Results for “Scanning Electron Microscopes” — Page 45

NASA NTRS1982

Plastic deformation and wear process at a surface during unlubricated sliding

The plastic deformation and wear of a 304 stainless steel surface sliding against an aluminum oxide rider with a spherical surface (the radius of curvature: 1.3 cm) were observed by using scanning electron and optical microscopes. Experiments were conducted in a vacuum of one million Pa and in an environment of fifty thousandth Pa of chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step shaped proturbances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. The mechanism for tearing away of the surface layer from the contact area and sliding track contour is explained assuming the simplified process of material removal based on the adhesion theory for the wear of materials.

Yamamoto, T.↗

NASA NTRS1982

SEM, optical, and Moessbauer studies of submicrometer chromite in Allende

New scanning electron and optical microscope results are presented showing that sub-micrometer chromite is abundant along healed cracks and grain boundaries in Allende chondrule olivine. Some wider healed cracks also contain pentlandite and euhedral Ni3Fe grains. Also reported are Moessbauer measurements on Allende HF-HCl residues confirming a high Fe(+++)/Fe(++) ratio.

Housley, R. M.↗

NASA NTRS1983

Plastic deformation and wear process at a surface during unlubricated sliding

The plastic deformation and wear of a 304 stainless steel surface sliding against an aluminum oxide rider with a spherical surface (the radius of curvature: 1.3 cm) were observed by using scanning electron and optical microscopes. Experiments were conducted in a vacuum of one million Pa and in an environment of fifty thousandth Pa of chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step shaped proturbances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. The mechanism for tearing away of the surface layer from the contact area and sliding track contour is explained assuming the simplified process of material removal based on the adhesion theory for the wear of materials. Previously announced in STAR as N82-32735

Yamamoto, T.↗

NASA NTRS1989

Microlesions - Theory and reality

Efforts to assess radiation risk in space have been complicated by the considerable unknowns regarding the biological effects of the heavy ion component (HZE particles) of the cosmic rays. The attention has focused primarily on the assignation of a quality factor (Q) which would take into account the greater effectiveness of heavy ions vis-a-vis other forms of ionizing radiation. If, however, as the so-called 'microlesion theory' allows, the passage of HZE particles through living tissue produces unique biological damage, the traditional use of Q becomes meaningless. Therefore, it is critical to determine if microlesions, in fact, do exist. While the concept does not necessarily require detectable morphological damage, 'tunnel-lesions' or holes in ocular tissues have been cited as evidence of microlesions. These data, however, are open to reinterpretation. Ongoing light, scanning and transmission electron microscopic studies of the corneas, lenses and retinas of rat eyes exposed to 450 MeV/amu Fe-56 ions thus far have not revealed tunnel-lesion damage. The morphological effects of the heavy ions have been found to be qualitatively similar to the changes following other kinds of ionizing radiation.

Worgul, Basil V.↗

NASA NTRS1991

Chemical characterization of selected LDEF polymeric materials

Chemical characterization of selected polymeric materials which received exposure on the Long Duration Exposure Facility (LDEF) is reported. The specimens examined include silvered fluorinated ethylene propylene Teflon thermal blanket material, polysulfone, epoxy, polyimide matrix resin/graphite fiber reinforced composites, and several high performance polymer films. These specimens came from numerous LDEF locations, and thus received different environmental exposures. The results to date show no significant change at the molecular level in the polymer that survived exposure. Scanning electron and scanning tunneling microscopes show resin loss and a texturing of some specimens which resulted in a change in optical properties. The potential effect of a silicon-containing molecular contamination on these materials is addressed. The possibility of continued post-exposure degradation of some polymeric films is also proposed.

Young, Philip R.↗

NASA NTRS1994

Bench-scale synthesis of nanoscale materials

A novel flow-through hydrothermal method used to synthesize nanoscale powders is introduced by Pacific Northwest Laboratory. The process, Rapid Thermal Decomposition of precursors in Solution (RTDS), uniquely combines high-pressure and high-temperature conditions to rapidly form nanoscale particles. The RTDS process was initially demonstrated on a laboratory scale and was subsequently scaled up to accommodate production rates attractive to industry. The process is able to produce a wide variety of metal oxides and oxyhydroxides. The powders are characterized by scanning and transmission electron microscopic methods, surface-area measurements, and x-ray diffraction. Typical crystallite sizes are less than 20 nanometers, with BET surface areas ranging from 100 to 400 sq m/g. A description of the RTDS process is presented along with powder characterization results. In addition, data on the sintering of nanoscale ZrO2 produced by RTDS are included.

Buehler, M. F.↗

NASA NTRS1994

A proposition for the classification of carbonaceous chondritic micrometeorites

Classification of interplanetary dust particles (IDP's) should be unambiguous and, if possible, provide an opportunity to interrelate these ultrafine IDP's with the matrices of undifferentiated meteorites. I prefer a scheme of chemical groupings and petrologic classes that is based on primary IDP properties that can be determined without prejudice by individual investigators. For IDP's of 2-50 microns these properties are bulk elemental chemistry, morphology, shape, and optical properties. The two major chemical groups are readily determined by energy dispersive spectroscopic analysis using the scanning or analytical electron microscope. Refinement of chondritic IDP classification is possible using the dominant mineral species, e.g. olivine, pyroxene, and layer silicates, and is readily inferred from FTIR, and automated chemical analysis. Petrographic analysis of phyllosilicate-rich IDP's will identify smectite-rich and serpentine-rich particles. Chondritic IDP's are also classified according to morphology, viz., CP and CF IDP's are aggregate particles that differ significantly in porosity, while the dense CS IDP's have a smooth surface. The CP IDP's are characterized by an anhydrous silicate mineralogy, but small amounts of layer silicates may be present. Distinction between the CP and CF IDP's is somewhat ambiguous, but the unique CP IDP's are fluffy, or porous, ultrafine-grained aggregates. The CP IDP's, which may contain silicate whiskers, are the most carbon-rich extraterrestrial material presently known. The CF IDP's are much less porous that CP IDP's. Using particle type definitions, CP IDP's in the NASA JSC Cosmic Dust Catalogs are approx. 15 percent of all IDP's that include nonchondritic spheres. Most aggregate particles are of the CF type.

Rietmeijer, Frans J. M.↗

NASA NTRS1999

Alteration of Rock Fragments from Columbia River Basalt Microcosms

During an earlier study, microorganisms were grown microcosms consisting of sterilized chips of Columbia River Basalt (CRB) and natural CRB ground water with its natural microflora; environmental conditions simulated a deep subsurface, anaerobic, dark environment. Subsequent scanning and transmission electron microscope (SEM and TEM) studies revealed the presence of several types of bacteria and biofilm, some of which were mineralized. Some of these biological features are very similar to possible biogenic features found in two meteorites from Mars, ALH84001 (found in Antarctica) and Nakhla (observed to fall in Egypt). Both ALH84001 and Nakhla contain traces of low-temperature aqueous alteration of silicates, oxides, and sulfides. The goals of this study are to use high-resolution field-emission SEM (FE-SEM) to examine the CRB samples for evidence of alteration features similar to those in the martian meteorites, to determine the extent of alteration during the CRB microcosm experiments, and to determine whether effects of biological activity can be distinguished from inorganic effects.

Wentworth, Susan J.↗

NASA NTRS2001

Ultrahigh Temperature Ceramics for Thermal Protection of Next Generation Space Vehicles

Materials with improved properties are needed for thermal protection of next generation space vehicles. Sharp leading edges on these vehicles will have to withstand exposure to high temperatures (> 2200 C or 4000 F) and severe thermal cycling in both neutral and oxidizing environments. These extreme conditions will require materials that possess superior oxidation resistance, low creep, and excellent thermal shock properties. This presentation will first discuss the system requirements for thermal protection of advanced space vehicles and then show how they are driving development of new materials systems. The presentation will focus on ultrahigh temperature ceramics (UHTCs) that are promising candidates for such applications. ZrB2 and HfB2 and composites of those ceramics with SiC are two particular families of UHTCs that are currently under development for sharp leading edges. These ceramics are appealing because their melting temperatures are 3245 C (5873 F) for ZrB2 and 3380 C (6116 F) for HfB2 and because they may form protective, oxidation resistant coatings in use. The mechanical properties of the UHTCs are strongly dependent on phase purity and the processing route used to make them, both of which factors are being actively investigated. For example, oxide impurities could form glassy grain boundary phases that soften at high temperatures and make the ceramic susceptible to creep deformation. Results from scanning and transmission electron microscopic studies of the UHTCs have shown how their processing can be improved to give better properties. This presentation will discuss the UHTC characterization results in some detail, focusing particularly on the structure and composition of the ceramic grain boundaries. The presentation will conclude with some remarks on how the properties of these promising UHTCs can be further improved and how they might be made more economically.

Loehman, R. E.↗

NASA NTRS1994

Microscopy in Space Research: Learning More About Gravitational Effects on Living Systems

Investigators are using light, scanning and transmission electron microscopic (TEM) methods to investigate the effects of microgravity on the development, maintenance and aging of biological systems. The capabilities of the spacelab for life sciences research in space will be described. Among the many results to be discussed are the effects of microgravity on amphibian fertilization and early development, and on the rodent musculoskeletal and neural systems. Xenopus laevis eggs fertilized in space developed normally during and after an eight day spaceflight. Ultrastructural studies of rodent tissue demonstrated that spaceflight-induced atrophy of antigravity skeletal muscles renders muscle fibers susceptible to structural failure upon return to weight bearing postflight. Principle TEM changes in neuromuscular junctions are the decrease or absence of synaptic vesicles and degeneration of axon terminals. In bone, architectural rather than compositional changes may be the primary perturbation. Thus, many techniques used on Earth (such as density determinations) would not detect significant changes in bone strength. An increment in synaptic number and changes in synapse distribution occur in peripheral gravity sensors. There is a decrease in muscarinic cholinergic receptor density in the striatum. Striatal receptor changes suggest spaceflight-related alterations in motor activity. Opportunities for future life sciences research in space will be discussed.

Ross, Muriel D.↗

NASA NTRS2015

Fe and O EELS Studies of Ion Irradiated Murchison CM2 Carbonaceous Chondrite Matrix

Introduction: The physical and chemical response of hydrated carbonaceous chondrite materials to space weathering processes is poorly understood. Improving this understanding is a key part of establishing how regoliths on primitive carbonaceous asteroids respond to space weathering processes, knowledge that supports future sample return missions (Hayabusa 2 and OSIRISREx) that are targeting objects of this type. We previously reported on He+ irradiation of Murchison matrix and showed that the irradiation resulted in amorphization of the matrix phyllosilicates, loss of OH, and surface vesiculation. Here, we report electron energy-loss spectroscopy (EELS) measurements of the irradiated material with emphasis on the Fe and O speciation. Sample and Methods: A polished thin section of the Murchison CM2 carbonaceous chondrite was irradiated with 4 kilovolts He(+) (normal incidence) to a total dose of 1 x 10(exp 18) He(+) per square centimeter. We extracted thin sections from both irradiated and unirradiated regions in matrix using focused ion beam (FIB) techniques with electron beam deposition for the protective carbon strap to minimize surface damage artifacts from the FIB milling. The FIB sections were analyzed using a JEOL 2500SE scanning and transmission electron microscope (STEM) equipped with a Gatan Tridiem imaging filter. EELS spectra were collected from 50 nanometer diameter regions with an energy resolution of 0.7 electronvolts FWHM at the zero loss. EELS spectra were collected at low electron doses to minimize possible artifacts from electron-beam irradiation damage. Results and Discussion: Fe L (sub 2,3) EELS spectra from matrix phyllosilicates in CM chondrites show mixed Fe(2+)/Fe(3+) oxidation states with Fe(3+)/Sigma Fe approximately 0.5. Fe L(sub 2,3) spectra from the irradiated/ amorphized matrix phyllosilicates show higher Fe(2+)/Fe(3+) ratios compared to spectra obtained from pristine material at depths beyond the implantation/amorphization layer. We also obtained O Ka spectra from phyllosilicates in both regions of the sample. The O Ka spectra show a pre-edge feature at approximately 530.5 electronvolts that is related to O 2p states hybridized with Fe 3d states. The intensity ratio of the O Ka pre-edge peak relative to the main part of the O Ka edge (that results from transitions of O 1s to 2p states) is lower in the irradiated layer compared to the pristine material and may reflect the loss of O (as OH) as was observed by IR spectroscopy. Conclusions: In addition to amorphization and OH loss, EELS spectra of He(+) irradiated matrix phyllosilicates in Murchison show that some of the Fe(3+) is reduced to Fe(2+). Spectral deconvolution is underway to extract quantitative ratios from the EELS spectra.

Keller, L. P.↗

NASA NTRSDate not supplied

Analysis of Samples from Asteroid Ryugu Returned by Hayabusa2

After returning to Earth in the winter of 2020, the samples from Cb-type asteroid Ryugu were stored under atmosphere-free conditions at the Extraterrestrial Materials Curation Center of ISAS/JAXA, and investigated for basic descriptions (sample imaging, weighing, etc.). They were distributed to six initial analysis teams in Japan in June 2021. The "Stone" team, in charge of analysis of coarse particles (>1 mm in size), conducted a series of analyses using a variety of techniques including reflectance spectra measurement, synchrotron-radiation three-dimensional elemental and mineralogical analysis, bulk elemental analysis using muon beam, Fe valence state measurement by XANES and Mössbauer spectroscopy, detailed mineralogical and petrological characterization by scanning and transmission electron microscopes. Physical and thermal properties of Ryiugu samples were measured to understand the response to shock and heating. In this talk, I would like to introduce summary of analysis results and what comes to be known about the formation and evolution of asteroid Ryugu.

Tomoki Nakamura↗

NASA NTRSDate not supplied

Bosch Carbon Catalyst Regeneration in Water II: Analysis of Bosch Catalyst Beads Throughout the Initial Regeneration Process

Catalyst integrity is an important factor in reactor longevity since it changes the effectiveness of a reaction. A Carbon Formation Reactor (CFR), used within Series Bosch (S-Bosch), utilizes an iron alloy catalyst to convert carbon monoxide and hydrogen into water and solid carbon. The catalyst promotes the formation of carbon to such an extent that pressure-causing clogs form within the reactor and reaction sites on the catalyst become limited. To remove carbon from both the reactor and the surface of the iron alloy catalyst, a technique was developed that utilizes water, an In-Situ Resource Utilization (ISRU) Resource, and agitation to regenerate the reactor. To ascertain catalyst integrity throughout this regenerative process, sample catalyst beads were taken before and after the carbon formation reaction, and then after the regeneration process. Additionally, wastewater from the regeneration process was sampled. The sampled beads and wastewater were observed under a Scanning Electron Microscopy (SEM) microscope and the beads were chemically etched to determine if the catalyst had degraded at any point during this process, and if catalyst was lost. Minimal catalyst degradation was observed after carbon formation in the CFR.

regeneration↗

NASA NTRSDate not supplied

Bosch Carbon Catalyst Regeneration in Water II: Analysis of Bosch Catalyst Beads Throughout the Initial Regeneration Process

Catalyst integrity is an important factor in reactor longevity since it changes the effectiveness of a reaction. A Carbon Formation Reactor (CFR), used within Series Bosch (S-Bosch), utilizes an iron alloy catalyst to convert carbon monoxide and hydrogen into water and solid carbon. The catalyst promotes the formation of carbon to such an extent that pressure-causing clogs form within the reactor and reaction sites on the catalyst become limited. To remove carbon from both the reactor and the surface of the iron alloy catalyst, a technique was developed that utilizes water, an In-Situ Resource Utilization (ISRU) Resource, and agitation to regenerate the reactor. To ascertain catalyst integrity throughout this regenerative process, sample catalyst beads were taken before and after the carbon formation reaction, and then after the regeneration process. Additionally, wastewater from the regeneration process was sampled. The sampled beads and wastewater were observed under a Scanning Electron Microscopy (SEM) microscope and the beads were chemically etched to determine if the catalyst had degraded at any point during this process, and if catalyst was lost. Minimal catalyst degradation was observed after carbon formation in the CFR.

Series Bosch↗

DOE OSTI2024

In Situ Liquid Electron Microscope Cells Strongly Attenuate Electrochemical Behavior

In situ electrochemical Scanning Transmission Electron Microscopy (ec-S/TEM) probes the dynamics of electrochemical processes in real time and at high spatial resolution. This method utilizes microfabricated electrochemical cells, with enclosed dimensions of 800 μm wide, 800 μm long, and 1–2 μm tall, with electron-transparent silicon nitride windows. Working, counter, and reference electrodes in the configuration studied are deposited Pt with a planar surface area of about 1 μm 2 and a height of 50 nm. The cell confines the electrolyte within a 1 μm tall channel, and the microfabricated electrodes have a non-standard geometry, are coplanar, and are not front-facing. As such, standard assumptions of electrochemical experiments do not apply. COMSOL modeling was used to compare and contrast differences in electrochemical behavior between conventional experimental setups and the in situ ec-S/TEM cells. Cell height strongly affected voltammogram measurements: peak magnitudes and shifts correlate directly to cell height. Reactant concentration above the electrode quickly decreases during deposition, leading to a planar diffusion-dominated regime. The concentration gradient prioritizes particle growth along the thin edges of the electrode and not on the planar part of the electrode. Experiments done in the ec-S/TEM ex situ of a TEM verify the model’s accuracy.

Wittman, Reed M. [Oak Ridge National Laboratory (O↗

DOE OSTI2020

Effects of Neutron Irradiation on the Micro/Nano Scale Structure and Fission Product Distribution of TRISO Coated Particle Fuel Kernels from AGR Experiments

The Advanced Reactor Technologies (ART) Program at Idaho National Laboratory (INL) includes the Advanced Gas Reactor (AGR) fuel development and qualification program that consists of fuel fabrication, experiment irradiations, post-irradiation examination (PIE) and safety testing to assess tristructural isotropic (TRISO) fuel performance during normal irradiation and under potential accident conditions. Advanced microscopy work on selected AGR-1 and AGR-2 unirradiated and irradiated fuel specimens is performed as part of the PIE effort. PIE work on fuel from the first experiment irradiation, AGR-1, began at INL in April 2010, and AGR-2 PIE began at INL in July 2014. This work scope includes University of Florida (UF) performing advanced electron microscopy examination and analysis using facilities at the Center for Advanced Energy Studies (CAES), INL or UF’s electron microscopy facilities. Electron microscopic examination and analysis may include scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), selected area diffraction (SAD), electron energy loss spectroscopy (EELS), electron dispersive spectroscopy (EDS) and atom probe tomography (APT) on the fuel kernels of TRISO-coated fuel particles. The electron microscopy lamellae will be provided by INL and will be available at CAES or Irradiated Materials Characterization Laboratory (IMCL).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRSDate not supplied

Variable Pressure - Scanning Electron Microscopy (VP-SEM)

Variable Pressure (or Environmental) Scanning Electron Microscopy (VP-SEM) combined with Energy Dispersive X-ray Spectroscopy (EDS) is one of the most powerful methods for characterizing the sub-micron topography and chemical composition of uncoated samples. Terrestrially, VP-SEM is extensively used to non-destructively study geologic and manufactured materials with high spatial resolution (tens of nanometers) and large depth-of-field. An SEM offers a geologist a first survey of microscopic mineral phases via secondary electron imaging (SEI), which provides a topographic look at a sample, as well as backscattered electron (BEI) imaging, which contrasts the phases present based on their geochemistry (atomic number). A VP-SEM utilizes a gas in the sample chamber as a charge dissipation and signal amplification method, allowing analysis of a sample without preparation in the form of a conductive coating. A miniaturized VP-SEM operating in-situ on a lander or rover would be able to use the CO2-rich Martian atmosphere (e.g., Nier et al., 1976; Williams 2016) as an imaging medium for this purpose. Adaptation of a VP-SEM for in-situ Mars surface studies will provide a new imaging capability (via SEI) that is at least an order of magnitude higher resolution than the Mars Hand Lens Imager (MAHLI) on the Mars Science Laboratory (Williams et al., 2015), and equal to or better than the achieved resolution of the Atomic Force Microscope on the Phoenix Mars lander (Pike et al., 2011). In addition, the MVP-SEM is capable of BSI and simultaneous chemical analysis of the imaged region. In this sense, the MVP-SEM can be regarded as an instrument suite that will provide a new set of information not achievable by any other instrument. The Miniaturized Variable Pressure Scanning Electron Microscope (MVP-SEM) was designed, built, and benchtop tested by a team at NASA’s Marshall Space Flight Center and Jet Propulsion Laboratory (JPL), Jacobs Space Exploration Group, Applied Physics Technologies, Inc. (AP-Tech), and Creare LLC, working with a team of technical and science collaborators. Benchtop testing was successful, proving concept feasibility. To date, the MVP-SEM has achieved an imaging resolution of <100 nm in the lab, and with continued optimization, even better performance (~50 nm resolution) is possible. Use in-situ on the lunar or other planetary surfaces would require some redesign to optimize instrument performance, but such an instrument would be equally useful.

Variable Pressure Scanning Electron Microscopy↗

NASA NTRSDate not supplied

Miniature Variable Pressure - Scanning Electron Microscopy (MVP-SEM)

Variable Pressure (or Environmental) Scanning Electron Microscopy (VP-SEM) combined with Energy Dispersive X-ray Spectroscopy (EDS) is one of the most powerful methods for characterizing the sub-micron topography and chemical composition of uncoated samples. Terrestrially, VP-SEM is extensively used to non-destructively study geologic and manufactured materials with high spatial resolution (tens of nanometers) and large depth-of-field. An SEM offers a geologist a first survey of microscopic mineral phases via secondary electron imaging (SEI), which provides a topographic look at a sample, as well as backscattered electron (BEI) imaging, which contrasts the phases present based on their geochemistry (atomic number). A VP-SEM utilizes a gas in the sample chamber as a charge dissipation and signal amplification method, allowing analysis of a sample without preparation in the form of a conductive coating. A miniaturized VP-SEM operating in-situ on a lander or rover would be able to use the CO2-rich Martian atmosphere (e.g., Nier et al., 1976; Williams 2016) as an imaging medium for this purpose. Adaptation of a VP-SEM for in-situ Mars surface studies will provide a new imaging capability (via SEI) that is at least an order of magnitude higher resolution than the Mars Hand Lens Imager (MAHLI) on the Mars Science Laboratory (Williams et al., 2015), and equal to or better than the achieved resolution of the Atomic Force Microscope on the Phoenix Mars lander (Pike et al., 2011). In addition, the MVP-SEM is capable of BSI and simultaneous chemical analysis of the imaged region. In this sense, the MVP-SEM can be regarded as an instrument suite that will provide a new set of information not achievable by any other instrument. The Miniaturized Variable Pressure Scanning Electron Microscope (MVP-SEM) was designed, built, and benchtop tested by a team at NASA’s Marshall Space Flight Center and Jet Propulsion Laboratory (JPL), Jacobs Space Exploration Group, Applied Physics Technologies, Inc. (AP-Tech), and Creare LLC, working with a team of technical and science collaborators. Benchtop testing was successful, proving concept feasibility. To date, the MVP-SEM has achieved an imaging resolution of <100 nm in the lab, and with continued optimization, even better performance (~50 nm resolution) is possible. Use in-situ on the lunar or other planetary surfaces would require some redesign to optimize instrument performance, but such an instrument would be equally useful.

Variable Pressure Scanning Electron Microscopy↗