‘Bad bubbles,’ semiconductors, new furnaces make Space Station ‘hotbed’ for
materials research

Scientists will soon turn the International Space Station into a materials
research laboratory to study “bad bubbles” that cause defects in metal
alloys used to produce engine turbine blades and semiconductor crystals that
are crucial components in electronic devices.

In a mission to the International Space Station this week, Space
Shuttle Endeavour will deliver two novel furnaces and more than 20 ampoules
filled with materials samples for the first two NASA materials science
experiments conducted on the Space Station.

“We can thank advances in materials science for everything from cell phones
to airplanes to computers to the next space ship in the making,” said Dr.
Donald Gillies, NASA’s discipline leader for materials science at the
Marshall Space Flight Center in Huntsville, Ala. “To improve materials
needed in our high-tech economy and help industry create the hot new
products of the future, NASA scientists are using low gravity to examine and
understand the role processing plays in creating materials.”

Bubbles are a good example of the way microgravity – the near-weightless
environment created as the Space Station orbits Earth – influences the
properties of materials as they are produced. On Earth when scientists melt
metals, bubbles that form in the molten material generally rise to the
surface, pop and disappear. In low-gravity, the bubbles may only move
slightly.

“Bubbles sound simple,” said Dr. Richard Grugel, lead scientist for
the Pore Formation and Mobility Investigation (PFMI) at the Marshall Center.
“But when bubbles are trapped in solid samples, they show up as internal
cracks that diminish a material’s strength and usefulness, whether it’s
processed on Earth or in space.”

Grugel’s furnace will melt and resolidify samples of a transparent
modeling material, succinonitrile and succinonitrile water mixtures.

“Bubbles are more likely to get trapped in samples processed in
microgravity, which makes it an excellent place to study their movements and
interactions,” said Grugel. “The information gleaned from the experiments
will promote our knowledge of bubble dynamics and provide needed insight
regarding materials processing of metals and alloys in space.”

Observing and controlling his Space Station experiment from the telescience
operations room at the Marshall Center, Grugel will scrutinize bubbles in
prepared samples and study their behavior. He’ll send commands to the
experiment in space, changing the processing temperature and other
parameters to systematically investigate the conditions that stimulate
bubble movement and eventual pore formation.

The other materials science experiment to be delivered on this
month’s STS-111 mission – the Solidification Using a Baffle in Sealed
Ampoules, or SUBSA — will study solidification of semiconductor crystals
from the melt. Semiconductors are used in electronic devices such as
computer chips and integrated circuits, medical imaging devices, and
detectors of nuclear and infrared radiation.

For this investigation, indium antimonide crystals previously
solidified on Earth are melted and then cooled to resolidify in microgravity
and form solid single crystals. To control the electronic properties of the
crystals, tiny quantities of tellurium or zinc is added to the indium
antimonide. The lead scientist for the experiment selected indium antimonide
because of its relatively low melting point of 512 degrees Celsius and
because it is useful for creating models that apply to a variety of
semiconductor materials.

“On Earth, buoyancy continuously deforms and moves fluids in complex
manners, making it difficult to study how materials that solidify from the
melt form semiconductors and other products,” said Dr. Aleksandar
Ostrogorsky, the SUBSA principal investigator who also teaches and conducts
research at the Rensselaer Polytechnic Institute in Troy, N.Y. “In
microgravity, the fluids are almost stagnant, resembling solids. The absence
of motion makes it easier to observe and mathematically describe what is
occurring when the crystals are melted, and how the materials solidify to
form a new crystal.”

The semiconductor crystals are contained in cylindrical glass tubes,
called ampoules, which astronauts insert into the SUBSA furnace for
processing. Ostrogorsky will observe each sample as it is processed and send
commands to his space furnaces — tweaking the experiment, much as he would
in a ground-based laboratory.

Ostrogorsky and Grugel will each process at least 10 samples.
Ostrogorsky’s samples are scheduled to be processed first and returned on
Space Shuttle Endeavour when it visits the Station this fall. Grugel’s
experiment will begin later during Expedition Five and continue until the
samples are returned on Space Shuttle Atlantis during the STS-114 mission
early next year.

These experiments are possible because the two high-temperature furnaces can
be enclosed inside the Microgravity Science Glovebox – a major new research
facility also being delivered to the Space Station this month. The glovebox
safely contains the materials being processed, and has a large front window
with built-in gloves allowing astronauts to change out samples and perform
other important tasks. The glovebox, built by the European Space Agency in
collaboration with engineers at the Marshall Center, makes it possible to do
many new types of hands-on science experiments.

“As the launch gets closer, my students and I are getting more excited that
our experiment is actually going to be one of the first materials science
experiments carried out on the Space Station,” said Ostrogorsky. “We have
done extensive work on the ground to prepare for the experiment, and we
believe that the prolonged processing times available on the Station will
allow scientists to do meaningful and reproducible materials research in
space,” added Ostrogorsky.

The new experiments will get under way during Expedition Five on the Space
Station – the next four-month research period on the orbiting laboratory
that starts with delivery of these and other experiments to the Station
during the STS-111 mission. The research is sponsored by NASA’s Microgravity
Research Program at the Marshall Center and by the Office of Biological and
Physical Research in Washington, D.C.