectedly homogeneous, strong, stable, and directionally clustered NRM, indicative of a unique original magnetizing event. The results support the assertion that both ureilites and carbonaceous chondrites have formed from related nebular material and provide further evidence for a strong external magnetic field during the accretional stages and throughout an early bombardment stage.
Brecher, A.↗