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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Novel Hydrogen Clathrate Hydrate

We report a new hydrogen clathrate hydrate synthesized at 1.2 GPa and 298 K documented by single-crystal x-ray diffraction, Raman spectroscopy, and first-principles calculations. The oxygen sublattice of the new clathrate hydrate matches that of ice II, while hydrogen molecules are in the ring cavities, which results in the trigonal R3c or R¯3c space group (proton ordered or disordered, respectively) and the composition of ( H 2 O) 6 H 2 . Raman spectroscopy and theoretical calculations reveal a hydrogen disordered nature of the new phase $C$$^{'}_{1}$, distinct from the well-known ordered C 1 clathrate, to which this new structure transforms upon compression and/or cooling. Furthermore, this new clathrate phase can be viewed as a realization of a disordered ice II, unobserved before, in contrast to all other ordered ice structures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Quantifications of growth rate and particle size of magnesium silicate hydrate cement using small‐angle X‐ray scattering

The focus of recent research on cement binders has shifted to alternatives such as magnesium silicate hydrate (M-S-H) to mitigate the environmental impact of conventional concrete production. However, a detailed understanding of the morphology and growth rate of M-S-H, which informs its applicability as a cementing agent, is lacking. These properties are important as they influence cement hydration and consequently the development of macroscopic properties. Here, in this study, the particle size distribution and growth rate of M-S-H synthesized by mixing aqueous stock solutions were analyzed using synchrotron-based small-angle X-ray scattering. The reaction solutions contained dissolved magnesium and silicon with concentrations ranging from 2 to 500 mM, corresponding to saturation indices with respect to M-S-H endmembers, M 0.75 -S-H and M 1.50 -S-H, between 5.8 and 10.3. The precipitation rates of M-S-H align with affinity-based kinetic models and can be described by the following equations: For M 0.75 -S-H: 𝑟 M 0.75 −S−H =10 −9.54±0.70 ⁢(Ω$^{0.59±0.08}_{M_{0.75}⁢\textrm{SH}}$−1), and for M 1.50 -S-H: 𝑟 M 1.50 −S−H =10 −7.56±0.37 ⁢(Ω$^{0.34±0.04}_{M_{1.50}⁢\textrm{SH}}$−1), where 𝑟 is the rate in mol/L/s, and Ω represents the saturation ratio with respect to M-S-H. Moreover, we observed that changing the [Mg]/[Si] ratio affects particle size, a trend that cannot be fully explained by changes in the saturation index alone. These insights are critical for improving the predictability and control of cementation in concrete that utilizes M-S-H-based binders.

M-S-H↗
DOE OSTI2023

The primary gas phase hydration shell of hydroxide

The number of water molecules in hydroxide’s primary hydration shell has been long debated to be three from the interpretation of experimental data and four from theoretical studies. Here, we provide direct evidence for the presence of a fourth water molecule in hydroxide’s primary hydration shell from a combined study based on high-resolution cryogenic experimental photoelectron spectroscopy and high-level quantum chemical computations. Well-defined spectra of OH - (H 2 O) n clusters (n = 2 to 5) yield accurate electron binding energies, which are, in turn, used as key signatures of the underlying molecular conformations. Although the smaller OH - (H 2 O) 3 and OH - (H 2 O) 4 clusters adopt close-lying conformations with similar electron binding energies that are hard to distinguish, the OH - (H 2 O) 5 cluster clearly has a predominant conformation with a four-coordinated hydroxide binding motif, a finding that unambiguously determines the gas phase coordination number of hydroxide to be four.

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

Insights into the thermo-hydraulic properties of compacted MX80 bentonite during hydration under elevated temperature

In high-level radioactive waste geological repositories, compacted bentonite undergoes coupled thermo-hydraulic processes due to heat released from a central waste canister and groundwater imbibition from the surrounding host rock. An understanding of these processes is essential for long-term simulations of radionuclide migration and canister corrosion, which requires an understanding of temperature effects on the coupled thermo-hydraulic properties governing these processes. In this study, a tank-scale radial infiltration test was used to investigate water imbibition processes in compacted bentonite under a central heater temperature of 200 °C that simulates high thermal gradients in a repository. Interpretation of this test focuses on evaluation of the liquid water wetting front during hydration and the interpretation of the temperature-dependent transient soil water retention curve (SWRC), thermal conductivity function (TCF), and hydraulic conductivity function (HCF). The SWRC during imbibition follows a temperature-dependent wetting path. Temperature effects on the hydraulic conductivity of bentonite in saturated conditions had the greatest effect on the shape of the HCF, with minimal temperature effects at higher suctions. The transient thermal conductivity data matched well with a new TCF linked with the SWRC shape. Although the bentonite layer was restrained, local deformations during hydration may have affected the shapes of the TCF and HCF.

Engineering↗
DOE OSTI2024

Dataset for manuscript "Consequences of the failure of equipartition for the p-V behavior of liquid water and the hydration free energy components of a small protein"

Previously, we showed that in the molecular dynamics simulation of a rigid model of water it is necessary to use an integration time-step dt that is less than or equal to 0.5 fs to ensure equipartition between translational and rotational modes. We extended that study in the NVT ensemble to NpT conditions and to an aqueous protein. We study neat liquid water with the rigid, SPC/E model and the protein BBA (PDB ID: 1FME) solvated in the rigid, TIP3P model. We examined integration time-steps ranging from 0.5 fs to 4.0 fs for various thermostat plus barostat combinations. We find that a small time-step, dt, is necessary to ensure consistent prediction of the simulation volume. Hydrogen mass repartitioning alleviates the problem somewhat, but is ineffective for the typical time-step used with this approach. The compressibility, a measure of volume fluctuations, is seen to be sensitive to dt. Using the mean volume estimated from the NpT simulation, we examined the electrostatic and van der Waals contribution to the hydration free energy of the protein in the NVT ensemble. These contributions are also sensitive to dt. In going from a time-step of 2 fs to a time-step of 0.5 fs, the change in the net electrostatic plus van der Waals contribution to the hydration of BBA is already in excess of the folding free energy reported for this protein. The data-set contains the simulation metadata and log files that support the claims noted above.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Hydration-driven stabilization and volume collapse of grain boundaries in Mg2SiO4 forsterite predicted by first-principles simulations

Grain boundaries in mantle minerals are of critical importance to geophysical and geochemical processes of the Earth’s interior. One of the fundamental issues is to understand how the water (H 2 O) component influences the properties of grain boundaries in silicate materials. Here, we report the results of the structure and stability of several tilt grain boundaries in Mg 2 SiO 4 forsterite over the pressure range 0 to 15 GPa using density functional theory-based first-principles simulations. Here, the results suggest greater energetic stability and hydration-driven volume collapse (negative excess volume) at zero pressure for the majority of hydrous grain boundaries relative to the anhydrous (dry) ones. All the hydrous grain boundaries become increasingly favorable at elevated pressures as the calculated hydration enthalpy systematically decreases with increasing pressure. The hydrous components at the interfacial regions are predominantly in the hydroxyl form and, to a lesser extent, in the molecular H 2 O form. Their calculated ratio ranges from 1.6 to 8.7 among the different grain boundary configurations. Our structural analysis also reveals that the hydroxyls are bound to either both Mg and Si or to Mg only. In comparison, the molecular species are bound only to Mg sites. Besides direct oxygen-hydrogen bonding, intermolecular hydrogen bonding becomes important with compression. On the basis of our results, we suggest that local atomic rearrangements caused by dissociative adsorption of water facilitate efficient compaction of the boundary interfaces, which, in turn, results in greater relative stability of hydrous grain boundaries. This means that water prefers to be incorporated within the grain boundaries over the bulk of silicate materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Probing Surface Hydration and Isotope Exchange Kinetics in Proton-Conducting Ceramics Using DRIFTS and EIS

This internship project investigates how water vapor partial pressure (pH2O) affects surface hydration and H/D isotope-exchange kinetics in BaZr0.4Ce0.4Y0.1Yb0.1O3?d (4411) proton-conducting ceramic electrolytes. Diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) is used to monitor surface hydroxyl and deuteroxyl species under controlled humidified atmospheres during gas-switching experiments. These surface kinetic trends are to be correlated with bulk, grain-boundary, and total electrolyte resistance measured by electrochemical impedance spectroscopy (EIS) under matching conditions. The future goals of this study are to clarify the relationship between surface hydration dynamics and proton conduction behavior, improving interpretation of EIS data and guiding the optimization of ceramic electrolytes for energy applications.

08 - HYDROGEN↗
DOE OSTI2022

Anodic Activity of Hydrated and Anhydrous Iron (II) Oxalate in Li-Ion Batteries

We discuss the applicability of the naturally occurring compound Ferrous Oxalate Dihydrate (FOD) (FeC2O4·2H2O) as an anode material in Li-ion batteries. Using first-principles modeling, we evaluate the electrochemical activity of FOD and demonstrate how its structural water content affects the intercalation reaction and contributes to its performance. We show that both Li0 and Li+ intercalation in FOD yields similar results. Our analysis indicates that fully dehydrated ferrous oxalate is a more promising anodic material with higher electrochemical stability: it carries 20% higher theoretical Li storage capacity and a lower voltage (0.68 V at the PBE/cc-pVDZ level), compared to its hydrated (2.29 V) or partially hydrated (1.43 V) counterparts.

Keshavarz, Fatemeh↗
DOE OSTI2022

Molecular Dynamics Simulation and Cryo-Electron Microscopy Investigation of AOT Surfactant Structure at the Hydrated Mica Surface

Structural properties of the anionic surfactant dioctyl sodium sulfosuccinate (AOT or Aerosol-OT) adsorbed on the mica surface were investigated by molecular dynamics simulation, including the effect of surface loading in the presence of monovalent and divalent cations. The simulations confirmed recent neutron reflectivity experiments that revealed the binding of anionic surfactant to the negatively charged surface via adsorbed cations. At low loading, cylindrical micelles formed on the surface, with sulfate head groups bound to the surface by water molecules or adsorbed cations. Cation bridging was observed in the presence of weakly hydrating monovalent cations, while sulfate groups interacted with strongly hydrating divalent cations through water bridges. The adsorbed micelle structure was confirmed experimentally with cryogenic electronic microscopy, which revealed micelles approximately 2 nm in diameter at the basal surface. At higher AOT loading, the simulations reveal adsorbed bilayers with similar surface binding mechanisms. Adsorbed micelles were slightly thicker (2.2–3.0 nm) than the corresponding bilayers (2.0–2.4 nm). Upon heating the low loading systems from 300 K to 350 K, the adsorbed micelles transformed to a more planar configuration resembling bilayers. The driving force for this transition is an increase in the number of sulfate head groups interacting directly with adsorbed cations.

58 GEOSCIENCES↗
DOE OSTI2020

Computational and Experimental 1H-NMR Study of Hydrated Mg-Based Minerals

Magnesium oxide (MgO) can convert to different magnesium-containing compounds depending on exposure and environmental conditions. Many MgO-based phases contain hydrated species allowing 1H-nuclear magnetic resonance (NMR) spectroscopy to be used in the characterization and quantification of proton-containing phases; however, surprisingly limited examples have been reported. Here, 1H-magic angle spinning (MAS) NMR spectra of select Mg-based minerals are presented and assigned. These experimental results are combined with computational NMR density functional theory (DFT) periodic calculations to calibrate the predicted chemical shielding results. This correlation is then used to predict the NMR shielding for a series of different MgO hydroxide, magnesium chloride hydrate, magnesium perchlorate, and magnesium cement compounds to aid in the future assignment of 1H-NMR spectra for complex Mg phases.

1H-NMR↗
NASA NTRS1967

Hydrated multivalent cations are new class of molten salt mixtures

Electrical conductance and activation energy measurements on mixtures of calcium and potassium nitrate show the hydrated form to be a new class of molten salt. The theoretical glass transition temperature of the hydrate varied in a manner opposite to that of the anhydrous system.

Angell, C. A.↗
NASA NTRS1970

Compact apparatus for photogeneration of hydrated electrons

Flash-photolysis instrument generates hydrated electrons and studies their reactions. It has a three-dimensional, multiple-reaction cell and the capacity to produce up to .1 micromole hydrated electron in a single 40 microsec light pulse.

Hart, E.↗
NASA NTRS1980

Infrared reflectance spectra of asteroids - A search for water of hydration

Infrared reflectance spectra have shown the presence of an absorption feature in the 3-4 micron region for seven C and U asteroids. By comparison with laboratory spectra of terrestrial silicates and meteorites, it is concluded that this band is probably due to water in the form of hydrated salts and silicates (clay minerals), implying that the surface material of these asteroids may be analogous to the CI and CM carbonaceous chondritic meteorites. The presence of other hydrated minerals, however, cannot be ruled out. The depths of the water bands in the spectra vary from asteroid to asteroid, though no asteroid spectrum shows a band as deep as was detected on 1 Ceres. On four other C asteroids, no water band was detected. The implications of these observations for the mineralogy of these asteroids are discussed

Lebofsky, L. A.↗
NASA NTRS1985

Hydrated interplanetary dust particle linked with carbonaceous chondrites?

The results of transmission electron microscope observations of a hydrated interplanetary dust particle (IDP) containing Fe-, Mg-rich smectite or mica as a major phase are reported. The sheet silicate appears to have formed by alteration of anhydrous silicates. Fassaite, a Ca, Al clinopyroxene, also occurs in this particle, and one of the crystals exhibits solar-flare tracks, clearly indicating that it is extraterrestrial. Fassaite is a major constituent of the Ca-, Al-rich refractory inclusions found in the carbonaceous chondrites, so its presence in this particle suggests that there may be a link between hydrated IDPs and carbonaceous chondrites in the early history of the solar system.

Tomeoka, K.↗
NASA NTRS1986

Effect of hydration on plasma vasopressin, renin, and aldosterone responses to head-up tilt

If plasma vasopressin (PVP), plasma renin (PRA), and plasma aldosterone (PA) responses to change in posture are mediated only by alterations in intrathoracic baroreceptor activity hydration status should have minimal influence on these responses. To test this hypothesis, six male subjects underwent 45 min of 70 deg head-up tilt (HUT) following 26 h dehydration, and again, 105 min later, following rehydration. Compared with preceding supine hydrated control values, PVP, PRA, and PA increased (p less than 0.001) during dehydrated HUT, but only PVP and PRA increased during rehydrated HUT (p less than 0.001). The dissociation during rehydrated HUT of PRA and PA may have been related more to the reduction (p less than 0.001) in plasma potassium concentration than to the accompanying decrease (p less than 0.001) in plasma osmolality and sodium concentration. Although increases in PVP and PRA during HUT were attenuated (p less than 0.01) following rehydration, this attenuation was associated with the absence of symptoms of overt hypotension following rehydration. However, since rehydration did not abolish the increases in PVP and PRA induced by HUT, it is concluded that the present observations support the concept of intrathoracic baroreceptor involvement in the regulation of vasopressin secretion and renin release.

Harrison, M. H.↗
NASA NTRS1986

Effect of hydration on plasma volume and endocrine responses to water immersion

The effect of hydration status on early endocrine responses and on osmotic and intravascular volume changes during immersion was determined in humans undergoing successive periods of dehydration, immersion, rehydration, and immersion. Immersion caused an isotonic expansion of plasma volume, as well as suppression of plasma renin activity and aldosterone, which all occurred independently of hydration status. On the other hand, the concentration of plasma vasopressin (PVP) was found to decrease during dehydrated immersion, but not during rehydrated immersion. It is concluded that plasma tonicity is not a factor influencing PVP suppression during water immersion.

Harrison, M. H.↗
NASA NTRS1990

Formation of nitric acid hydrates - A chemical equilibrium approach

Published data are used to calculate equilibrium constants for reactions of the formation of nitric acid hydrates over the temperature range 190 to 205 K. Standard enthalpies of formation and standard entropies are calculated for the tri- and mono-hydrates. These are shown to be in reasonable agreement with earlier calorimetric measurements. The formation of nitric acid trihydrate in the polar stratosphere is discussed in terms of these equilibrium constants.

Smith, Roland H.↗
NASA NTRS1991

Low-pressure clathrate-hydrate formation in amorphous astrophysical ice analogs

In modeling cometary ice, the properties of clathrate hydrates were used to explain anomalous gas release at large radial distances from the Sun, and the retention of particular gas inventories at elevated temperatures. Clathrates may also have been important early in solar system history. However, there has never been a reasonable mechanism proposed for clathrate formation under the low pressures typical of these environments. For the first time, it was shown that clathrate hydrates can be formed by warming and annealing amorphous mixed molecular ices at low pressures. The complex microstructures which occur as a result of clathrate formation from the solid state may provide an explanation for a variety of unexplained phenomena. The vacuum and imaging systems of an Hitachi H-500H Analytical Electron Microscope was modified to study mixed molecular ices at temperatures between 12 and 373 K. The resulting ices are characterized by low-electron dose Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED). The implications of these results for the mechanical and gas release properties of comets are discussed. Laboratory IR data from similar ices are presented which suggest the possibility of remotely observing and identifying clathrates in astrophysical objects.

Blake, D. F.↗