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Facemire, B. R.

Publications and source records attributed to Facemire, B. R..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Evolution of Local Microstructures: Spatial and Temporal Correlation in Clusters Undergoing 2-Dimensional Diffusion

Diffusion-limited, capillarity-driven, coarsening of precipitates is an important and intensively studied phenomenon. Coarsening can occur among several microstructural constituents ranging from the primary phases to widely dispersed precipitates. Moreover, coarsening of three-dimensional (3-D) phase domains, occurring via mass transport through a two-dimensional (2-D) diffusion field (called mixed-dimensional phase coarsening) is a cooperative phenomenon that is of practical importance, especially in thin film technologies and catalysis. A primary objective of our current work is to focus on the details of evolving microstructures through a study of 'island' formation in heteroepitaxial film/substrate systems. Whereas this work has been designed for space-based coarsening studies, which require long-duration quality microgravity to observe 3-D Ostwald ripening, a significant amount of work has been performed during ground-based studies to observe diffusional coarsening in a liquid-liquid two-phase system. We have performed the experiment at an isopycnic point to maximize exclusion of gravity-based system disturbance. This has allowed observations of 3-D droplets, immobilized by container wall contact, undergoing coarsening by 2-D diffusion for the required long times (approximately 4 months) using a holographic imaging technique. Although such systems may not be as reliant on long-duration microgravity processing as 3-D systems are, they are of direct relevance to so-called mixed-dimensional coarsening and to the study of heterostructures grown by thin-film technique

Curreri, Peter A.↗
NASA NTRS1989

Non-ideality near the monotectic composition of a miscibility-gap type system - Succinonitrile-water

Differential scanning calorimetry (DSC) of near monotectic succinonitrile-water solutions, fast-quenched in hydrophilic and hydrophobic DSC pans, indicate, by degree of undercooling, thst there may be significant dependence of final ingot microstructure on the pre-quench equilibration temperature. Partial molal-volume determinations from density data, along with DSC data, suggest the nature of temperature dependent component associations from 20 to 55 C in homogeneous solutions. The undercooling profile in a hydrophilic container is explained in terms of solution-composition shifts arising from the Gibbs surface excess. The evidence shows that temperature-dependent preferred component aggregates may modulate surface-composition gradients. Similar effects may be present through intermetallic compound formation in metallic monotectic alloys.

Frazier, D. O.↗
NASA NTRS1986

Separation in Binary Alloys

Studies of monotectic alloys and alloy analogs reviewed. Report surveys research on liquid/liquid and solid/liquid separation in binary monotectic alloys. Emphasizes separation processes in low gravity, such as in outer space or in free fall in drop towers. Advances in methods of controlling separation in experiments highlighted.

Frazier, D. O.↗
NASA NTRS1986

Surface effects on phase distributions of a fast-quenched miscibility gap type system - Succinonitrile-water

If a binary homogeneous melt is cooled into an immiscible region, the newly formed second phase will generally have a density different from the parent phase, and will separate readily by sedimentation. Observation of solidification processes in microgravity indicates that outside of sedimentation, at least two other important effets can separate the phases: (1) preferential wetting, and (2) thermal migration of second-phase droplets due to interfacial tension gradients. The latter effect would drive the minority phase along the thermal gradient toward the hottest part (assuming the interfacial tension decreases with increasing temperature), which is usually away from the crucible wall. On the other hand, if the minority phase preferentially wets the crucible, a minority phase layer which thickens as initial solution compositions approach critical, will form adjacent to the solid surface and remain in the coldest region of the ingot. This study presents compelling preliminary evidence that these two effects do exist and that they compete with one another. However, the temperature dependence of preferential wetting below T(c) for the current system of study is, as yet, undetermined. These effects are sensitive to the initial concentration of a hypermonotectic solution cooling through a miscibility gap.

Frazier, D. O.↗
NASA NTRS1985

Studies of Model Immiscible Systems

The objectives are to use model transparent monotectics to obtain fundamental information applicable to two-phase systems in general, to apply this understanding to materials of interest in the Microgravity Science and Applications program, and to interpret results of flight experimental involving monotectic alloys. A number of model immiscible systems are in use to study various aspects of two-phase behavior within the miscibility gap and during solidification. Particle growth, coalescence and particle motions are under investigation using a holographic microscopy system. The system is capable of working with particle densities up to 10 to the 7th power particles/cubic centimeters through a 100 micron depth and can resolve particles of the order of 2 to 3 micron in diameter throughout the entire cell volume. Particle size, distribution changes with respect to time and temperature are observable from sequential holograms. Initial experiments using diethylene glycol/ethyl salicylate (DEG/ES) have demonstrated the usefulness of the technique. The thermal system controls temperature to at least plus or minus 0.001 K over the course of an experiment. A time-lapse film, made from holograms, of a succinonitrile/water solution shows particle size and number distribution changes with time under isothermal conditions. The observations are consistent with Ostwald ripening theory.

Frazier, D. O.↗
NASA NTRS1985

Optical studies of a binary miscibility gap system

Model transparent fluids are being studied to develop a better understanding of phase separation processes in binary miscibility-gap metal alloys. The model selected for the reported work is diethylene glycol-ethyl salicylate. This system is well characterized with respect to its phase diagram, density, surface and interfacial tensions, viscosity, and other pertinent physical properties. Minority phase growth, coalescence, and droplet motions are observed using holographic microscopy which is capable of recording particle densities up to 10 to the 7th particles/cu cm and is able to resolve particles as small as 2 to 3 microns in diameter throughout the entire volume of the test cell. Sequential holograms allow determination of droplet size distribution changes throughout the total volume with respect to time and temperature. This allows a direct method for testing various theories of droplet growth and ripening phenomena.

Witherow, W. K.↗
NASA NTRS1984

Separation processes during binary monotectic alloy production

Observation of microgravity solidification processes indicates that outside of sedimentation, at least two other important effects can separate the phases: critical-point wetting and spreading; and thermal migration of second-phase droplets due to interfacial tension gradients. It is difficult to study these surface tension effects while in a unit gravity field. In order to investigate the processes occurring over a temperature range, i.e., between a consolute point and the monotectic temperature, it is necessary to use a low-gravity environment. The MSFC drop tube (and tower), the ballistic trajectory KC-135 airplane, and the Space Shuttle are ideal facilities to aid formation and testing of hypotheses. Much of the early work in this area focuses on transparent materials so that process dynamics may be studied by optical techniques such as photography for viewing macro-processes; holography for studying diffusional growth; spinodal decomposition and coalescence; ellipsometry for surface wetting and spreading effects; and interferometry and spectroscopy for small-scale spatial resolution of concentration profiles.

Frazier, D. O.↗
NASA NTRS1982

Optical Studies of model binary miscibility gap system

In order to develop a better understanding of separation processes in binary miscibility gap metal alloys, model transparent fluid systems were studied. The system selected was diethylene glycol-ethyl salicylate which has convenient working temperatures (288 to 350 K), low toxicity, and is relatively easy to purify. The system is well characterized with respect to its phase diagram, density, surface and interfacial tensions, viscosity and other pertinent physical properties. Studies of migration of the dispersed phase in a thermal gradient were performed using conventional photomicroscopy. Velocities of the droplets of the dispersed phase were measured and compared to calculated rates which included both Stokes and thermal components. A holographic microscopy system was used to study growth, coalescence, and particle motions. Sequential holograms allowed determination of particle size distribution changes with respect to time and temperature. Holographic microscopy is capable of recording particle densities up to 10 to the 7th power particles/cu cm and is able to resolve particles of the order of 2 to 3 microns in diameter throughout the entire volume of the test cell. The reconstructed hologram produces a wavefront that is identical to the original wavefront as it existed when the hologram was made. The reconstructed wavefront is analyzed using a variety of conventional optical methods.

Lacy, L. L.↗
NASA NTRS1978

Liquid spreading ASTP Science Demonstration

Wetting and spreading phenomena are significant in a wide variety of processes. This report discusses the results of an ASTP Science Demonstration, 'Liquid Spreading', and compares these results to theoretical predictions. On earth the initial spreading of large liquid drops on solid surfaces is always dominated by gravity; in this demonstration the effect of gravity is greatly reduced so that surface energy forces are the controlling factor.

Bourgeois, S. V.↗
NASA NTRS1978

Chemical reactions in low-g

The Apollo-Soyuz flight experiment, 'Chemical Foams' demonstrated that foams and air/liquid dispersions are much more stable in low-gravity than on the ground. It thus should be possible to conduct unique chemical reactions in space foams. The low-g results and subsequent ground work on the formaldehyde clock reaction indicate that the reaction is strongly influenced by (1) dissociated and undissociated solution species being adsorbed at solid/liquid and gas/liquid surfaces and (2) chemical reaction rates apparently being affected by long-range forces determined by the liquid mass and the extent and nature of all surface interfaces.

Grodzka, P. G.↗
NASA NTRS1976

Electrochemical deposition of silver crystals aboard Skylab 4

Silver crystals were grown aboard Skylab 4 by an electro-chemical reaction and subsequently returned to earth for comparison with crystals grown at 1- and 5-g. Both the Skylab and earth-grown crystals show a variety of structures. Certain tendencies in structure dependency on gravity level, however, can be discerned. In addition, downward growing dendrite streamers; upward growing chunky crystal streamers; growth along an air/liquid interface; and ribbon, film, and fiber crystal habits were observed in experiments conducted on the ground with solutions of varying concentrations. It was also observed that the crystal structures of space and ground electro-deposited silver crystals were very similar to the structures of germanium selenide and germanium telluride crystals grown in space and on the ground by a vapor transport technique. Consideration of the data leads to the conclusions that: (1) the rate of electrochemical displacement of silver ions from a 5 percent aqueous solution by copper is predominantly diffussion controlled in space and kinetically controlled in 1- and higher-g because of augmentation of mass transport by convection; (2) downward and upward crystal streamers are the result of gravity-driven convection, the flow patterns of which can be delineated. Lateral growths along an air/liquid interface are the result of surface-tension-driven convection, the pattern of which also can be delineated; (3) electrolysis in space or low-g environments can produce either dendritic crystals with more perfect microcrystalline structures or massive, single crystals with fewer defects than those grown on ground or at higher g-levels. Ribbons or films of space-grown silicon crystals would find a ready market for electronic substrate and photocell applications. Space-grown dendritic, metal crystals present the possibility of unique catalysts. Large perfect crystals of various materials are desired for a number of electronic and optical applications; and (4) vapor transport growth of germanium selenide and germanium telluride is affected by convection mechanisms similar to the mechanisms hypothesized for the electrochemical deposition of silver crystals. Evidence and considerations leading to the preceding summaries and conclusions are presented. The implications of the findings and conclusions for technological applications are discussed, and recommendations for further experiments are presented.

Grodzka, P. G.↗
NASA NTRS1975

Studies of rotating liquid floating zones on Skylab IV

Liquid zones of water, soap solution and soap foam were deployed between two aligned circular disks which were free to rotate about the zone axis in the microgravity environment of Skylab IV. Such a configuration is of interest in the containerless handling of melts for possible future space processing crystal growth experiments. Three basic types of zone surface deformation and instability were observed for these rotational conditions; axisymmetric shape changes under single disk rotation, nonaxisymmetric, whirling, C-modes for long zones with equal rotation of both disks, and capillary wave phenomena for short zones with equal rotation of both disks. The sources of these instabilities and the conditions promoting them are analyzed in detail from video tape recordings of the Skylab experiments.

Carruthers, J. R.↗
NASA NTRS1975

Tracking transient temperatures with liquid crystals

The theoretical basis of the use of the liquid crystal technique to obtain transient thermal data is discussed. Results of calibrations of liquid crystal temperature sensors are given. The effects of crystal aging, lighting effects, observer bias, etc., on accuracy are discussed. The sensitivity of liquid crystal tapes as sensors of dynamic temperature changes is quite high. The accuracy of the technique is determined primarily by the type of calibration apparatus used.

Grodzka, P. G.↗
NASA NTRS1973

Apollo 17 heat flow and convection experiments: Final data analyses results

A group of experiments called the Apollo 17 heat flow and convection (HFC) experiments was conducted, aboard the Apollo 17 spacecraft while in translunar coast on the way to the moon. These experiments together with the HFC experiments flown on Apollo 14 demonstrated and provided data on two types of low-g natural convection: cellular, surface tension-driven convection and convection in confined fluids caused by spacecraft and astronaut movements. Observed convection onset times show that surface tension-driven convection occurs at lower temperature gradients in low-g than in one-g environments. Data on heat flow in confined fluids show that spacecraft and astronaut movements can cause significant degrees of convection.

Bannister, T. C.↗