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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

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

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

Blake, D. F.↗
NASA NTRS1991

Quantitative nondestructive evaluation of materials and structures

An experimental investigation was undertaken to quantify damage tolerance and resistance in composite materials impacted using the drop-weight method. Tests were conducted on laminates of several different carbon-fiber composite systems, such as epoxies, modified epoxies, and amorphous and semicrystalline thermoplastics. Impacted composite specimens were examined using destructive and non-destructive techniques to establish the characteristic damage states. Specifically, optical microscopy, ultrasonic, and scanning electron microscopy techniques were used to identify impact induced damage mechanisms. Damage propagation during post impact compression was also studied.

Smith, Barry T.↗
NASA NTRS1987

Ketimine modifications as a route to novel amorphous and derived semicrystalline poly(arylene ether ketone) homo- and copolymers

A series of amine terminal amorphous poly(arylene ether ketone) oligomers of controlled molecular weights (2-15 K) were synthesized. These oligomers have been found to undergo 'self-crosslinking' reactions upon heating above 220 C, via the reaction of the terminal amine groups with the in-chain keto carbonyl functionalities. The resulting networks are ductile, chemically resistant, and nonporous. The networks obtained via generated ketimine functionality were characterized by solid state NMR. They have also been found to be remarkably stable toward hydrolysis. Ketimine functional bishalide monomers have also been synthesized. Such monomers have been utilized to synthesize a wide variety of amorphous poly(arylene ether) ketimine polymers. A high molecular weight hydroquinone functional poly(arylene ether) ketimine has been acid treated to regenerate a poly(arylene ether ketone) backbone in solution. This novel procedure thus allows for the synthesis of important matrix resins under relatively mild conditions.

Mohanty, D. K.↗
NASA NTRS1992

Characterization of damage modes in impacted thermoset and thermoplastic composites

Composite materials remain extremely vulnerable to out-of-plane impact loads, which may lead to severe losses in strength and stiffness. Impact induced damage is often a complex mixture of transverse cracks, delaminations and fiber failures. An experimental investigation was undertaken to quantify damage tolerance and resistance in composite materials impacted using the drop-weight method. Tests were conducted on laminates of several different carbon-fiber composite systems such as epoxies, modified epoxies, and amorphous and semicrystalline thermoplastics. In this paper, impacted composite specimens have been examined using destructive and nondestructive techniques to establish the characteristic damage states. Specifically, optical microscopy, ultrasonic and scanning electron microscopy techniques have been used to identify impact induced damage mechanisms. Damage propagation during post impact compression was also studied.

Srinivasan, K.↗
NASA NTRS1987

Structure and dynamics of amorphous water ice

Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.

NASA Program Exobiology↗
NASA NTRS1987

Reactions of Atomic Oxygen (O(3P)) with Polybutadienes and Related Polymers

Thin films of the following polymers were exposed at ambient temperature to ground-state oxygen atoms (O(3P)), generated by a radio-frequency glow discharge in O2: cis- and trans-1,4-polybutadienes (CB and TB), amorphous 1,2-polybutadiene (VB), polybutadienes with different 1,4/1,2 contents, trans polypentenamer (TP), cis and trans polyoctenamers (CO and TO), and ethylene-propylene rubber (EPM). Transmission infrared spectra of CB and TB films revealed extensive surface recession, or etching, unaccompanied by any microstructural changes within the films, demonstrating that the reactions were confined to the surface layers. Contrary to the report by Rabek, Lucki, and Ranby (1979), there was no O(3P)-induced cis-trans isomerization in CB or TB. From weight-loss measurements, etch rates for polybutadienes were found to be markedly dependent on vinyl content, decreasing by two orders of magnitude from CB (2% 1,2) to structures with 30 to 40% 1,2 double bonds, thereafter increasing by half an order of magnitude to VB (97% 1,2). Relative etch rates for EMP and the polyalkenamers were in the order: EMP is greater than CO (or TO) is greater than TP is greater than CB. The sole non-elastomer examined, TB, had an etch rate about six times that of CB, ascribable to a morphology difference. Cis/trans content had a negligible effect on the etch rate of the polyalkenamers. Mechanisms involving crosslinking through units are proposed for the unexpected protection imparted to polybutadienes by the 1,2 double bonds.

Golub, Morton A.↗
NASA NTRS1987

Binary synaptic connections based on memory switching in a-Si:H for artificial neural networks

A scheme for nonvolatile associative electronic memory storage with high information storage density is proposed which is based on neural network models and which uses a matrix of two-terminal passive interconnections (synapses). It is noted that the massive parallelism in the architecture would require the ON state of a synaptic connection to be unusually weak (highly resistive). Memory switching using a-Si:H along with ballast resistors patterned from amorphous Ge-metal alloys is investigated for a binary programmable read only memory matrix. The fabrication of a 1600 synapse test array of uniform connection strengths and a-Si:H switching elements is discussed.

Thakoor, A. P.↗
NASA NTRS2010

Experimental Investigation of Space Radiation Processing in Lunar Soil Ilmenite: Combining Perspectives from Surface Science and Transmission Electron Microscopy

Energetic ions mostly from the solar wind play a major role in lunar space weathering because they contribute structural and chemical changes to the space-exposed surfaces of lunar regolith grains. In mature mare soils, ilmenite (FeTiO3) grains in the finest size fraction have been shown in transmission electron microscope (TEM) studies to exhibit key differences in their response to space radiation processing relative to silicates [1,2,3]. In ilmenite, solar ion radiation alters host grain outer margins to produce 10-100 nm thick layers that are microstructurally complex, but dominantly crystalline compared to the amorphous radiation-processed rims on silicates [1,2,3]. Spatially well-resolved analytical TEM measurements also show nm-scale compositional and chemical state changes in these layers [1,3]. These include shifts in Fe/Ti ratio from strong surface Fe-enrichment (Fe/Ti >> 1), to Fe depletion (Fe/Ti < 1) at 40-50 nm below the grain surface [1,3]. These compositional changes are not observed in the radiation-processed rims on silicates [4]. Several mechanism(s) to explain the overall relations in the ilmenite grain rims by radiation processing and/or additional space weathering processes were proposed by [1], and remain under current consideration [3]. A key issue has concerned the ability of ion radiation processing alone to produce some of the deeper- penetrating compositional changes. In order to provide some experimental constraints on these questions, we have performed a combined X-ray photoelectron spectroscopy (XPS) and field-emission scanning transmission electron (FE-STEM) study of experimentally ion-irradiated ilmenite. A key feature of this work is the combination of analytical techniques sensitive to changes in the irradiated samples at depth scales going from the immediate surface (approx.5 nm; XPS), to deeper in the grain interior (5-100 nm; FE-STEM).

Christoffersen, R.↗
NASA NTRS1980

Effect of W and WC on the oxidation resistance of yttria-doped silicon nitride

The effect of tungsten and tungsten carbide contamination on the oxidation and cracking in air of yttria-doped silicon nitride ceramics is investigated. Silicon nitride powder containing 8 wt % Y2O3 was doped with 2 wt % W, 4 wt % W, 2 wt % WC or left undoped, and sintered in order to simulate contamination during milling, and specimens were exposed in air to 500, 750 and 1350 C for various lengths of time. Scanning electron and optical microscopy and X-ray diffraction of the specimens in the as-sintered state reveals that the addition of W or WC does not affect the phase relationships in the system, composed of alpha and beta Si3N4, melilite and an amorphous phase. Catastrophic oxidation is observed at 750 C in specimens containing 2 and 4 wt % W, accompanied by the disappearance of alpha Si3N4 and melilite from the structure. At 1350 C, the formation of a protective glassy oxide layer was observed on all specimens without catastrophic oxidation, and it is found that pre-oxidation at 1350 C also improved the oxidation resistance at 750 C of bars doped with 4 wt % W. It is suggested that tungsten contamination from WC grinding balls may be the major cause of the intermediate-temperature cracking and instability frequently observed in Si3N4-8Y2O3.

Schuon, S.↗
NASA NTRS2016

Space Weathering of Olivine: Samples, Experiments and Modeling

Olivine is a major constituent of chondritic bodies and its response to space weathering processes likely dominates the optical properties of asteroid regoliths (e.g. S- and many C-type asteroids). Analyses of olivine in returned samples and laboratory experiments provide details and insights regarding the mechanisms and rates of space weathering. Analyses of olivine grains from lunar soils and asteroid Itokawa reveal that they display solar wind damaged rims that are typically not amorphized despite long surface exposure ages, which are inferred from solar flare track densities (up to 10 (sup 7 y)). The olivine damaged rim width rapidly approaches approximately 120 nm in approximately 10 (sup 6 y) and then reaches steady-state with longer exposure times. The damaged rims are nanocrystalline with high dislocation densities, but crystalline order exists up to the outermost exposed surface. Sparse nanophase Fe metal inclusions occur in the damaged rims and are believed to be produced during irradiation through preferential sputtering of oxygen from the rims. The observed space weathering effects in lunar and Itokawa olivine grains are difficult to reconcile with laboratory irradiation studies and our numerical models that indicate that olivine surfaces should readily blister and amorphize on relatively short time scales (less than 10 (sup 3 y)). These results suggest that it is not just the ion fluence alone, but other variable, the ion flux that controls the type and extent of irradiation damage that develops in olivine. This flux dependence argues for caution in extrapolating between high flux laboratory experiments and the natural case. Additional measurements, experiments, and modeling are required to resolve the discrepancies among the observations and calculations involving solar wind processing of olivine.

Keller, L. P.↗
NASA NTRS1974

Solid state polymerization and crystallography of polyimide precursors

Although the production of crystallinity in a polymeric system has historically led to commerically useful properties, the polyimides, prized for their high temperature characteristics, as customarily synthesized by melt or solution casting, are amorphous. It is shown that polymide containing residual crystallinity can be synthesized by isothermal annealing of crystals of the salt of the diisopropyl ester of pyromellitic acid and phenylene diamine. The reaction is topochemical in that the geometry of the polymer product is dependent upon that of the crystalline precursor. Infrared spectroscopy reveals the presence of imide absorption in the polymer, while powder diffractometry suggests residual crystallinity. Single crystal X-ray analysis of the monomer yields a structure of chains of alternating acid and base suggesting that the monomer is amenable to polymerization with a minimum of geometrical disruption.

Wakelyn, N. T.↗
NASA NTRS2010

Comparison of the Mineralogy of Comet Wild 2 Coma Grains to Other Astromaterials

We propose that Kuiper Belt samples (in this case comet coma grains from the Jupiter family comet Wild 2) are recognizably different from the bulk of materials in outer belt asteroids, because of their different formation positions and times in the early solar system. We believe this despite similarities found between some Wild 2 grains and components of carbonaceous chondrites (i.e. some CAI and chondrules). Kuiper Belt samples must preserve measurable mineralogical and compositional evidence of formation at unique positions and times in the early solar nebula, and these formational differences must have imparted recognizable special characteristics. We hypothesize that these characteristics include: (1) Unique major element compositional ranges of common astromaterial minerals, especially olivine and pyroxene; (2) Unique minor element compositions of major silicate phases, especially olivine and low-Ca pyroxene; (3) Degree and effects of radiation processing -- including amorphous rims, metal coatings, and Glass with Embedded Metal and Sulfides (GEMS); (4) Presence of abundant presolar silicate grains as recognized by anomalous oxygen in silicates; (5) Oxidation state of the mineral assemblage. We are working our way through all available Wild 2 samples, selecting 1-2 non-consecutive viable TEM grids from each possible extracted Wild 2 grain. We especially prefer TEM grids from grains for which complete mineralogical details have not been published (which is to say the majority of the extracted grains). We are performing a basic mineralogic survey by E-beam techniques, to establish the essential features of the extracted Wild 2 grains. We are making a particular effort to carefully and accurately measure minor elements of olivine and pyroxene, as these minerals are widespread in astromaterials, and comparisons of their compositions will serve to place the Wild 2 silicates in contact with asteroids, meteorites and chondritic interplanetary dust particles processing. We are also making a special effort to search for mineralogical products of aqueous alteration, since their presence would reveal that Wild 2 was once internally heated, a result with dramatic implications for models of early solar system primitive bodies. Thus far carbonates are the only potential evidence for aqueous alteration for Wild 2.

Frank, David↗
NASA NTRS1976

Developments in new aircraft tire tread materials

Comparative laboratory and field tests were conducted on experimental and state-of-the-art aircraft tire tread materials in a program aimed at seeking new elastomeric materials which would provide improved aircraft tire tread wear, traction, and blowout resistance in the interests of operational safety and economy. The experimental stock was formulated of natural rubber and amorphous vinyl polybutadiene to provide high thermal-oxidative resistance, a characteristic pursued on the premise that thermal oxidation is involved both in the normal abrasion or wear of tire treads and probably in the chain of events leading to blowout failures. Results from the tests demonstrate that the experimental stock provided better heat buildup (hysteresis) and fatigue properties, at least equal wet and dry traction, and greater wear resistance than the state-of-the-art stock.

Yager, T. J.↗
NASA NTRS2021

Dissolution Rates of Allophane with Variable Fe Contents: Implications for Aqueous Alteration and the Preservation of X-ray Amorphous Materials on Mars

Recent measurements from Mars document X-ray amorphous/nano-crystalline materials in multiple locations across the planet. However, despite their prevalence, little is known about these materials or what their presence implies for the history of Mars. The X-ray amorphous component of the martian soil in Gale crater has an X-ray diffraction pattern that can be partially fit with allophane (approximately Al2O3•(SiO2)1.3-2•(H2O)2.5-3), and the low-temperature water release data are consistent with allophane. The chemical data from Gale crater suggest that other silicate materials similar to allophane, such as Fe-substituted allophane (approximately (Fe2O3)0.01-0.5(Al2O3)0.5-0.99•(SiO2)2•3H2O), may also be present. In order to investigate the properties of these potential poorly crystalline components of the martian soil, Fe-free allophane (Fe:Al = 0), Fe-poor allophane (Fe:Al = 1:99), and Fe-rich allophane (Fe:Al = 1:1) were synthesized and then characterized using electron microscopy and Mars-relevant techniques, including infrared spectroscopy, X-ray diffraction, and evolved gas analysis. Dissolution experiments were performed at acidic (initial pH values pH0 = 3.01, pH0 = 5.04), near-neutral (pH0 = 6.99), and alkaline (pH0 = 10.4) conditions in order to determine dissolution kinetics and alteration phases for these poorly crystalline materials. Dissolution rates (rdiss), based on the rate of Si release into solution, show that these poorly crystalline materials dissolve approximately an order of magnitude faster than crystalline phases with similar compositions at all pH conditions. For Fe-free allophane, logrdiss = -10.65 – 0.15 × pH; for Fe-poor allophane, logrdiss = -10.35 – 0.22 × pH; and for Fe-rich allophane, logrdiss = -11.46 – 0.042 × pH at 25°C, where rdiss has the units of mol m-2 s-1. The formation of incipient phyllosilicate-like phases was detected in Fe-free and Fe-rich allophane reacted in aqueous solutions with pH0 = 10.4 (steady-state pH ≈ 8). Mars-analog instrument analyses demonstrate that Fe-free allophane, Fe-poor allophane, and Fe-rich allophane are appropriate analogs for silicate phases in the martian amorphous soil component. Therefore, similar materials on Mars must have had limited interaction with liquid water since their formation. Combined with chemical changes expected from weathering, such as phyllosilicate formation, the rapid alteration of these poorly crystalline materials may be a useful tool for evaluating the extent of aqueous alteration in returned samples of martian soils.

S J Ralston↗
NASA NTRS1985

Magnetron-Sputtered Amorphous Metallic Coatings

Amorphous coatings of refractory metal/metalloid-based alloys deposited by magnetron sputtering provide extraordinary hardness and wear resistance. Sputtering target fabricated by thoroughly mixing powders of tungsten, rhenium, and boron in stated proportions and pressing at 1,200 degrees C and 3,000 lb/in. to second power (21 MPa). Substrate lightly etched by sputtering before deposition, then maintained at bias of - 500 V during initial stages of film growth while target material sputtered onto it. Argon gas at pressure used as carrier gas for sputter deposition. Coatings dense, pinhole-free, extremely smooth, and significantly resistant to chemical corrosion in acidic and neutral aqueous environments.

Thakoor, A. P.↗
NASA NTRSDate not supplied

Indigenous Organic Matter Associated with Unusual Low Temperature Aqueous Secondary Phases in the Mars Meteorite Nakhla

In freshly fractured chips of the Mars meteorite Nakhla, we found carbonaceous phases intimately associated with secondary aqueous alteration phases, both mineral and amorphous, interpreted to have formed through the low-temperature, mineral-water dissolution of the host Martian basalt.We have characterized the nature of carbonaceous matter and spatially associated secondary phases within Nakhla using a multidisciplinary suite of optical and electron beam instrumentation(Thomas-Keprta et al., 2022). Secondary Phases: The preserved secondary mineral phases are best described as ‘juvenile’ hydrated amorphous silica formed when water interacts with mafic rocks. Although amorphous silica on Earth rarely persists through geologic time due to alteration into other phases, e.g.,microcrystalline opal-CT and eventually quartz, the lack of maturation of primarily amorphous silica with embedded nano phase ferrihydrite in Nakhla infers these phases formed in a limited water environment by low temperature, circumneutral pH fluids stabilized by the presence of coexisting amorphous silica.Additionally, we report the presence of the ferrous hydroxycarbonate mineral chukanovite (Fe2(OH)2CO3)within some of the secondary mineral aggregates studied. Organic Matter:Indigenous Nakhla carbonaceous matter is present both in condensed phases and in a dispersed state spatially associated with secondary alteration phases. In the former, discrete refractory micron to submicron assemblages were identified that appear macromolecular in nature and, in several cases, associated with F and, in one case, significant N. While organically bound Fhas yet to be detected remotely on Mars, the identification of organic N within one of the carbonaceous phases is considered a prerequisite for Martian astrobiological potential. Summary: Neither the intimate association of carbonaceous matter with secondary phases nor the identification of chukanovite have been previously reported in any of the Martian meteorites.A variety of habitability-related metastable solid-phase, oxidation-reduction, and organic-molecular sample attributes in Nakhla formed hundreds of millions of years ago near Mars’ surface; these alteration products persisted on Mars until very recentlyand resemble the amorphous materials observed at Gale crater by Mars Science Laboratory CuriosityRover (Rampe et al., 2020).Similar phases may be expected to occur elsewhere on Mars (e.g., Jezerocrater). References: Rampe E. B. et al.(2020) Mineralogy and geochemistry of sedimentary rocks and eolian sediments in Gale crater, Mars: A review after six Earth years of exploration with Curiosity.Geochemistry80, 125605; Thomas-Keprta K.L. et al. (2022) Indigenous carbon-rich matter associated with unusual aqueous alteration features in Nakhla: Complex formation and preservation history. Geochim. et Cosmochim. Acta320, 41-78 (online).

Mars meteorite↗
NASA NTRS2015

Solar Ion Processing of Itokawa Grains: Constraints on Surface Exposure Times

Analytical TEM observations obtained to date reveal that a significant sub-population of grains returned from the surface of asteroid Itokawa have had their outer 30-100 nm processed by space weathering effects. Although the effects include some surface deposition of condensed impact vapor and isolated impact melt splashes, much of the width of the space weathered outer margins or "rims" on grains is derived from solar wind processing of the original host grain. Similar to what has long been reported for some lunar grains, the ion-processed rims on Itokawa grains exhibit varing degrees and depths of penetration of atomic-displacement ion damage, resulting in complete amorphization for some rims (particularly in plagioclase), or formation of highly defective but still crystalline structures in others (particularly in pyroxene and olivine). Possibly different from lunar grains, however, is the presence of isolated internal cavities or voids in Itokawa grain rims, which may be implantation "bubbles" due to accumulating implanted solar wind H and/or He. For a given mineral exposed at a particular set of long term solar wind conditions, the level of ion damage in a given grain rim, the depth of damage penetration represented by the rim width, and the formation or lack of formation of implantation bubbles can all be linked to the time spent by the grain in an uncovered state on the topmost, space-exposed, regolith surface. For the lunar case, we have previously shown that with reasonable assumptions about solar wind characteristics over time, a model can be developed to estimate this exposure time based on the width of amorphous rims on lunar grains. Here we report on an expansion of the model to cover exposure time information contained in the array of solar ion-induced features in Itokawa grains.

Christoffersen, R.↗
NASA NTRS1992

Shock-induced transformations in the system NaAlSiO4-SiO2 - A new interpretation

New internally consistent interpretations of the phases represented by the high pressure phase shock wave data for an albite-rich rock, jadeite, and nepheline in the system NaAlSiO4-SiO2, are obtained using the results of static high pressure investigations, and the recent discovery of the hollandite phase in a shocked meteorite. We conclude that nepheline transforms directly to the calcium ferrite structure, whereas albite transforms possibly to the hollandite structure. Shock Hugoniots for the other plagioclase and alkali feldspars also indicate that these transform to hollandite structures. The pressure-volume data at high pressure could alternatively represent the compression of an amorphous phase. Moreover, the shock Hugoniot data are expected to reflect the properties of the melt above shock stresses of 60-80 GPa. The third order Birch-Murnaghan equation of state parameters are given for the calcium ferrite type NaAlSiO4 and for albite-rich, orthoclase-rich, and anorthite-rich hollandites.

Sekine, Toshimori↗