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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Unexpected Hydride: Ce 4 B 2 C 2 H 2.42 , a Stuffed Variant of the Nd 2 BC Structure Type

Ce 4 B 2 C 2 H 2.42 was grown as large crystals from a cerium/copper eutectic flux. The structure was characterized by single-crystal X-ray and neutron diffraction and was found to be a stuffed variant of Nd 2 BC with the addition of two interstitial hydrogen positions. The tetrahedral hydrogen position is fully occupied, while the octahedral position has an occupancy of 42(3)%. Initial synthesis was due to hydrogen contamination of the cerium metal but has been successfully repeated using anthracene as a carbon and hydrogen source. Density of states calculations suggest that the incorporation of hydrogen stabilizes the compound with respect to the nonhydrided model. Magnetic susceptibility data show a complex magnetic ordering at 7.7 K that originates from the localized electron on the Ce 3+ in the structure. The trivalent state is also supported by X-ray photoelectron spectroscopy measurements. Heat capacity and electrical resistivity data show that the phase transition is broad in temperature, which may be due to structural disorder. Furthermore, the large low temperature value of C/T also indicates possible heavy fermion behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2019

One-Dimensional Quaternary and Penternary Alkali Rare Earth Thiophosphates Obtained via Alkali Halide Flux Crystal Growth

Single crystals of nine new quaternary and penternary rare earth containing thiophosphates, Cs 2 KLn(PS 4 ) 2 , Rb 3-x Na x Ln(PS 4 ) 2 (Ln = La, Nd), Rb 2 NaNd(PS 4 ) 2 , Cs 3 La(PS 4 ) 2 , Rb 3 Gd(PS 4 ) 2 , and Cs 5 NaLn 2 (PS 4 ) 4 (Ln = Gd, Tb), were grown in alkali halide eutectic fluxes. All title compounds were structurally characterized by single crystal X-ray diffraction and were found to crystallize in pseudo-one-dimensional structure types, reminiscent of those found for other known alkali rare earth thiophosphates, in a variety of space groups including monoclinic P2 1 /c, P2 1 /m, P2 1 , and orthorhombic Ccca. The crystal structures of the reported compounds are characterized by the formation of complex one-dimensional [(Ln(PS 4 ) 2 )3–] and [(Ln 2 (PS 4 ) 4 ) 6– ] anionic chains that run along the crystallographic α-axis in Cs 2 KLn(PS 4 ) 2 , Rb 3-x NaxLn(PS 4 ) 2 (Ln = La, Nd) and Rb 2 NaNd(PS 4 ) 2 , b-axis in Cs 3 La(PS 4 ) 2 and Rb 3 Gd(PS 4 ) 2 , and c-axis in Cs 5 NaLn 2 (PS 4 ) 4 (Ln = Gd, Tb). Cs 2 KLn(PS 4 ) 2 , Rb 3-x Na x Ln(PS 4 ) 2 (Ln = La, Nd), Rb 2 NaNd(PS 4 ) 2 , Rb 3 Gd(PS 4 ) 2 , and Cs 3 La(PS 4 ) 2 feature two crystallographically unique thiophosphate tetrahedra that face- and edge-share with the LnS x polyhedra forming infinite one-dimensional zigzag-like chains. This unusual face-sharing or face-grafting coordination mode of the thiophosphate group is however absent in Cs 5 NaLn 2 (PS 4 ) 4 (Ln = Gd, Tb), which exhibit only one unique phosphorus site. The magnetic susceptibility and the field-dependent magnetization were measured for Rb 2 NaNd(PS 4 ) 2 and Cs 2 KNd(PS 4 ) 2 which were found to be paramagnetic over the entire 2–300 K temperature range. Finally, optical properties of Cs 2 KNd(PS 4 ) 2 and Rb 2.65 Na 0.35 La(PS 4 ) 2 were measured by UV–vis diffuse reflectance spectrometry which revealed numerous weak absorption bands in the 300–900 nm range characteristic of the f–f electronic transitions in Nd 3+ ; Rb 2.65 Na 0.35 La(PS 4 ) 2 was found to be a semiconductor with a direct band gap of 3.60 eV.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Function of Tetrahedral ZnS 3 O Building Blocks in the Formation of SrZn 2 S 2 O: A Phase Matchable Polar Oxysulfide with a Large Second Harmonic Generation Response

Single crystals of a new zinc oxysulfide SrZn 2 S2O were grown in a eutectic KF-KCl flux and the structure was determined by single-crystal X-ray diffraction. SrZn 2 S 2 O crystallizes in the non-centrosymmetric polar space group Pmn2 1 with lattice parameters of a = 3.87440(10) Å, b = 9.9847(3) Å, and c = 6.0916(2) Å. In the crystal structure, close-packed corrugated double layers of ZnS3O tetrahedra, which are derived from the wurtzite structure, are vertically separated by Sr 2+ ions. In addition, the O/S anion ordered arrangement in each close-packed layer yields two distinct orientations of the Zn-centered tetrahedra. The crystals of SrZn 2 S 2 O are colorless and transparent and the oxysulfide has a band gap of 3.86 eV, based on UV-vis-NIR diffuse reflectance measurements. Thermogravimetric measurements showed that SrZn 2 S 2 O is stable up to 650 °C in O 2 gas atmosphere. First-principle calculations indicate that the valence band maximum is mainly composed of O-2p and S-3p states, whereas the conduction band minimum is derived from Zn-4s, Zn-4p, and Sr-4d states. The calculated band dispersion reveals a direct band gap corresponding to a transition between S-3p and Zn-4s energy levels. Second harmonic generation (SHG) measurements determined that SrZn 2 S 2 O is phase matchable with twice the SHG intensity of potassium dihydrogen phosphate (KDP) in contrast to CaZnSO with similar ZnS 3 O building units, which exhibits non-phase matching behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Electrochemical Salt Wasteform Development: A Review of Salt Treatment and Immobilization Options

Electrochemical reprocessing, also referred to as pyroprocessing, is a technique for recycling actinides from used nuclear fuel (UNF) to produce fuel for future reactors. Here, UNF is dissolved in a molten salt (e.g., LiCl-KCl eutectic) within an electrorefiner. After UNF dissolution, fission products are released into the electrolyte salt and converted to chlorides. This paper discusses wasteform options for processing the base electrolyte salt with the fission product salts as well as just the rare-earth fission products (as RECl 3 , REOCl, or REO x ) with the intent of finding optimal methods for reducing total waste salt volumes or partitioning the salt for alternate wasteform options. Furthermore, two of the more detailed partitioning options discussed herein include halide removal from the salt (dehalogenation), which accounts for more than half of the salt on a molar basis, and RE fission product removal for wasteforms with high-RE loadings. Wasteform properties are compared with emphasis on wasteform volume starting from a given amount of (1) total salt cations or (2) RE cations. Comparisons are also made of wasteform chemical durabilities, with the data available from like testing methods. A main conclusion from this work is the justification of subsequent salt processing after electrorefiner operations for achieving significant wasteform volume reduction.

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

Exploring the Complex Chemistry of Uranium within Molten Chloride Salts

Harsh environments represent a unique opportunity to explore new frontiers in chemistry while developing novel tools to meet global needs. Exploring the chemistry of uranium within molten salts is a key example. Actinide chemistry within the highly ionic environment of a molten salt is poorly understood, particularly in the presence of common salt impurities or without active oxidation state control. Delving into this chemistry can provide new insight into actinide and f-electron interactions. Furthermore, expanding our chemical knowledge can also enable advances in and deployment of molten salt reactors or molten salt recycle schemes. Both molten salt applications aim towards providing green, reliable, and equitable energy as well as critical materials for the world. Here the utilization of visible absorbance and Raman spectroscopies to understand and quantify U within chloride-based salt eutectics is discussed. Furthermore, machine learning techniques in the form of chemometric modelling are developed and described, providing advanced analytical tools to quantify and characterize the U present. In conclusion, these tools are then leveraged to monitor and explore the dynamic fundamental chemistry of U within chloride-based salt melts.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Flux Synthesis of a Metal Carbide Hydride Using Anthracene As a Reactant

In this study, La 15 (FeC 6 ) 4 H was synthesized from the reaction of iron and anthracene in La/Ni eutectic flux. Anthracene was the source of both the carbon and hydrogen in the product. The structure of this metal carbide hydride features hydride ions in tetrahedral interstitial sites surrounded by lanthanum ions, which was confirmed by single-crystal neutron diffraction studies. The trigonal planar FeC 6 units in which the central iron atom is coordinated by three ethylenide groups are similar to those found in La 3.67 FeC 6 , a previously reported compound that is formed in the absence of a hydride source. Magnetic susceptibility data confirm that the iron sites do not have magnetic moments. Density of states calculations indicate that La 15 (FeC 6 ) 4 H is metallic and is stabilized by the incorporation of hydride anions.

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

Refined Classical Force Field for Choline Chloride and Ethylene Glycol Mixtures over Wide Composition Range

In this work, a classical force field based on the General Amber Force Field (GAFF) was refined for the simulation of choline chloride (ChCl) and ethylene glycol (EG) mixtures over a wide composition range by scaling the partial charges and van der Waals parameters. The scaling factors were derived by fitting the simulation results to only eight experimental density and viscosity data points of pure EG, and ChCl/EG mixtures at 1:2, 1:4, and 1:6 molar ratios. Using the refined force field, properties essential for electrochemical applications such as density, viscosity, self-diffusion coefficient, and ionic conductivity were calculated, and excellent agreement to experimental results was found even for compositions and temperatures not used in the fitting procedure. In addition, new experimental data for density, viscosity, and ionic conductivity are reported as a function of temperature and composition for this mixture. To the best of our knowledge, this is the first classical force field developed for the study of ChCl/EG mixtures over a composition range that includes the eutectic point. Using the new model, the liquid dynamics was studied in terms of ionic conductivity. It was found that the dynamics in ChCl/EG mixtures with ChCl mole fraction higher than 20% is similar to that of ionic liquids, high temperature molten salts, and highly concentrated water-in-salt electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2019

Water in Solutions of Chaotropic and Kosmotropic Salts: A Differential Scanning Calorimetry Investigation

We report the use of aqueous phase separations via aqueous biphasic systems (ABS) has been widely explored in the recent decades. For wider and more “intelligent” applications, it is important to look below the surface and study these systems thoroughly at a fundamental level. Two important questions still unsolved are how do polymers and ions of different types organize water (if they in fact they do so) and how does it affect the separation of phases? In the present work, differential scanning calorimetry (DSC) was used to relate ABS phase diagrams and the behavior of water in aqueous solutions containing kosmotropic salts (K 3 PO 4 or (NH 4 ) 2 SO 4 ), a chaotropic ionic liquid ([C 4 mim]Cl), or a polymer (PEG-2000), all of which are reported components of ABS, and their mixtures. Additional DSC transitions were observed for the two classes of salts which could be assigned based on the fundamental differences between their interactions with water, suggesting that it is the differences in the abilities of kosmotropic and chaotropic salts to interact with water which result in the phase separation phenomena observed. The DSC measurements of solutions of PEG-2000 and (NH 4 ) 2 SO 4 indicate that aqueous solutions of PEG-2000 supercool and potentially enter a glassy state that exhibits devitrification upon heating. The devitrified state exhibits a clear eutectic with water. Mixtures of the polymer and salt continue to exhibit all the features observed for the pure components. These results suggest that the mixtures are phase separated and consist of largely separate concentrated solutions of PEG-2000 and (NH 4 ) 2 SO 4 , indicating an entropy-driven phase separation. The DSC analysis of these systems further refines the understanding of kosmotropic and chaotropic solutes into more specific phenomena for each compound. Lastly, this work suggests that DSC can be used to understand the role of each salt/component in ABS.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

NMR Relaxometry and Diffusometry Analysis of Dynamics in Ionic Liquids and Ionogels for Use in Lithium-Ion Batteries

Solvation and transport properties of methlyviologen dichloride in mixtures of choline chloride (ChCl) and ethylene glycol (EG) including the deep eutectic solvent (DES) ethaline were studied through physical property measurements, cyclic voltammetry, and Raman spectroscopy. The transport properties of the solvate structures in ethaline and ChCl:EG mixtures were compared to a well-studied ionic liquid (IL), 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [PYR13][TFSI] through the lens of hole theory. Exchanging the chloride anion of ethaline with bis(trifuoromethylsufonyl)imide) anion, [TFSI], is found to increase the fluidity of the solvent and promoted stronger solute-solvent interactions. Raman spectroscopy shows that methylviologen is solvated by EG in solutions with ChTFSI but interstitially accommodated in void spaces in both ChCl solutions and [PYR13][TFSI]. Complex solvents such as DESs are regarded as “designer solvents” and we demonstrate that the physical properties and solvation characteristics of these fluids can be varied by anion exchange of hydrogen bond acceptors.

25 ENERGY STORAGE↗
DOE OSTI2021

Concentration-Dependent Solvation Structure and Dynamics of Aqueous Sulfuric Acid Using Multinuclear NMR and DFT

Sulfuric acid is a ubiquitous compound for industrial processes and aqueous sulfate solutions also play a critical role in electrolytes for many prominent battery chemistries. While the thermodynamic literature for it is quite well-developed, comprehensive studies of the solvation structure, and particularly molecular-scale dynamical and transport properties, are less available. This study applies a multinuclear NMR approach to the elucidation of the solvation structure and dynamics over a wide temperature (-10 – 50?C) and concentration (0 – 18 M) range, combining 17O shift, linewidth, and T1 relaxation measurements, 33S shift and linewidth measurements, and 1H PFG-NMR measurements of the proton self-diffusivity. In conjunction, these results indicate a crossover between two regimes of solvation structure and dynamics, occurring above the concentration associated with the deep eutectic point (~ 4.5 M), with the high-concentration regime dominated by strong water-sulfate correlation. This description was borne out in detail by the activation energy trends with increasing concentration derived from the relaxation of both the H2O/H3O+ and H2SO4/HSO4-/SO42- 17O resonances and the 1H self-diffusivity. However, the 17O chemical shift difference between the H2O/H3O+ and H2SO4/HSO4-/SO42- resonances across the entire temperature range is nevertheless strikingly linear. A computational approach coupling MD simulations and DFT NMR shift calculations to reproduce this trend is presented, which will be the subject of further development. This combination of multinuclear, dynamical NMR and computational methods, and the results furnished by this study, will provide a platform for future studies on battery electrolytes where aqueous sulfate chemistry plays a central role in the solution structure.

Bazak, Jonathan D.↗
DOE OSTI2022

Structure of Sulfuric Acid Solutions Using Pair Distribution Function Analysis

Solvation and mesoscale ordering of sulfuric acid and other strong acid solutions leads to suppressed freezing points and strong rheological changes with varying concentration. While the solid-state structures are well-understood, studies focused on the evolving solvation structure in the solution phase have probed a limited concentration range (~1–6 M). This study applies a total scattering approach in both the wide-angle X-ray scattering (WAXS) and pair distribution function (PDF) regimes to elucidate the evolving solvation structure over its full range of acid concentration (0–18 M). The emergence of a prepeak in the WAXS regime at intermediate concentrations indicates a transition from noninteracting sulfate molecules in the dilute limit to sterically limited sulfates at concentrations near its deep eutectic point. Fits to the PDF data quantify this trend, showing a transition from octahedrally hydrated sulfates up to 6–7 M concentrations, followed by gradual dehydration, and eventually reaching a solution structure similar to that of water-in-salt electrolyte systems at high acid concentrations.

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

60 Years of Betaine 30–From Solvatochromic Discovery to Future Frontiers

Betaine-30 (B30) was reported by Karl Dimroth and Christian Reichardt et al. in 1963 as a solvatochromic probe that can be easily synthesized, shows good solubility, and remains stable in various organic solvents and solutions. Its strongly negatively solvatochromic behavior arises from differential solvation between its electronic ground and excited states, making it a valuable tool for assessing solvent polarity using the E T (30) polarity scale, also devised by Dimroth and Reichardt. In addition, advancements in femtosecond laser spectroscopy in the 1990s greatly improved the understanding of B30’s relaxation dynamics following photoexcitation. In solvents capable of hydrogen bonding, such as alcohols, intermolecular hydrogen-bond rearrangement contributes to the multiple relaxation components observed. Since the 1990s, the applications of B30 have expanded beyond simple organic solvents to include complex solvent mixtures, such as electrolyte solutions for battery technologies and eutectic solvent mixtures. Furthermore, given the growing importance of these complex solvent mixtures, B30 is becoming an increasingly valuable tool for studying previously unexplored solvation properties.

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

Temperature-Dependent Speciation of Ni(II) in Molten Chloride, Bromide, and Iodide Salts

Understanding the fundamental speciation and local structure of metal cations─such as nickel, which is present as a corrosion product─in molten salt media is essential for assessing their impact on the thermal and physical properties of salts used for advanced nuclear energy applications. In this study, we employed an integrated approach of combining X-ray absorption spectroscopy (XAS), UV–vis spectroscopy, and ab initio molecular dynamics (AIMD) to investigate the halide-dependent speciation of divalent nickel ions, Ni(II), in LiCl–KCl, LiBr–KBr, and LiI–KI eutectic salt mixtures from room temperature to 600 °C. Our findings show that both halide type and temperature significantly influence the local coordination of nickel in these molten salt systems. A notable aspect of Ni(II) speciation in LiI–KI salts is the formation of a polyiodide species. In conclusion, our findings provide critical insights into metal ion speciation in molten salt systems, enhancing our understanding of the factors that govern the physicochemical properties of these complex fluids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Addition of Chloroform in a Solvent-in-Salt Electrolyte: Outcomes in the Microscopic Dynamics in Bulk and Confinement

Solvent-in-salt electrolytes (SISEs) are a promising alternative to the electrolytes currently used in commercial devices. Despite the SISEs’ advantages, their utilization is not yet realized due to the poor mobility of their chemical species. Here, we explore this problem by adding chloroform to a SISE formed by acetonitrile and a Li-salt. First, we performed illustrative cycling experiments to highlight the potential of this approach. Then, we focused on the description of the microscopic dynamics of the electrolytes and exposed the relevant aspects to be considered for their optimal performance. While the conductivity at low temperatures may be enhanced by the addition of chloroform, only subtle changes occur at room temperature. As revealed by molecular dynamics simulations and quasielastic neutron scattering (QENS) experiments, this effect is related to the preservation of the structure expected for a highly concentrated solution and promotion of the formation of ionic aggregates. These outcomes occur despite the increase in the overall mobility of the chemical species. The dynamics of the electrolytes in porous carbon was also investigated using QENS. In these circumstances, low concentrations of chloroform lead to diffusivities of the molecular species higher than those observed for the bulk electrolytes. As chloroform’s concentration increases, no further changes in the diffusivities are observed. Nonetheless, chloroform is mostly immobilized on the carbon surfaces and this behavior may be intensified at compositions closer to the eutectic mixture.

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

Probing Complex Chemical Processes at the Molecular Level with Vibrational Spectroscopy and X-ray Tools

Understanding the origins of structure and bonding at the molecular level in complex chemical systems spanning magnitudes in length and time is of paramount interest in physical chemistry. Here, we have coupled vibrational spectroscopy and X-ray based techniques with a series of microreactors and aerosol beams to tease out intricate and sometimes subtle interactions, such as hydrogen bonding, proton transfer, and noncovalent interactions. This allows for unraveling the self-assembly of arginine-oleic acid complexes in an aqueous solution and growth processes in a metal–organic framework. Terahertz and infrared spectroscopy provide an intimate view of the hydrogen-bond network and associated phase changes with temperature in neopentyl glycol. The hydrogen-bond network in aqueous glycerol aerosols and levels of protonation of nicotine in aqueous aerosols are visualized. Future directions in probing the hydrogen-bond networks in deep eutectic solvents and organic frameworks are described, and we suggest how X-ray scattering coupled to X-ray spectroscopy can offer insight into the reactivity of organic aerosols.

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

Assessing Melting and Solid–Solid Transition Properties of Choline Chloride via Molecular Dynamics Simulations

Choline chloride (ChCl) is used extensively as a hydrogen bond donor in deep eutectic solvents (DESs). However, determining its melting properties experimentally is challenging due to decomposition upon melting, leading to widely varying literature values. Accurate melting properties are crucial for understanding the solid–liquid phase behavior of ChCl-containing DESs. Here, we employ molecular dynamics simulations to compute the phase transitions of ChCl, testing a variety of atomistic force fields. We find that the results are sensitive to the choice of force field, but a melting temperature of 627 K and a melting enthalpy of 7.8 kJ/mol seem most reasonable, in good agreement with some literature values. Furthermore, we suggest these as the likely melting properties of ChCl, though the results are tentative due to limited experimental data for the liquid ChCl phase.

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

Four-Dimensional Probing of Phase-Reaction Dynamics in Au/GaAs Nanowires

Nanoeutectic phase reaction covers the fundamental study of a chemical and physical reaction of multiple phases at the nanoscale. We report the direct visualization of phase-reaction dynamics in Au/GaAs nanowires (NWs) using four-dimensional (4D) electron microscopy. The NW phase reactions were initiated with a pump laser pulse, while the following dynamics in the Au/GaAs NW was probed by a precisely time-delayed electron pulse. Single-pulse imaging reveals that the cubic zinc-blende NW presents a transient length increase within the time duration of ~150 ns, giving the appearance of intermediate phase reactions at an early stage. A final length reduction of the NW is observed after the phase reactions have fully ended. In contrast, only length reduction is seen throughout the entire process in GaAs/AlGaAs core–shell and hexagonal wurtzite GaAs NWs. The reasons for the above intriguing phenomena are discussed. The eutectic-related phenomena in both zinc-blende and wurtzite materials offer a comprehensive understanding of phase-reaction dynamics in polytypic structures commonly available in compound semiconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Thermal Property Modeling and Assessment of the Physical Properties of FLiNaK

Here, the thermodynamic properties of the LiF–NaF–KF system and its subsystems were re-evaluated using the CALPHAD method, focusing on the deviations from ideality in the heat capacity [C p (T)] of mixtures, temperature-dependence of mixing enthalpies (Δ mix H), vapor pressures of mixtures, and enthalpies of fusion (ΔH fus ) using reported values and measurements. The results of this work confirmed a pseudoternary eutectic at 732.9 K and 46.5LiF–11.5NaF–42KF mol % (FLiNaK) with determined Cp(T) = 69.822 + 0.000679T + 2,137,152T –2 J mol –1 K –1 (732.9 < T < 1200 K) and ΔH fus = 18,051 J mol –1 in good agreement to the experimental values. The resulting accurate thermodynamic representation can be used to find relevant excess thermochemical properties in the whole pseudoternary space and provide insights into their composition and temperature dependence. A detailed evaluation of select thermophysical properties was also conducted to determine recommended density, thermal diffusivity, thermal conductivity, vapor pressures, and boiling point with calculated uncertainties over the temperature range of interest for FLiNaK–salt energy applications.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗