SEARCH · Search NASA

Results for “Scanning microscopy”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS2018

Results of the Aerosol Sampling Experiment on the International Space Station

The indoor air quality of the International Space Station (ISS), in terms of particulate matter, has been assessed through a sampling experiment that collected airborne debris for return to Earth. The Aerosol Sampling Experiment took place on ISS in December 2016 and January 2017, with sample return in February 2017. For redundancy, two different aerosol samplers collected particles in two size ranges spanning from 10 nm to hundreds of micrometers. Multiple analysis techniques have been used to characterize the particles, such as reflective light microscopy, manual scanning electron microscopy (SEM) analysis (secondary and backscattered imaging) with energy dispersive spectroscopy (EDS) x-ray analysis, computer controlled scanning electron microscopy (CCSEM) and Raman spectroscopy. Sampling took place in five locations on ISS, with the greatest deposition of particles in Node 3, followed by Node 1, the US Lab and Node 2. The PMM had very few airborne particles, as expected, owing to the lack of human presence. A large proportion of the sampled material consisted of fibers from clothing. Many particles had complex morphologies or contained multiple metals in a carbonaceous matrix. Metal particles were analyzed for each sampling location in terms of both weight and number percent, with 27 heavy metals detected. Fiberglass and TiO2 particles were present in every location. Quantitative analysis results are presented, and where possible, particle emission sources are identified with the intention to fuel discussions on mitigation.

Meyer, Marit E.↗

NASA NTRS1991

Biofilm formation and control in a simulated spacecraft water system - Two-year results

The ability of iodine to maintain microbial water quality in a simulated spacecraft water system is being studied. An iodine level of about 2.0 mg/L is maintained by passing ultrapure influent water through an iodinated ion exchange resin. Six liters are withdrawn daily and the chemical and microbial quality of the water is monitored regularly. Stainless steel coupons used to monitor biofilm formation are being analyzed by culture methods, epifluorescence microscopy, and scanning electron microscopy. Results from the first two years of operation show a single episode of high bacterial colony counts in the iodinated system. This growth was apparently controlled by replacing the iodinated ion exchange resin. Scanning electron microscopy indicates that the iodine has limited but not completely eliminated the formation of biofilm during the first two years of operation. Significant microbial contamination has been present continuously in a parallel noniodinated system since the third week of operation.

Schultz, John R.↗

NASA NTRS1992

Pyrolytic boron nitride coatings on ceramic yarns and fabrication of insulations

Pyrolytic boron nitride (PBN) was deposited on Nicalon NL 202 silicon carbide yarns at 1000 to 1200 C with the goal of improving the resistance of the Nicalon to deterioration in an aerodynamic environment at temperatures up to 1000 C. For continuous coating, the yarns were fed through the deposition chamber of a pilot plant sized CVD furnace at a rate of about 2 feet per minute. PBN coatings were obtained by reacting boron trichloride and ammonia gases inside the deposition chamber. Most of the PBN coatings were made at around 1080 C to minimize thermal degradation of the Nicalon. Pressures were typically below 0.1 Torr. The coated yarns were characterized by weight per unit length, tensile strength and modulus, scanning electron microscopy, and scanning Auger microscopy. The PBN coated Nicalon was woven into cloth, but was not entirely satisfactory as a high temperature sizing. Several 13 in. square pieces of Nicalon cloth were coated with PBN in a batch process in a factory sized deposition furnace. Samples of cloth made from the PBN coated Nicalon were sewn into thermal insulation panels, whose performance is being compared with that of panels made using uncoated Nicalon.

Moore, Arthur W.↗

NASA NTRS1987

Nondestructive evaluation of structural ceramics

A review is presented on research and development of techniques for nondestructive evaluation and characterization of advanced ceramics for heat engine applications. Highlighted in this review are Lewis Research Center efforts in microfocus radiography, scanning laser acoustic microscopy (SLAM), scanning acoustic microscopy (SAM), scanning electron acoustic microscopy (SEAM), and photoacoustic microscopy (PAM). The techniques were evaluated by applying them to research samples of green and sintered silicon nitride and silicon carbide in the form of modulus-of-rupture bars containing seeded voids. Probabilities of detection of voids were determined for diameters as small as 20 microns for microfucus radiography, SLAM, and SAM. Strengths and limitations of the techniques for ceramic applications are identified. Application of ultrasonics for characterizing ceramic microstructures is also discussed.

Klima, Stanley J.↗

NASA NTRS2005

Two-Photon Fluorescence Microscope for Microgravity Research

A two-photon fluorescence microscope has been developed for the study of biophysical phenomena. Two-photon microscopy is a novel form of laser-based scanning microscopy that enables three-dimensional imaging without many of the problems inherent in confocal microscopy. Unlike one-photon optical microscopy, two-photon microscopy utilizes the simultaneous nonlinear absorption of two near-infrared photons. However, the efficiency of two-photon absorption is much lower than that of one-photon absorption, so an ultra-fast pulsed laser source is typically employed. On the other hand, the critical energy threshold for two-photon absorption leads to fluorophore excitation that is intrinsically localized to the focal volume. Consequently, two-photon microscopy enables optical sectioning and confocal performance without the need for a signal-limiting pinhole. In addition, there is a reduction (relative to one-photon optical microscopy) in photon-induced damage because of the longer excitation wavelength. This reduction is especially advantageous for in vivo studies. Relative to confocal microscopy, there is also a reduction in background fluorescence, and, because of a reduction in Rayleigh scattering, there is a 4 increase of penetration depth. The prohibitive cost of a commercial two-photon fluorescence-microscope system, as well as a need for modularity, has led to the construction of a custom-built system (see Figure 1). This system includes a coherent mode-locked titanium: sapphire laser emitting 120-fs-duration pulses at a repetition rate of 80 MHz. The pulsed laser has an average output power of 800 mW and a wavelength tuning range of 700 to 980 nm, enabling the excitation of a variety of targeted fluorophores. The output from the laser is attenuated, spatially filtered, and then directed into a confocal scanning head that has been modified to provide for side entry of the laser beam. The laser output coupler has been replaced with a dichroic filter that reflects the longer-wavelength excitation light and passes the shorter-wavelength fluorescence light. Also, the confocal pinhole has been removed to increase the signal strength. The laser beam is scanned by a twoperpendicular- axis pair of galvanometer mirrors through a pupil transfer lens into the side port of an inverted microscope. Finally, the beam is focused by a 63-magnification, 1.3-numerical- aperture oil-immersion objective lens onto a specimen. The pupil transfer lens serves to match the intermediate image planes of the scanning head and the microscope, and its location is critical. In order to maximize the quality of the image, (that is, the point spread function of the objective lens for all scan positions), the entire system was modeled in optical-design software, and the various free design parameters (the parameters of the spatial-filter components as well as the separations of all of the system components) were determined through an iterative optimization process. A modular design was chosen to facilitate access to the optical train for future fluorescence correlation spectroscopy and fluorescence-lifetime experiments.

Fischer, David G.↗

NASA NTRS1991

Microstress contrast in scanning electron acoustic microscopy of ceramics

A mathematical model of image contrast in scanning electron acoustic microscopy (SEAM) due to the effect of residual stresses in materials is presented. It is found that in regions near the ends of the radial cracks induced by Vickers indentation the SEAM micrographs reveal a rather large variation of the acoustic output signal.

Cantrell, John H.↗

NASA NTRS1986

Reliability of scanning laser acoustic microscopy for detecting internal voids in structural ceramics

The reliability of 100 MHz scanning laser acoustic microscopy (SLAM) for detecting internal voids in sintered specimens of silicon nitride and silicon carbide was evaluated. The specimens contained artificially implanted voids and were positioned at depths ranging up to 2 mm below the specimen surface. Detection probability of 0.90 at a 0.95 confidence level was determined as a function of material, void diameter, and void depth. The statistical results presented for void detectability indicate some of the strengths and limitations of SLAM as a nondestructive evaluation technique for structural ceramics.

Roth, D. J.↗

NASA NTRS1986

Reliability of scanning laser acoustic microscopy for detecting internal voids in structural ceramics

Roth, D. J.↗

NASA NTRS1990

Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics

The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms the interpretation of the strong contrast.

Cantrell, John H.↗

NASA NTRS1977

Ultrastructural changes in tracheal epithelial cells exposed to oxygen

White albino rats were sacrificed after 24, 36, 48, 72, and 96 h of exposure to 100% O2 at 1 atm. Tissue was prepared for the scanning electron microscope (SEM) by Critical Point Drying and for the transmission electron microscope (TEM) by plastic embedding. Scanning microscopy showed a loss of microvilli after 48 h of exposure. Cilia appeared relatively normal with SEM, but TEM revealed changes in the outer membrane. In TEM, nonciliated cells appeared swollen and often encroached on the ciliated cells. A heavy mucous blanket remained even after processing. All the changes observed that are induced by oxygen exposure contribute to mucostasis, reducing and/or halting mucociliary clearance.

Philpott, D. E.↗

NASA NTRS1980

Effect of starting powder characteristics on density, microstructure and low temperature oxidation behavior of a Si3N48w/o Y2O3 ceramic

The densification and oxidation behavior of Si3N4 - 8w/oY2O3 prepared from three commercial starting powders were studied. Bars of SN 402, SN 502, and CP 85/15 were sintered for 3 to 4.5 hours at 1750 C. A second set was hot pressed for 2 hours at 1750 C. The microstructures were studied by transmission electron microscopy and scanning electron microscopy, densities were determined, and the phase compositions were determined by X-ray diffraction. Densification and microstructure were greatly influenced by the starting powder morphology and impurity content. Although SN 402 exhibited the maximum weight lose, the highest sintered and hot pressed densities were obtained with this powder. All powders had both equiaxed and elongated grains. Sintered bars were composed of beta silicon nitride and n-melelite. In contrast, hot pressed bars contained beta silicon nitride, H-phase, and J-phase, but no melelite. Yttria distribution in sintered bars was related to the presence of cation impurities such as Ca, Fe, and Mg. A limited oxidation study at 750 C in air showed no instability in these Si3N4 - 8 w/oY2O3 specimens, regardless of startin powder.

Schuon, S.↗

NASA NTRS1982

An unusual layered mineral in chondrules and aggregates of the Allende carbonaceous chondrite

Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X ray (EDS) and electron energy loss (EELS) spectroscopy examinations of the microstructures and phase relationships of minerals in opaque spherules in the Allende chondrules and aggregates are reported. The studies were carried out on petrographic thin sections which were ion-thinned. A significant metasomatic effect was observed in a highly oxidizing condition of a later cooled stage. An unusually layered Fe-, Ni-, and O-rich mineral related to serpentine was found to occur in the opaque specimen, and was judged to occur by alteration of olivine. It is noted that low temperature and a hydrous condition would have been required for the formation of the serpentine in the spherules, the first observed in Allende. It is suggested that the aqueous conditions occurred before the final stage of the meteorite formation, and proceeded in a nonterrestrial manner.

Tomeoka, K.↗

NASA NTRS1983

Mineralogy and petrology of chondrules and inclusions in the Mokoia CV3 chondrite

The inclusions and chondrules of the Mokoia CV3 chondrite are studied systematically and compared with those in the Allende meteorite. Five polished thin sections of Mokoia were examined by optical microscopy, backscattered scanning electron microscopy, and electronprobe microanalysis, and objects greater than about 100 microns in apparent diameter were measured and classified petrographically. Three major types of olivine chondrules are distinguished: igneous chondrules, which evidently crystallized from droplets of silicate melt; recrystallized chondrules, apparently metamorphosed at relatively high temperatures; and accretional aggregates, which are probably fragments of igneous chondrules. Refractory inclusions in Mokoia are generally similar to those found in Allende, although Mokoia inclusions include phyllosilicates rather than feldspathoids and melilite-rich Ca, Al-rich inclusions (CAIs) are more abundant in Allende. The small, fine-grained CAIs, which are more abundant than coarse-grained CAIs in both meteorites, are observed to represent aggregates of three distinct constituents: concentric objects, chaotic material and inclusion matrix. It is concluded that most of the CAIs probably formed during metamorphism, partial melting, and incomplete distillation of primitive dust aggregates heated in the solar nebula.

Cohen, R. E.↗

NASA NTRS1986

Solidification of Nb-Ge alloys in long drop tubes

The 30-m and 100 m-long drop tubes at the Marshall Space Flight Center have been used to obtain large undercooling in Nb-Ge alloys. Electron beam melting has been used to obtain drops approximately 2.5 mm in diam. In the 30-m tube, many specimens fell the length of the tube without solidifying, and were ultimately liquid-quenched in oil. The amount of undercooling prior to the quench was usually around 0.13 T(m). In the 100-m tube, freezing generally initiated during free fall, and the maximum undercooling was around 0.22 T(m). Microstructures were characterized by a combination of X-ray diffraction, optical microscopy, and scanning electron microscopy with energy dispersive analysis by X-rays. A variety of interesting microstructures was observed.

Bayuzick, R. J.↗

NASA NTRS1987

Mechanisms of rolling contact spalling

The results of a study aimed at analyzing the mechanical material interactions responsible for rolling contact spalling of the 440 C steel, high pressure oxygen turbopump bearings are presented. A coupled temperature displacement finite element analysis of the effects of friction heating under the contact is presented. The contact is modelled as a stationary, heat generating, 2 dimensional indent in an elastic perfectly plastic half-space with heat fluxes up to 8.6 x 10000 KW/m sq comparable to those generated in the bearing. Local temperatures in excess of 1000 C are treated. The calculations reveal high levels of residual tension after the contact is unloaded and cools. Efforts to promote Mode 2/Mode 3 fatigue crack growth under cyclic torsion in hardened 440 C steel are described. Spalls produced on 440 C steel by a 3 ball/rod rolling contact testing machine were studied with scanning microscopy. The shapes of the cyclic, stress strain hysteresis loops displayed by hardened 440 C steel in cyclic torsion at room temperature are defined for the plastic strain amplitudes encountered in rolling/sliding contact. Results of these analyses are discussed in detail.

Kumar, A. M.↗

NASA NTRS1988

Effect of electric discharge machining on the fatigue life of Inconel 718

The effect of electric discharge machining on the fatigue life of Inconel 718 alloy at room temperature was investigated. Data were generated in the uniaxial tension fatigue mode at ambient temperature using flat 3.175 mm thick specimens. The specimens were machined on a wire-cut electric discharge machine at cutting speeds ranging from 0.5 to 2 mm per minute. The specimens were fatigued at a selected stress, and the resulting fatigue lives compared with that of the virgin material. The surfaces of the fatigued specimens were examined under optical and scanning electron microscopes, and the roughness of the surfaces was measured using a standard profilometer. From the results of the investigation, it was concluded that the fatigue life of the specimens machined using EDM decreased slightly as compared with that of the virgin material, but remained unchanged as the cutting speed was changed. The results are explained using data produced employing microhardness measurements, profilometry, and optical and scanning microscopy.

Jeelani, S.↗

NASA NTRS1992

The microscopic world: A demonstration of electron microscopy for younger students

The purpose is to excite students about the importance of scientific investigation and demonstrate why they should look at things in greater detail, extending beyond superficial examination. The topics covered include: microscopy, scanning electron microscopes, high magnification, and the scientific method.

Horton, Linda L.↗

NASA NTRS1992

Preliminary results of an experimental study of the interactions of basalt glass and a water vapor atmosphere: Implications for weathering on Mars

Models of weathering processes on the surface of Mars invoke hydrothermal alteration as the primary mechanism responsible for clay formation. Previous experimental studies of basalt glass interactions with water under hydrothermal conditions demonstrate that phyllosilicates and zeolites are the primary alteration minerals. Gas-solid weathering is thought to be less thermodynamically favorable and relatively unimportant, however, the experimental alteration of basalt glass under vapor ion conditions (large SA/V) can result in the formation of clay minerals, zeolites, and hydrated calcium silicates. We have undertaken a study of the reacted layers formed on basalt glasses experimentally altered under vapor hydration conditions to resolve this issue. High SA/V ratios promote reaction product buildup in solution and promote alteration mineral formation. It was previously shown that these reaction conditions promote weathering processes similar to those found in nature for tektite glasses, rhyolitic glasses, and basalt glasses. The hydration of basalt glass is described for 100 percent relative humidity experiments at temperatures of 150, 175, and 200 C for up to 400 days. Preliminary characterization of the alteration layers with analytical electron and scanning microscopy suggest that the reaction mechanism includes precipitation of a smectite clay on the outermost surface of the glass. Between the clay and the unreacted glass is an amorphous gel-like phase (palagonite). Our results provide an experimental basis for proposing that basalt glass interactions with vapor atmospheres can be an important source of clay minerals.

Mazer, J. J.↗