I
then k minus nine eight seven six five
four three two one solid rocket ignition
and liftoff liftoff of Columbia on a
voyage to the future
the isothermal dendritic growth
experiment or idge is a microgravity
material science experiment plan to fly
on board the space shuttle Columbia as
part of the United States microgravity
payload mission it is a fundamental
materials research experiment to help
better understand and correlate what
parameters affect the size and shape of
crystals which determine the final
properties of materials idge was
conceived at the Rensselaer Polytechnic
Institute in Troy New York which is
responsible for the science and
dendritic growth chamber development dr.
Martin a gliksin of rpi is the idge
principal investigator well what we hope
to accomplish in the idg experiment is
to be able to observe the growth rates
and
krystal morphologies of dendritic
crystals as they form and develop in the
microgravity environment of low-earth
orbit this experiment will constitute a
basic check of the physics theories of
dendritic growth and provide some
critical data for the assessment of the
scientific concepts that form the
framework of our understanding of this
rather important metallurgical
phenomenon the experiment will take
place inside this experiment apparatus
container which will be mounted on the
support structure inside the cargo bay
of the spacecraft the experiment
apparatus is a miniaturized automated
space laboratory that was designed and
built by a team of engineers at the NASA
Lewis Research Center in Cleveland Ohio
the specific objective of this space
experiment is to improve the quality of
metals through the study of sixy known
nitrile this material was chosen because
it mimics the behavior of iron in its
melting and solidifying process with one
additional advantage it is clear and
transparent metals are not transparent
we cannot see what is happening to their
structure when they solidify if we were
able to better understand what is
occurring to the crystalline structure
of the metal we would stand a much
greater chance of improving its
qualities that then is the objective of
this space experiment this containment
vessel houses the device through which
we will attempt to learn and understand
the internal changes taking place inside
these solidifying materials inside the
containment vessel of the automated
space laboratory there is an isothermal
bath it is a two gallon tank filled with
a mixture of ethylene glycol and water
in which the temperature can be
maintained to within two thousandth of a
degree it has a heater coil in it and a
small impeller down at the
to assure good mixing of the ethylene
glycol and water so that there is an
even temperature distribution within the
vessel the isothermal tank also has four
windows on it to accommodate the
necessary photography mounted to the
tank are 2 35 millimeter cameras which
record the dendritic growth and to slow
scan television cameras the television
cameras monitor the dendritic growth and
activate the 35 millimeter cameras when
growth and the experiment begins the
rack around the tank provides a place to
mount the circuit boards the experiments
will take place inside this growth
chamber which was conceived and
developed at Rensselaer Polytechnic
Institute the chamber is constructed out
of stainless steel and glass their
misters extend from the bottom of the
growth chamber up into the volume of 16
Oh nitrile they measure the temperature
of the dendritic growth with an accuracy
of two thousandth of a degree Celsius
sixy no nitrile or SCM is encapsulated
in the volume of the growth chamber the
scn is 99.9 percent pure and was chosen
because it mimics the behavior of iron
in its melting and solidifying process
Sen is a solid at room temperature and
melts at 58 degrees centigrade that's
136 degrees Fahrenheit
now let's take a closer look at what we
expect to achieve and learn through
these experiments during the
solidification process dendrites are
formed dendrites are branching tree like
crystals that form during industrial
metal production understanding and
correlating what parameters affect the
size and shape of this crystallization
will help us to understand and
subsequently be able to predict the
final properties of many metals alloys
and super alloys and how we propose
gathering that information is through
this isothermal dendritic growth
experiment the growth chamber is filled
with scn material and contains a stinger
that is used to form the dendrites first
the scn material is melted by raising
the temperature of the isothermal bath
the molten scn is then cooled to just
below its freezing point by reducing the
temperature of the isothermal bath the
scn will not solidify at this
temperature because it is such a pure
material the stinger is a hollow shaft
which is also filled with the polymer
scn and extends right into the volume of
this scn material in the growth chamber
using thermal electric coolers
additional chilling is started at the
top of the stinger shaft which is
located outside of the growth chamber
as the Stinger cools too far below the
freezing point the scn inside the shaft
solidifies the solidification process
moves down the shaft and pops out at the
stinger tip which is being monitored by
the slow scan television cameras when
the SS TV and associated software spot a
dendrite forming the 35 millimeter
cameras are triggered the cameras are
set to expose six pictures at regular
intervals as the dendrite grows to fill
the field of view this entire process is
monitored in Huntsville Alabama at
NASA's Marshall Space Flight Center to
assure that the experiment is
progressing as expected in the payload
operations control center or POC the
growth velocity of the dendrite is
measured if necessary timing of the
experiment can be adjusted and remelted
to repeat the experiment as often as
might be required after the flight the
35 millimeter photos will be analyzed
for size and shape information these are
dendrites which were grown on earth you
can see the effects of gravity in their
formation there are no arms or branches
on top of the stand right as this
material solidifies it gives off the
heat of fusion the heat works upward
causing the top of the sample to stay a
little bit hotter as a result the bottom
solidifies a little sooner than the top
as the bottom cools gravity is creating
a force which speeds up the downward
growth of the arms of the dendrite these
convective forces confound the effect of
dendritic growth and make it difficult
to understand the formation of these
dendrites the space environment will
simplify this process and enable us to
better understand the process of
crystallization
the dendrites will be more symmetrical
because gravity will not be distorting
the solidification process these
experiments will be most beneficial to
metal manufacturers they will provide a
fundamental understanding of how
dendrites grow so that we can better
understand how to make predictions of
the quality of an end product if we
understand the process we can improve it
if we can improve it we will be able to
reduce scrap and produce stronger and
more ductile materials it will be
possible to achieve whatever kind of
property may be needed to satisfy the
consumer everyone making products out of
any metal will benefit from what has
learned from these experiments in the
future automobiles airplanes ships and
many other metal products will be a
little better and somewhat less
expensive because of the isothermal
dendritic growth experiment
you