National Academies Press: OpenBook

Future Materials Science Research on the International Space Station (1997)

Chapter: 3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment

« Previous: 2 NASA's Microgravity Research Solicitation and Selection Process
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
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3
Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment

This chapter contains descriptions of the broad categories of microgravity materials-science experiments that could yield significant information that is unattainable in a terrestrial gravity field. It also contains assessments of the ability of the current SSFF Core concept to support research on metals and alloys, semiconductors, ceramics and glasses, and polymers. The chapter ends with the committee's overarching conclusions and recommendations about the current SSFF Core concept.

The committee's evaluations of the applicability of the current SSFF Core concept to the needs of the metals and alloys research area and the electronic and photonics (semiconductor) research area are largely based on the 13 projects NASA has already selected as candidate investigations for the ISS (Table 3-1). Because the ceramics, glasses, and polymers areas are underrepresented in the current microgravity materials-science program, potential areas of high-impact research were suggested by the committee and thus are more speculative. Core capabilities required by expanding the program to accommodate areas not included in the current list of 13 are then specified in the report.

The committee also attempted to evaluate the ability of the SSFF Core to support biomaterials research but could not identify any areas in which the Core could directly serve the needs of this research community. Biomaterials researchers will be more likely to exploit the

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
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TABLE 3-1 Principal Investigators, Affiliations, and Program Titles for the Research Projects Selected in Response to 1991 and 1994 NRAs

Principal Investigator

Affiliation

Title

Materials

Prof. B. Andrews

University of Alabama, Birmingham

Coupled Growth in Hypermonotectics

Al-Mn

Prof. D. Stefanescu

University of Alabama, Birmingham

Particle Engulfment and Pushing by Solidifying Interfaces

Al and Al-Ni + SiC and zirconia particles

Prof. D. Mattiesen

Case Western Reserve University

Diffusion Processes in Molten Semiconductors

Ge:Ga; Ge:Sb; Ge:(Si, Ga)

Prof. K. Bachmann

North Carolina State University

Fundamental Aspects of Vapor Deposition and Etching under Diffusion Controlled Transport Conditions

GaxIn1-xP and GaxIn1-xN on Si, Ge, sapphire, and III-V

Prof. R. Bayuzick

Vanderbilt University

Investigation of the Relationship between Undercooling and and Solidification Velocity

NiSn; NiSi; NiTi; TiAl; Ti-Oxygen

Prof. C. Beckermann

University of Iowa

Equiaxed Dendritic Solidification Experiment

ultrapure succinonitrile

Prof. W. Johnson

California Institute of Technology

Physical Properties and Processing of Undercooled Metallic Glass Forming Liquids

metallic glasses containing Zr, Ti, Be, Ni, Nb, Cu, Co

Prof. D. Larson

State University of New York, Stony Brook

Orbital Processing of Eutectic Rod-Like Arrays

Bi/MnBi

Prof. A. Ostrogorsky

Rensselaer Polytechnic Institute

Space-Based and Ground-Based Crystal Growth Using Magnetically Coupled Baffle

Doped GaSb and Ge (possibly GaInSb)

Prof. D. Poirier

University of Arizona

Comparison of Structure and Segregation in Alloys Directionally Solidified in Terrestrial and Microgravity Environments

Pb:23%Sn; Al:15%Cu

Prof. F. Rosenberger

University of Alabama, Huntsville

Self-Diffusion in Liquid Elements

up to 20 elements

Dr. C.-H. Su

NASA/Marshall Space Flight Center

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

ZnSe, ZnSxSe1-x; ZnSe1-xTex; Zn1-xCdxSe

Prof. R. Trivedi

Iowa State University

Interface Pattern Selection Criterion for Cellular Structures in Directional Solidification

Al:4wt%Cu; Al:15wt%Cu

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

unique microgravity capabilities of the space station through specifically designed experimental modules that will be housed outside the SSFF Core. NASA should continue to monitor this potentially high-impact materials-science research area, however.

Metals and Alloys

An analysis of the entire microgravity materials-science research program (Table 2-1) and the candidate investigations selected for the ISS (Table 3-1) shows that the subdiscipline of metals and alloys currently constitutes a substantial portion of the entire MRD materials-science research program. The importance of metals and alloys in NASA-sponsored microgravity research was recognized in the National Research Council report, Microgravity Research Opportunities for the 1990s: ''The microgravity environment, by reducing . . . gravity-driven phenomena, clearly offers new opportunities to metallurgists to understand and enhance control of materials processing'' (NRC, 1995).

Nucleation and Metastable States in the Microgravity Environment

In many materials systems, phase transformation occurs through a nucleation and growth process. In heterogeneous nucleation, nuclei form on heterogeneities in the system, such as container walls, impurity particles, or line defects. In homogeneous nucleation, nuclei form spontaneously through thermodynamic fluctuations within the volume of the parent phase. In almost all cases, heterogeneous nucleation occurs before conditions are reached that would permit homogeneous nucleation. Containerless processing eliminates many of the nucleation sites that prevent significant undercooling of the melt. Deep supercooling may lead to the formation of new, nonequilibrium crystalline and amorphous phases. A microgravity environment makes containerless processing possible without resorting to levitation by induced currents or acoustic pressure gradients. Research on containerless processing to attain deep undercoolings in metals and alloys is a key sector of the current MRD flight program (Bayuzick, 1997a; Flemings, 1997a), as well as of the extensive ground-based research program (Arnold, 1997; Bayuzick, 1997b; Flemings, 1997b; Robinson, 1997; Spaepen, 1997).

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

Microstructures Resulting from Solidification in a Microgravity Environment

Understanding of the microstructures that result from alloy solidification can be increased by critical experiments conducted in a microgravity environment. Microstructures in cast materials, for example, can be manipulated by controlling the alloy composition and rate at which solidification takes place. During solidification, an initially smooth liquid/solid interface can behave in an unstable manner, developing an interface structure containing bumps or even tree-like structures called dendrites. A mixed-phase region known as a "mushy zone" develops before the portion solidifies. Heat and mass transfer processes that occur in the mixed-phase zone determine the final microstructure and properties of the solid (Chalmers, 1964).

A considerable body of theoretical and experimental research has been accumulated on interfacial instabilities and microstructure formation upon solidification (e.g., Glicksman and Marsh, 1993; Martin et al., 1997). Theories generally ignore the influence of fluid convection, although it occurs in experiments carried out in a terrestrial environment. A series of experiments conducted on sounding rockets, aircraft flying in parabolic orbits, and space shuttles have shown that the microstructure is indeed affected by a reduced gravity environment (Johnston and Parr, 1982; Glicksman and Koss, 1994; Fripp, 1996; Abbaschian, 1997).

Most engineering alloys contain two or more phases in the solid state. If certain eutectic (Pirich and Larson, 1982), peritectic (Lograsso, 1997), or monotectic (Andrews, 1997) alloys are directionally solidified in either terrestrial or reduced gravity, aligned microstructures result. These alloys may be regarded as in situ composites. A technologically important example of a eutectic alloy with an aligned microstructure is manganese-bismuth, which has an extraordinarily high magnetic coercivity that approaches the theoretical limit (Pirich and Larson, 1982). The size and spacing of the magnetic phase in material solidified on earth with a strong convective flow agree with theory, whereas a pronounced discrepancy is found in samples solidified in a microgravity environment. Similar discrepancies have been observed in other low-gravity experiments (Spacelab-I and D-1, which flew in 1985). There is still much to be learned about eutectic solidification.

Phase coarsening (or Ostwald ripening) is another phenomenon that can contribute to the microstructural evolution of an alloy. Prolonged exposure to elevated temperatures causes the larger particles in a particle-strengthened alloy to coarsen at the expense of the

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

smaller ones. This process, which is driven by a reduction in the free energy associated with the interfacial energy, degrades the strength of the alloy. Similar changes occur to dendrite arms in castings. On a recent shuttle flight that was terminated prematurely, a "glove-box" style experiment was attempted to obtain convection-free kinetic and microstructural coarsening data on tin-lead alloys (Voorhees, 1997). Similar, well defined microgravity experiments conducted at larger scales and for longer durations are needed to quantify the underlying physics of phase coarsening under purely diffusive solute transport. These experiments might require relatively long durations (many weeks) at microgravity levels (10-6g) to gather data of sufficient quality to draw meaningful scientific conclusions.

Phase-Separating Systems and Interfacial Phenomena

Another class of multiphase materials of interest in microgravity research are immiscible systems. At any temperature below a critical temperature, a range of compositions exists for which the melt separates into two distinct liquids. In the Earth's gravity, the two liquids will stratify before they solidify because of mass-density differences. The result is a macroscopically segregated solid. However, buoyancy-driven sedimentation should be largely eliminated in a microgravity environment. So far, microgravity experiments have been only partially successful in producing uniform dispersions (Lacy and Otto, 1975), indicating that effects other than buoyancy-driven sedimentation are also important. An extensive series of ground-based experiments has uncovered a rich variety of interfacial effects, such as critical wetting and particle pushing (Stefanescu, 1997a). The microstructures of immiscible alloys have now been scientifically classified with the help of microgravity research (Grugel et al., 1982).

Brazing, soldering, and welding are technologically important processes for the Human Exploration and Development of Space enterprise that are influenced by interfacial phenomena (Boatner, 1997). Both wetting and surface-driven flows are primary factors in the successful production of a join.

Solutal Transport

Convective mixing of solute-enriched melt adjacent to an advancing solid/melt interface causes segregation to occur throughout the solidified specimen. When the flow rate varies in time, a solid may result

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

with a composition profile that exhibits periodic bands of composition. These important but complex phenomena have been studied throughout the entire history of microgravity research. MRD research currently supports experimental flight programs on solutal segregation (Lehoczky, 1997; Matthiessen, 1997). MRD also supports ground-based studies on the modeling and measurement of complex solutal transport phenomena (Brown, 1997; Stefanescu, 1997b; Alexander, 1997). In a microgravity environment, unique microstructures could potentially be produced in a variety of systems (e.g., off-eutectic compositions, monotectics, syntectics, and peritectics) that would normally separate into different phases in terrestrial gravity as well as in solid solutions that are subject to double-diffusive convection. Liquid-phase sintering of heavy metal particles dispersed in lower-density transition alloys (typically cobalt-based) is the basis of the hard-materials industry for machine tools and a good example of a commercially important process that was recently investigated as a small-scale microgravity experiment (German, 1997).

Ability of Space Station Furnace Facility Core to Support Microgravity Metallurgical Research

The current SSFF Core concept is particularly useful for high-temperature metals and alloys research. However, the concept does not support studies on low-temperature metals and alloys, which are not only scientifically and technologically important but can also serve as models for high-temperature materials, thus reducing the cost and time of experimenting at high temperatures. In addition, the current SSFF Core concept does not have the levitation capabilities required for containerless experiments. Some of the candidate experiments require containerless environments, however, so the Core should incorporate provisions for levitation capabilities in both gaseous and vacuum environments.

Semiconductors

Five of the 13 research projects selected by NASA as candidate investigations for the ISS (Table 3-1) are directly pertinent to semiconductor crystal growth. Based on these five investigations and the 1996 NRA, this section discusses the relevance of the type of semiconductor

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

research to be conducted in the microgravity environment and the ability of the current SSFF Core concept to support this research.

Microgravity Semiconductor Research

The two goals of studies of semiconductor growth should be to provide information that improves the understanding of the crystal growth process and/or improves the growth of terrestrial bulk crystals. The three fundamental physical phenomena identified by the DWG (Chapter 1) as worthy of study under long-duration microgravity conditions that are directly relevant to semiconductor growth are transport phenomena, defect generation control, and surface tension gradient driven flows. The same consideration of the effects of interfacial instabilities during solidification and the advantages of eliminating buoyancy-driven convection discussed in the section on the growth of metals applies to the growth of semiconductors. In the case of single-crystal growth of semiconductors, simply providing crystals that are grown in space, that have lower defect densities, or that are clearly grown in the diffusion regime is not particularly useful to the crystal growth community, even for semiconductors that are difficult to grow on Earth. Unfortunately, previous studies of semiconductor growth in space have only occasionally achieved the two goals specified above.

The section on crystal growth and defect generation control in the December 4, 1996, NRA clearly shows that the elimination of fluid flow in the microgravity environment is complicated by surface-tension-driven convective flow and density-driven flows that might actually be suppressed at one g but are enhanced by g-jitter and by residual low g in directions not normally encountered in terrestrial growth. The suggested solution is the application of magnetic damping during crystal growth in the microgravity environment. This presumably would permit reproducible diffusion-controlled growth.

The NRA goes on to explain that defects, "whether they are impurity atoms or lattice defects, have a major impact on electrical and optical properties." Defects are generated at the container wall/solid/liquid interface, and the degree of fluid motion affects defect concentration and distribution. The detailed relationships between the various parameters for any material, growth method, or container material are unknown, however. The announcement suggests that microgravity experiments "should provide an excellent method for learning more

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

about this important topic." In fact, it is not clear that microgravity studies are required or have a significant chance of generating significant new and useful knowledge in semiconductor research. Careful terrestrial studies using the advanced characterization methods mentioned in the announcement (e.g., atomic force microscopy and synchrotron x-ray topography, along with magnetic damping and even the magnetically coupled baffle) might provide more useful opportunities in semiconductor research, given the scarceness of space-based research opportunities compared with terrestrial ones. The committee hopes that NASA will vigorously support such terrestrial studies and be particularly careful in selecting for flight only studies for which a successful outcome can reasonably be expected to lead to a deeper understanding of the growth process and the formation of defects.

Also included in the NRA is a section on transport phenomena. The study of transport properties in the liquids from which crystals are grown can provide important experimental data for modeling crystal growth from the liquid. These data are extremely difficult to obtain on earth because of buoyancy convection, and even in the microgravity environment residual g effects and surface-tension-driven convection can cause severe problems. However, magnetic damping could be beneficial in this respect.

Three of the five semiconductor-related candidate investigations for the ISS (Table 3-1) are entirely or partly for the study of transport properties in molten semiconductor materials. These experiments could provide valuable data for modeling terrestrial growth. The other two experiments are studies of crystal growth from the vapor. One is intended to provide organometallic chemical vapor deposition growth in the diffusion-controlled regime with reflectance spectroscopy as a diagnostic. The other is presumably a sealed tube experiment for the growth of II–VI compounds, the constituent elements of which are volatile at the growth temperature. It is not obvious in either of these latter studies how studying the growth parameters will provide insights into the fundamentals of how and why defects are formed.

Ability of Space Station Furnace Facility Core to Support Semiconductor Research

The current design for the SSFF Core is particularly well suited to studies of the growth of inorganic crystals by methods conventionally

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

used to grow semiconductors from a melt. These methods generally employ sealed tubes, and growth takes place within the temperature range currently specified for the Core. These methods do not generally require gases or vacuum pumping. The current Core design is also well suited for experiments to determine the diffusivities of the components of the semiconductor (including impurities) in the liquid source because the research projects can be designed as sealed-tube experiments. NASA should consider adding levitation capabilities to the Core concept to support the containerless experiments discussed above, however. Three of the five candidate experiments should be able to take advantage of the current SSFF Core concept. One, or possibly two, require or might benefit from the use of magnetic suppression of residual convection. Two may have requirements beyond the SSFF Core or EM specifications.

Ceramics and Glass

None of the 13 research projects selected by NASA as candidate investigations for the ISS (Table 3-1) can be classified as a true ceramic or glass experiment. One, however, involves semiconductors and crystal growth by vapor phase, which is a process related to some potential ceramic studies, and one is related to metallic glasses. There are eight ongoing and six recently completed ground-based studies that could be classified as ceramic or glass experiments. Current and potential microgravity projects in ceramics and glass, including both high-and low-temperature processing or characterization, and the ability of the SSFF Core to support them are reviewed in this section.

Ceramics Research in Microgravity

Microgravity research in ceramics tends to be less prominent than microgravity research in other materials areas because the major effects of the microgravity environment (e.g., suppression of density-driven transport and reduced convection) are more important in systems that contain a liquid or are in a low-viscosity molten state at some point in the process. Ceramics processing is generally performed in the solid state because the very high melting point and dissociation behavior of ceramics make them unsuitable for processing from melts. Even for processes in which ceramic-metal or other composites are

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

produced via some molten phase, the effect of convection tends to be minimal because of the high viscosities of the melts.

Ongoing ground-based studies provide some insight into the kinds of ceramics research that might be included in the microgravity flight program and would require support by the SSFF Core. Research areas are vapor-phase sintering; oxide melts, including glass synthesis and diffusion; and superconductor processing. Of the six recently completed ground-based projects, two are concerned with vapor-phase sintering, one is based on ambient or low-temperature processing in a liquid, and three concern molten-state glasses or ceramics. The vapor-phase sintering studies require elevated temperatures and possibly reactive atmospheres. The liquid-phase study does not require high temperatures but does require convection and sedimentation control. The melt processing and diffusion studies require elevated temperatures, and one also requires levitation. Of the eight ground-based programs that are currently being conducted, three concern solution processing, one concerns modeling, four concern processing or investigation of oxide melts, and one concerns both oxide melts and metallic glasses. The modeling study appears to have no experimental component at this stage. All of the other projects require elevated temperatures, and at least some will require an oxygen atmosphere. For example, the oxygen content of superconductors is critical, and some processing in air or oxygen will be required in relevant studies. The investigation of immiscibility gaps in mullite may also require an oxygen atmosphere.

There are two areas in which microgravity ceramics research could be important: (1) vapor-phase convection in sintering and degradation and (2) low-temperature solution processing. Convection in the vapor phase is important to certain ceramic sintering processes and in the degradation of ceramics. Vapor-phase sintering studies that have been supported by the microgravity program are relevant. Possible oxidation, corrosion, or vaporization studies would also be important where a gas phase either interacts with a ceramic or vaporizes from a ceramic.

The effects of microgravity on ceramics are most relevant to processes that involve a liquid phase. These are often low-temperature processes that involve solutions or suspensions in which convection and density gradients and differences play a major role in determining homogeneity and final properties. For example, some powder syntheses and certain shape-forming processes are performed in a liquid environment (e.g., sol-gel, coprecipitation, sedimentation and filtration, and hydrothermal synthesis). Although convection is often used

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

to promote mixing thereby producing homogeneous powders or materials, it is possible that processing in microgravity could lead to improved ground-based processing by elucidating the effects of sedimentation and agglomeration on the microstructure of ceramics. Low temperatures also play a role in the use of preceramic polymers for processing ceramics and forming new composite materials or coatings.

In line with the above discussion, the benefits of microgravity research in ceramics are specialized, and the ceramics community in general does not appear to be substantially involved in the program. However, this is only true for ceramic synthesis and processing as it is generally done at this time. There is considerable interest in the ceramics community in developing new, inexpensive methods of fabricating ceramics. Recent trends in ceramics research suggest that additional candidate studies could involve ceramic-metal composites, especially if the metal phase is molten; further work in oxides; and diffusion either in melts or from melts into ceramic preforms, as is done in some composite processing. In many of these experiments, microgravity would elucidate mechanisms. It is possible that future ceramics research might benefit substantially from microgravity research, so it is incumbent upon NASA to provide as fully as possible for ceramics research in the current SSFF Core concept.

Glass Research in Microgravity

Because glasses are processed from melts, melting and crystallization (also called devitrification) of glass are research areas that might benefit from the microgravity environment. Ceramic-glass melting is a capital-intensive process; therefore, modeling is an industrially important prelude to building or modifying a glass tank. Empirical data obtained in a microgravity environment might provide better input for models that are used to predict thermal convection and bubble movement in glass melts. Containerless processing, which would eliminate interactions with crucibles or nucleation from crucibles, could allow for the formation of new glasses with potentially useful properties. The suppression of volatilization of certain species from glass melts because of the suppression of convection may also allow new glass compositions to be produced. Thus, two research trends may be germane to microgravity research: the development of glass compositions with novel properties and the measurement of some thermophysical properties.

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

Ability of Space Station Furnace Facility Core to Support Ceramic and Glass Research

The committee has four major concerns about the ability of the current SSFF Core concept to support ceramics and glass microgravity research: the lack of levitation capability; the lack of environmental control, especially the lack of gases other than argon and nitrogen (specifically, the lack of oxidizing gases) and the poor vacuum capabilities; the amount of power available to allow a furnace to reach high temperatures (greater than 1200 to 1500°C); and the lack of temperature control from ambient to 500°C.

The current concept design for the Core does not have the levitation capability required to conduct containerless processing experiments on glass. The ground-based experiments also require controlled atmospheres (e.g., inert gases, air/oxygen, and other reactive gases) or vacuum. Gas availability in the current Core concept, both type and quantity, and vacuum quality are also limited. Relatively small quantities of inert gas will be available according to the present Core concept, and no provision has been made for oxygen, air, or other gases in the Core itself. Space and weight considerations clearly prevent the use of large volumes of gas, and fire-containment constraints will limit the use of some gases. Unless suitable alternatives can be devised within the EMs, the lack of oxidizing gases in the Core will preclude some of the current ground-based experiments from becoming flight experiments, and the relatively poor vacuum capabilities will affect experiments that require high-purity conditions.

Many of the current studies require high temperatures. Although none of the temperatures is beyond the current specifications for the SSFF Core (higher than 2300°C), considerable power will be needed to produce the required high temperatures. Actual temperature capability will depend on the furnace design, volume, insulation, gas, and gas throughput. There will clearly be restrictions on running more than one high-temperature (greater than 1200 to 1500°C) furnace at a time, and careful planning will be required to ensure that sufficient power can be delivered to each unit.

Many ceramic experiments are performed at temperatures between ambient and 500°C, a regime for which the current SSFF Core is not designed. To make the current SSFF Core concept more generally useful for ceramics, the temperature capability would have to be extended by the installation of cooling circuits and control strategies that would permit temperature ramps and temperature control in

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

lower temperature ranges. Although the current SSFF Core was designed generally to support higher-temperature studies, the importance of microgravity to low-temperature ceramic processes, the limited volume available in the EMs for experimental hardware, and the lack of other suitable services (e.g., gas availability) make it important to consider changes to the current Core concept to accommodate more ceramic and glass experiments.

Polymeric Materials

None of the 13 research projects selected by NASA as candidate investigations for the ISS (Table 3-1) can be classified as a polymeric materials experiment. There are six ongoing ground-based studies that could be classified as polymeric experiments, however. Potential microgravity projects in polymeric materials, including low-temperature processing, and the ability of the SSFF Core to support them are reviewed in this section.

Polymeric Materials Research in Microgravity

A previous National Research Council report (NRC, 1995) concluded that NASA's polymer microgravity materials research was not as well developed as metals and alloys and semiconductor materials because polymers and their solutions are usually too viscous for gravity-driven convection to play an important role in their phase formation or processing. This view is overly simplistic, however. Polymers and their assemblies can be constituted in diverse, complex forms that exhibit low viscosities. Even when non-fluid phases are employed, gravitationally mediated deformations may be of substantial concern. Indeed, there are many reasons to suppose that research conducted in microgravity will enable significant progress in the field of polymeric materials. Given the breadth of this class of materials, it should be considered a strong candidate for further study.

Gravity does affect diverse areas of polymer and organic materials structural development in terms of crystallization and polymerization. Notable examples include the effects of gravitationally mediated shear flows on chain orientation during crystallization, size and shape distributions in emulsion polymerization, and thin-film formation by vapor-phase-transport crystallization of metal coordination complexes. New program directions identified by NASA via the NRA process include aspects of transport and fluid mechanics that impact polymerization

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

processes involving liquid monomers, suspensions, and other complex fluid phases.

Polymers and related materials also present many issues of interest beyond crystallization and polymerization, the understanding of which might benefit from research conducted in a microgravity environment. For example, mesoscale self-assembly is currently an important theme in broad areas of materials research and could constitute the basis for new initiatives in polymer microgravity materials research. These systems, which aggregate particles into large assemblies via forces determined by molecular recognition, also have close analogies in the research themes identified in the colloids and biomaterials initiatives of NASA's microgravity research program. Polymer microfabrication is another area in which structure is affected by mechanical or interface directed deformations, effects that might be subject to manipulation in microgravity.

Ability of Space Station Furnace Facility Core to Support Polymer Research

A major concern in microgravity polymer research is how well the current SSFF Core design will be able to contribute to establishing a broader program in this area. Unless the definition for NASA's microgravity materials science research program is revised, it seems likely that the current polymeric microgravity materials-science program will simply migrate to the Space Station platform in its present form. The availability of the SSFF Core is not likely to have a major impact.

To support a more generalized program of polymer microgravity materials research, three shortcomings would have to be corrected in the current design of the SSFF Core. First, the gas-handling capabilities of the present SSFF Core design are limited. As in ceramics research, the amounts and varieties of gases, including oxygen, would have to be expanded to support polymer research. Second, the ability to control liquid mixing and flows is not included in the Core's envisioned control functions. These capabilities may be essential to studies involving the synthesis of macromolecules. Third, temperature control for polymer research is generally required within the ambient to 500°C range, for which the SSFF Core was not originally designed. Extending the temperature capability by installing cooling circuits and control strategies would be necessary for control within these lower temperature ranges.

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

Conclusions and Recommendations

The current SSFF Core concept was intended to function as a dedicated facility for high-temperature materials-science research. The question now is whether its capabilities could be extended in order for it to become a general facility for microgravity research in materials science and engineering.

Most of the scientific and engineering issues of concern in high-temperature materials processing have relevant counterparts in more modest temperature ranges. All experiments in microgravity materials science and engineering will require data input/output and storage capabilities, control hardware, power distribution, and active vibration isolation. These capabilities are already included in the current SSFF Core concept. Therefore, there is every reason to believe that with some redesigning, the Core could support significant research in broader areas of materials science and engineering. Although the committee can only speculate about microgravity research in areas other than those for which the SSFF Core was originally designed, any concerns are likely to be more than offset by the broader range of experiments that could become possible and materials classes that could become involved.

Recommendation. To expand the range of experiments and classes of materials that the SSFF Core can support, the current concept should be adapted to serve a broader range of experimental instruments than the modular furnaces for which it was originally designed.

To support an expanded research program, NASA should re-examine the facilities in the current SSFF Core with the view of eliminating highly specialized capabilities. For example, a Peltier pulser will serve only a fraction of the experiments in the metals and alloys research area. Its presence should be weighed against the benefit of equipment (e.g., vacuum pump, fire-suppression, or levitation systems) that could be applicable to a larger number of experiments in more materials science research areas.

Recommendation. All equipment in the current SSFF Core concept should be re-examined in terms of its applicability to the broadest range of materials research areas and experiments.

NASA should consider redesigning the current SSFF Core concept in the following ways to facilitate microgravity materials-science

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

research: extending the temperature-control capabilities, adding levitation capabilities, improving vacuum quality, adding gas handling capabilities, adding liquid handling capabilities, and re-examining power availability.

Temperature-Control Capabilities

The temperature-control hardware in the current SSFF Core concept is designed to maintain and program temperature conditions between 500°C and 2300°C. For certain types of experiments in all of the materials research areas, however, it will be important to control temperatures and program conditions well below 500°C (i.e., at temperatures of 25°C to 500°C). The SSFF Core was not originally designed to support experiments in this lower temperature range.

Recommendation. The following changes to the current SSFF Core concept should be considered in order to increase the temperature-control capabilities to lower temperatures and expand the range of experiments in all materials science research areas: increasing the variety of temperature-measuring and temperature-control sensors (e.g., resistance thermometers, thermistors, and pyrometers) that can be accommodated; and adding a coolant loop (e.g., using water or freon) to support low-to moderate-temperature experiments.

Levitation Capabilities

The space environment offers unique opportunities for more precise measurements of some thermophysical properties by allowing the production of containerless or float-zone environments. The current SSFF concept, however, does not have the capability to support levitation research.

Recommendation. NASA should consider adding levitation capabilities to the SSFF Core to support containerless experiments.

Vacuum Quality

The relatively poor vacuum (10-3 torr) available in the current SSFF Core concept will have an adverse impact on materials science

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

experiments that require high-purity conditions, unless suitable alternatives can be devised within the EMs.

Recommendation. NASA should consider installing a suitable vacuum system in the SSFF Core.

Gas Handling

In the current SSFF Core concept, only relatively small quantities of inert gas will be available, and no provision has been made for handling oxygen, air, or other gases. Space and weight considerations clearly preclude the use of large volumes of gas, and fire-containment constraints will limit the use of some gases. Nevertheless, the lack of oxidizing gases will limit flight experiments, especially in ceramics and solution research.

Recommendation. NASA should consider methods for accommodating the following in the SSFF Core: small quantities of gases other than argon (e.g., oxygen or air), within safety guidelines; fire-suppression systems to allow for the use of oxidizing gases; and larger quantities of gases and the associated crew time required to change gas cylinders. Control elements for gas handling (e.g., mass flow control and venting systems control) should also be considered.

Liquid Handling

The control functions of the current SSFF Core concept do not include controlling liquid mixing and flows. The effects of microgravity on ceramics will be most relevant to processes that involve solutions or suspensions in which convection and density gradients and differences play a major role in determining homogeneity and final properties. Liquid-control capabilities may also be essential for studies involving the synthesis of polymers, the growth of crystals, and the precipitation from solutions.

Recommendation. NASA should consider adding liquid-mixing and liquid-flow control capabilities to the current SSFF Core concept to support materials research that involves a liquid state.

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×

Power Availability

Considerable power will be required to produce the high temperatures, levitation, and magnetic damping required for many of the experiments currently planned for the SSFF Core. Careful planning will be required to ensure that sufficient power can be delivered to each unit.

Recommendation. NASA should review the power supply to ensure that it is adequate for producing high temperatures, levitation, and damping.

Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 29
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 30
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 31
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 32
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 33
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 34
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 35
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 36
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 37
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 38
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 39
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 40
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 41
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 42
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 43
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 44
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 45
Suggested Citation:"3 Ability of the Space Station Furnace Facility Core to Support Materials Science Experiments that Require a Microgravity Environment." National Research Council. 1997. Future Materials Science Research on the International Space Station. Washington, DC: The National Academies Press. doi: 10.17226/5971.
×
Page 46
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