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NASA NTRS2017

Chemical and Microstructural Changes in Metallic and Ceramic Materials Exposed to Venusian Surface Conditions

The chemical and microstructural behavior of steels (304, 310, 316, and 1018), nickel-based alloys (beta-NiAl, G30, and 625), gold, coatings (4YSZ, SilcoNert(TradeMark) 1040 (SilcoTek Co.), Dursan(TradeMark) (SilcoTek Co.), and porcelain), and bulk ceramics (alpha-Al2O3, fused quartz, beta-SiC, and alpha-Si3N4) were probed after exposure to supercritical fluid with temperature, pressure, and composition mimicking the Venus lower atmosphere. Exposures were carried out in the Glenn Extreme Environments Rig (GEER) chamber with the Venusian gas mixture (96.5% CO2, 3.5% N2, 30 ppm H2O, 150 ppm SO2, 28 ppm CO, 15 ppm OCS, 3 ppm H2S, 0.5 ppm HCl, and 5 ppb HF) at 92 bar (1330 psi) and 467 C (873 F) for durations of 10 and 42 days. An additional 21-day exposure was done to stainless steel uncoated and coated with SilcoNert(TradeMark) and Dursan(TradeMark). Samples were characterized before and after the experiment by gravimetric analysis, X-ray diffraction, X-ray photoelectron and Auger electron spectroscopies, and cross section electron microscopy analysis. All steels exposed for 10 and 42 days formed double-layered scales consisting mainly of metal (Cr, Fe, Ni) oxides and sulfides showing different chemistry, microstructure, and crystalline phases. The alloys G30 and 625 formed double-layered scales consisting mainly of nickel sulfides. After 10 days, the beta-NiAl exhibited no detectable scale, suggesting only a very thin film was formed. The 304 and 316 stainless steels coated with 4YSZ that were exposed for 10 and 42 days exhibited no significant oxidation. Steel 1018 coated with 4YSZ exhibited a corrosion scale of iron and/or chromium oxide formed at the base of the alloy. The 304 steel coated with porcelain did not exhibit corrosion, although the coating exhibited recession. SilcoNert(TradeMark) exposed for 10 and 42 days exhibited recession, although no oxidation was found to occur at the base of the alloy. Stainless steel 316 coated with Dursan(TradeMark)  exhibited corrosion at the base of the alloy. All ceramics tested showed no clear evidence of reaction. The weight-gain-per-area performance of the materials exposed in the GEER for 10 and 42 days are reported from the lowest to the highest weight gain per area as follows: gold did not exhibit any weight change; nickel-based alloys: beta- NiAl < G30 < 625; steels: 304 < 310 < 316 < 1018; ceramics: considering the experimental uncertainties, no weight change was observed for all ceramics of this work (alpha-Al2O3, Si3N4, SiC, and amorphous SiO2).

Costa, Gustavo C. C.↗
NASA NTRS2017

Interstellar and Solar Nebula Materials in Cometary Dust

Laboratory studies of cometary dust collected in the stratosphere and returned from comet 81P/Wild 2 by the Stardust spacecraft have revealed ancient interstellar grains and molecular cloud organic matter that record a range of astrophysical processes and the first steps of planetary formation. Presolar materials are rarer meteorites owing to high temperature processing in the solar nebula and hydrothermal alteration on their asteroidal parent bodies. The greater preservation of presolar materials in comets is attributed to their low accretion temperatures and limited planetary processing. Yet, comets also contain a large complement of high temperature materials from the inner Solar System. Owing to the limited and biased sampling of comets to date, the proportions of interstellar and Solar System materials within them remains highly uncertain. Interstellar materials are identified by coordinated isotopic, mineralogical, and chemical measurements at the scale of individual grains. Chondritic porous interplanetary dust particles (CP IDPs) that likely derive from comets are made up of 0.1 - 10 micron-sized silicates, Fe-Ni-sulfides, oxides, and other phases bound by organic material. As much as 1% of the silicates are interstellar grains that have exotic isotopic compositions imparted by nucleosynthetic processes in their parent stars. Crystalline silicates in CP IDPs dominantly have normal isotopic compositions and probably formed in the Solar System. 81P samples include isotopically normal refractory minerals that resemble Ca-Al rich inclusions and chondrules common in meteorites. The origins of sub-micron amorphous silicates in IDPs are not certain, but at least a few % of them are interstellar grains. The remainder have isotopic compositions consistent with Solar System origins and elemental compositions that are inconsistent with interstellar grain properties, thus favoring formation in the solar nebula [4]. The organic component in comets and primitive meteorites has large enrichments in D/H and N-15/N-14 relative to terrestrial materials. These isotopic signatures are probably due to low temperature chemical processes in cold molecular clouds or the outermost reaches of the protoplanetary disk. The greatest isotopic anomalies are found in sub-micron organic nanoglobules that show chemical signatures of interstellar chemistry. The observation that cometary dust is mostly composed of isotopically normal minerals within isotopically anomalous organic matter is difficult to reconcile with the formation models of each component. The mineral component likely formed in high temperature processes in the inner Solar System, while the organic fraction shows isotopic and chemical signatures of formation near 10 K. Studying more primitive remnants of the Solar System starting materials would help in resolving this paradox. Comets formed across a vast expanse of the outer disk under differing thermal and collisional regimes, and some are likely to be better preserved than others. Finding truly pristine aggregates of presolar materials may require return of a pristine sample of comet nucleus material.

Messenger, Scott↗
NASA NTRS2017

Jet Fuel Thermal Stability Investigations Using Ellipsometry

Jet fuels are typically used for endothermic cooling in practical engines where their thermal stability is very important. In this work the thermal stability of Sasol IPK (a synthetic jet fuel) with varying levels of naphthalene has been studied on stainless steel substrates using spectroscopic ellipsometry in the temperature range 385-400 K. Ellipsometry is an optical technique that measures the changes in a light beam’s polarization and intensity after it reflects off of a thin film to determine the film’s thickness and optical properties. All of the tubes used were rated as thermally unstable by the color standard portion of the Jet Fuel Thermal Oxidation Test, and this was confirmed by the deposit thicknesses observed using ellipsometry. A new amorphous model on a stainless steel substrate was used to model the data and obtain the results. It was observed that, as would be expected, increasing the temperature of the tube increased the overall deposit amount for a constant concentration of naphthalene. The repeatability of these measurements was assessed using multiple trials of the same fuel at 385 K. Lastly, the effect of increasing the naphthalene concentration in the fuel at a constant temperature was found to increase the deposit thickness.In conclusion, ellipsometry was used to investigate the thermal stability of jet fuels on stainless steel substrate. The effects of increasing temperature and addition of naphthalene on stainless steel tubes with Sasol IPK fuel were investigated. It was found, as expected, that increasing temperature lead to an increase in deposit thickness. It wasAmerican Institute of Aeronautics and Astronautics6also found that increasing amounts of naphthalene increased the maximum deposit thickness. The repeatability of these measurements was investigated using multiple tests at the same conditions. The present work provides as a better quantitative tool compared to the widely used JFTOT technique. Future work will expand on the fuel types, temperature, and substrate materials.

thermal stability↗
NASA NTRS2017

Investigating Weathering of Basaltic Materials in Gale Crater, Mars: A Combined Laboratory, Modeling and Terrestrial Field Approach

Recent observations from Gale Crater, Mars document past aqueous alteration both in the formation of the Stimson sandstone unit, as well as in the formation of altered fractures within that unit. Geochemical and mineralogical data from Curiosity also suggest Fe-rich amorphous weathering products are present in most samples measured to date. Here we interpret conditions of possible past weathering in Gale Crater using a combination of field, laboratory, and modeling work. In order to better understand secondary Fe-rich phases on Mars, we are examining formation of weathering products in high Fe and Mg and low Al serpentine soils in the Klamath Mountains, CA. We have isolated potential weathering products from these soils, and are analyzing them using synchrotron μXRF and μXRD as well as FullPat for a direct comparison to analyses from Gale Crater. In order to interpret the implications of the persistence of potential secondary Fe-containing phases on Mars, we are also measuring the dissolution rates of the secondary weathering products allophane, Fe-rich allophane, and hisingerite. Ongoing dissolution experiments of these materials suggest that they dissolve significantly more rapidly than more crystalline secondary minerals with similar chemical compositions. Finally, to quantify the specific conditions of past aqueous alteration in Gale Crater we are performing reactive transport modeling of a range of possible past environmental conditions. Specifically, we are testing the conditions under which a Stimson unit-like material forms from a parent material similar to Rocknest or Bagnold eolian deposits, and the conditions under which observed altered fracture zones form from a Stimson unit-like parent material. Our modeling results indicate that the formation of the Stimson unit is consistent with leaching of an eolian deposit with a solution of pH = 6-8, and that formation of the altered fracture zones is consistent with leaching with a very acidic (pH = 2-3) high sulfate solution containing Ca. These results suggest circumneutral pH conditions during authigenesis or early diagenesis in the Stimson formation sediments followed by diagenetic alteration by very acidic solutions along fracture zones.

Hausrath, Elisabeth↗
NASA NTRS2018

The Diversity of Carbon in Cometary Refractory Dust Particles

When comparing the dark icy surfaces of outer solar system small bodies and the composition of carbonaceous chondrites derived from dark asteroids we find a significant discrepancy in the assessed amounts of elemental carbon: up to 80% amorphous carbon is used to model the dark surfaces of Kuiper Belt Objects and Centaurs whereas at most 5% of elemental carbon is found in carbonaceous chondrites. If we presume that regimes of comet nuclei formation are analogous to disk regimes where other outer solar system ice-rich bodies formed then we can turn to comet dust to gain insights into the diversity in the concentration and forms of carbon available in the outer disk. Comet dust offers important insights into the diversity in the amounts and forms of carbon that were incorporated into aggregate dust particles in the colder parts of the protoplanetary disk out of which comet nuclei accreted. Comet nuclei are amongst the most primitive bodies because they have remained cold and unequilibrated. Comet dust particles reveal the presence of forms of elemental carbon and of soluble and insoluble organic matter, and in a great diversity of concentrations from very little, e.g., Stardust samples of comet 81P/Wild 2, to 80% by volume for Ultra Carbonaceous Antarctic Micro Meteorites (UCAMMs). Cometary outbursts and/or jet activity also demonstrate variations in the concentration of carbon in the grains at different grain sizes within a single comet. We review the diversity of carbon-bearing dust grains in cometary samples, flyby measurements and deduced from remote-sensing to enrich the discussion about the diversity of carbonaceous matter available in the outer ice-rich disk at the time of comet nuclei formation.

Wooden, D. H.↗
NASA NTRS2018

A D- and N-15-Rich Micrometer-Sized Aggregate of Organic Matter in a Xenolithic Clast from the Zag Ordinary Chondrite

The nature and origin of extraterrestrial organic matter are still under debate despite the significant progress in the analyses and experimental approaches in this field over the last five decades. Xenolithic clasts are often found in a wide variety of meteorite groups, some of which contain exotic organic matter (OM). The Zag meteorite is a thermally-metamorphosed H ordinary chondrite. It contains a primitive xenolithic clast that has been proposed to have originated from Ceres, which was accreted to the Zag host asteroid after metamorphism. The cm-sized clast contains abundant large carbon-rich (mostly organic) grains or aggregates up to 20 microns. Such large OM grains are unique among astromaterials with respect to the size. Here we report organic and isotope analyses of a large (approx.10 microns) aggregate of solid OM in the Zag clast. The X-ray micro-spectroscopic technique revealed that the OM has sp2 bonded carbon with no other functional groups nor graphitic feature (1s-sigma exciton), and thus it is distinguished from most of the OM in carbonaceous meteorites. The apparent absence of functional groups in the OM suggests that it is composed of hydrocarbon networks with less heteroatoms, and therefore the OM aggregate is similar to hydrogenated amorphous carbon (HAC). The OM aggregate has high D/H and 15N/14N ratios, suggesting that it originated in a very cold environment such as the interstellar medium or outer region of the solar nebula, while the OM is embedded in carbonate-bearing matrix resulting from aqueous activities. Thus the high D/H ratio must have survived the extensive late-stage aqueous processing. It is not in the case for OM in carbonaceous chondrites of which the D/H ratio was reduced by the alteration via the D-H exchange of water. It indicates that both the OM precursors and the water had high D/H ratios, similar to the water in Enceladus. Our results support the idea that the clast originated from Ceres, or at least, a hydrovolcanically active body similar to Ceres, and further imply that Ceres originally formed in the outer Solar System and migrated to the main belt asteroid region as suggested by the "Grand tack" scenario.

Kebukawa, Yoko↗
NASA NTRS2018

Reactive Transport and Mass Balance Modeling of the Stimson Sedimentary Formation and Altered Fracture Zones Constrain Diagenetic Conditions at Gale Crater, Mars

On a planet as cold and dry as present-day Mars, evidence of multiple aqueous episodes offers an intriguing view into very different past environments. Fluvial, lacustrine, and eolian depositional environments are being investigated by the Mars Science Laboratory Curiosity in Gale crater, Mars. Geochemical and mineralogical observations of these sedimentary rocks suggest diagenetic processes affected the sediments. Here, we analyze diagenesis of the Stimson formation eolian parent material, which caused loss of olivine and formation of magnetite. Additional, later alteration in fracture zones resulted in preferential dissolution of pyroxene and precipitation of secondary amorphous silica and Ca sulfate. The ability to compare the unaltered parent material with the reacted material allows constraints to be placed on the characteristics of the altering solutions. In this work we use a combination of a mass balance approach calculating the fraction of a mobile element lost or gained, tau, with fundamental geochemical kinetics and thermodynamics in the reactive transport code CrunchFlow to examine the characteristics of multiple stages of aqueous alteration at Gale crater, Mars. Our model results indicate that early diagenesis of the Stimson sedimentary formation is consistent with leaching of an eolian deposit by a near-neutral solution, and that formation of the altered fracture zones is consistent with a very acidic, high sulfate solution containing Ca, P and Si. These results indicate a range of past aqueous conditions occurring at Gale crater, Mars, with important implications for past martian climate and environments.

Gale↗
NASA NTRS2018

Corrosion of Bare Carbon Steel as a Passive Sensor to Assess Moisture Availability for Biological Activity in Atacama Desert Soils

In this work we suggest the corrosion of polished bared metal coupons as a passive sensor to detect or identify the lower limit of water availability that could be suitable for biological activity in the Atacama Desert on soil or solid substrates. For this purpose, carbon steel coupons were deposited in selected sites along a west-east transect and removed at predetermined times for morphological inspection. The advantage of this procedure is that the attributes of the oxide layer (corrosion extent, morphology and oxide phases) can be considered as a fingerprint of the atmospheric moisture history at a given time interval. Two types of coupons were used, a long rectangular shape that are half-buried in a vertical position, and square shape that are deposited on the soil surface. The morphological attributes observed by SEM inspection is correlated to the so-called humectation time which is determined from local meteorological parameters. The main result is that the decreasing trend of atmospheric moisture along the transect is closely related to corrosion behavior and water soil penetration. For instance, while in the coastal site oxide phases formed on the coupon surface rapidly evolve to well- crystallized species, in the driest inland site Lomas Bayas only amorphous oxide is observed.

Caceres, Luis↗
NASA NTRS2018

Multiscale Modeling of PEEK Using Reactive Molecular Dynamics Modeling and Micromechanics

Polyether ether ketone (PEEK) is a high-performance, semi-crystalline thermoplastic that is used in a wide range of engineering applications, including some structural components of aircraft. The design of new PEEK-based materials requires a precise understanding of the multiscale structure and behavior of semi-crystalline PEEK. Molecular Dynamics (MD) modeling can efficiently predict bulk-level properties of single phase polymers, and micromechanics can be used to homogenize those phases based on the overall polymer microstructure. In this study, MD modeling was used to predict the mechanical properties of the amorphous and crystalline phases of PEEK. The hierarchical microstructure of PEEK, which combines the aforementioned phases, was modeled using a multiscale modeling approach facilitated by NASA's MSGMC. The bulk mechanical properties of semi-crystalline PEEK predicted using MD modeling and MSGMC agree well with vendor data, thus validating the multiscale modeling approach.

Pisani, William A.↗
NASA NTRS2017

Radiation Chemistry of Solid Acetone in the Interstellar Medium - A New Dimension to an Old Problem

A laboratory investigation of acetone, an interstellar and cometary molecule, has produced new results concerning its decomposition in a radiation environment. Mid-infrared spectroscopy has been used to follow amorphous acetone's destruction by ionizing radiation (1 MeV protons) at 20 K. Radiation products identified are the CH4, CO, and CO2 usually made in such experiments, along with ketene, allene, and the acetonyl radical, all identified here for the first time in irradiated solid acetone. Evidence for the reduction product 2-propanol was suggestive, but a firm identification could not be made either for it or for the C2 hydrocarbons (i.e., C2H6, C2H4, C2H2). The acetyl radical was not observed as a radiation product. Isotopically labeled reagents were used to demonstrate ketene formation and to emphasize that multiple approaches are needed for robust assignments of infrared spectral features of irradiated icy solids. Results from a supporting radiation experiment with isotopically labeled acetic acid are described. Comparisons are made to a previous study of acetone's stability in extraterrestrial radiation environments, and caution is urged in measuring and interpreting CO abundances in irradiated icy solids.

cometary molecule↗
NASA NTRS2016

Yield and Failure Behavior Investigated for Cross-linked Phenolic Resins Using Molecular Dynamics

Molecular dynamics simulations were conducted to fundamentally evaluate the yield and failure behavior of cross-linked phenolic resins at temperatures below the glass transition. Yield stress was investigated at various temperatures, strain rates, and degrees of cross-linking. The onset of non-linear behavior in the cross-linked phenolic structures was caused by localized irreversible molecular rearrangements through the rotation of methylene linkers followed by the formation or annihilation of neighboring hydrogen bonds. The yield stress results, with respect to temperature and strain rate, could be fit by existing models used to describe yield behavior of amorphous glasses. The degree of cross-linking only indirectly influences the maximum yield stress through its influence on the glass transition temperature (Tg), however there is a strong relationship between the degree of cross-linking and the failure mechanism. Low cross-linked samples were able to separate through void formation, whereas the highly cross-linked structures exhibited bond scission.

Stress-strain curves↗
NASA NTRS2014

Sulfur-bearing Phases Detected by Evolved Gas Analysis of the Rocknest Aeolian Deposit, Gale Crater, Mars

The Sample Analysis at Mars (SAM) instrument suite detected SO2, H2S, OCS, and CS2 from ~450 to 800degC during evolved gas analysis (EGA) of materials from the Rocknest aeolian deposit in Gale Crater, Mars. This was the first detection of evolved sulfur species from a Martian surface sample during in situ EGA. SO2 (~3-22 μmol) is consistent with the thermal decomposition of Fe sulfates or Ca sulfites, or evolution/desorption from sulfur-bearing amorphous phases. Reactions between reduced sulfur phases such as sulfides and evolved O2 or H2O in the SAM oven are another candidate SO2 source. H2S (~41-109 nmol) is consistent with interactions of H2O, H2 and/or HCl with reduced sulfur phases and/or SO2 in the SAM oven. OCS (~1-5nmol) and CS2 (~0.2-1 nmol) are likely derived from reactions between carbon-bearing compounds and reduced sulfur. Sulfates and sulfites indicate some aqueous interactions, although not necessarily at the Rocknest site; Fe sulfates imply interaction with acid solutions whereas Ca sulfites can form from acidic to near-neutral solutions. Sulfides in the Rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source. The presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering. The possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage. Understanding the sulfur mineralogy in Rocknest materials, which exhibit chemical similarities to basaltic fines analyzed elsewhere on Mars, can provide insight in to the origin and alteration history of Martian surface materials.

Gale Crater↗
NASA NTRS2018

Qualifying Bulk Metallic Glass Gear Materials for Spacecraft Applications

NASA is evaluating bulk metallic glass (BMG) gears for extreme environment (cryogenic) applications; e.g., Europa Lander. The main purpose of this report is to recommend a quality assurance (QA) protocol for the production of consistent and reliable gear castings. Currently, there are two, separate manufacturers involved; Materion Corporation produces re-melt stock and Visser Precision Cast, Inc. produces BMG castings. Division of the existing alloy specifications document into material supplier-specific documents is proposed. Until a composition-based specification is established, processability- and performance-based methodologies may be an option during manufacturing development. It is recommended that each of the documents has a distinct focus; the processing behavior of crystalline feedstock, and the mechanical behavior of amorphous castings. The report addresses the “gray area” in QA testing between these materials suppliers by outlining an equitable division of responsibilities. The use of a number of dedicated reference dies to produce witness materials for physical and mechanical property evaluation is strongly recommended. Allocation of QA tests between screen testing of gear castings, and formal testing of witness materials, including cryogenic properties, is also proposed. The most effective suite of tests for both physical and mechanical property determination are down-selected from available national and international standards. The contents of this report create a solid basis for selection of QA tests, thereby setting the stage for negotiations between the materials suppliers and the customer.This technical paper:a) provides recommendations to advance materials specifications document JPL D-56223,Rev. A from “draft” to “preliminary” status;b) proposes division of the current document into two supplier-specific documents;c) separates testing methods by “ingots/castings” and “witness materials”;d) classifies test methodology based on “processability” and “performance”;e) assembles candidate ASTM specifications for “screen testing” and “formal testing”;f) identifies standard tests compatible with evaluation of BMG flexspline gears;g) suggests division of responsibilities for processability and performance testing; andh) addresses the QA “gray area” between production of ingots and castings.The report recommends that:a) processability- and performance-based QA methods might be used in lieu ofcompositional specifications during manufacturing development only;b) reference dies be designed for “acceptance” and “qualification” castings;c) witness materials provide physical and mechanical property data;d) formal testing be conducted at ambient and cryogenic temperatures; ande) processing/properties be correlated with compositional variations.

Hales, Stephen J.↗
NASA NTRS2019

Molecular Identifications in Experiments with Astronomical Ice Analogues: New Data, Old Strategies, and the N2 + Acetone System

A recent publication on the radiation chemistry and IR spectroscopy of N2 plus acetone ices is used to illustrate some of the difficulties encountered in the study of astronomical ice analogues. Concerns and problems are identified and suggestions for their solution are presented, including new infrared (IR) spectra of amorphous ices. The hazards of using peak positions alone for assignments of the IR spectra of irradiated ices are illustrated, and the importance of considering the underlying reaction chemistry is shown. Several experiments are proposed as a way to investigate the behaviour of acetone in cold, extraterrestrial environments. Electronic versions of IR spectra are provided and several new refractive indices of ices are reported.

Hudson, Reggie L.↗
NASA NTRS2019

Evolved Gas Analyses of Mudstones from the Vera Rubin Ridge

The Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) rover has been essential in understanding volatile-bearing phases in Gale Crater materials. SAM’s evolved gas analysis mass spectrometry (EGA-MS) has detected H2O, CO2, O2, H2, SO2, H2S, HCl, NO, and other trace gases, including organic fragments, in many samples. The identity and evolution temperature of evolved gases can support CheMin instrument mineral detection and place constraints on trace volatile-bearing phases or phases difficult to characterize with X-ray diffraction (e.g., amorphous phases). For the past ~500 sols, MSL has been exploring the Vera Rubin Ridge (VRR), which exhibits a striking hematite signature in orbital remote sensing data, in order to understand the depositional and diagenetic history recorded in the rocks and how it relates to the underlying Murray Formation. Four rock samples were drilled, one from the Blunts Point Member (Duluth, DU), one from the Pettegrrove Point Member (Stoer, ST), and two from the Jura Member. The Jura Member displays differences in color, summarized as grey and red, and a key goal was to constrain the cause of this color difference and the associated implications for depositional or post-depositional conditions. To investigate, a grey (Highfield, HF) and a red (Rock Hall, RH) Jura sample were drilled. Here we will give an overview of results from SAM EGA-MS analyses of VRR materials, with some comparisons to analyses of samples of the underlying Murray.

McAdam, A. C.↗
NASA NTRS2019

Spectral Properties of Hydrated Poorly Crystalline Materials for Spectral Analysis of the Moon and Mars

Visible/near-infrared (VNIR) reflectance spectra of both Mars [1] and the Moon [2] include hydration bands that vary across the planet and are not well explained in some cases. Poorly crystalline phases have been found at ~30-70 wt.% by CheMin in Gale crater, Mars in all samples measured to date [3]. Here we report on VNIR reflectance spectra of a large collection of amorphous and poorly crystalline materials. These include opal, allophane, imogolite, iron hydroxides/ oxyhydroxides (FeOx), and several synthetic materials containing Si, Al and/or Fe. All of these contain hydration bands due to water and OH that can be used to identify these materials remotely on planetary bodies.

Bishop, J. L.↗
NASA NTRS2019

Simulating Space Weathering in the Transmission Electron Microscope via Dynamic in Situ Heating and Helium Irradiation of Olivine

The chemical composition, microstructure, and optical properties of grains on the surfaces of airless bodies are predominantly altered by micrometeorite impacts and solar wind irradiation. These processes drive space weathering and result in the formation of features including chemically-altered, amorphous grain rims, Fe nanoparticles (npFe), and vesiculated grain textures. These characteristics have been identified in returned samples from the surfaces of the Moon and asteroid Itokawa. In order to advance our understanding of the formation of these microstructural and chemical features in returned samples, we have simulated space weathering processes for a variety of materials via laboratory experiments. These experiments include ion irradiation to simulate solar wind exposure and laser irradiation and in situ heating to simulate micrometeorite impacts. While these experiments have provided considerable insight into the formation mechanisms of many space weathering features, they are predominantly static and typically performed separately. Here we present results from the simulated space weathering of olivine grains via He irradiation and dynamic heating, both performed in situ inside the transmission electron microscope (TEM). These experiments allow for the real-time observation of chemical and microstructural changes resulting from the superposed effects of ion irradiation and pulsed heating.

Thompson, M. S.↗
NASA NTRS2016

Fabricating with Crystalline Si to Improve Superconducting Detector Performance

We built and measured radio-frequency (RF) loss tangent, tan δ, evaluation structures using float-zone quality silicon-on-insulator (SOI) wafers with 5 μm thick device layers. Superconducting Nb components were fabricated on both sides of the SOI Si device layer. Our main goals were to develop a robust fabrication for using crystalline Si (c-Si) dielectric layers with superconducting Nb components in a wafer bonding process and to confirm that tan δ with c-Si dielectric layers was reduced at RF frequencies compared to devices fabricated with amorphous dielectrics, such as SiO2 and SixNy, where tan δ ~ 10(exp -3). Our primary test structure used a Nb coplanar waveguide (CPW) readout structure capacitively coupled to LC resonators, where the capacitors were defined as parallel-plate capacitors on both sides of a c-Si device layer using a wafer bonding process with benzocyclobutene (BCB) wafer bonding adhesive. Our control experiment, to determine the intrinsic tan δ in the SOI device layer without wafer bonding, also used Nb CPW readout coupled to LC resonators; however, the parallel-plate capacitors were fabricated on both sides of the Si device layer using a deep reactive ion etch (DRIE) to access the c-Si underside through the buried oxide and handle Si layers in the SOI wafers. We found that our wafer bonded devices demonstrated F· δ = (8 +/- 2) × 10(exp -5), where F is the filling fraction of two-level states (TLS). For the control experiment, F· δ = (2.0 +/- 0.6) × 10(exp -5), and we discuss what may be degrading the performance in the wafer bonded devices as compared to the control devices.

Beyer, A. D↗