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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

How the Hydrophobic Interface between a Perfluorosulfonic Acid Polymer and Water Vapor Controls Membrane Hydration

Stable hydration in perfluorinated polyelectrolyte membranes such as Nafion is essential to maintain good ion conductivity and manage permeation, especially in vapor-fed devices where water content depends on relative humidity in a gas stream. Extensive studies in the literature have shown that Nafion hydration in water vapor is controlled by its interfacial transport resistance. Nafion forms a fluorine-rich layer at the polymer-gas interface, and it has been proposed that this layer blocks water transport due to its hydrophobicity. To develop a molecular-level description of the physics underlying transport resistance in this system, we have performed a computational reaction-diffusion kinetics study of water evaporation from Nafion. Two distinct models are examined, one mimicking the blocking function proposed in the literature and the other assuming that there is no blocking, treating instead water evaporation as a dynamic balance between uptake from the gas and desorption from the polymer surface. Simulation results are compared to time-dependent infrared data over a range of 100-0% relative humidity from the literature. Only the dynamic model successfully reproduces experimental observations. This indicates that the physical nature of interfacial transport resistance is not slow diffusion across an interfacial layer; rather, it is due to the competition between dehydration and rehydration. The simulation data provide details on the accompanying water distributions throughout the membrane and on interfacial kinetics, showing that they are characterized by strong fluctuations.

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

Determining the hydration energetics on carbon-supported Ru catalysts: An adsorption calorimetry and density functional theory study

Fundamental knowledge on the energetics at the interface between a water layer and a metal catalyst is essential so as to understand the roles that water can play in the synthesis, activation and regeneration of noble metal-based catalysts. Here, we report the direct measurement of the enthalpy of water adsorption (Δh ads ) on activated carbon (C) and activated C-supported Ru nanoparticles, which are promising catalyst as applied to the hydrogenation/hydrodeoxygenation (HDO) of oxygenates (phenolics, aldehydes, etc.). Specifically, the near-zero coverage enthalpy of water adsorption on a C-supported Ru catalyst is -75.3 ± 0.4 kJ/(mol water), suggesting favorable water–metal binding. This is much more exothermic than that on C, which has an enthalpy of adsorption of -50.3 ± 1.3 kJ/(mol water). Despite the favorable initial binding, the magnitudes of enthalpies of water condensation on C and Ru-C indicate that overall, their surfaces are both hydrophobic. Moreover, the experimentally-measured near-zero coverage water adsorption enthalpy at the Ru sites is in very good agreement with our density functional theory based calculations. At low coverages, we obtain a water binding energy of -61.7 kJ/(mol water), which increases to -78.1 kJ/(mol water) at saturation. Complementary results are also obtained from a thermal analysis, which employed a thermogravimetric analysis–differential scanning calorimetry–mass spectrometry (TG-DSC-MS), a spectroscopic investigation using ex situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and a morphological evaluation with transmission electron microscopy (TEM). We point out that in carbon-supported metal catalysts, such as Ru-C, a strong hydration at near-zero coverage and relative weak water-surface interactions occurs upon saturation. Such heterogeneity is essential and crucial for catalytic hydrogenation/HDO reactions that involve balanced interactions among the water-rich reactant mixture and nonpolar organic products.

09 BIOMASS FUELS↗
NASA NTRS2007

Clay Bearing Units in the Region around Mawrth Vallis: Stratigraphy, Extent, and Possible Alteration Fronts

The largest exposure of phyllosilicates on Mars occurs on the highland plains around Mawrth Vallis. This exposure extends for about 300 km southward from the edge of the dichotomy boundary, covering an area greater than 200 x 300 kilometers over an elevation range of approximately 2000 meters. At least two different types of hydrated phyllosilicates (Fe/Mg-rich and Al-rich phyllosilicates) have been identified in OMEGA data based on absorption bands near 2.3 and 2.2 micrometers, respectively. These clay-bearing units are associated with layered, indurated light-toned units with complex spatial and stratigraphic relationships, and are unconfomably overlain by a darker, indurated, more heavily cratered unit. Ongoing analysis of OMEGA (approximately 1 kilometer/pixel) and CRISM multi-spectral (MSP, 200 meters/pixel) data reveal hydrated minerals with absorptions at approximately 2.2 or 2.3 micrometers in locations up to 300 kilometers away from the borders of the previously identified extent of clay-bearing units. We seek to: 1) further constrain the mineralogy of the hydrated species identified in [5], and 2) understand spatial and stratigraphic relationships between the different hydrated minerals and the cratered plains units in which they are found. In this work we perform mineralogical and stratigraphic comparisons between units to test whether these extended units may be related, in order to establish a broad zone of alteration.

Dobrea, E. Z. Noe↗
NASA NTRS1991

Effect of sinter fracture and ohmic resistance on capacity retention in the nickel oxide electrode

The lifetime of batteries which utilize the nickel oxide electrode is often limited because this electrode loses a significant portion of its capacity as it is cycled. It is asserted that this capacity loss may often be attributed to cracking or separation of the conductive nickel sinter in the electrode, which forces electronic current to pass through the poorly conducting hydrated oxide and thus imposes a significant ohmic resistance. The model indicates that the oxide develops a nearly insulating layer which prevents complete discharge in the cycled electrode at usable rates. The capacity retention can be improved by reducing the cyclic stresses or strengthening the current collecting structure, redistributing it to provide a shorter current path through the solid phase, or by increasing the conductivity of the oxide to delay the formation of an insulating layer.

Lanzi, Oscar↗
NASA NTRS2012

Initial Observations by the Mars Exploration Rover Opportunity at Cape York, Meridiani Planum

Since the beginning of its mission, the MER rover Opportunity has visited a sequence of progressively larger impact craters in order to characterize rocks that represent an ever broader stratigraphic range. Endeavour Crater is by far the largest crater that this rover has visited, therefore the crater rim provides materials from strata that are much deeper and older than any materials yet sampled. Indeed, the Mars Reconnaissance Orbiter CRISM instrument detected spectral signatures of hydrated phyllosilicates in several rim segments, consistent with a Noachian provenance. In addition, the crater rim might have recorded the effects of the original impact as well as the thermal processes that occurred in its aftermath. This report summarizes initial observations of geologic structures and the fabrics, chemistry and mineralogy of rocks. Cape York is an N/NE - S/SW-trending segment of crater rim that is bounded by rim segments that are more deeply eroded, forming embayments. Opportunity drove onto the southwest margin of Cape York and has traversed across the Cape to a ridge near its northern end. The rim of Endeavour Crater was severely degraded and then on lapped by Meridiani sulfate-rich deposits, indicating that Cape York deposits experienced extensive erosion prior to the deposition of Meridiani Planum sulfate-rich sediments. Cape York consists of impact-uplifted rocks that are surrounded by a younger bedrock bench that might represent sediments shed from Cape York. The uplifted rock "Tisdale-2," located near the southern end of Cape York, is a polymict lithic breccia. Its elemental composition resembles a mixture of basalt plus bedrock encountered previously at Meridiani Planum, and it is relatively enriched in Ni, Zn, P, characteristic of hydrothermal fluids. "Chester Lake" and "Greeley Haven" are bedrock surfaces located near the southern and northern ends of Cape York, respectively, and they exhibit fabrics reminiscent of suevites. The rocks that were analyzed so far are quite different from any rocks previously encountered by Opportunity and Spirit. Several light-toned vein deposits (approx 1 cm) were discovered in the bench that borders the western flanks of Cape York. The vein "Homestake" is rich in Ca and S, and it exhibits a spectral feature near 1000 run caused by hydration, indicating that "Homestake" consists substantially of gypsum. The relationship(s) between these veins and the sulfate-rich layered deposits at Meridiani Planum remains uncertain. The veins might have been deposited by sulfate-rich fluids perhaps either in the immediate aftermath of the impact that formed Endeavour Crater or at some later time. Current uncertainties notwithstanding, the novel lithologies at Cape York are significantly older than the sulfate-rich sedimentary rocks at Meridiani Planum, and these lithologies have recorded episodes of aqueous activity from earlier epochs, perhaps during the Noachian. The author acknowledges the contributions of the Athena Science Team, the MER engineering team, JPL and NASA.

Marais, David J.↗
DOE OSTI2020

Petrophysical and geomechanical properties of gas hydrate-bearing sediments recovered from Alaska North Slope 2018 Hydrate-01 Stratigraphic Test Well

Knowledge of petrophysical and geomechanical properties of gas hydrate-bearing sediments are essential for predicting reservoir response due to gas production from gas hydrate reservoirs. That information will be critical parameters for designing production well completion such as specification of depressurization pump, water storage tank, and mesh size of sand screen. In December 2018, Stratigraphic Test Well Hydrate-01 was drilled in the western part of the Prudhoe Bay Unit, Alaska North Slope as part of the technical planning effort for a future long-term production test by collaborative team of DOE/NETL, USGS, and MH21-S (Boswell et al., 2020, Collett et al., 2020, Okinaka et al., 2020). Data set of logging-while-drilling (LWD) were acquired (Haines et al., 2020, Suzuki et al., 2019) and core sampling depth was determined on-site.Side-wall pressure coring was conducted to recover gas hydrate-bearing sediments from two reservoir sections named Unit-B and Unit-D. A total of 34 cores were successfully recovered by 5 runs of a wire-line deployed pressure corer (CoreVault® System - Halliburton). Core analysis scheme of this project are shown in Figure 1. All cores were quenched in liquid nitrogen while at high pressure in the laboratory of Stratum Reservoir, LLC. at Anchorage (Figure 1, a)). And the cores were removed from the pressure corer autoclave with temperature support of dry ice and stored under liquid nitrogen at atmospheric pressure. 19 damaged cores were processed to index property measurements directly such as grain size, grain density. 4 of another 17 cores were depressurized and trimmed for making a plug to analyze petrophysical properties of host sediments. Unsteady-state permeability test was conducted to obtain relative water permeability to gas and core scale NMR T2 distribution measurement was performed for evaluating pore size distribution at Houston (Figure 1, b)). Remained high quality 13 cores were preserved with gas hydrate for advanced laboratory analysis. National Institute of Advanced Industrial Science and Technology, as a part of the Japanese National Hydrate Research Program (MH21-S, funded by Ministry of Economy, Trade and Industry), received the samples at Sapporo, Japan for advanced core analysis. High-resolution X-ray CT was used to analyze the quality of the samples, which showed undisturbed lithological layers. Cores were lathed into cylindrical shape and distributed for multi property measurements (Figure 1, c)).<p>As a result, sediment from Unit-D is categorized as silty sand at ~37% porosity with ~80% gas hydrate saturation. An average hydration number n = 6.16 was measured by Raman spectroscopy. An average intrinsic permeability of ~400 mD and in situ effective permeability (with hydrate) on the order of ~10 mD. The Unit B recovered cores consisted of well sorted sand at ~40% porosity with ~95% gas hydrate saturation. An average intrinsic permeability of ~1 Darcy and in situ effective permeability on the order of ~30 mD was measured for the Unit B cores. There was a small permeability reduction due to porosity loss with increasing effective stress that simulated consolidation behavior along with depressurization in the highly permeable sandy sediment. The apparent minimum change in porosity and permeability may be caused by the low compressibility of quartz sand grains in the recovered cores. XRD and thermal conductivity analysis also suggested high quartz content. Triaxial compression tests established internal friction angles based on the Mohr-Coulomb's failure criterion, which are 40° for hydrate-bearing sediment and 29.8° for hydrate free sediment.</p>

Yoneda, Jun↗
DOE OSTI2020

PDADMAC/PSS Oligoelectrolyte Multilayers: Internal Structure and Hydration Properties at Early Growth Stages from Atomistic Simulations

We analyze the internal structure and hydration properties of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) oligoelectrolyte multilayers at early stages of their layer-by-layer growth process. Our study is based on large-scale molecular dynamics simulations with atomistic resolution that we presented recently [Sánchez et al., Soft Matter 2019, 15, 9437], in which we produced the first four deposition cycles of a multilayer obtained by alternate exposure of a flat silica substrate to aqueous electrolyte solutions of such polymers at 0.1M of NaCl. In contrast to any previous work, here we perform a local structural analysis that allows us to determine the dependence of the multilayer properties on the distance to the substrate. We prove that the large accumulation of water and ions next to the substrate observed in previous overall measurements actually decreases the degree of intrinsic charge compensation, but this remains as the main mechanism within the interface region. We show that the range of influence of the substrate reaches approximately 3 nm, whereas the structure of the outer region is rather independent from the position. This detailed characterization is essential for the development of accurate mesoscale models able to reach length and time scales of technological interest.

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

Time-resolved 3D characterisation of early-age microstructural development of Portland cement

Abstract Time-resolved in-situ synchrotron X-ray microtomography reveals new levels of detail about the chemical and physical processes that take place as Portland cement hardens. The conversion of a fluid paste into a hardened product can be monitored on a sub-minute time-scale, and with sample movement/settlement corrections applied to enable individual particles to be tracked as they react, hydrate, and become interconnected into a single strong monolith. The growth of the strength-giving hydrate phases surrounding cement grains, and of the fluid-filled pore network that surrounds them, is able to be directly viewed at the level of individual cement particles through the application of this tracking protocol. When cement is brought into contact with water, a layer which differs in density from the bulk of the cement grains becomes observable on the grain surfaces during the induction period (during which time the heat evolution from the paste is relatively low). As hydration continues, reaction products grow both from particle surfaces into the initially fluid-filled region, and also into the space originally occupied by the cement particles, forming a density gradient within the microstructure. As the reaction accelerates and larger volumes of solid phases precipitate, the newly-formed solid structure percolates via interconnection of agglomerated low-density outer hydrates, which then densify as hydration continues. This eventually leads to solidification of the structure into a hardened porous matrix. Graphical abstract

36 MATERIALS SCIENCE↗
NASA NTRS1991

Water on Mars: Volatile history and resource availability

The existence of water on Mars is undisputed today. Measurements of atmospheric water vapor have shown that the abundance varies with location and season in a systematic way which depends on processes of exchange with the polar caps, regolith, and atmosphere. Channels, which give the appearance of having been carved by water or of having had water involved in their formation, appear in various locations on the surface; some were formed by catastrophic outflow of water from beneath the surface, while others form valley networks which give the appearance of having formed over long periods of time primarily early in the planet's history. The north polar residual cap consists of water ice, possibly containing an amount of water equivalent to a global layer several tens of meters thick. Finally, water is observed within the regolith, as adsorbed water or as water of hydration.

Jakosky, Bruce M.↗
NASA NTRS1990

Automated thin-film analyses of hydrated interplanetary dust particles in the analytical electron microscope

A 200 keV electron microscope was used to obtain elemental analyses from over 4000 points on thin sections of eight 'layer silicate' class interplanetary dust particles (IDPs). Major and minor element abundances from a volume approaching that of a cylinder 50 nm in diameter were observed. Mineral phases and their relative abundances in the thin sections were identified and petrographic characteristics were determined. Three of the particles contained smectite (1.0-1.2 nm basal spacing) and two contained serpentine (0.7 nm basal spacing). The point count analyses and Mg-Si-Fe ternary diagrams show that one of the serpentine-containing IDPs is similar to CI and CM chondritic meteorites. The IDPs exhibit evidence of aqueous processing, but they have typically experienced only short range, submicrometer scale alteration. The IDPs may provide a broad sampling of the asteroid belt.

Germani, M. S.↗
DOE OSTI2024

Development of Low-Cost, High-Performance, Easy-To-Apply, Non-Flammable, Inorganic Phase Change Material (PCM) Technology (Project Final Report)

This report describes a 45-months long research program focused on the development of novel, easy-to-apply, non-flammable, and high-performance inorganic phase change materials (PCMs) for building and industrial applications. The University of Massachusetts Lowell (UML) formed a world-class team consisting of researchers form InsolCorp (only N. American manufacturer of inorganic PCM systems for building applications), and a group of industrial advisors, to develop a universal/multipurpose, simple-to-manufacture and cost-effective PCM technology. The project team expects that the results of this work will spur in the future the adoption of thermal storage materials – a key building energy saving technology as identified by DOE BTO – for a variety of building envelope applications. The main goal of this project was to demonstrate a suite of low-cost, multipurpose, and durable inorganic PCM formulations with phase transition temperatures encompassing typical building applications (between +5 o C and +55 o C). The first objective was to design, fabricate, and experimentally validate a performance of inexpensive, durable, highly efficient, non-flammable, and easy to manufacture PCMs. To allow a variety of building applications, the project team focused on formulations that exhibit repeatable phase transitions between +5 o C and +55 o C. To follow the DOE BTO cost efficiency target without compromising thermal performance, our work was based on inorganic compounds (mostly salt hydrates) and their blends, which represent a fraction of the cost of most of organic PCMs with about twice as high density as well as significantly higher thermal conductivity and phase change enthalpy. The second objective was to develop easy-to-manufacture and -install packaging/encapsulation designs that are 1) a superior barrier to current state-of-the-art macro-packaging, which significantly reduces the risk of loss of hydration water and PCM leak, and 2) optimal in enhancing the heat exchange rates with the surroundings and within the PCM core to ensure complete charging/discharging of the entire PCM within the product. Finally, the project’s intend was to scale-up the fabrication process to demonstrate installation on system-scale applications, and to validate the performance under field conditions. This work aimed at developing low-cost, high-energy storage, and reliable latent heat storage technology for building applications. This development was realized by formulating and integrating the following two technology components: 1) inorganic salt hydrate based PCMs that have high latent enthalpies and are low-cost and durable, and 2) PCM encapsulation (packaging) technology that maximizes PCM concentration and enhances heat transport characteristics in the product and with the external environment/materials. High thermal storage capacity, low cost and fire resistance are key to the building market entry for PCM technology. Therefore, the project’s focus was on salt-hydrate-based formulations which satisfy all these criteria. Packaging and/or encapsulation of PCM is a key processing step. The project team recognized that a low-cost and simple-to-manufacture salt hydrate-based PCM technology holds the best chance to be successful in the building construction market, a market which is traditionally extremely sensitive to cost and where commodity thermal insulations are the benchmark for envelope-related energy saving measures. That is why, in this project, the main intention was to minimize the production cost and maximize the product energy storage density without sacrificing the PCM performance. It was achieved through: 1. Minimizing the non-PCM components (plastics, additives, packaging/encapsulation materials, etc.) because they are significantly more expensive than salt hydrates, 2. Using highly thermally conductive and lightweight PCM carrier (packaging material) to facilitate more complete phase cycling, and 3. Optimizing the thickness and minimizing air spaces in product design (such as in pouched PCM). For this purpose, our approach was to enable an easy system design, including selection of the PCM operating temperatures, optimizing the necessary heat storage capacity (by stacking together several layers of PCM products), and if needed, a synchronized usage of PCM products of different temperatures. A specially designed, robust, highly thermally conducting and highly impermeable packaging (to retain salt hydrate water during phase transition cycles) was designed and tested to increase the overall system thermal performance and durability. All PCM products developed during this project were tested in both lab scale and in full scale field conditions. It is expected that, after further developments and commercialization, the developed PCM technologies may be also applied in space conditioning, energy storage technologies, and heat transfer applications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Does Confinement Mediate Cerium Exchange and Its Impact on Ionomer Properties?

Thin-film ionomers, pivotal in the function of fuel-cell catalyst layers (CLs), are undercharacterized compared to their bulk membrane counterparts, especially with respect to cation effects. Cerium cations, used as an additive in fuel-cell membranes, tend to migrate from the membrane into the CL ionomer during operation. Further, this study investigates whether cerium doping of perfluorinated sulfonic acid ionomer changes under confinement (to a nanometer thin film) and affects the hydration behavior. Confinement has a negligible effect on the ionomer’s cerium partitioning, yet it reduces the ionomer water uptake. Thus, cerium replaces protons similarly in a membrane or CL ionomer; however, its presence affects the thermodynamics of hydration differently.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Hydrated doped-BaZrO 3 proton conductors studied by positron annihilation lifetime spectroscopy

The study of defect chemistry for doped BaZrO 3 proton conductors is of particular interest because of defect interactions that can affect the proton conductivity of the material. Protons incorporated due to the material's hydration can be trapped by negatively charged immobile dopants, reducing proton mobility. The reduction of the proton conduction impedes using BaZrO 3 materials in energy conversion applications at intermediate temperatures (300°C – 600°C). The probing of proton trapping in doped BaZrO 3 is hindered by the limited availability of techniques sensitive to defect chemistries. In this work, we used positron annihilation lifetime spectroscopy (PALS) to study the defect chemistry of Y-doped and Sc-doped BaZrO 3 . Using a two-state positron trapping model we showed that PALS can be used to study the defect chemistry of hydrated dense proton conductors. Positron trapping rates and lifetimes were correlated with doping levels of the materials. Probability significance t-tests were carried out for PALS parameters to verify whether there are differences/similarities for various populations: non-doped/doped, level and type of doping, high temperature, and surface effects. Further, the results revealed that the initial doping generates a significant number of traps available for positrons. Doping in yttrium increased the positron trapping rate, while this effect was not observed with scandium. Low-temperature hydration affects specimens significantly inhibiting positron trapping at undoped BaZrO 3 material and highly doped specimens. Positronium formation in rough surface layers, and highly doped specimens was detected but does not exceed 1%.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Surface Hydration and Hydroxyl Configurations of Gibbsite and Boehmite Nanoplates

Discontinuation of the bulk structure at the interface between metal oxide particles and water leads to altered bonding characteristics and unique facet-dependent molecular environments. Surface hydration and consequent hydroxylation adds further complexity to the interface, details that for metal (oxy)hydroxides are especially difficult to isolate from the background signal of bulk structural hydroxyls. Here we probe for the first time the hydroxylation and hydration structures on basal surfaces of gibbsite (?-Al(OH)3) and boehmite (?-AlOOH) nanoplates at ambient conditions, using the interface-sensitive technique vibrational sum frequency generation spectroscopy (VSFG). Hydroxyl stretching modes at the interfaces with adsorbed water layers compared directly to Raman and infrared bulk modes show that while gibbsite surface frequencies were sharp and nearly identical to those in the bulk, boehmite surface hydroxyls displayed a very different broad spectrum of states. Ab initio molecular dynamics simulations of both basal surfaces with and without hydration waters reveal that gibbsite surface hydroxyls interact only weakly with overlying hydration waters remaining essentially unperturbed, whereasthose on boehmite can interact more strongly facilitated by higher configurational degrees of freedom at the interface. The findings clearly unveil substantial differences in the hydrated interfacial dynamics of these two otherwise similar materials, with implications for their interfacial chemistry and wettability.

Sassi, Michel JPC↗
DOE OSTI2020

Thin Cation-Exchange Layers Enable High-Current-Density Bipolar Membrane Electrolyzers via Improved Water Transport

With suitable water dissociation (WD) catalysts, bipolar membranes (BPMs) can efficiently dissociate water into H + and OH – at the junction between anion- and cation-exchange layers (AEL and CEL, respectively). First, however, water must be transported through the AEL or CEL and thus against the outward flow of hydrated H + and OH – . This is a challenge intrinsic to the BPM architecture and limits operation to current densities typically less than ~0.5 A·cm –2 . Here we explore how water transport affects durability and performance in reference alkaline and acidic membrane electrolyzers, and we use the insight gained to design BPMs with improved water transport. We demonstrate a thin-CEL BPM (2-μm Nafion CEL|~200 nm TiO 2 |~200 nm NiO + ionomer|50 μm Sustainion AEL) which maintains a pH difference of ~14 units between the anode and cathode for current densities of up to 3.4 A·cm –2 with a total water electrolysis voltage of ~4 V and an estimated WD overpotential of ~1.5 V. Finally, such high-current-density operation is crucial for key emerging BPM applications, including in water and carbon-dioxide electrolyzers and in (regenerative) fuel cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

The Origin of Chondrites: Metal-Silicate Separation Experiments Under Microgravity Conditions, Experiment 2

Chondrites are categorized into different groups by several properties, including the metal-to-silicate ratio. Various processes have been suggested to produce distinct metal/silicate ratios, some based on sorting in the early solar nebular and others occurring after accretion on the parent body. Huang et al. suggested that a weak gravitational field accompanied by degassing, could result in metal/silicate separation on parent bodies. We suggest that asteroids were volatile-rich, at least early in their histories. Spectroscopic evidence from asteroid surfaces indicates that one-third of all asteroids maybe rich in clays and hydrated minerals, similar to carbonaceous chondrites. Internal and/or external heating could have caused volatiles to evaporate and pass through a surface dust layer. Spacecraft images of asteroids show they have a thick regoliths. Housen, and Asphaug and Nolan proposed that even a 10 km diameter asteroid could potentially have a significant regolith. Grain size and grain density sorting could occur in the unconsolidated layer by the process known as fluidization. This process occurs when an upward stream of gas is passed through a bed of particles which are lifted against a gravitational force. Fluidization is commonly used commercially to sort particulates. This type of behavior is based upon the bed, as a whole, and differs from aerodynamic sorting. Two sets of reduced gravity experiments were conducted during parabolic flights aboard NASA's KC-135 aircraft. The first experiment employed 310 tubes of 2.5 cm diameter, containing mixtures of sand and metal grains. A gas source was used to fluidize the mixture at reduced gravity conditions and mixtures were analyzed after the flight. However, this experiment did not allow a description of the fluidization as a function of gravity. A second experiment was conducted on the KC-135 aircraft in the summer of 2001, consisting of two Plexiglas cylinders containing a metal/silicate mixture, and video cameras to record the experiment on tape. Here we summarize this experiment and discusses the implications for metalsilicate separation on asteroid bodies.

Moore, S. R.↗
DOE OSTI2021

Ion correlations drive charge overscreening and heterogeneous nucleation at solid–aqueous electrolyte interfaces

Significance Ion distributions at charged solid–water interfaces, referred to as the electrical double layer (EDL), are poorly understood at high ion concentrations, in part due to the lack of molecular-scale descriptions of the interactions between adsorbed hydrated ions. Here, direct visualization of the salinity-dependent evolution of EDL structure reveals molecular origins of nonclassical transformation of the EDL, in which charge overscreening and heterogeneous nucleation are driven by ion–ion correlations at the interfaces. This manifestation of the atomistic basis of nonclassical behaviors provides a much-needed understanding of the impact of ion cooperativity at charged interfaces for the development of predictive models for element transport in natural environments and advanced technologies for material growth and synthesis in saline environments.

36 MATERIALS SCIENCE↗