Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “electron microscope”

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.

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

At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Angular particle impingement studies of thermoplastic materials at normal incidence

Scanning electron microscope studies were conducted to characterize the erosion resistance of polymethyl methacrylate (PMMA), polycarbonate (PC), polytetrafluorethylene (PTFE), and ultra-high-molecular-weight polyethylene (UHMWPE). Erosion was caused by a jet of angular microparticles of crushed glass at normal incidence. Material built up above the original surface on all of the materials. As erosion progressed, this buildup disappeared. UHMWPE was the most resistant material and PMMA the least. The most favorable properties for high erosion resistance were high values of ultimate elongation, maximum service temperature, and strain energy and a low value of the modulus of elasticity. Erosion-rate-versus-time curves of PC and PTFE exhibited incubation, acceleration, and steady-state periods. PMMA also exhibited a deceleration period, and an incubation period with deposition was observed for UHMWPE.

Rao, P. V.↗
NASA NTRS1986

An ultrahigh vacuum multipurpose specimen chamber with sample introduction system for in situ transmission electron microscopy investigations

A commercial transmission electron microscope (TEM), with flat-plate upper pole piece configuration of the objective lens, and top-entry specimen introduction was modified by introducing an ultrahigh vacuum (UHV) specimen chamber for in situ TEM experimentation. The pumping and design principles and special features of this UHV chamber, which makes it possible to obtain 5 x 10 to the -10th mbar pressure at the site of the specimen, while maintaining the airlock system that allows operation in the 10 to the -10th mbar range within 15 min after specimen change, are described. Design operating pressures and image quality (resolution of metal particles smaller than 1 nm in size) were achieved. Schematic drawings and design dimensions are included.

Heinemann, K.↗
NASA NTRS1985

Microgravity changes in heart structure and cyclic-AMP metabolism

The effects of microgravity on cardiac ultrastructure and cyclic AMP metabolism in tissues of rats flown on Spacelab 3 are reported. Light and electron microscope studies of cell structure, measurements of low and high Km phosphodiesterase activity, cyclic AMP-dependent protein kinase activity, and regulatory subunit compartmentation show significant deviations in flight animals when compared to ground controls. The results indicate that some changes have occurred in cellular responses associated with catecholamine receptor interactions and intracellular signal processing.

Philpott, D. E.↗
NASA NTRS1986

Cometary particles - Thin sectioning and electron beam analysis

Thin sections (500 to 1000 angstroms thick) of individual micrometeorites (5 to 15 micrometers) have been prepared with an ultramicrotome equipped with a diamond knife. Electron microscope examination of these sections has revealed the internal structures of chondritic micrometeorites, and a subset of highly porous, fragile particles has been identified. Delicate meteoritic materials such as these are characteristic of debris from cometary meteors.

Bradley, J. P.↗
NASA NTRS1985

Analytical/experimental correlations of failure modes in composites

During the past decade, significant progress has been made in the development and refinement of finite element micromechanics analyses of unidirectional composite materials. The current status is summarized here, and example results are presented. These are correlated with available experimental data, and with scanning electron microscope observations.

Adams, D. F.↗
NASA NTRS1986

Progressive fracture of fiber composites

Refined models and procedures are described for determining progressive composite fracture in graphite/epoxy angleplied laminates. Unique Lewis Research Center capabilities are utilized including the Real-Time Ultrasonic C-San (RUSCAN) experimental facility and the Composite Durability Structural Analysis (CODSTRAN) computer code. CODSTRAN is used to predict the fracture progression based on composite mechanics, finite element stress analysis, and fracture criteria modules. The RUSCAN facility, CODSTRAN computer code, and scanning electron microscope are used to determine durability and identify failure mechanisms in graphite/epoxy coomposites. Results indicate that RUSCAN/CODSTRAN is an effective method of Studying progressive fracture of composites.

Irvine, T. B.↗
NASA NTRS1986

Shock-induced CO2 loss from CaCO3 - Implications for early planetary atmospheres

Recovered samples from shock recovery experiments on single crystal calcite were subjected to thermogravimetric analysis to determine the amount of post-shock CO2, the decarbonization interval and the activation energy, for the removal of remaining CO2 in shock-loaded calcite. Comparison of post-shock CO2 with that initially present determines shock-induced CO2 loss as a function of shock pressure. Incipient to complete CO2 loss occurs over a pressure range of approximately 10 to approximately 70 GPa. Optical and scanning electron microscopy reveal structural changes which are related to the shock-loading. The occurrence of dark, diffuse areas, which can be resolved as highly vesticular areas as observed with a scanning electron microscope are interpreted as representing quenched partial melts, into which shock-released CO2 was injected. The experimental results are used to constrain models of shock-produced, primary CO2 atmospheres on the accreting terrestrial planets.

Lange, M. A.↗
NASA NTRS1985

Development of otoconia in the embryonic chick (Gallus domesticus)

In the chick (Gallus domesticus) embryo, otoconium formation started first over the macula sacculi around the 4th day of incubation, and a day later over the macula utriculi. It was determined that each otoconium formed as a result of the segmentation of the immature otolithic membrane, and that the calcium responsible for otoconium calcification was incorporated into the organic matrix of each otoconium in the form of small electron-dense granules (20-150 nm in. diameter). The presence of calcium in these granules was confirmed by histochemical staining with osmic-potassium pyroantimonate, by EDTA chelation, and by X-ray micronanalysis under the electron microscope.

Fermin, C. D.↗
NASA NTRS1986

An in-situ study in SEM of delamination in several graphite/epoxy composite material systems

A three point bend fixture compatible with the current loading stage for the Scanning Electron Microscope was designed and fabricated. End-notched flexure tests were run on several materials. Work to date was on AS4/3502, T6T145/F155, and T6T145/F185. Fracture toughness was measured. Fracture of neat resin specimens was begun. The decrease in delaminatin fracture toughness, compared to neat resin toughness, due to rigid fiber filler and interlaminar failure is addressed. An experimental program was designed to try to determine the proper interpretatin for apparent microcracking in neat resin specimens.

Bradley, W. L.↗
NASA NTRS1985

Analysis of micrometeorite material captured by the solar max satellite

A Solar Maximum satellite was retrieved and repaired after being subjected for four years and 55 days to impacts by micrometeorites and Earth-orbiting space debris. The chemical variety and physical condition of particles associated with two particular impact structures in the insulation blanket of the main electronics box are studied. A scanning electron microscope equipped with an energy dispersive X ray analyzer was used to determine morphology and chemistry of impacted areas and associated particles. Some details are discussed.

Schramm, L. S.↗
NASA NTRS1985

SSM atomic oxygen reactions on Kapton and silverized Teflon

Surface morphology studies using scanning electron microscopy on Kapton and Inconel silver coated Teflon material samples retrieved from the Solar Maximum Mission spacecraft revealed significant changes attributed to orbital atomic oxygen induced reactions. The Kapton recession observed on the aluminized Kapton material samples appeared equivalent in nature with that observed on previous Space Shuttle LEO missions. SSM Teflon taped material samples, coated on the back side with films of Inconel protected silver were observed degraded on both sides. Visibly severe reactions on the back side produced total blackening, generally restricted to areas of tape with a narrow direct view-factor of the external orbital environment. High magnification scanning electron microscope views provided evidence of near total silver reaction, flaking, and subsequent erosion of the underlying Teflon itself. Only three of the extensive S.E.M. photographs illustrating the basic reactions observed are included pending further detailed investigations.

Roger Linton↗
NASA NTRS1986

Performance of textured carbon on copper electrode multistage depressed collectors with medium-power traveling wave tubes

Performance of multistage depressed collectors (MDCs) using textured carbon on copper substrate electrode surfaces was evaluated in conjunction with medium-power traveling wave tubes (TWTs). The MDC and TWT overall efficiencies for these electrodes were measured and compared with those obtained with the same TWT and a copper electrode MDC of identical design. Long-term stability of the carbon-coated copper electrode surfaces was investigated by periodic evaluation of TWT-MDC performance over an extended period of continuous wave (CW) operation. Application of textured carbon coating on copper MDC electrode surfaces produced a 13% improvement in both MDC and TWT overall efficiencies for the TWT-MDC tests. During 1600 hr of CW operation with a medium power TWT, no significant changes in MDC performance were noted. This indicated good stability of the textured carbon electrode surfaces. This stability was confirmed by scanning electron microscope examinations of the electrode surfaces before assembly of the MDC and after completion of the test program.

Ramins, Peter↗
NASA NTRS1987

Aeolian abrasion on Venus: Preliminary results from the Venus simulator

The role of atmospheric pressure on aeolian abrasion was examined in the Venus Simulator with a constant temperature of 737 K. Both the rock target and the impactor were fine-grained basalt. The impactor was a 3 mm diameter angular particle chosen to represent a size of material that is entrainable by the dense Venusian atmosphere and potentially abrasive by virtue of its mass. It was projected at the target 10 to the 5 power times at a velocity of 0.7 m/s. The impactor showed a weight loss of approximately 1.2 x 10 to the -9 power gm per impact with the attrition occurring only at the edges. Results from scanning electron microscope analysis, profilometry, and weight measurement are summarized. It is concluded that particles can incur abrasion at Venusian temperatures even with low impact velocities expected for Venus.

Marshall, J. R.↗
NASA NTRS1987

Pulsed source of energetic atomic oxygen

A pulsed high flux source of nearly monoenergetic atomic oxygen was designed, built, and successfully demonstrated. Molecular oxygen at several atmospheres pressure is introduced into an evacuated supersonic expansion nozzle through a pulsed molecular beam valve. An 18 J pulsed CO2 TEA laser is focused to intensities greater than 10(9) W/sq cm in the nozzle throat to generate a laser-induced breakdown. The resulting plasma is heated in excess of 20,000 K by a laser supported detonation wave, and then rapidly expands and cools. Nozzle geometry confines the expansion to provide rapid electron-ion recombination into atomic oxygen. Average O atom beam velocities from 5 to 13 km/s were measured at estimated fluxes to 10(18) atoms per pulse. Preliminary materials testing has produced the same surface oxygen enrichment in polyethylene samples as obtained on the STS-8 mission. Scanning electron microscope examinations of irradiated polymer surfaces reveal an erosion morphology similar to that obtained in low Earth orbit, with an estimated mass removal rate of approx. 10(-24) cu cm/atom. The characteristics of the O atom source and the results of some preliminary materials testing studies are reviewed.

Caledonia, George E.↗
NASA NTRS1987

Nondestructive SEM for surface and subsurface wafer imaging

The scanning electron microscope (SEM) is considered as a tool for both failure analysis as well as device characterization. A survey is made of various operational SEM modes and their applicability to image processing methods on semiconductor devices.

Propst, Roy H.↗
NASA NTRS1987

Analysis of NiAlTa precipitates in beta-NiAl + 2 at. pct Ta alloy

Results are reported from experiments performed to identify the precipitates, and their orientation in the matrix, in a beta-NiAl alloy containing 2 at. pct. Ta after undergoing creep test at 1300 K. Test specimens formed by extruding hot powders were compressed at 1300 K for about 50 hr at a strain rate averaging 6/1 million per sec. The specimens were then thinned and examined under an electron microscope and by X-ray diffractometry. An intermetallic NiAlTa compound with a hexagonal Cl4 structure appeared as second phase precipitates in the samples, exhibiting plate-like shapes and a habit plane close to (012). The prism planes of the hexagonal NiAlTa precipitates paralleled the closest packed planes in the cubic beta-NiAl matrix.

Pathare, V.↗
NASA NTRS1988

Fatique crack growth behavior of a single crystal alloy as observed through an in situ fatigue loading stage

An in situ fatigue loading stage inside a scanning electron microscope (SEM) was used to determine the fatigue crack growth behavior of a PWA 1480 single-crystal nickel-based superalloy. The loading stage permits real-time viewing of the fatigue damage processes at high magnification. The PWA 1480 single-crystal, single-edge notch specimens were tested with the load axis parallel to the (100) orientation. Two distinct fatigue failure mechanisms were identified. The crack growth rate differed substantially when the failure occurred on a single slip system in comparison to multislip system failure. Two processes by which crack branching is produced were identified and are discussed. Also discussed are the observed crack closure mechanisms.

Telesman, Jack↗
NASA NTRS1988

As-received microstructure of a SiC/Ti-15-3 composite

A silicon carbide fiber reinforced titanium (Ti-15V-3Cr-3Sn-3Al) composite is metallographically examined. Several methods for examining composite materials are investigated and documented. Polishing techniques for this material are described. An interference layering method is developed to reveal the structure of the fiber, the reaction zone, and various phases within the matrix. Microprobe and transmission electron microscope (TEM) analyses are performed on the fiber/matrix interface. A detailed description of the fiber distribution as well as the microstructure of the fiber and matrix are presented.

Lerch, Bradley A.↗