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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Mars Aqueous Chemistry Experiment (MACE)

The concept of an aqueous-based chemical analyzer for Martian surface materials has been demonstrated to be feasible. During the processes of analysis, design, breadboarding, and most importantly, testing, it has become quite apparent that there are many challenges in implementing such a system. Nonetheless, excellent progress has been made and a number of problems which arose have been solved. The ability to conduct this work under a development environment which is separate and which precedes the project-level development has allowed us to find solutions to these implementation realities at low cost. If the instrument had been selected for a mission without this laboratory pre-project work, the costs of implementation would be much higher. In the four areas covered in Sections D, E, F, and G of this Final Report, outstanding progress has been made. There still remains the task of flight-qualifying certain of the components. This is traditionally done under the aegis of a Flight Project, but just as the concept development can be done at much lower cost when kept small and focused, so could the qualification program of critical parts benefit. We recommend, therefore, that NASA consider means of such qualifications and brass-boarding, in advance of final flight development. This is a generic recommendation, but hardware such as the Mars aqueous chemistry experiment (MACE) and other similarly-new concepts are particularly applicable. MACE now has wide versatility, in being able to reliably dispense both liquids and solids as chemical reagents to an entire suite of samples. The hardware and the experiment is much simpler than was developed for the Viking Biology instrument, yet can accomplish all the inorganic chemical measurements that the Viking desing was capable of. In addition, it is much more flexible and versatile to new experiment protocols (and reagents) than the Viking design ever could have been. MACE opens up the opportunity for many different scientific disciplines to design sub- experiments and to benefit from the investigations that can be conducted. In this sense, it will have the value of a facility, although our recommendation would be that it be under the stewardship of a single lead investigator to insure that conflicting requirements not compromise the straight-forward design that have been achieved. MACE is an excellent candidate for upcoming Mars missions, including the Mars Surveyor Program (MSP) lander missions in 2001 and 2003. In addition, it could be used for any mission to the surface of any other planet or planetary body (including small bodies). An important next step is to encourage various investigators to propose specific uses for this experiment that specifically address their major scientific objectives for upcoming missions.

Benton, Clark C.↗
NASA NTRS1997

Liquid-Liquid Phase Separation in Supersaturated Lysozyme Solutions and Associated Precipitate Formation/Crystallization

Using cloud point determinations, the phase boundaries (binodals) for metastable liquid-liquid (L-L) separation in supersaturated hen egg white lysozyme solutions with 3%, 5%, and 7% (wlv) NaCl at pH= 4.5 and protein concentrations c between 40 and 400 mg/ml were determined. The critical temperature for the binodal increased approximately linearly with salt concentration. The coexisting liquid phases both remained supersaturated but differed widely in protein concentration. No salt repartitioning was observed between the initial and the two separated liquid phases. After the L-L separation, due to the presence of the high protein concentration phase, crystallization occurred much more rapidly than in the initial solution. At high initial protein concentrations, a metastable gel phase formed at temperatures above the liquid binodal. Both crystal nucleation and gel formation were accelerated in samples that had been cycled through the binodal. Solutions in the gel and L-L regions yielded various types of precipitates. Based on theoretical considerations, previous observations with other proteins, and our experimental results with lysozyme, a generic phase diagram for globular proteins is put forth. A limited region in the (T,c) plane favorable for the growth of protein single crystals is delineated.

Muschol, Martin↗
NASA NTRS2007

Status of Superheated Spray and Post Combustor Particulate Modeling for NCC

At supersonic cruise conditions, high fuel temperatures, coupled with low pressures in the combustor, create potential for superheated fuel injection leading to shorter fuel jet break-up time and reduced spray penetration. Another issue particularly important to the supersonic cruise is the aircraft emissions contributing to the climate change in the atmosphere. Needless to say, aircraft emissions in general also contribute to the air pollution in the neighborhood of airports. The objectives of the present efforts are to establish baseline for prediction methods and experimental data for (a) liquid fuel atomization and vaporization at superheated conditions and (b) particle sampling systems and laboratory or engine testing environments, as well as to document current capabilities and identify gaps for future research.

Liu, Nan-Suey↗
NASA NTRS2007

Binary Colloidal Alloy Test-3 and 4: Critical Point

Binary Colloidal Alloy Test - 3 and 4: Critical Point (BCAT-3-4-CP) will determine phase separation rates and add needed points to the phase diagram of a model critical fluid system. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

Weitz, David A.↗
NASA NTRS2008

Binodal Colloidal Aggregation Test - 4: Polydispersion

Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) will use model hard-spheres to explore seeded colloidal crystal nucleation and the effects of polydispersity, providing insight into how nature brings order out of disorder. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

Chaikin, Paul M.↗
NASA NTRS2020

Microscopic Object Classification through Passive Motion Observations with Holographic Microscopy

Digital holographic microscopy provides the ability to observe throughout a volume that is large compared to its resolution element without the need to refocus through the volume. This capability enables simultaneous observations of large numbers of small objects within such a volume. We have constructed a microscope that can observe a volume 0.4 x 0.4 x 1.0 µm with submicrometer resolution for observation of microorganisms and minerals in liquid environments in earth and on potential planetary missions. Because environmental samples are likely to contain mixtures of inorganics and microorganisms that are of comparable sizes near the resolution limit of the instrument, discrimination of living and non-living objects may be difficult. The motion of motile organisms can be used to readily distinguish them from non-motile objects (live or inorganic), but additional methods are required to distinguish non-motile organisms and inorganic objects that are of comparable size, but different composition and structure. In this paper we evaluate the use of passive motion to make this discrimination by evaluating diffusion and buoyancy characteristics of objects in the field of view.

Lindensmith, Christian↗
NASA NTRS2018

Mars Ecopoiesis Testbed

Mars surface conditions where liquid water is absent were simulated for the purposes of laboratory research. A pressure-temperature (P-T) profile was maintained in which no combination of pressure or temperature corresponds to the liquid region of the water phase diagram. The triple point of pure water occurs at T = 0.1oC and P(H2O) = 6.01 mbar; therefore all temperatures and pressures must be kept below these values, respectively. A 35-day test was performed in a commercial planetary simulation system (Techshot, Inc., Greenville, IN) in which the minimum night-time temperature was -80oC, the maximum daytime temperature was +26oC, the simulated day-night light cycle in earth hours was 12-on and 12-off, and the total pressure of the pure CO2 atmosphere was maintained below 11 mbar. Any water present was allowed to equilibrate with the changing temperature and pressure. The gas phase was sampled into a CR1-A condensation-mirror low-pressure hygrometer, which uses liquid nitrogen (down to 77oK) to determine the dew point (Buck Technologies, Boulder, CO). Dew point was measured once every hour and recorded on a data logger, along with the varying temperature in the chamber, from which the partial pressure of water was calculated. The resulting calculated daily cycles were tracked on the water P-T diagram, and no points were found to fall within the liquid-phase region of the diagram. It is concluded that there was no liquid water present throughout the test except during the initial pump-down period when aqueous specimens were introduced on the first day (less than 1 hour). Mars regolith simulant was present during this test, and further investigation is needed to determine whether liquid water could have been present or absent in the regolith in the form of brine. Biological samples consisting of Cyanobacteria: Anabena sp., Chroococcidiopsis CCMEE171, Plectonema boryanum; Eubacteria: Bacillus subtilis, Pseudomonas aeruginosa, and Eukaryota: Chlorella ellipsoidia were maintained in the simulator under the above-described conditions. The exposed specimens were tested for intracellular esterase activity, chlorophyll content (where appropriate) and reproductive survival. All tests yielded low-level positive results in all cases. In parallel to these terrestrial studies a planned design study was undertaken for the proposed test bed. Design requirements include compact assembly for transport and installation on the planetary surface (multiple units per mission would be expected), protective internal package for the release of organisms, a means of atmosphere exchange, access to sunlight, a means of penetrating the planetary surface, and most importantly a means of acquiring regolith while meeting the requirements of planetary protection. In consultation with advisers a design was created, and a large-scale mock-up of this design was fabricated by additive manufacturing at Techshot, Inc. with moving parts that simulated the components of the design. The mock-up assembly has been demonstrated to interested parties. A means of detecting live metabolism will also be included in the test bed. Several options were reviewed, and it is concluded that, by the time the ecopoiesis test bed is ready for testing the optimum instrument will be the equivalent of a hand-held mass spectrometer for metabolic gas analysis. This will maximize versatility and reveal much more information than could a detector of a single product (such as molecular oxygen), and the

Ecopoiesis↗
NASA NTRS1996

Magneto-Hydrodynamic Damping of Convection During Vertical Bridgman-Stockbarger Growth of HgCdTe

In order to quantify the effects of convection on segregation, Hg(0.8)Cd(0.2)Te crystals were grown by the vertical Bridgman-Stockbarger method in the presence of an applied axial magnetic field of 50 kG. The influence of convection, by magneto-hydrodynamic damping, on mass transfer in the melt and segregation at the solid-liquid interface was investigated by measuring the axial and radial compositional variations in the grown samples. The reduction of convective mixing in the melt through the application of the magnetic field is found to decrease radial segregation to the diffusion-limited regime. It was also found that the suppression of the convective cell near the solid-liquid interface results in an increase in the slope of the diffusion-controlled solute boundary layer, which can lead to constitutional supercooling.

Watring, D. A.↗
NASA NTRS1995

Partical Melting of bulk Bi-2212

Dense and textured Bi-2212 bulk samples have been produced by the partial melting process. The appropriate amount of liquid phase necessary for complete densification has been adjusted by controlling the maximum processing temperature. The maximum temperature itself has to be adapted to several parameters as powder stoichiometry, silver addition and oxygen partial pressure. Prolonged annealing at 850 and 820 C and cooling in N2 atmosphere led to nearly single phase material with T(sub c) = 92 K. Critical current densities j(sub c) of 2'200 A/sq cm at 77 K/0 T have been achieved in samples of more than 1 mm thickness. Reducing the thickness below 0.4 mm enhances j(sub c) considerably to values is greater than 4'000 A/sq cm. The addition of 2 wt% Ag decreases the solidus temperature of the Bi-2212 powder by 21 C. Therefore, the maximum heat treatment temperature of Ag containing samples can be markedly lowered leading to a reduction of the amount of secondary phases. In addition, Ag enhances slightly the texture over the entire cross section and as a result j(sub c) at 77 K/0 T.

Heeb, B.↗
NASA NTRSDate not supplied

Analysis of Integrated Spacecraft Performance Using A Rotating Detonation Rocket Engine

For spacecraft with especially stringent mass fraction constraints, the use of a rotating detonation rocket engine (RDRE) may yield potentially significant system mass savings. The pressure gain combustion inherent to RDREs provides higher thrust than traditional rocket engines for a given supply pressure and throat area. This opens multiple avenues for reducing system mass via higher specific impulse, reduced gravity losses, and reduced feed pressures. To highlight the potentially weight-saving characteristics of RDRE systems, the integrated performance of representative spacecraft designs using either a conventional rocket engine or an RDRE was assessed. This paper details the assumptions, methods, and results of this trade study. Two representative spacecraft were assessed. The first is a Liquid Mars Ascent Vehicle (MAV). This spacecraft was designed by NASA in 2011 for the Mars Sample Return Campaign but was not selected for flight due in part to it exceeding the mass requirements by 119 lbm. The second is MIURA-1, a kerolox sounding rocket developed by Payload Aerospace S.L.. The Liquid MAV assessment showed that an RDRE powered design met the mass requirements with a total vehicle mass 46 lbm below the limit. The MIURA-1 assessment showed that wall heat transfer and regenerative cooling are significant challenges for kerolox RDREs, but these challenges may be mitigated by reducing mixture ratio and using both propellants to cool the chamber. The assessment showed that an RDRE powered sounding rocket could achieve 12% more microgravity time than a conventional sounding rocket with the same payload and total vehicle mass. Alternately, if the payload mass and target apogee are held constant, then an RDRE powered sounding rocket can be 8% shorter and 11% lighter than a conventional sounding rocket. These results suggest that the advent of RDREs for in-space propulsion may unlock new missions for which conventional propulsion is not feasible.

Rotating Detonation Rocket Engine↗
NASA NTRSDate not supplied

Analysis of Integrated Spacecraft Performance Using Rotating Detonation Rocket Engine

For spacecraft with especially stringent mass fraction constraints, the use of a rotating detonation rocket engine (RDRE) may yield potentially significant system mass savings. The pressure gain combustion inherent to RDREs provides higher thrust than traditional rocket engines for a given supply pressure and throat area. This opens multiple avenues for reducing system mass via higher specific impulse, reduced gravity losses, and reduced feed pressures. To highlight the potentially weight-saving characteristics of RDRE systems, the integrated performance of representative spacecraft designs using either a conventional rocket engine or an RDRE was assessed. This paper details the assumptions, methods, and results of this trade study. Two representative spacecraft were assessed. The first is a Liquid Mars Ascent Vehicle (MAV). This spacecraft was designed by NASA in 2011 for the Mars Sample Return Campaign but was not selected for flight due in part to it exceeding the mass requirements by 119 lbm. The second is MIURA-1, a kerolox sounding rocket developed by Payload Aerospace S.L.. The Liquid MAV assessment showed that an RDRE powered design met the mass requirements with a total vehicle mass 46 lbm below the limit. The MIURA-1 assessment showed that wall heat transfer and regenerative cooling are significant challenges for kerolox RDREs, but these challenges may be mitigated by reducing mixture ratio and using both propellants to cool the chamber. The assessment showed that an RDRE powered sounding rocket could achieve 12% more microgravity time than a conventional sounding rocket with the same payload and total vehicle mass. Alternately, if the payload mass and target apogee are held constant, then an RDRE powered sounding rocket can be 8% short and 11% lighter than a conventional sounding rocket. These results suggest that the advent of RDREs for in-space propulsion may unlock new missions for which conventional propulsion is not feasible.

Rotating Detonation Rocket Engine↗
NASA NTRS2002

PCS: The First Fluid Physics Payload on ISS

The Physics of Colloids in Space (PCS) experiment was accommodated within International Space Station (ISS) EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack 2 and was remotely operated from early June 2001 until February 2002 from NASA Glenn Research Center's Telescience Support Center in Cleveland, Ohio and from a remote site at Harvard University in Cambridge, Massachusetts. PCS is an experiment conceived by Professor David A. Weitz of Harvard University (the Principal Investigator), focusing on the behavior of three different classes of colloid mixtures. The sophisticated light scattering instrumentation comprising PCS is capable of color imaging, and dynamic and static light scattering from 11 to 169 degrees, Bragg scattering over the range from 10 to 60 degrees, and laser light scattering at low angles from 0.3 to 6.0 degrees. The PCS instrumentation performed remarkably well, demonstrating a flexibility that enabled experiments to be performed that had not been envisioned prior to launch. While on-orbit, PCS accomplished 2400 hours of science operations, and was declared a resounding success. Each of the eight sample cells worked well and produced interesting and important results. Crystal nucleation and growth and the resulting structures of two binary colloidal crystal alloys were studied, with the long duration microgravity environment of the ISS facilitating extended studies on the growth and coarsening characteristics of the crystals. In another experiment run, the de-mixing of the colloid-polymer critical-point sample was studied as it phase-separates into two phases, one that resembles a gas and one that resembles a liquid. This process was studied over four decades of length scale, from 1 micron to 1 centimeter, behavior that cannot be observed in this sample on Earth because sedimentation would cause the colloids to fall to the bottom of the cell faster than the de-mixing process could occur. Similarly, the study of gelation and aging of another colloid-polymer sample, the colloid-polymer gel, also provided valuable information on gelation mechanisms, as did investigations on the extremely the low concentration silica and polystyrene fractal gel samples.

Doherty, M.↗
NASA NTRS2014

Liquid Chromatography-Mass Spectrometry Interface for Detection of Extraterrestrial Organics

The OASIS (Organics Analyzer for Sampling Icy surfaces) microchip enables electrospray or thermospray of analyte for subsequent analysis by the OASIS time-of-flight mass spectrometer. Electrospray of buffer solution containing the nucleobase adenine was performed using the microchip and detected by a commercial time-of-flight mass spectrometer. Future testing of thermospray and electrospray capability will be performed using a test fixture and vacuum chamber developed especially for optimization of ion spray at atmosphere and in low pressure environments.

extraterrestrial organics↗
NASA NTRS1999

Coarsening in Solid-Liquid Mixtures Studied on the Space Shuttle

Ostwald ripening, or coarsening, is a process in which large particles in a two-phase mixture grow at the expense of small particles. It is a ubiquitous natural phenomena occurring in the late stages of virtually all phase separation processes. In addition, a large number of commercially important alloys undergo coarsening because they are composed of particles embedded in a matrix. Many of them, such as high-temperature superalloys used for turbine blade materials and low-temperature aluminum alloys, coarsen in the solid state. In addition, many alloys, such as the tungsten-heavy metal systems, coarsen in the solid-liquid state during liquid phase sintering. Numerous theories have been proposed that predict the rate at which the coarsening process occurs and the shape of the particle size distribution. Unfortunately, these theories have never been tested using a system that satisfies all the assumptions of the theory. In an effort to test these theories, NASA studied the coarsening process in a solid-liquid mixture composed of solid tin particles in a liquid lead-tin matrix. On Earth, the solid tin particles float to the surface of the sample, like ice in water. In contrast, in a microgravity environment this does not occur. The microstructures in the ground- and space-processed samples (see the photos) show clearly the effects of gravity on the coarsening process. The STS-83-processed sample (right image) shows nearly spherical uniformly dispersed solid tin particles. In contrast, the identically processed, ground-based sample (left image) shows significant density-driven, nonspherical particles, and because of the higher effective solid volume fraction, a larger particle size after the same coarsening time. The "Coarsening in Solid-Liquid Mixtures" (CSLM) experiment was conducted in the Middeck Glovebox facility (MGBX) flown aboard the shuttle in the Microgravity Science Laboratory (MSL-1/1R) on STS-83/94. The primary objective of CSLM is to measure the temporal evolution of the solid particles during coarsening.

Caruso, John J.↗
NASA NTRS1996

A Noncontact Measurement Technique for the Density and Thermal Expansion Coefficient of Solid and Liquid Materials

A noncontact measurement technique for the density and the thermal expansion refractory materials in their molten as well as solid phases is presented. This technique is based on the video image processing of a levitated sample. Experiments were performed using the high-temperature electrostatic levitator (HTESL) at the Jet Propulsion Laboratory in which 2-3 mm diameter samples can be levitated, melted, and radiatively cooled in a vacuum. Due to the axisymmetric nature of the molten samples when levitated in the HTESL, a rather simple digital image analysis can be employed to accurately measure the volumetric change as a function of temperature. Density and the thermal expansion coefficient measurements were made on a pure nickel sample to test the accuracy of the technique in the temperature range of 1045-1565 C. The result for the liquid phase density can be expressed by p = 8.848 + (6.730 x 10(exp -4)) x T (degC) g/cu cm within 0.8% accuracy, and the corresponding thermal expansion coefficient can be expressed by Beta=(9.419 x 10(exp -5)) - (7.165 x 10(exp -9) x T (degC)/K within 0.2% accuracy.

Chung, Sang K.↗
NASA NTRS1990

Thermodynamic properties and crystallization kinetics at high liquid undercooling

The heat capacities of liquid and crystalline Au-Pb-Sb alloys in the glass-forming composition range were measured with droplet emulsion and bulk samples. Based on the measured C(sub p) data, the entropy, enthalpy, and Gibbs free energy functions of the eutectic, solid mixture, and undercooled liquid were determined as a function of undercooling and compared with theoretical predictions. The results indicate an isentropic temperature at 313 + or - 5 K, which agrees well with experimental data for the glass transition. A kinetics analysis of the nucleation undercooling response suggests that the proper choice for the Gibbs free energy change during crystallization is most important in analyzing the nucleation kinetics. By classical nucleation theory, the prefactors obtained, based on a variety of theoretical predictions for the driving force, can differ by six orders of magnitude. If the nucleation rates are extrapolated to high undercooling, the extrapolations based on measured heat capacity data show agreement, whereas the predicted nucleation rates are inconsistent with results from drop tower experiments. The implications for microg experiments are discussed.

Fecht, Hans J.↗
NASA NTRSDate not supplied

rHealth One Demonstration Aboard ISS: A Microfluidic Bioanalyzer Based on Sheath/Hydrodynamic Focusing Flow Cytometry

The Exploration Medical Capability (ExMC) element aims to provide astronauts with the means for their own health monitoring, diagnosis, and treatment during exploration missions. As space flight ventures further from earth, the need for autonomous medical care increases under greater constraints on size, mass, and resources. One pillar for diagnosis that crew would be separated from is laboratory analysis. Even now on ISS, blood samples must be collected and returned to earth for testing. In response, ExMC is assessing how assays for hematology, bone health, radiation exposure etc. could be addressed through commercial-off-the-shelf (COTS) and Small Business Innovation Research (SBIR) funded bioanalyzers that are miniaturizing lab technology. Since missions will reach distances where there are no timely replacements, validation on the International Space Station (ISS) is a necessary part of that assessment. In partnership with NASA Johnson Space Center (JSC) Immunology Lab and the Research Operations and Integration (ROI) element, ExMC conducted a technology demonstration on ISS of the rHEALTH ONE, a flow cytometry based bioanalyzer, to assess future devices based on this design. In flow cytometry, there are predominantly three ways to focus the cells (or particles) into a single file stream: hydrodynamic focusing, microcapillary, and acoustic focusing. The rHEALTH ONE utilizes the commercial standard, sheath-based hydrodynamic focusing. rHEALTH itself represents both a company and a suite of medical tools NASA has funded through SBIR grants towards the development of a promising diagnosis instrument for exploration missions. rHEALTH ONE is the interim version of the technology, functional as a benchtop analyzer and test bed for the next generation of rHEALTH in development. Several modifications were made to the rHEALTH ONE analyzer for operation in microgravity. For function, fluid management was key. A sheath-based analyzer uses sheath fluid to flow the sample, cleaning fluid to prevent biological contamination, and a reservoir to collect the liquid waste. The rHEALTH ONE analyzer uses bottles dependent on gravity to separate the air and liquid pathways and keep the liquids contained. It uses only 1 psig of air pressure to directly push the liquid through the device, requiring little-to-no resistance at inlet and outlet. A microtubing assembly with self-sealing luer connectors was designed – featuring 0.014 mm thick durable medical balloons to hold water inside the supply bottles – to create safe containment and easy access for the crew while maintaining the analyzer’s function. For safety, copper tape was added to the interior of the plastic housing to reduce electromagnetic interference, fluid and electrical connections were secured against vibration and leaks, and gaps were further sealed to ensure containment of the optical block and lasers. Water as the sheath and cleaning fluid and TOX 0 samples were used to reduce the biohazard risk to the crew. In May 2022, European Space Agency astronaut Samantha Cristoforetti demonstrated the rHEALTH ONE aboard ISS for its sample loading, flow cytometry, and data collection capability in microgravity. The JSC Immunology Lab provided flow cytometry expertise, designed the sample test protocol, and manufactured and benchmarked the flight samples on a ‘gold-standard’ flow cytometer. The analyzer was primed with water, purged of air, and four calibration solutions of polystyrene microparticles were tested to characterize its performance. Tightly controlled procedures and excellent execution prevented air bubble interference during air/water separation, fluid transfer, sample mixing and loading. Data showed a slight increase in signal noise on 3 of 5 channels and an anomaly of fluorophores migrating in one sample (confirmed by JSC post-flight). Flight results correctly detected the change in sample, matched the analyzer’s ground performance, and were consistent with the gold-standard’s ground results. Although areas were noted for improvement, these outcomes signified complete mission success.

R. S. Miller↗
NASA NTRS1999

Influence of Applied Thermal Gradients and a Static Magnetic Field on Bridgman-Grown GeSi Alloys

The effect of applied axial and radial thermal gradients and an axial static magnetic field on the macrosegregation profiles of Bridgman-grown GeSi alloy crystals has been assessed. The axial thermal gradients were adjusted by changing the control setpoints of a seven-zone vertical Bridgman furnace. The radial thermal gradients were affected by growing samples in ampoules with different thermal conductivities, namely graphite, hot-pressed boron nitride (BN), and pyrolytic boron nitride (PBN). Those samples grown in a graphite ampoule exhibited radial profiles consistent with a highly concave interface and axial profiles indicative of complete mixing in the melt. The samples grown in BN and PBN ampoules had less radial variation. Axial macrosegregation profiles of these samples fell between the predictions for a completely mixed melt and one where solute transport is dominated by diffusion. All of the samples were grown on Ge seeds. This resulted in a period of free growth until the Si concentration in the solid was in equilibrium with the Si concentration in the liquid. The length of crystal grown during this period was inversely proportional to the applied axial thermal gradient. Several samples were grown in an axial 5 Tesla magnetic field. Measured macroscopic segregation profiles on these samples indicate that the magnetic field did not, in general, reduce the melt flow velocities to below the growth velocities.

Volz, M. P.↗