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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Luminescent Bimetallic Two-Coordinate Gold(I) Complexes Utilizing Janus Carbenes

A series of bimetallic carbene-metal-amide (cMa) complexes have been prepared with bridging biscarbene ligands to serve as a model for the design of luminescent materials with large oscillator strengths and small energy differences between the singlet and triplet states (ΔE ST ). The complexes have a general structure (R 2 N)Au(:carbene—carbene:)Au(NR 2 ). The bimetallic complexes show solvation-dependent absorption and emission that is analyzed in detail. It is found that the molar absorptivity of the bimetallic complexes is correlated with the energy barrier to rotation of the metal–ligand bond. The bimetallic cMa complexes also exhibit short emission lifetimes (τ = 200–300 ns) with high photoluminescence efficiencies (Φ PL > 95%). The radiative rates of bimetallic cMa complexes are 3–4 times faster than that of the corresponding monometallic complexes. Analysis of temperature-dependent luminescence data indicates that the lifetime for the singlet state (τS 1 ) of bimetallic cMa complexes is near 12 ns with a ΔE ST of 40–50 meV. Here the presented compounds provide a general design for cMa complexes to achieve small values for ΔE ST while retaining high radiative rates. Solution-processed organic light-emitting devices (OLEDs) made using two of the complexes as luminescent dopants show high efficiency and low roll-off at high luminance.

14 SOLAR ENERGY↗
DOE OSTI2021

Interplays of electron and nuclear motions along CO dissociation trajectory in myoglobin revealed by ultrafast X-rays and quantum dynamics calculations

Significance In this multidisciplinary study, we investigated local and global structural responses upon carbon monoxide (CO) dissociation from the heme iron(II) in myoglobin in solution using ultrafast X-ray absorption and scattering. CO dissociation was optically triggered and pulsed X-rays probed structural and electronic changes as a function of time, revealing an iron(II) spin state transition and nuclear motions propagating from the active site throughout the entire protein. Quantum mechanical computational results were used to assign the iron K-edge absorption features, and to map out electronic and nuclear trajectories during Fe–CO bond elongation and heme macrocycle doming. The study has important implications for heme–protein function and the interaction of small molecule substrates with the metal active centers in enzymes.

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

C136A and C138A Report of Analysis

In this work the isotopic ratios and weight percentages of 238 Pu, 239 Pu, 240 Pu, 241 Pu and 242 Pu were determined using Isotope Dilution Mass Spectrometry. Two samples of C136A and C138A were sent to the Analytical Research laboratories by the National Nuclear Security Administration Nuclear Reference Material Program. The four samples were dissolved in concentrated hydrochloric acid. From the parent solutions, eight aliquots were taken, diluted, spiked with 244 Pu and submitted to separations. After the samples were separated, they were analyzed using Multicollector Inductively Coupled Plasma Mass Spectrometry. Along with the samples, two C126A Quality Control Samples were analyzed each day. Mass bias standards were also analyzed at the beginning, during and at the end of the analysis. GUM Workbench Pro software Version 2.4.1.406 was used to calculate the isotopic ratios relative to 239 Pu, and total Pu mass and the correlated expanded uncertainties.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2024

Generalized Quasi-Static Mooring System Modeling with Analytic Jacobians

This paper presents a generalized and efficient method for quasi-static analysis of mooring systems, including complex scenarios such as when shared mooring lines interconnect multiple floating wind or wave energy devices. While quasi-static mooring models are well established, most published formulations are focused on specific applications, and no publicly available implementations provide efficient handling of large mooring system networks. The present formulation addresses these gaps by: (1) formulating solutions for edge cases not typically supported by quasi-static models; (2) creating a fully generalized model structure such that any combination of mooring lines, point masses, and floating bodies can be assembled; and (3) deriving analytic expressions for the system Jacobians (stiffness matrices) so that systems with many degrees of freedom can be solved efficiently. These techniques form the theory basis of MoorPy, an open-source mooring analysis library. The model is demonstrated on nine scenarios of increasing complexity with features of interest for offshore renewable energy applications. When compared with steady-state results from a lumped-mass dynamic model, the results show that the quasi-static formulation accurately calculates profiles and tensions and that its analytic approach provides more efficient and reliable computation of system stiffness matrices than finite-differencing methods. These results verify the accuracy of the MoorPy model.

16 TIDAL AND WAVE POWER↗
DOE OSTI2021

De Sitter decays to infinity

Bubbles of nothing are a class of vacuum decay processes present in some theories with compactified extra dimensions. We investigate the existence and properties of bubbles of nothing in models where the scalar pseudomoduli controlling the size of the extra dimensions are stabilized at positive vacuum energy, which is a necessary feature of any realistic model. We map the construction of bubbles of nothing to a four-dimensional Coleman-De Luccia problem and establish necessary conditions on the asymptotic behavior of the scalar potential for the existence of suitable solutions. We perform detailed analyses in the context of five-dimensional theories with metastable dS 4 x S 1 vacua, using analytic approximations and numerical methods to calculate the decay rate. We find that bubbles of nothing sometimes exist in potentials with no ordinary Coleman-De Luccia decay process, and that in the examples we study, when both processes exist, the bubble of nothing decay rate is typically faster. Our methods can be generalized to other stabilizing potentials and internal manifolds.

classical theories of gravity↗
DOE OSTI2023

High-order finite element method for atomic structure calculations

We introduce featom, an open source code that implements a high-order finite element solver for the radial Schrödinger, Dirac, and Kohn-Sham equations. The formulation accommodates various mesh types, such as uniform or exponential, and the convergence can be systematically controlled by increasing the number and/or polynomial order of the finite element basis functions. The Dirac equation is solved using a squared Hamiltonian approach to eliminate spurious states. Here, to address the slow convergence of the $κ=±1$ states due to divergent derivatives at the origin, we incorporate known asymptotic forms into the solutions. We achieve a high level of accuracy (10 -8 Hartree) for total energies and eigenvalues of heavy atoms such as uranium in both Schrödinger and Dirac Kohn-Sham solutions. We provide detailed convergence studies and computational parameters required to attain commonly required accuracies. Finally, we compare our results with known analytic results as well as the results of other methods. In particular, we calculate benchmark results for atomic numbers (Z) from 1 to 92, verifying current benchmarks. We demonstrate significant speedup compared to the state-of-the-art shooting solver dftatom. An efficient, modular Fortran 2008 implementation, is provided under an open source, permissive license, including examples and tests, wherein particular emphasis is placed on the independence (no global variables), reusability, and generality of the individual routines.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Solvent Effects on Catalytic Reactions and Related Phenomena at Liquid-Solid Interfaces

Catalytic reactions involve the direct interaction of reactants, intermediates and products with the catalyst surface. We not only need to control the atomic structure and electronic properties of the active site, but also explore the multiple molecular interactions that occur beyond the active site; they play an essential role in altering the binding and reactivity of surface species. In liquid-phase catalysis, solvents provide additional degrees of freedom in the design of the catalytic process for desirable activity and selectivity. Here, the multi-faceted effects of solvents have a profound impact on the catalyst performance by restricting the mass transfer to the site, tuning the chemical potential of the surface species, competing for active sites, stabilizing the initial and transition states, and causing mechanistic changes by participating in the kinetically relevant elementary steps. This review addresses the different aspects of solvent effects, using a few prototype solid-liquid interfaces to illustrate these fundamental features. Recent experimental and computational studies that provide new insight at the molecular level are examined. Solvent structures in the proximity of the catalyst surface are discussed along with their influence in molecular binding and reaction at the solid-liquid interfaces. Furthermore, opportunities to alter such a solid-liquid interaction by tuning the wettability of the catalyst surfaces are explored.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Metal Complex Molecular Solids Showing Band-like Transport Driven by In Situ Ligand Exchange

Transition-metal complexes exhibit excellent charge transport properties in solid films, rendering them promising for application in modern electronics. Although the charge transport mechanism of metal complex solids with multiple redox states is considered to be governed by self-exchange hole hopping, the effect of additives, such as Lewis bases, has not been identified. Herein, we describe the effect of 4- tert -butylpyridine (TBP) on the charge transport mechanism and film properties of [Cu(dmbpy) 2 ] 2 + / + (dmbpy = 6,6'-dimethyl-2,2'-bipyridine)-based molecular solids. The formation of [Cu(TBP) 4 ] 2 + , excess TBP, and free dmbpy from the ligand-exchange reaction between [Cu(dmbpy) 2 ] 2 + and TBP increases the film conductivity and changes the transport mechanism from hopping to band-like transport through a combination of chemical composition, film morphology, and crystallographic changes. In conclusion, these findings advance our understanding of the fundamental properties of molecular metal complex solids and enable optoelectronic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Lyapunov exponent as a signature of dissipative many-body quantum chaos

A distinct feature of Hermitian quantum chaotic dynamics is the exponential increase of certain out-of-time-order correlation (OTOC) functions around the Ehrenfest time with a rate given by a Lyapunov exponent. Physically, the OTOCs describe the growth of quantum uncertainty that crucially depends on the nature of the quantum motion. Here, we employ the OTOC in order to provide a precise definition of dissipative quantum chaos. For this purpose, we compute analytically the Lyapunov exponent for the vectorized formulation of the large- q limit of a q -body Sachdev-Ye-Kitaev model coupled to a Markovian bath. These analytic results are confirmed by an explicit numerical calculation of the Lyapunov exponent for several values of q ≥ 4 based on the solutions of the Schwinger-Dyson and Bethe-Salpeter equations. We show that the Lyapunov exponent decreases monotonically as the coupling to the bath increases and eventually becomes negative at a critical value of the coupling signaling a transition to a dynamics which is no longer quantum chaotic. Therefore, a positive Lyapunov exponent is a defining feature of dissipative many-body quantum chaos. The observation of the breaking of the exponential growth for sufficiently strong coupling suggests that dissipative quantum chaos may require in certain cases a sufficiently weak coupling to the environment. Published by the American Physical Society 2024

García-García, Antonio M.↗
DOE OSTI2023

Quantitative chemical assay of nanogram-level particulate matter using aerosol mass spectrometry: characterization of particles collected from uncrewed atmospheric measurement platforms

Abstract. Aerosol generation techniques have expanded the utility of aerosol mass spectrometry (AMS) for offline chemical analysis of airborne particles and droplets. However, standard aerosolization techniques require relatively large liquid volumes (e.g., several milliliters) and high sample masses that limit their utility. Here we report the development and characterization of a micronebulization AMS (MN-AMS) technique that requires as low as 10 µL of sample and can provide the quantification of the nanogram level of organic and inorganic substances via the usage of an isotopically labeled internal standard (34SO42-). Using standard solutions, the detection limits for this technique were determined at 0.19, 0.75, and 2.2 ng for sulfate, nitrate, and organics, respectively. The analytical recoveries for these species are 104 %, 87 %, and 94 %, respectively. This MN-AMS technique was applied successfully to analyze filter and impactor samples collected using miniature particulate matter (PM) samplers deployable on uncrewed atmospheric measurement platforms, such as uncrewed aerial systems (UASs) and tethered balloon systems (TBSs). Chemical composition of PM samples collected from a UAS field campaign conducted at the Department of Energy's (DOE) Southern Great Plains (SGP) observatory was characterized. The offline MN-AMS data compared well with the in situ PM composition measured by a co-located aerosol chemical speciation monitor (ACSM). In addition, the MN-AMS and ion chromatography (IC) agreed well for measurements of sulfate and nitrate concentrations in the PM extracts. This study demonstrates the utility of combining MN-AMS with uncrewed measurement platforms to provide quantitative measurements of ambient PM composition.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Parametric study and speciation analysis of rare earth precipitation using oxalic acid in a chloride solution system

Oxalic acid precipitation is a common step in the purification of rare earth elements (REE) from a concentrated pregnant leach solution (PLS). However, the presence of contaminants such as Al, Fe, and Ca in given amounts decreases the REE precipitation efficiency and product purity while also increasing the amount of oxalic acid needed to maximize recovery. As such, a statistically designed test program was performed to identify the optimal conditions necessary for a relatively low REE content PLS containing elevated concentrations of contaminant ions. The performance objective was maximization of REE precipitation efficiency while minimizing the oxalic acid dosage. A central composite design was utilized to quantify performance impacts and identify the ultimate set of parameter values for oxalic acid dosage, Fe(III) contamination concentration, solution pH, and reaction temperature. The resultant model suggested that oxalic acid dosage and reaction pH are the most significant factors for the REE precipitation efficiency, followed by the interaction of oxalic dosage and Fe concentration. Test results indicate that increasing the oxalic acid concentration from 0 g/L to 80 g/L improved the REE precipitation efficiency from approximately 4.2% to 95.0%. Furthermore, raising the solution pH from 0.5 to 2.5 considerably enhanced the precipitation efficiency from 0.0% to 98.9%. A solution temperature elevation decreased REE recovery, which indicated an exothermic reaction between REEs and oxalate anions. Finally, a high level of Fe contamination adversely impacted REE precipitation efficiency. Here, to further the understanding of the REE-oxalate system, a fundamental solution chemistry study was performed using the equilibrium constants of the reactions. The study resulted in the development of oxalate speciation diagrams and provided an analysis of the REE precipitation characteristics at various oxalate anion concentrations and Fe(III) contamination levels using MINTEQ software. The dominant Fe(III) species in the solution system were found to be Fe-(C 2 O 4 ) 3 3- , Fe-(C 2 O 4 ) 2- , and Fe-(C 2 O 4 ) + , which consume the majority of the oxalate anions. The simulated model was found to be in agreement with the experimental findings and helped to explain the adverse impact of increased iron concentrations on REE precipitation efficiency.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ultrasound-Assisted Nonthermal, Nonequilibrium Separation of Organic Molecules from Their Binary Aqueous Solutions: Effect of Solute Properties on Separation

The separation of organic molecules in downstream processes, such as distillation, plays a vital role in biobased chemical production. A comprehensive study was performed here using ultrasonic energy to separate 11 organic molecules from their binary aqueous solutions under nonthermal, nonequilibrium, and phase-change free conditions. A batch sonoseparator with a three-stage mist collection unit allowed direct analysis of ultrasound-generated mist with an HPLC/GC and differentiation and quantification of the vapor and mist. The results showed that the alcohols (1-butanol, ethanol, 1-propanol, and methanol) and acetone were enriched in the ultrasound-generated mist with enrichment ratios of 3.2–5. On the other hand, ethylene glycol, glycerol, γ-valerolactone (GVL), glucose, and sucrose were diluted with dilution ratios in the range of 2.04–15.7 in the mist and vapor generated by ultrasound (or concentrated in the bulk solution). No enrichment nor dilution of acetic acid was observed. The role of various physicochemical parameters such as dynamic viscosity, surface tension, Henry’s law of solubility constant, vapor pressure, and octanol–water partition coefficient in the enrichment was examined. Furthermore, the hydrophobicity of the organic molecules represented by the octanol–water partition coefficient was found to play a crucial role in determining the separation characteristics of the molecules in ultrasound-generated mist and vapor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Anti-electrostatic hydrogen-bonded tellurate dimers captured and stabilized by crystallization of a bis-iminoguanidinium salt

Anionic Te 2 O 6 (OH) 4 4– dimers have been captured by crystallization of a hydrated salt of glyoxal-bis-iminoguanidinium (GBIG), and structurally characterized by single-crystal X-ray diffraction and vibrational spectroscopy. The crystal structure reveals anti-electrostatic hydrogen-bonded chains of Te 2 O 6 (OH) 4 4– dimers, consisting of edge-sharing TeO 6 octahedra, stabilized by hydrogen bonding from the GBIG cations and the water molecules included in the crystal. FTIR spectroscopy confirms the presence of TeO 6 octahedra with characteristic Te–O stretching modes at 755 cm -1 and 689 cm -1 , while the observed stretching mode at 3459 cm-1 confirms the presence of axially-bonded hydroxyl groups. Raman spectroscopy and DFT calculations confirm the presence of the Te 2 O 6 (OH) 4 4– dimers in the crystalline phase and of the TeO(OH) 5 – monomers in solution.

36 MATERIALS SCIENCE↗
DOE OSTI2020

N -Arylimide Molecular Balances: A Comprehensive Platform for Studying Aromatic Interactions in Solution

Noncovalent interactions of aromatic surfaces play a key role in many biological processes and in determining the properties and utility of synthetic materials, sensors, and catalysts. However, the study of aromatic interactions has been challenging because these interactions are usually very weak and their trends are modulated by many factors such as structural, electronic, steric, and solvent effects. Recently, N-arylimide molecular balances have emerged as highly versatile and effective platforms for studying aromatic interactions in solution. These molecular balances can accurately measure weak noncovalent interactions in solution via their influence on the folded–unfolded conformational equilibrium. The structure (i.e., size, shape, π-conjugation, and substitution) and nature (i.e., element, charge, and polarity) of the π-surfaces and interacting groups can be readily varied, enabling the study of a wide range of aromatic interactions. These include aromatic stacking, heterocyclic aromatic stacking, and alkyl–π, chalcogen–π, silver–π, halogen–π, substituent–π, and solvent–π interactions. The ability to measure a diverse array of aromatic interactions within a single model system provides a unique perspective and insights as the interaction energies, stability trends, and solvent effects for different types of interactions can be directly compared. Some broad conclusions that have emerged from this comprehensive analysis include: (1) The strongest aromatic interactions involve groups with positive charges such as pyridinium and metal ions which interact with the electrostatically negative π-face of the aromatic surface via cation–π or metal–π interactions. Attractive electrostatic interactions can also form between aromatic surfaces and groups with partial positive charges. (2) Electrostatic interactions involving aromatic surfaces can be switched from repulsive to attractive using electron-withdrawing substituents or heterocycles. These electrostatic trends appear to span many types of aromatic interactions involving a polar group interacting with a π-surface such as halogen–π, chalcogen–π, and carbonyl–π. (3) Nonpolar groups form weak but measurable stabilizing interactions with aromatic surfaces in organic solvents due to favorable dispersion and/or solvophobic effects. Furthermore, a good predictor of the interaction strength is provided by the change in solvent-accessible surface area. (4) Solvent effects modulate the aromatic interactions in the forms of solvophobic effects and competitive solvation, which can be modeled using solvent cohesion density and specific solvent–solute interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Metal–Oxo Cluster Formation Using Ammonium and Sulfate to Differentiate M IV (Th, U, Ce) Chemistries

Isolating isostructural compounds of tetravalent metals M IV (Zr, Hf, Ce, Th, U, Pu, Np) improves our understanding of metal hydrolysis and coordination behavior across the periodic table. These metals form polynuclear clusters typified by the hexamer [M IV 6 O 4 (OH) 4 ] 12+ . Exploiting the ammonium M IV -sulfate (Ce IV , Th IV , and U IV ) phase space targeting rapid crystallization, we isolate the common hexamer [M IV 6 (OH) 4 (O) 4 ] 12+ but with different numbers of capping sulfates and water molecules for Ce IV , Th IV , and U IV . Furthermore, these phases allowed a direct comparison of bonding trends across the series. Upon cocrystallization with the hexamers, higher complex structures can be identified. Thorium features assemblies with monomer-linked hexamer chains. Uranium features assemblies with sulfate-bridged hexamers and the supramolecular assembly of 14 hexamers into the U 84 , [U 6 (OH) 4 (O) 4 ) 14 (SO 4 ) 120 (H 2 O) 42 ] 72– . Last, cerium showcases the isolation from monomers to the Ce 62 , [Ce 62 (OH) 30 (O) 58 (SO 4 ) 71 (H 2 O) 33.25 ] 41– . Furthermore, small-angle X-ray scattering (room temperature) shows ammonium-induced cluster assembly for Ce IV but minimal reactivity for U IV and Th IV . In this study, because the phases crystallized at elevated temperature demonstrates favorable cluster assembly, these solution phase results were surprising and suggest some other characteristics such as Ce’s facile redox behavior, contributes to its solution-phase speciation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Roles of Hydrogen Bonds and Alignment in Oriented Attachment of Gibbsite Nanoparticles: Insights from Molecular Dynamics

Oriented attachment (OA) of nanoparticles is an important crystal growth pathway in the synthesis of hierarchical structures. Although a significant understanding of OA has been made, the effect of atomistic misalignment and the roles of solvent/particle and particle/particle interactions on the structure–energy relationship during an OA remain elusive. In this study, we perform molecular dynamics simulations to calculate the potential of mean force (PMF) profile for gibbsite particle translation on a gibbsite slab with 1 or 2 intervening water layers (1W or 2W). The structures of the gibbsite surfaces and the confined water are analyzed to determine how the number and type of hydrogen bonds (H-bonds) influence the free energy profile during the translation. The PMF profile exhibits a periodicity of length 5.078 Å, consistent with the gibbsite unit cell size along the translation direction. The changes in the surface–water and water–water hydrogen bond network and water and surface OH groups’ orientations during the translation are strongly coupled with the changes in the PMF profile in the 1W case. However, when increasing the number of intervening water layers from 1W to 2W, the particle/slab misalignment becomes a dominant factor controlling the behavior of the PMF profile. We also establish a method to quantify misalignment between the particle and the slab, which exhibits a strong correlation with the free energy for the 2W case. These results shed more light into the roles of particle/slab misalignment and hydrogen bond network in the OA of mineral particles in aqueous solution.

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

High Pressure DME-Driven Fractional Crystallizations

Rare Earth Elements (REEs), include the 15 lanthanides plus yttrium and scandium and are crucial for various technologies and applications. Their low concentrations in the earth's crust require alternative sources. This study explores antisolvent fractional crystallization (FC) using dimethyl ether (DME) under high pressures to extract REEs from secondary sources such as mining waste, coal byproducts, and e-waste. DME's properties, including its solubility in water, small molecular size, and high vapor pressure, make it an effective antisolvent that can be easily recovered and reused. The method involves pressurizing DME to 1000-2000 psi in a reaction chamber with the test solution, followed by sample collection and analysis using ICP-MS and ICP-OES. This approach aims to address the limitations of current extraction methods, such as high energy consumption, chemical usage, and waste production, offering a potentially more efficient and sustainable solution for REE extraction.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗