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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

On the Discovery of CO Nighttime Emissions on Titan by Cassini/VIMS: Derived Stratospheric Abundances and Geological Implications

We present a quantitative analysis of CO thermal emissions discovered on the nightside of Titan by Baines et al. [2005. The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/VIMS. Earth, Moon, and Planets, 96, 119-147] in Cassini/VIMS spectral imagery. We identify these emission features as the P and R branches of the 1-0 vibrational band of carbon monoxide (CO) near 4.65 microns. For CH3D, the prominent Q branch of the nu(2) fundamental band of CH3D near 4.55 microns is apparent. CO2 emissions from the strong nu(3) vibrational band are virtually absent, indicating a CO2 abundance several orders of magnitude less than CO, in agreement with previous investigations. Analysis of CO emission spectra obtained over a variety of altitudes on Titan's nightside limb indicates that the stratospheric abundance of CO is 32 +/- 15 ppm, and together with other recent determinations, suggests a vertical distribution of CO nearly constant at this value from the surface throughout the troposphere to at least the stratopause near 300 km altitude. The corresponding total atmospheric content of CO in Titan is similar to 2.9 +/- 1.5 x 10(exp 14) kg. Given the long lifetime of CO in the oxygen-poor Titan atmosphere (similar to 0.5-1.0 Gyr), we find a mean CO atmospheric production rate of 6 +/- 3 x 10(exp 5) kg yr(exp -1). Given the lack of primordial heavy noble gases observed by Huygens [Niemann et al., 2005. The abundances of constituents of Titan's atmosphere from the GCMS on the Huygens probe. Nature, 438, 779-784], the primary source of atmospheric CO is likely surface emissions. The implied CO/CH4 mixing ratio of near-surface material is 1.8 +/- 0.9 x 10(exp -4), based on an average methane surface emission rate over the past 0.5 Gyr of 1.3 x 10(exp -13) gm cm(exp -2) s(exp -1) as required to balance hydrocarbon haze production via methane photolysis [Wilson and Atreya, 2004. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. J. Geophys. Res. 109, E06002 Doi: 10.1029/2003JE002181]. This low CO/CH4 ratio is much lower than expected for the sub-nebular formation region of Titan and supports the hypothesis [e.g., Atreya et al., 2005. Methane on Titan: photochemical-meteorological-hydrogeochemical cycle. Bull. Am. Astron. Soc. 37, 735] that the conversion of primordial CO and other carbon-bearing materials into CH4-enriched clathrate-hydrates occurs within the deep interior of Titan via the release of hydrogen through the serpentinization process followed by Fischer-Tropsch catalysis. The time-averaged predicted emission rate of methane-rich surface materials is approximately 0.02 km(exp 3) yr (exp -1), a value significantly lower than the rate of silicate lava production for the Earth and Venus, but nonetheless indicative of significant geological processes reshaping the surface of Titan.

carbon compounds↗
NASA NTRS2009

One-Hundred-km-Scale Basins on Enceladus: Evidence for an Active Ice Shell

Stereo-derived topographic mapping of 50% of Enceladus reveals at least 6 large-scale, ovoid depressions (basins) 90-175 km across and 800-to-1500 m deep and uncorrelated with geologic boundaries. Their shape and scale are inconsistent with impact, geoid deflection, or with dynamically supported topography. Isostatic thinning of Enceladus ice shell associated with upwellings (and tidally-driven ice melting) can plausibly account for the basins. Thinning implies upwarping of the base of the shell of 10-20 km beneath the depressions, depending on total shell thickness; loss of near-surface porosity due to enhanced heat flow may also contribute to basin lows. Alternatively, the basins may overly cold, inactive, and hence denser ice, but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice. In contrast to the basins, the south polar depression (SPD) is larger (~350 wide) and shallower (~0.4-to-0.8 km deep) and correlates with the area of tectonic deformation and active resurfacing. The SPD also differs in that the floor is relatively flat (i.e., conforms roughly to the global triaxial shape, or geoid) with broad, gently sloping flanks. The relative flatness across the SPD suggests that it is in or near isostatic equilibrium, and underlain by denser material, supporting the polar sea hypothesis of Collins and Goodman. Near flatness is also predicted by a crustal spreading origin for the "tiger stripes (McKinnon and Barr 2007, Barr 2008); the extraordinary, high CIRS heat flows imply half-spreading rates in excess of 10 cm/yr, a very young surface age (~250,000 yr), and a rather thin lithosphere (hence modest thermal topography). Topographic rises in places along the outer margin of the SPD correlate with parallel ridges and deformation along the edge of the resurfaced terrain, consistent with a compressional, imbricate thrust origin for these ridges, driven by the spreading.

Schenk, Paul M.↗
NASA NTRS2009

Liquid Water on Enceladus from Observations of Ammonia and Ar-40 in the Plume

Jets of water ice from surface fractures near the south pole of Saturn's icy moon Enceladus produce a plume of gas and particles. The source of the jets may be a liquid water region under the ice shell-as suggested most recently by the discovery of salts in E-ring particles derived from the plume-or warm ice that is heated, causing dissociation of clathrate hydrates. Here we report that ammonia is present in the plume, along with various organic compounds, deuterium and, very probably, Ar-40. The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180 K have been measured near the fractures from which the jets emanate. We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice. As part of a general comprehensive review of the midsize saturnian satellites at the conclusion of the prime Cassini mission, PI McKinnon and co-I Barr contributed to three review chapters.

Waite, J. H., Jr.↗
NASA NTRS2004

NASA Tech Briefs, February 2004

Topics include: Simulation Testing of Embedded Flight Software; Improved Indentation Test for Measuring Nonlinear Elasticity; Ultraviolet-Absorption Spectroscopic Biofilm Monitor; Electronic Tongue for Quantitation of Contaminants in Water; Radar for Measuring Soil Moisture Under Vegetation; Modular Wireless Data-Acquisition and Control System; Microwave System for Detecting Ice on Aircraft; Routing Algorithm Exploits Spatial Relations; Two-Finger EKG Method of Detecting Evasive Responses; Updated System-Availability and Resource-Allocation Program; Routines for Computing Pressure Drops in Venturis; Software for Fault-Tolerant Matrix Multiplication; Reproducible Growth of High-Quality Cubic-SiC Layers; Nonlinear Thermoelastic Model for SMAs and SMA Hybrid Composites; Liquid-Crystal Thermosets, a New Generation of High-Performance Liquid-Crystal Polymers; Formulations for Stronger Solid Oxide Fuel-Cell Electrolytes; Simulation of Hazards and Poses for a Rocker-Bogie Rover; Autonomous Formation Flight; Expandable Purge Chambers Would Protect Cryogenic Fittings; Wavy-Planform Helicopter Blades Make Less Noise; Miniature Robotic Spacecraft for Inspecting Other Spacecraft; Miniature Ring-Shaped Peristaltic Pump; Compact Plasma Accelerator; Improved Electrohydraulic Linear Actuators; A Software Architecture for Semiautonomous Robot Control; Fabrication of Channels for Nanobiotechnological Devices; Improved Thin, Flexible Heat Pipes; Miniature Radioisotope Thermoelectric Power Cubes; Permanent Sequestration of Emitted Gases in the Form of Clathrate Hydrates; Electrochemical, H2O2-Boosted Catalytic Oxidation System; Electrokinetic In Situ Treatment of Metal-Contaminated Soil; Pumping Liquid Oxygen by Use of Pulsed Magnetic Fields; Magnetocaloric Pumping of Liquid Oxygen; Tailoring Ion-Thruster Grid Apertures for Greater Efficiency; and Lidar for Guidance of a Spacecraft or Exploratory Robot.

Source record↗
NASA NTRS2003

NASA Tech Briefs, December 2003

Topics covered include: Organic/Inorganic Hybrid Polymer/Clay Nanocomposites; Less-Toxic Coatings for Inhibiting Corrosion of Aluminum; Liquid Coatings for Reducing Corrosion of Steel in Concrete; Processable Polyimides Containing APB and Reactive End Caps; Rod/Coil Block Copolyimides for Ion-Conducting Membranes; Techniques for Characterizing Microwave Printed Antennas; Cylindrical Antenna With Partly Adaptive Phased-Array Feed; Command Interface ASIC - Analog Interface ASIC Chip Set; Predicting Accumulations of Ice on Aerodynamic Surfaces; Analyzing Aeroelasticity in Turbomachines; Software for Allocating Resources in the Deep Space Network; Expert Seeker; High-Speed Recording of Test Data on Hard Disks; Functionally Graded Nanophase Beryllium/Carbon Composites; Thin Thermal-Insulation Blankets for Very High Temperatures; Aerostructures Test Wing; Flight-Test Evaluation of Flutter-Prediction Methods; Piezoelectrically Actuated Microvalve for Liquid Effluents; Larger-Stroke Piezoelectrically Actuated Microvalve; Innovative, High-Pressure, Cryogenic Control Valve: Short Face-to-Face, Reduced Cost; Safer Roadside Crash Walls Would Limit Deceleration; Improved Interactive Medical-Imaging System; Scanning Microscopes Using X Rays and Microchannels; Slotting Fins of Heat Exchangers to Provide Thermal Breaks; Methane Clathrate Hydrate Prospecting; Automated Monitoring with a BSP Fault-Detection Test; Automated Monitoring with a BCP Fault-Decision Test; Vector-Ordering Filter Procedure for Data Reduction; Remote Sensing and Information Technology for Large Farms; Developments at the Advanced Design Technologies Testbed; Spore-Forming Bacteria that Resist Sterilization; and Acoustical Applications of the HHT Method.

Source record↗
NASA NTRS2012

Impact-Induced Climate Change on Titan

Titan's thick atmosphere and volatile surface cause it to respond to big impacts like the one that produced the prominent Menrva impact basin in a somewhat Earth-like manner. Menrva was big enough to raise the surface temperature by 100 K. If methane in the regolith is generally as abundant as it was at the Huygens landing site, Menrva would have been big enough to double the amount of methane in the atmosphere. The extra methane would have drizzled out of the atmosphere over hundreds of years. Conditions may have been favorable for clathrating volatiles such as ethane. Impacts can also create local crater lakes set in warm ice but these quickly sink below the warm ice; whether the cryptic waters quickly freeze by mixing with the ice crust or whether they long endure under the ice remains a open question. Bigger impacts can create shallow liquid water oceans at the surface. If Titan's crust is made of water ice, the putative Hotei impact (a possible 800-1200 km diameter basin, Soderblom et al 2009) would have raised the average surface temperature to 350-400 K. Water rain would have fallen and global meltwaters would have averaged 50 m to as much as 500 m deep. The meltwaters may not have lasted more than a few decades or centuries at most, but are interesting to consider given Titan's organic wealth.

Zahnle, Kevin↗
NASA NTRS2013

Transient Climate Effects of Large Impacts on Titan

Titan's thick atmosphere and volatile-rich surface cause it to respond to big impacts in a somewhat Earth-like manner. Here we construct a simple globally-averaged model that tracks the flow of energy through the environment in the weeks, years, and millenia after a big comet strikes Titan. The model Titan is endowed with 1.4 bars of N2 and 0.07 bars of CH4, methane lakes, a water ice crust, and enough methane underground to saturate the regolith to the surface. We find that a nominal Menrva impact is big enough to raise the surface temperature by approx. 80 K and to double the amount of methane in the atmosphere. The extra methane drizzles out of the atmosphere over hundreds of years. An upper-limit Menrva is just big enough to raise the surface to water's melting point. The putative Hotei impact (a possible 800-1200 km diameter basin, Soderblom et al., 2009) is big enough to raise the surface temperature to 350-400 K. Water rain must fall and global meltwaters might range between 50 m to more than a kilometer deep, depending on the details. Global meltwater oceans do not last more than a few decades or centuries at most, but are interesting to consider given Titan's organic wealth. Significant near-surface clathrate formation is possible as Titan cools but faces major kinetic barriers.

Titan↗
NASA NTRS2014

Big Impacts and Transient Oceans on Titan

We have studied the thermal consequences of very big impacts on Titan [1]. Titan's thick atmosphere and volatile-rich surface cause it to respond to big impacts in a somewhat Earth-like manner. Here we construct a simple globally-averaged model that tracks the flow of energy through the environment in the weeks, years, and millenia after a big comet strikes Titan. The model Titan is endowed with 1.4 bars of N2 and 0.07 bars of CH4, methane lakes, a water ice crust, and enough methane underground to saturate the regolith to the surface. We assume that half of the impact energy is immediately available to the atmosphere and surface while the other half is buried at the site of the crater and is unavailable on time scales of interest. The atmosphere and surface are treated as isothermal. We make the simplifying assumptions that the crust is everywhere as methane saturated as it was at the Huygens landing site, that the concentration of methane in the regolith is the same as it is at the surface, and that the crust is made of water ice. Heat flow into and out of the crust is approximated by step-functions. If the impact is great enough, ice melts. The meltwater oceans cool to the atmosphere conductively through an ice lid while at the base melting their way into the interior, driven down in part through Rayleigh-Taylor instabilities between the dense water and the warm ice. Topography, CO2, and hydrocarbons other than methane are ignored. Methane and ethane clathrate hydrates are discussed quantitatively but not fully incorporated into the model.

methane↗
NASA NTRS2016

Martian Methane From a Cometary Source: A Hypothesis

In recent years, methane in the martian atmosphere has been detected by Earth-based spectroscopy, the Planetary Fourier Spectrometer on the ESA Mars Express mission, and the NASA Mars Science Laboratory. The methane's origin remains a mystery, with proposed sources including volcanism, exogenous sources like impacts and interplanetary dust, aqueous alteration of olivine in the presence of carbonaceous material, release from ancient deposits of methane clathrates, and/or biological activity. An additional potential source exists: meteor showers from the emission of large comet dust particles could generate martian methane via UV pyrolysis of carbon-rich infall material. We find a correlation between the dates of Mars/cometary orbit encounters and detections of methane on Mars. We hypothesize that cometary debris falls onto Mars during these interactions, generating methane via UV photolysis.

Fries, M.↗
NASA NTRS2016

Martian Atmospheric Methane Plumes from Meteor Shower Infall: A Hypothesis

Methane plumes in the martian atmosphere have been detected using Earth-based spectroscopy, the Planetary Fourier Spectrometer on the ESA Mars Express mission, and the NASA Mars Science Laboratory. The methane's origin remains a mystery, with proposed sources including volcanism, exogenous sources like impacts and interplanetary dust, aqueous alteration of olivine in the presence of carbonaceous material, release from ancient deposits of methane clathrates, and/or biological activity. To date, none of these phenomena have been found to reliably correlate with the detection of methane plumes. An additional source exists, however: meteor showers could generate martian methane via UV pyrolysis of carbon-rich infall material. We find a correlation between the dates of Mars/cometary orbit encounters and detections of methane on Mars. We hypothesize that cometary debris falls onto Mars during these interactions, depositing freshly disaggregated meteor shower material in a regional concentration. The material generates methane via UV photolysis, resulting in a localized "plume" of short-lived methane.

Fries, M.↗
NASA NTRS2019

New Estimates of Ice and Oxygen Fluxes Across the Entire Lid of Lake Vostok From Observations of Englacial Radio Wave Attenuation

Over deep Antarctic subglacial lakes, spatially varying ice thickness and the pressure‐dependent melting point of ice result in distinct areas of melting and freeze‐on at the ice‐water interface, that is, at the lake lid. These ice mass fluxes drive lake circulation and, because basal Antarctic ice contains air clathrate, affect the input of oxygen to the lake, with implications for subglacial life. Inferences of rates of melting and freeze‐on, that is, accretion rates, from radar layer tracking and geodesy are limited in spatial coverage and resolution. Here we develop a new method to estimate accretion rate, and the resulting oxygen input at a lake lid, using airborne radar data over Lake Vostok together with ice‐temperature and chemistry data from the Vostok ice core. Because the lake lid is a coherent reflector of known reflectivity (at our radar frequency), we can infer depth‐averaged radio wave attenuation in the ice, with a spatial resolution of ~1 km along flight lines. Spatial variation in attenuation depends mostly on variation in ice temperature near the lid, which in turn varies strongly with ice mass flux at the lid. We model ice temperature versus depth with ice mass flux as a parameter, thus linking that flux to observed depth‐averaged attenuation. The resulting map of melt and accretion rates independently reproduces features known from earlier studies but now covers the entire lid. We find that freeze‐on is dominant when integrated over the lid, with an ice imbalance of 0.05 to 0.07 cu.km/year, which is robust against uncertainties.

Dale P. Winebrenner↗
NASA NTRS2022

Defining and Characterizing Habitable Environments in Ocean World Systems

We explore the major characteristics of habitable environments on ocean worlds and how we can study them using Earth analogs and autonomous instru-mentation. Earth analogs for habitable regions on ocean worlds include interfaces (e.g., ice-water and seafloor-water boundaries), hydrothermal systems, and inside of ice, snow, clathrates, and crustal rocks. These analogs are best known in Earth’s ocean, but they may also exist on Earth’s land, particularly in polar regions. Importantly, ocean habitability requires that parts of the planetary body interact dynamically with the ocean. Probing the habitability of currently inaccessible extraterrestrial ocean worlds will require establishing biogenicity and abiotic reference frames for organic com-pounds on ocean worlds and technological advances to explore subsurface liquid water environments beyond Earth. Next generation studies of ocean world habitability will also require integrated modeling tools and coordination between the Earth/ocean sci-ences and the planetary science communities.

Jennifer B Glass↗
NASA NTRS2021

Cold Traps of Hypervolatiles in the Protosolar Nebula at the Origin of the Peculiar Composition of Comet C/2016 R2 (PanSTARRS)

Recent observations of the long-period comet C/2016 R2 (PanSTARRS; hereafter R2) indicate an unusually high N2/CO abundance ratio, typically larger than ∼0.05, and at least 2–3 times higher than the one measured in 67P/Churyumov–Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H2O (H2O/CO ∼ 0.32%), compared to other comets. Here we investigate the formation circumstances of a generic comet whose composition reproduces these two key features. We first envisage the possibility that this comet agglomerated from clathrates, but we find that such a scenario does not explain the observed low water abundance. We then alternatively investigate the possibility that the building blocks of R2 agglomerated from grains and pebbles made of pure condensates via the use of a disk model describing the radial transport of volatiles. We show that N2/CO ratios reproducing the value estimated in this comet can be found in grains condensed in the vicinity of the CO and N2 ice lines. Moreover, high CO/H2O ratios (>100 times the initial gas-phase value) can be found in grains condensed in the vicinity of the CO ice line. If the building blocks of a comet assembled from such grains, they should present N2/CO and CO/H2O ratios consistent with the measurements made in R2's coma. Our scenario indicates that R2 formed in a colder environment than the other comets that share more usual compositions. Our model also explains the unusual composition of the interstellar comet 2l/Borisov.

Olivier Mousis↗
NASA NTRS2026

Tracing the Source of Carbon Oxides on the Large Moons of Uranus

The Uranian moons Ariel, Umbriel, Titania, and Oberon are enriched in CO 2 mixed with CO, but the origin(s) of these carbon oxides, be they primarily native or radiolytic, remain(s) uncertain. Using data collected by NIRSpec on the James Webb Space Telescope (JWST), we measured the spectral signature of CO 2 and other carbon oxides to help disentangle these hypotheses. Through comparison to laboratory data, we find that many of the detected spectral features are consistent with CO 2 ice, including 12 CO2 scattering peaks (4.15–4.26 μm), multilobe 13 CO 2 bands (4.35–4.43 μm), and CO 2 biphonon and triphonon modes (4.80–5.25 μm). Our measurements show that CO 2 and CO are concentrated on the trailing hemispheres of the inner moons Ariel and Umbriel, potentially supporting a radiolytic production hypothesis, consistent with prior ground-based results. However, many of the identified spectral features are only observed in thick crystalline ice deposits measured in the laboratory, which may be difficult to form via radiolysis of carbon-bearing material mixed in icy regoliths. Similarly, the data exhibit weak 4.02 and 4.40 μm bands, hinting at the presence of carbonate minerals and 13 CO 2 clathrates, respectively, possibly formed in the interiors of these moons. Furthermore, JWST has revealed that CO 2 is widespread at Uranus, present in its system of rings, ring moons, and irregular satellites, consistent with its largest moons accreting CO 2 and other carbon oxides from the Uranian subnebula. We conclude that exposed carbon oxides are potentially native, with their surface distributions shaped by charged particle irradiation and seasonal sublimation–condensation cycles.

Ice spectroscopy↗
DOE OSTI2021

Autogenous formation and smart behaviors of nitrite- and nitrate-intercalated layered double hydroxides (LDHs) in Portland cement-metakaolin-dolomite blends

In this work, the influence of sodium nitrite (NaNO{sub 2}) and sodium nitrate (NaNO{sub 3}) corrosion inhibitors on the composition, structure, and chloride binding behaviors of layered double hydroxides (LDHs) formed in ternary ordinary Portland cement-metakaolin-dolomite (OPC-MK-DM) systems is studied. The results show that the nitrite and nitrate anions are preferably intercalated in the CaAl LDHs (AFm phases), but not in the MgAl LDHs (hydrotalcite-type phases) due to its limited formation in these ternary cementitious systems cured at ambient temperature. The autogenously formed nitrate- and nitrite-AFm phases are decomposed upon chloride exposure accompanied by Friedel's salts formation, potentially releasing corrosion inhibitive ions to the pore solution in a progressive manner. The NaNO{sub 2} and NaNO{sub 3} incorporation in ternary OPC-MK-DM binders marginally lowers chloride binding capacity but reduces its penetration resistance mainly due to pore coarsening. Nevertheless, a strong linear correlation can be established between the water-soluble and total chloride contents in ternary OPC-MK-DM systems, regardless of OPC replacement level and corrosion inhibitor incorporation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Sequestration and release of nitrite and nitrate in alkali-activated slag: A route toward smart corrosion control

Intercalating the corrosion inhibitive ions in hydrotalcite is a promising approach to improve the long-term efficiency of inhibitors in corrosion protection of steel in reinforced concrete. In this work, the potential of autogenously generating nitrite- and nitrate-intercalated hydrotalcite in alkali-activated slag (AAS) is investigated. The results show that the added nitrite and nitrate ions are preferably uptaken in the interlayer structure of hydrotalcite in AAS, and the sequestered nitrite and nitrate are released upon chloride exposure in seawater and NaCl solution. The incorporation of nitrite and nitrate has little detrimental effects on the chloride binding capacity of AAS but slightly enhances the chloride ingress due to the pore coarsening effect. Similar to ordinary Portland cement (OPC), AAS is more permeable to the chloride in seawater than NaCl solution. However, unlike the release of bound chloride contributed by ettringite formation in seawater-exposed OPC, the enhanced chloride ingress in seawater-exposed AAS is primarily attributed to the aggravated pH reduction at the exposure front due to brucite formation. This study contributes to the design of alkali-activated binders with a smart inhibitor releasing ability for mitigating corrosion of steel in concrete.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Specific molecular design of polycarboxylate polymers exhibiting optimal compatibility with clay contaminants in concrete

Highlights: • Allyl ether-based PCEs with short side chain length and low side chain density presented superior clay resistance. • PCEs with medium side chain density exhibited best clay robustness when compared at the absolute dosed quantities. • The proportion of PCE being intercalated into the layered structure of clay was quantified. It is widely recognized that the dispersing ability of polycarboxylate superplasticizers (PCEs) could be hindered due to the presence of clay contaminants in concrete. In this study, a series of allyl ether-based polycarboxylate superplasticizers possessing short polyethylene glycol side chains was successfully synthesized and probed for their clay tolerance. The resulting PCE polymers were characterized via Size Exclusion Chromatography (SEC) to obtain their molecular properties. Thereafter, their dispersing ability was probed in the absence and presence of sodium bentonite. Allyl ether-based polycarboxylate (APEG) polymers possessing short side chains were found to exhibit enhanced clay resistance as compared to that of conventional MPEG PCEs holding long pendant chains. The mode of interaction between APEG PCEs and bentonite was investigated via sorption and XRD measurements. The data revealed that APEG PCEs possessing a lower side chain density intercalate less into the interlayer space of bentonite than those exhibiting higher side chain density.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Water content of carbon dioxide at hydrate forming conditions

There is an interest to ensure sub-saturated water content in lines containing carbon dioxide in applications such as enhanced oil recovery and carbon sequestration, to reduce risks of hydrate blockage and corrosion. The water content of carbon dioxide at various temperatures and pressures has been measured in the past, but there is no consistent set of measurements that could be used for carbon dioxide storage and transportation design work. The solubility of water in a carbon dioxide rich gas phase at hydrate forming conditions was measured in this work. Pressures ranged from 12.06 to 29.30 bar along two isotherms, 1 °C and -7 °C, all within the gaseous carbon dioxide and hydrate stability zone. For the first time in these types of measurements, the solid phase was also characterized and confirmed to be carbon dioxide hydrate via X-ray computed tomography, simultaneous with water content measurements of the gas phase. Once carbon dioxide hydrate conversion had reached a maximum value (65% estimated by X-ray computed tomography), the equilibrium water content was measured. Prior to reaching this maximum carbon dioxide hydrate conversion, the water content in carbon dioxide was observed to decrease as liquid water converted to carbon dioxide hydrate. Furthermore, this slow conversion to hydrate, metastability of the hydrate phase, or unexpected phases may be responsible for the large discrepancy between prior data sets for similar carbon dioxide water content measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗