Containerless processing of materials at elevated temperatures is discussed with emphasis on high temperature chemistry, thermophysical properties, materials science, and materials processing. Acoustic and electromagnetic positioning of high temperature melts are discussed. Results from recent ground based experiments, including KC-135 testing of an acoustic levitator, are presented. Some current positioning technologies and the potential for enhancing them are considered. Further, a summary of these technologies and their science capabilities for the development of future experiments is given

Danley, T. J.

Merkley, D. R.

Rey, Charles A.

English

NASA Technical Reports Server

SOME CONSIDERATIONS FOR VARIOUS POSITIONING SYSTEMS
AND THEIR SCIENCE CAPABILITIES
C. A. Rey, D. R. Merkley and T. J. Danley
Intersonics, Inc.
Northbrook, Illinois
Abstract
Containerless processing of materials at elevated temperatures is discussed
with emphasis on i) high temperature chemistry and thermophysical properties and
2) materials science and materials processing. Acoustic and electromagnetic
positioning of high temperature melts are discussed. Results from recent ground-
based experiments, including KC-135 testing of an acoustic levitator, are
presented. Some current positioning technologies and the potential for enhancing
them are considered. Further, a summary of these technologies and their science
capabilities for the development of future experiments is given in this paper.
Need for Containerless Processing
The capability of conducting materials research in a containerless state
at high temperatures is of significant interest to the scientific community.
In a typical materials process, contaminants from the crucible can alter or even
invalidate results of the investigation. As the processing temperature
increases, there is an increase in the probability and the rate of unwanted
reactions occurring between the crucible and its contents. Containerless
processing eliminates the crucible, thus eliminating the dominant source of
contamination. In acoustic levitation, the materials being investigated come
in contact only with the medium in which the acoustic waves propagate. This
medium typically may be dry air or an inert gas, such as argon, or even a special
gas for specific reactions. In electromagnetic levitation the specimen
investigated can be processed in either vacuum or some suitable gas, but the
specimen must have sufficient electrical conductivity.
Nonresonant Acoustic Levitator Systems
Fig. IA illustrates the basic concept central to a single-axis resonant
system. I The nonresonant system shown in Fig. IB uses an acoustic transducer
at the bottom, which produces a primary, nearly plane wave, which impinges on
a small reflector. 2 The approximately spherical reflected wave interferes with
the primary wave and the resulting acoustic field produces continuous restoring
forces on a specimen. The magnitude of these forces is quite small. While
sufficient to levitate small objects at ambient temperatures, it is not strong
enough when the supporting gas is at a high temperature. However, in the
microgravity of space these restoring forces are more than adequate to position
a research specimen. 3
One configuration of the Single Axis Acoustic Levitator, called SAAL, is
shown in cross section in Fig. lB. Three levitation experiments using the SAAL
on an October, 1985 Space Shuttle flight successfully demonstrated for the first
time containerless processing of glass specimens at high temperatures and
attained some scientific and engineering objectives. 4 Positioning of both solids
and liquids without a container at temperatures from 800 to 1500°C was achieved.
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In each case a specimen was injected and captured in the acoustic potential
energy well. Specimens were positioned in the containerless state while being
heated, melted, cooled, and solidified.
Acoustic Levitation Furnace (ALF)
The acoustic levitation furnace (ALF) facility under development will use
a hotwall furnace and acoustic positioning for containerless processing of
materials up to 1750°C. The facility is capable of processing a substantial
number of experimental specimens under a variety of conditions thus enabling
multiple research efforts. The ALF is designed with six opposed acoustic sources
in three orthogonal axes to provide acoustic control of both solid and liquid
specimens. 5 Fig. IC shows the schematic arrangement of these acoustic
transducers. The resulting acoustic field produces an energy well that is
symmetric and stable, providing excellent translational stability for the
specimen. These features can ensure that the containerless state is maintained
throughout processing and that the specimen remains both centered and spherical
when melted.
High Temperature Acoustic Levitator (HAL)
The high temperature acoustic levitator (HAL) is a facility designed for
containerless processing of materials at temperatures up to 2000°C or above.
The facility employs an array of six high power acoustic transducers which
produce a very symmetric acoustic field promoting a stable levitating
environment. A beam heating technique is used to obtain temperatures in excess
of 2000°C. In one version of this approach radiation emitted from compact xenon
arc lamps are focused onto a levitated sample using ellipsoidal reflectors.
Fig. 2 shows a brassboard version of HAL which has been designed to be flown
aboard the KC-135 microgravity test facility.
Fig. 3A shows sound positioning versus time data for a density 2.2 gm/cm 3
sample. Good damping of residual motion is apparent within a time constant of
about 2 seconds. Figure 3B shows a similar plot for a specimen density of 8.9
heated to over 1400K.
Stabilized Electromagnetic Levitator (SEL)
The Stabilized Electromagnetic Levitator is a highly stable multi-coil
levitator for melting and undercooling studies in a microgravity environment.
The module design is shown in Fig. 2. SEL is characterized by independent
control of heating and positioning. Both highly or poorly conductive materials,
metallic or non-metallic, may be levitated. High frequency induction heating
of samples to 2700°C or greater will be possible. Heating and cooling rates of
at least 200°C/sec. would be available. By varying the signals between coils,
sample stability and oscillation can be controlled. Independent heating will
allow undercooling studies without sample instability.
The basic design and development work for a SEL test module has been
completed at Intersonics under a SBIR grant from NASA. The test module is a
single-axis system powered by modified, commercially available, high efficiency,
solid-state, radio frequency amplifiers. Techniques for coil construction,
transmission line fabrication and insulation are under development at
Intersonics.
439
Summary and Conclusion
Acoustic levitation in space is providing the experimenter and eventually
the manufacturer with new techniques for high-temperature containerless materials
processing. In acoustic levitation the technology has evolved from a single-
axis resonance tube levitator in 1971 to the nonresonant, three-axis, opposed
source system now under development in ALF and HAL. An electromagnetic system
is being developed which may have greater flexibility than previous designs.
A summary of the science capabilities for these systems is given in Table i.
With the availability of these new techniques for high-temperature
containerless materials processing, a vastly expanded range of materials from
processing up to (and perhaps beyond) 2700°C are envisioned. It is reasonable
to anticipate that significant advances in the production of new materials, new
ceramics, alloys, and optical and electronic materials will result.
Acknowledgment
This work was supported by the NASA, George C. Marshall Space Flight
Center.
References
I. Whymark, R. R., "Acoustic Field Positioning for Containerless Processing,"
Ultrasonics, Nov. 1975, pp.251-261.
2. R. Whymark, C. Rey, J. Yearnd, and R. Broz, "Acoustic Levitation Materials
Processing Systems," AIAA Aerospace Sciences Meeting, #79-0870 (Jan. 1979)
3. C.A. Rey, R. R. Whymark, T. J. Danley, and D. R. Merkley, "Present and
Future Capabilities of Acoustic Levitation and Positioning Devices," Materials
Processing in Reduced Gravity Environment of Space, Proceedings of the Materials
Research Society Annual Meeting, edited by Guy Rindone, 1982 p. 137, Elsevier
Science, New York, NY.
4. Rey, C. A., Merkley, D. R., Hammarlund, G. R., and Danley, T. J.,
Metallurgical Transactions VoI.19A, Nov. 1988 pp. 2619-2623; Ray, C. S., and Day,
D. E., Proceedings of the Materials Research Society Symposium Vol. 87, 1987,
pp. 239-251; and Gac, F. D., Rept. LA-UR-86-2732, Los Alamos National Laboratory,
Los Alamos, NM, 1986.
5. Merkley, D. R., Rey, C. A., Hammarlund, G. R., and Danley, T. J., "Specimen
Translational Control Capabilities Using an Opposed Radiator Acoustic Levitation
System," ll4th Meeting of the Acoustical Society of America, Miami FI, Nov. 20,
1987.
440
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Figure D
FIGURE 1
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HIGH TEMPERATURE ACOUSTIC LEVITATOR GENERAL ASSEMBLY
FIGURE 2
442
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MICROGRAVTTY SCIENCE CAPABILITIES SUMMARY FOR
HIGH TEMPERATURE CONTAINERLESS PROCESSING MODULE tHTCPM)
A High Temperature Contalneriess Processing Module (HTCPM) could be one of
the modules supported by the DPM package for SpaceIM). lind could be •
precursor module for the Modular Contalnerless Processing Fscility(MCPF) for the
space station. Depending on the science requirements, It may utilize one or more
of the following technologies:
PARAMETER ACOUSTIC ACOUSTIC STABILIZED
(HOT WALL) (BEAM HEATED) E L E C T R O -
(ALF) (HAL) MAGNETIC
(SEL)
Temperatures 800-1750 "C 30-2000 "C 30 to 2700 "C
or higher or higher
Specimen Very Good Good Good
Isothermality (+_ 2 ,C/cm)
Processing Gas Inert, Reducing, Inert. Reducing. Inert, Reducing,
Oxidizing Oxidizing Oxid_Vacuum
Gas Pud_ Good Excellent Excellent
Particulate Class 1000 or
ContaminaUon Better
Heating and Slow to Very Fast Very Fast
Cooling Rates Moderate (-tZ00 "C/sec.) (-_00 "C/sec.)
(( 2 "C/sec.)
ConductJve No No Yes
Specimen
Required
Liquid or Solid Yes Yes Yes
Processed
Specimen Size 2 - 10ram 2 - 6ram 2 - 6mm
SOME POSSIBLE APPUCATION$ FOR CONTAINERLESS PROCESSING
AT HIGH TEMPERATURES IN MICROGRAVITY
HIGH TEMPERATURE CHEMISTRY
o Cp VS TEMPERATURE, UNDERCOOIJED UQUIDS
o OPTICAL PROPERTY MEASUREMENT - It, If., e, E'TC
o SURFACE RIM BEHAVIOR, GROWTH RATES, ETC
o THERMODYNAMICS ANO KINETICS (OF OX]DIE AND NITRIOES)
o VAPOR PRESSURES BY UF, ETC
o PASSNATION/CORROSION EFFECTS
MATERIAL S PROCESSING
o PURIFY, REMOVE OXIDES, IN METALS/AlLOYS
o HIGH PURITY SEMICONDUCTORS
o MICRO ALLOYING, SUPER ALLOYS
o CONTROLLED MICRO SiTIUCTURES
o HIGH Tc SUPERCONDUCTORS
o DEEP UNDERCOOUNG, AMORPHOUS MATERIALS
o NON-EQUILIBRIUM STUDIES
o OXIDE DISPERSION STRENGTHENING
o OPTICAL MATERIALS. BENCHMARK MATERIALS
TABLE l


Some considerations for various positioning systems and their science capabilities

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