During the International Microgravity Laboratory-1 (IML-1) mission it is planned to grow triglycine sulfate (TGS) crystals from aqueous solution using the modified Fluids Experiment System (FES). A special cooled sting technique will be used for solution crystal growth. The objectives of the experiment are as follows: (1) to grow crystals of TGS using the modified FES; (2) to perform holographic interferometric tomography of the fluid field in three dimensions; (3) to study the fluid motion due to g-jitter by multiple exposure holography of tracer particles; and (4) to study the influence of g-jitter on the growth rate

Lal, Ravindra B.

English

NASA Technical Reports Server

N92-23 30
A STUDY OF SOLUTION CRYSTAL GROWTH IN LOW-g
(2-IML-1)
Ravindra B. Lal
Alabama A&M University
Huntsville, AL USA
I. INTRODUCTION
During the International Micmgravity Laboratory-1 (IML-1) mission it is planned to
grow triglycine sulfate (TGS) crystals from aqueous solution using the modified Fluids Experi-
ment System (FES). A special cooled sting technique I will be used for solution crystal growth.
The objectives of the experiment are: (a) to grow crystals of TGS using the modified fluids
experiment system, (b) to perform holographic interferometric tomography of the fluid field in
three dimensions, (c) to study the fluid motion due to g-jitter by multiple exposure holography of
tracer particles, and (d) to study the influence of g-jitter on the growth rate.
TGS cystals have technological interest as a pyroelectric infrared detector that can be
used with no cooling devices. There are many applications for improved infrared detectors in
military systems, astronomical telescopes, Earth observation cameras, and environmental
analysis monitors. When grown to useful sizes on Earth, the crystals develop defects that limit
their performance.
II. EXPERIMENT
During the IML-1 mission it is planned to have two experiment runs.
1. TGS-1 run (Isothermal) Sting and fluid temperature same and near saturation
temperature. (010) oriented polyhedral seed (Figure 1).
2. TGS-2 run (Polynomial) The sting follows a predetermined polynomial. (001)
oriented polyhedral seed (Figure 1).
A. Short Description of the Two Experiments
These experiments will be performed in the Fluids Experiment System (FES). The
details of the FES are given elsewhere. 2 The FES is a windowed and instrumented crystal
growth research cell designed to allow a variety of holographic diagnostics and schlieren viewing
of the crystal and surrounding fluid as the crystal grows in space. Two types of images are
recorded: schlieren images (transmitted on down-link as black and white video that reveals flow
patterns and variations in fluid density) and holograms (recordings of three dimensional images
that lead to quantitative determination of the concentration of the solution surrounding the
crystal). TGS solution is nearly transparent, so it is possible to record holographic images
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throughthefluid around a growing crystal. Using holographic interferornetry, temperature and
concentration gradients in the fluid and their motion can be monitored to determine how they are
reduced in space and to determine how the crystal growth takes place in a low gravity environ-
ment. The FES has been slightly modified since the Spacelab 3 mission in 1985. The following
modifications have been made to the FES. The knife edge has been realigned to avoid blackout
at certain angles; holographic optical elements (HOE) have been added to the test cell windows
for three-dimensional reconstruction of concentration gradients; a new software has been added;
a viewing window has been added to view the test cell without opening the doors of the test cell
enclosure; test cell bladder in the cap assembly has been reworked; a gold coated stainless steel
pump has been replaced by a titanium pump; and the inside of the test cells has been coated with
silicone RTV to reduce metallic contamination of TGS solutions.
The FES optical diagnostic system was modified for IML- 1 after its last use in Spacelab 3
to incorporate holographic tomography (the ability to take optical data through the cell at
multiple angles) as shown in Figure 2. Specially designed holographic optical elements (HOEs)
have been added to the main test cell windows to provide a capability to illuminate and view the
crystal at three different angles. The straight through view remains unchanged and two views at
23.5 ° are made possible by the HOEs. The schlieren system operation remains essentially the
same while the hologram now records all three views on a single frame in a manner that allows
them to be separated later back on Earth. The availability of the three views will lead to a more
accurate quantitative understanding of the solution concentration and crystal growth.
Holograms and video data will be recorded during mechanical operations and critical
phases of the crystal growth. Acceleration of the seed particles can be observed in real time on
the video down link and will be determined accurately from the analysis of the holography data.
During the experiment, the principal investigator and his team will monitor the down link video
of the crystal and the growth solution and may instruct the crew to adjust some growth
parameters.
In the first experiment a TGS crystal oriented in (010) direction will be grown for ap-
proximately 23 hours. The (010) face is the fastest growing face in TGS and is also the face
required for detector fabrication. The growing face is uncut and unpolished and is about 1 cm x
1 cm in size. The solution of TGS will be seeded with buoyant particles of three different sizes
(300 _tm, 400 _tm, and 600 lain). The main objective for this experiment run is to determine the
effects of g-jitter and other g-variations on the fluid flow. Holograms will be taken at a
programmed rate especially during any crew activities, and other Microgravity Vestibular
Investigation (MVI) activities.
The second experiment run is basically a crystal growth run. The time allotted for this
run is about 43 hours. No particles will be added to the TGS solution. The seed crystal will be
(001) oriented polyhedral crystal which is uncut and unpolished on the growing side. This seed
is about 1.5 cm x 1.5 cm in size. The experiment will follow a predetermined polynomial 3, but
depending upon actual space conditions, the growth rate can be modified by changing the
194
constants in the polynomial by crew interface. After the growth, the sting and the grown crystal
will be removed from the test cell and will be stored in a specially designed container.
The payload crew will begin each run by placing a pre-stored sting with attached TGS
seed crystal in a test cell filled with about 1.0 liter of TGS solution. The seed and the fluid will
be separated by a cap assembly that will be retracted when the experiment begins. To dissolve
all crystallites that will have formed in the solution at room temperature, the test cell will be
preheated to a temperature of 70 °C on the optical bench, while keeping the sting temperature at
42 °C. The cell and the optical bench will then be cooled while the sting is heated to an
appropriate temperature to bring the sting and the fluid to around 46 °C. At this temperature the
cap will be retracted. A part of the seed will be dissolved to remove any surface imperfections
and spurious nuclei. After that the experiment will follow a predetermined schedule. A typical
time line profile is given in Figure 3. At the end of the run the cap will again be closed, the test
cell removed from the optical bench, and the sting removed from the cell and stored in a specially
designed container such that the crystal cools slowly to room temperature.
After the mission, the crystals will be returned to our laboratory for extensive
investigations for their structural and electrical properties, including their capability for infrared
detection. The space grown crystals will be compared with the laboratory grown crystals.
Holograms taken during the mission will be reconstructed on ground for detailed optical analysis
of fluid behavior. Data on the particle studies will be analyzed and correlated with "g"
measurements on the shuttle.
On the IML-1 mission, accelerations that may cause convection and disturb the crystal
growth will be carefully monitored. In addition to an internal FES accelerometer that will
measure acceleration above 5 Hz, the Space Acceleration Monitoring System (SAMS) has two
accelerometers located in the FES rack and one mounted in the Spacelab aisles. The special set
of accelerometers are expected to provide information on low frequency (0 to 5 Hz) vibrations.
Because the effects of g-jitter are believed to be extremely important in the crystal growth
experiment we chose to incorporate optical techniques to monitor these effects directly.
III. UNDERLYING SCIENCE FOR THE GROWTH OF TGS CRYSTAL
A. Growth of TGS Crystals
The dielectric loss in TGS is due to the following: domain relaxation, microscopic
solution and air inclusions incorporated during growth, and dislocations/strain centers which pin
the domains. In space grown crystals we expect the growth to be mainly diffusion controlled and
so we expect ordered deposition, fewer microscopic solution and air inclusions (solution is
degassed before filling) and less strain centers and so domains will be more mobile. So we
expect low dielectric loss (e") and improved figure of merit.
The ultimate use of these crystals is for IR detectors for 8 p.m-14 i.tm range. The detec-
tors will be fabricated at EDO/Barnes Engineering Division in Shelton, CT. All other electrical
195
propertieswill bemeasuredin our laboratory at Alabama A & M University. A section of both
crystals will be analyzed by high resolution synchrotron X-radiation diffraction imaging at
Brookhaven National Laboratory with the help of NIST.
A study of the effects of microgravity on TGS crystal growth in space by computer
simulation is underway to help in the design of control parameters of spaceflight experiments.
A mathematical model of TGS crystal growth in space has been established including the
field model, the interface model, and various boundary conditions. 4 The behaviors of the TGS
aqueous solution follow the basic conservation laws of continuity, momentum, energy and
concentration which are time dependent. The liquid-solid interface follows the growth kinetics
and the mass balance. A finite volume code called COM-MIX has been employed and exten-
sively modified to implement the simulation.
A series of two-dimensional cases are tested with different steady background g level
(10-1 - 10-4 go) and different orientations (horizontal and verticai). Some cases of g-jitter are also
simulated. Alternative boundary conditions are being tested. The results will be compared with
the flight data.
B. Experiment with Seed Particles in the FES
Seed particles of three different monodisperse sizes will be added to the fluid in the FES.
These will be observed on TV downlink in real time (only the largest particles are expected to
show up clearly on the TV image). Their positions will be noted during each downlink and
compared with later values to give us preliminary information on fluid and particle motion. The
TV image will provide limited resolution and accuracy. Image processing will be done on line
on the downlink image to help improve this. Holograms of the particle distribution will be made
at preselected times during the experiments to later allow an accurate three-dimensional location
on the particles as a function of time. Preliminary ground based results of particles image
displacement velocity experiments were presented by Trolinger et al. 5
1. Primary Science Objective
The primary science objective is to observe and quantify minute convection currents in
the vicinity of the crystal and to correlate these with crystal growth processes. We will attempt
to observe, isolate, and quantify the following components of fluid convection:
(a) Growth driven convection
(b) Convection due to g-jitter-random forces
(c) Convection due to other quasi-steady state acceleration forces - water dumps, etc.
(d) Convection due to residual microgravity - air drag, gravity gradient, etc.
The use of different particle sizes should allow us to make these measurements accurately and
196
with highspatialresolution.Thediffusioncoefficientin g-jitter variesasthefourthpowerof
radius,while terminalvelocity variesassecondpowerof radius.
We shouldbeableto correlatethepresenceof convectionwith crystalgrowthanomalies
andprocesses,andweshouldbeableto correlatethepresenceof convectionwith otherevents.
Namely,weshouldbeableto moreaccuratelycharacterizethespaceshuttleenvironment,how
energyis coupledto anexperiment,andits effectoncrystalgrowth.
An accuratemeasurementof convection will be made in a regime never measured before.
This will allow the validation of both theory and CFD codes.
2. Secondary Science Objectives
The dynamics of three ensembles of monodisperse particles in suspension will be
observed in microgravity. This will provide important basic scientific information about inertial
random walk, two phase flow, particle dynamics, and residual gravitational field in the Spacelab.
Testing the theory of intertial random walk - Inertial random walk, a novel type of
diffusion, has been predicted by Regel et al. 6 to exist in microgravity, but has never been ob-
served. It may have a significant effect on certain types of materials processing in space. It has
been simulated (in one dimension) in ground experiments but only when measured in space will
the theory truly be tested. Our particle experiments are almost ideal for testing the theory of
inertial random walk. Requirements of particle sizes and types are fortunately similar for both
the primary science objective and this objective, allowing us to pursue this objective with no
added cost.
Testin_ two-phase flow and particle dynamics theory - Two phase flow has been studied
very little in microgravity. The general equations of two phase flow are surprisingly untested
because of the difficulty of testing many regimes. The microgravity environment will allow us to
examine two phase flow in an extremely low Reynolds number regime where convection would
normally dominate the results. The use of multiple particle sizes will allow us to test a variety of
two phase flow effects.
Materials processing which involves free-floating particles depends heavily on particle
dynamics and interaction. The statistics of particle diffusion and collision rates have been
developed but have not been tested in microgravity. Although our selected particle number
density is somewhat low, the study of particle dynamics and interaction should be enhanced by
the tracking of all particles in three-dimensions in microgravity.
Residual gravitational field in Spacelab - The equations of motion of the particles lead
us to the conclusion that we will be able to accurately measure the residual gravitational field on
the Spacelab by tracking these suspended particles. The selection of the size and density range
has increased the accuracy of the measurement. We should also be able to measure relatively
low frequency changes in g. High frequency changes in g will be filtered out of our measure-
197
ment. The measurement will be correlated with other recorded events in the IML- 1 mission.
This should provide a significantly improved characterization of the Spacelab environment.
C. Holographic Optical Elements (HOEs, holograms that emulate optical components)
First space application of HOEs - HOEs expand the FES optical system capability from a
single angle of view to three angles of view without any significant weight or volume changes in
the FES. The HOEs, thin materials which are attached to the FES windows, split the input light
beam into three beams traversing the crystal surface at three angles. This is important to resolve
any non-axially symmetric diffusion fronts. The HOE on the output window collects the three
beams and bends them back to allow their collection in the same recording camera. To achieve
the same thing with conventional optics would have required a major redesign and configuration
change in the FES and would have added considerable weight and volume. The concept is likely
to find application in other optical diagnostics requirements for space experiments where weight
and volume are critical parameters, and where a wider angle of view is needed for viewing.
ACKNOWLEDGEMENTS
Help given by Rudolph Ruff, Todd MacLeod, David Johnston, and David Mclntosh of
NASA/MSFC and other Teledyne Brown Engineering company personnel during development
of this experiment is gratefully acknowledged.
.
.
References
Lal, R. B., Aggarwal, M. D., Kroes, R. L., and Wilcox, W. R., Phys. Stat. Sol (a) 80, 547
(1983).
Materials Processing in Spacelab 3-Fluid Experiment System, Vapor Crystal Growth System,
Applications Payload Projects, NASA/MSFC, Code JA84, Marshall Space Flight Center, AL
35812.
.
.
.
.
Liu, L. C., Wilcox, W. R., Kroes, R. L. and Lal, R. B., Proc. Mat. Res. Soc., Vol. 9, p. 339
(Ed., Guy E. Rindone) North Holland, NY (1982).
Sun, J., Carlson, F. M., and Wilcox, W. R., 42nd Congress of the International Astronautical
Federation, October 5-11, 1991, Montreal, Canada.
Trolinger, J. D., Mclntosh, D., Witherow, W. K., Lal, R. B., and Batra, A. K., Proc. SPIE,
1557 (1990).
Regel, L. L., Vedernikov, A. A., Ilinski, R. V., and Melikhov, I. M., Proc. 6th European
Symposium on Materials Sciences Under Microgravity Conditions, Bordeaux, France,
December 2-5, 1986.
198
(121)
CRYSTALLOGRAPHIC FACES OF TGS CRYSTAL
STING
TGS-1
Figure l.
TGS-2
Triglycine Sulfate Growth Runs on the IML-1 Mission.
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A study of solution crystal growth in LOW-g (2-IML-1)

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