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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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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Comparison of characterization methods for differently atomized nickel-based alloy 625 powders

The deployment of additive manufacturing depends on the quality of the produced part, specifically the absence of internal defects, impurities and compositional gradient. In this paper, differently atomized nickel-based alloy 625 powder particles were systematically characterized with different methods and results were compared. Powder properties were studied to understand the effect of different atomization methods on the properties of the powder particles. Morphology, shape and size of water and argon atomized powders were observed using optical microscopy, scanning electron microscopy and micro-computed X-ray tomography (μCT); μCT with different resolution and sample setup. As expected, water atomized powder particles have irregular morphology in contrast to spherical gas atomized particles. Phase and elemental analysis were conducted with X-ray diffraction and energy dispersive spectroscopy; thermal properties were measured with differential scanning calorimetry. Gas atomized powder shows composition and melting temperature close to nominal bulk alloy 625. Particle size analysis was carried out using sieving, laser particle size analysis and μCT. It is found that the average particle size obtained from μCT depends on scan resolution. Additionally, porosity of the powders was observed in SEM micrographs and investigated in detail using μCT. In conclusion, μCT with higher resolution results in collecting accurate shape, size, porosity and morphology of the powder particles. Finally, considering the large number of particles that can be investigated with μCT and ability to observe internal porosity, μCT is found to be an appropriate if not superior substitution for other powder characterization methods such as optical/electron microscopies, sieving and laser particle size analysis if time of characterization is not a concern.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Charge Transport in Solvated Donor–Acceptor Functionalized Peptoids: Molecular Dynamics and Rate Theory

Scalable solar-energy conversion requires photoactive materials that combine the efficiency of natural photosynthetic systems with the stability and processability needed for practical applications. Achieving reliable charge transport in soft, self-assembled organic materials remains challenging, as structural fluctuations and environmental effects strongly influence charge-transfer (CT) rates. Here, we present a broadly applicable computational framework for evaluating CT rates in the condensed phase, combining Fermi’s golden rule rate theory with inputs from all-atom molecular dynamics (MD) simulations and first-principles electronic-structure calculations. The approach does not rely on system-specific parametrization and is applicable to a wide range of soft and disordered materials. We demonstrate the applicability and usefulness of the framework on redox-active peptoids functionalized with iron–porphyrin (Fe–P) complexes, a bioinspired platform with programmable donor–acceptor units and tunable three-dimensional organization. The calculated CT rates exhibit strong sensitivity to molecular conformation, with variations spanning several orders of magnitude. This dependence is shown to arise from the pronounced variation in diabatic electronic coupling with the relative orientations and separations of the Fe–P complexes across the conformational ensemble. The framework provides a consistent route for connecting atomistic structure to CT kinetics in the condensed phase and enables analysis of structure–rate relations in organic semiconducting systems.

Charge transfer↗
DOE OSTI2016

Determination of Interfacial Mixing in Tapered Block Polymer Thin Films: Experimental and Theoretical Investigations

Tapered block polymers are an emerging class of macromolecules with unique and diverse self-assembly behavior and properties. Here, we directly examine the manipulation of self-assembled interfaces in poly(isoprene- b -styrene) (I-S)-based block polymers (BPs) by synthesizing non-tapered (I-S), normal tapered (I-IS-S), and inverse tapered (I-SI-S) BPs with controlled monomer segment distributions. We provide the first direct measurements of interfacial mixing for these tapered polymers through X-ray reflectivity (XRR). The density profiles from XRR are compared to results from fluids density functional theory (fDFT) with good agreement. We find that our normal tapered BPs (30 vol % tapering) have similar interfacial mixing to diblock polymers, while our inverse tapered BPs (30 vol % tapering) have much wider interfaces. Additionally, differential scanning calorimetry (DSC) studies elucidate the influence of tapering on the glass transition temperature (T g ) and change of heat capacity (ΔC P ) for each BP phase, and quantitative analysis from ΔC P also indicates enhanced mixing in the inverse tapered I-SI-S BPs. Finally, we investigate the free surface morphologies of these tapered polymers in thin film geometries. The inverse tapered BP form larger island/hole structures likely due to decreased surface elasticity from mixing as a result of the modified interblock interfacial characteristics. These results demonstrate that BPs with similar molecular weights and compositions can exhibit different thermodynamic properties and free surface morphologies in thin film geometries, as influenced by monomer sequence.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Atmospheric β-Caryophyllene-Derived Ozonolysis Products at Interfaces

By integrating organic synthesis, secondary organic aerosol synthesis and collection, DFT calculations, and vibrational sum frequency generation spectroscopy, we identify close spectral matches between the surface vibrational spectra of ß-caryophyllene-derived secondary organic material and those of ß-caryophyllene aldehyde and ß-caryophyllonic acid at various interfaces. Combined with the record high surface tension depression described previously for these same oxidation products, we discuss possibilities for an intrinsically chemical origin for cloud activation by terpene-derived surfactants. Although the present study does not unequivocally identify the synthesized and analyzed oxidation products on the ß-caryophyllene derived SOM surfaces, these two compounds appear to be the most surface active out of the series, and have also been foci of previous ß-caryophyllene field and laboratory studies. An orientation analysis by phase-resolved SFG spectroscopy reveals a “pincer-like” configuration of the ß-caryophyllene oxidation products, albeit on a model quartz surface, that somewhat resembles the orientation of inverse double-tailed surfactants at the surfaces biological systems. The structural information suggests that the less polar moiety of a surface-localized oxidation product, such as those studied here, may be the first site-of-contact for a gas-phase molecule approaching an SOA particle containing surface-active ß-caryophyllene oxidation products.

vibrational sum frequency generation spectroscopy,↗
DOE OSTI2020

Flash Graphene from Plastic Waste

In this work, an approach to upcycling plastic waste (PW) products is presented. The method relies on flash Joule heating (FJH) to convert PW into flash graphene (FG). In addition to FG, the process results in the formation of carbon oligomers, hydrogen, and light hydrocarbons. In order to make high quality graphene, a sequential alternating current (AC) and direct current (DC) flash is used. Here, the FJH process requires no catalyst and works for PW mixtures, which makes the process suitable for handling landfill PW. The energy required to convert PW to FG is ~ 23 kJ/g or ~ $125 in electricity per ton of PW, potentially making this process economically attractive for scale-up. The FG was characterized by Raman spectroscopy and had a I 2D /I G peak ratio up to 6 with a low-intensity D band. Moreover, transmission electron microscopy and X-ray diffraction analysis show that the FG is turbostratic with an interlayer spacing of 3.45 Å. The large interlayer spacing will facilitate its dispersion in liquids and composites. Analysis of FG dispersions in 1% Pluronic aqueous solution shows that concentrations up to 1.2 mg/mL can be achieved. The carbon oligomers that distilled from the process were characterized by Fourier-transform infrared spectroscopy and have chemical structures similar to the starting PW. Initial analysis of gas phase products shows the formation of considerable amounts of hydrogen along with other light hydrocarbons. Since graphene is naturally occurring and it shows a low toxicity profile, this could be an environmentally beneficial method to upcycle PE.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Pore‐Scale Visualization of Methane Hydrate‐Bearing Sediments With Micro‐CT

Abstract X‐ray computed tomography (CT) has become a critical technique in the study of porous media. It has attracted growing attention for analyzing hydrate‐bearing sediment, but this has been done using surrogates (Xe/Kr) only due to difficulties in distinguishing methane hydrate from water. This study presents the successful imaging of methane hydrate coexisting with pore liquid, gas, and sediments. We used potassium iodide (KI) solutions and in‐line propagation‐based phase‐contrast CT analysis of X‐ray attenuation and diffraction to distinguish the four materials. Thus, consideration for CT‐related X‐ray physics was necessary to optimize KI concentrations, improve material separation with X‐ray propagation, and properly interpret artifacts within the images. The images clearly show methane hydrate in the pore space of sand (~250 μm) coexisting with KI solution and gas. Following this, X‐ray CT can now be used to visualize pore habits of natural methane hydrate in sediment cores.

Lei, Liang↗
DOE OSTI2021

Alloying–realloying enabled high durability for Pt–Pd-3d-transition metal nanoparticle fuel cell catalysts

Abstract Alloying noble metals with non-noble metals enables high activity while reducing the cost of electrocatalysts in fuel cells. However, under fuel cell operating conditions, state-of-the-art oxygen reduction reaction alloy catalysts either feature high atomic percentages of noble metals (>70%) with limited durability or show poor durability when lower percentages of noble metals (<50%) are used. Here, we demonstrate a highly-durable alloy catalyst derived by alloying PtPd (<50%) with 3d-transition metals (Cu, Ni or Co) in ternary compositions. The origin of the high durability is probed by in-situ/operando high-energy synchrotron X-ray diffraction coupled with pair distribution function analysis of atomic phase structures and strains, revealing an important role of realloying in the compressively-strained single-phase alloy state despite the occurrence of dealloying. The implication of the finding, a striking departure from previous perceptions of phase-segregated noble metal skin or complete dealloying of non-noble metals, is the fulfilling of the promise of alloy catalysts for mass commercialization of fuel cells.

25 ENERGY STORAGE↗
DOE OSTI2025

Unconventional solitonic high-temperature superfluorescence from perovskites

Fast thermal dephasing limits macroscopic quantum phenomena to cryogenic conditions and hinders their use at ambient temperatures. For electronic excitations in condensed media, dephasing is mediated by thermal lattice motion. Therefore, taming the lattice influence is essential for creating collective electronic quantum states at high temperatures. Although there are occasional reports of high-T c quantum effects across different platforms, it is unclear which lattice characteristics and electron–lattice interactions lead to macroscopically coherent electronic states in solids. Here we studied intensity fluctuations in the macroscopic polarization during the emergence of superfluorescence in a lead halide perovskite and showed that spontaneously synchronized polaronic lattice oscillations accompany collective electronic dipole emission. We further developed an effective field model and theoretically confirmed that exciton–lattice interactions lead to a new electronically and structurally entangled coherent extended solitonic state beyond a critical polaron density. The analysis shows a phase transition with two processes happening in tandem: incoherent disordered polaronic lattice deformations establish an order, while macroscopic quantum coherence among excitons simultaneously emerges. Recombination of excitons in this state culminates in superfluorescence at high temperatures. Our study establishes fundamental connections between the transient superfluorescence process observed after the impulsive excitation of perovskites and general equilibrium phase transitions achieved by thermal cooling. By identifying various electron–lattice interactions in the perovskite structure and their respective role in creating collectively coherent electronic effects in solids, our work provides unprecedented insight into the design and development of new materials that exhibit high-temperature macroscopic quantum phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Combined Plasmonic Au-nanoparticle and Conducting Metal Oxide High-temperature Optical Sensing with LSTO

<span style="color: rgba(0, 0, 0, 0.79); font-family: &quot;Source Sans Pro&quot;, source-sans-pro, museo_sans300, museo-sans, Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);">Fiber optic sensor technology offers several advantages for harsh-environment applications. However, the development of optical gas sensing layers that are stable under harsh environmental conditions is an ongoing research challenge. In this work, electronically conducting metal oxide lanthanum-doped strontium titanate (LSTO) films embedded with gold nanoparticles are examined as a sensing layer for application in reducing gas flows at high temperature (600–800 °C). A strong localized surface plasmon resonance (LSPR) based response to hydrogen is demonstrated in the visible region of the spectrum, while a Drude free electron-based response is observed in the near-IR. Characteristics of these responses are studied both on planar glass substrates and on silica fibers. Charge transfer between the oxide film and the gold nanoparticles is explored as a possible mechanism governing the Au LSPR response and is considered in terms of the corresponding properties of the conducting metal oxide-based matrix phase. Principal component analysis is applied to the combined plasmonic and free-carrier based response over a range of temperatures and hydrogen concentrations. It is demonstrated that the combined visible and near-IR response of these films provides improved versatility for multiwavelength interrogation, as well as improved discrimination of important process parameters (concentration and temperature) through application of multivariate analysis techniques.</span>

Wuenschell, Jeffrey K.↗
DOE OSTI2015

Light scattering by epitaxial VO{sub 2} films near the metal-insulator transition point

Experimental observation of metal-insulator transition in epitaxial films of vanadium dioxide is reported. Hemispherical angle-resolved light scattering technique is applied for statistical analysis of the phase transition processes on mesoscale. It is shown that the thermal hysteresis strongly depends on spatial frequency of surface irregularities. The transformation of scattering indicatrix depends on sample morphology and is principally different for the thin films with higher internal elastic strain and for the thicker films where this strain is suppressed by introduction of misfit dislocations. The evolution of scattering indicatrix, fractal dimension, surface power spectral density, and surface autocorrelation function demonstrates distinctive behavior which elucidates the influence of structural defects and strain on thermal hysteresis, twinning of microcrystallites, and domain formation during the phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Surface modification of Ti alloy by electro-explosive alloying and electron-beam treatment

By methods of modern physical metallurgy the analysis of structure phase states of titanium alloy VT6 is carried out after electric explosion alloying with boron carbide and subsequent irradiation by pulsed electron beam. The formation of an electro-explosive alloying zone of a thickness up to 50 µm, having a gradient structure, characterized by decrease in the concentration of carbon and boron with increasing distance to the treatable surface has been revealed. Subsequent electron-beam treatment of alloying zone leads to smoothing of the alloying area surface and is accompanied by the multilayer structure formation at the depth of 30 µm with alternating layers with different alloying degrees having the structure of submicro - and nanoscale level.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structure-substitution limit correlation study on Cr{sup 3+} substituted polycrystalline yttrium iron garnet

Polycrystalline samples of Cr{sup 3+} - substituted yttrium iron garnet (Y{sub 3}Fe{sub 5}O{sub 12}) system with general chemical formula, Y{sub 3}Fe{sub 5-x}Cr{sub x}O{sub 12}, x = 0.0, 0.2, 0.4 and 0.6 were synthesized by double sintering ceramic technique and characterized by X-ray powder diffractometry. The Rietveld fitted X-ray diffraction patterns analysis revealed mono phase formation for x = 0.0 - 0.4 compositions while x = 0.6 composition possesses mixed phase character. The observed substitution limit has been discussed in the light of ionic size of substituent, electrostatic energy, electronic configuration and synthesis parameters. These observations strongly suggest that the electronic configuration of Cr{sup 3+}, which is favorable to the formation of d2sp3 (octahedral) type bonds, must be important. In the case of Cr{sup 3+}, the substitution does not appear to proceed well for x much greater than 0.5, this limitation probably is a consequence of the strong preference of a smaller ion Cr{sup 3+}, for a larger octahedral site which quickly leads to a condition not comparable with the requirement of the structure. The distribution of cations, mean ionic radii and theoretical lattice constant values have been determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Molecular structure of vapor-deposited amorphous selenium

The structure of amorphous selenium is clouded with much uncertainty and contradictory results regarding the dominance of polymeric chains versus monomer rings. The analysis of the diffraction radial distribution functions are inconclusive because of the similarities between the crystalline allotropes of selenium in terms of the coordination number, bond length, bond angle, and dihedral angle. Here, we took a much different approach and probed the molecular symmetry of the thermodynamically unstable amorphous state via analysis of structural phase transformations. We verified the structure of the converted metastable and stable crystalline structures using scanning transmission electron microscopy. In addition, given that no experimental technique can tell us the exact three-dimensional atomic arrangements in glassy semiconductors, we performed molecular-dynamic simulations using a well-established empirical three-body interatomic potential. In this work, we developed a true vapor-deposited process for the deposition of selenium molecules onto a substrate using empirical molecular vapor compositions and densities. We prepared both vapor-deposited and melt-quenched samples and showed that the simulated radial distribution functions match very well to experiment. The combination of our experimental and molecular-dynamic analyses shows that the structures of vapor- and melt-quenched glassy/amorphous selenium are quite different, based primarily on rings and chains, respectively, reflecting the predominant structure of the parent phase in its thermodynamic equilibrium.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Exploring connections between statistical mechanics and Green’s functions for realistic systems: Temperature dependent electronic entropy and internal energy from a self-consistent second-order Green’s function

Including finite-temperature effects from the electronic degrees of freedom in electronic structure calculations of semiconductors and metals is desired; however, in practice it remains exceedingly difficult when using zero-temperature methods, since these methods require an explicit evaluation of multiple excited states in order to account for any finite-temperature effects. Using a Matsubara Green’s function formalism remains a viable alternative, since in this formalism it is easier to include thermal effects and to connect the dynamic quantities such as the self-energy with static thermodynamic quantities such as the Helmholtz energy, entropy, and internal energy. However, despite the promising properties of this formalism, little is known about the multiple solutions of the non-linear equations present in the self-consistent Matsubara formalism and only a few cases involving a full Coulomb Hamiltonian were investigated in the past. In this study, to shed some light onto the iterative nature of the Green’s function solutions, we self-consistently evaluate the thermodynamic quantities for a one-dimensional (1D) hydrogen solid at various interatomic separations and temperatures using the self-energy approximated to second-order (GF2). At many points in the phase diagram of this system, multiple phases such as a metal and an insulator exist, and we are able to determine the most stable phase from the analysis of Helmholtz energies. Additionally, we show the evolution of the spectrum of 1D boron nitride to demonstrate that GF2 is capable of qualitatively describing the temperature effects influencing the size of the band gap.

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

Molecular insights into ionic liquid/aqueous interface of phosphonium based phase-separable ionic liquids

Phosphonium based phase-separable ionic liquids (PSILs) are promising green solvents for dissolution of cellulose and lignin, a necessary step for conversion of biomass to fuels and chemicals. The knowledge of interfacial behavior of ionic liquid/solvent systems is critical for designing efficient separation processes. Here, molecular dynamics simulations are carried out for aqueous interface of tetraalkylphosphonium ionic liquids with chloride and acetate as anions to investigate IL miscibility with water. The transition zone from miscible to immiscible behavior was observed for alkyl chain lengths of 6 to 8. Emulsion phase was observed for [P8888]+ ion and multiple IL/water interface was observed for [P12121212]+ phosphonium cation. IL/water interface is observed to be enriched with solvated anions with phosphorous atom oriented towards the aqueous phase. The potential of mean force calculations suggest that as the alkyl chain of the phosphonium cations increase, so does the driving force for aggregation of cations in the aqueous phase. Due to the difference in the molecular shape and size, anions are better solvated by the water molecules, and these ions diffuse into the aqueous phase. Furthermore, the analysis of selected pair interactions provides insights into the nature of intermolecular forces and the role of the alkyl side chains on the interfacial properties.

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

Reaction intermediates during operando electrocatalysis identified from full solvent quantum mechanics molecular dynamics

Electrocatalysis provides a powerful means to selectively transform molecules, but a serious impediment in making rapid progress is the lack of a molecular-based understanding of the reactive mechanisms or intermediates at the electrode–electrolyte interface (EEI). Recent experimental techniques have been developed for operando identification of reaction intermediates using surface infrared (IR) and Raman spectroscopy. However, large noises in the experimental spectrum pose great challenges in resolving the atomistic structures of reactive intermediates. To provide an interpretation of these experimental studies and target for additional studies, we report the results from quantum mechanics molecular dynamics (QM-MD) with explicit consideration of solvent, electrode–electrolyte interface, and applied potential at 298 K, which conceptually resemble the operando experimental condition, leading to a prototype of operando QM-MD (o-QM-MD). With o-QM-MD, we characterize 22 possible reactive intermediates in carbon dioxide reduction reactions ( C O 2 RRs). Furthermore, we report the vibrational density of states (v-DoSs) of these intermediates from two-phase thermodynamic (2PT) analysis. Accordingly, we identify important intermediates such as chemisorbed C O 2 ( b - C O 2 ), *HOC-COH, *C-CH, and *C-COH in our o-QM-MD likely to explain the experimental spectrum. Indeed, we assign the experimental peak at 1,191 cm −1 to the mode of C-O stretch in *HOC-COH predicted at 1,189 cm −1 and the experimental peak at 1,584 cm −1 to the mode of C-C stretch in *C-COD predicted at 1,581 cm −1 . Interestingly, we find that surface ketene (*C=C=O), arising from *HOC-COH dehydration, also shows signals at around 1,584 cm −1 , which indicates a nonelectrochemical pathway of hydrocarbon formation at low overpotential and high pH conditions.

36 MATERIALS SCIENCE↗