Today on MSL-1
we highlight some of the materials science research being done in space.
Metals and alloys are virtually everywhere in our daily lives. From
them, we make aircraft engines, automobiles, bridges, buildings - even paper
clips. Certain metals are appropriate for use in certain functions, while
not suitable in others.
Before we can effectively use metals and alloys in products that we need, many questions must be answered through scientific investigation and experimentation:
The research on MSL-1 in the area of metals and alloys helps us to begin to answer just a few of these questions.
This fascinating process of undercooling and rapid freezing or "solidification" of material, which we observe any time we see snow fall, allows us to study and manufacture solid metals of a form that cannot be made anywhere else. These are Super-materials!!!
If you heat a metal in microgravity, and allow it to cool without touching any container walls, it will continue to cool below its freezing point, but still remain as a liquid. The water in your ice-cube trays in the freezer at home first freeze to the sides of the tray, eventually freezing through to the center to make an ice-cube. But the liquid metals in the TEMPUS facility have nothing to "freeze" onto, and remain as a liquid right through the freezing temperature and down to lower temperatures. In some cases, we can have liquid metals that are at temperatures several hundred degrees below the normal freezing point of the metal.
When the metal eventually does
freeze, it does so in just a fraction of a second emitting a pulse of light
(pictured at right from a previous shuttle mission). The central bright
blob is a sample from TEMPUS, at the moment of solidification. You can also
view a 3 second video clip, in avi
format (480 KB) or quicktime
(540 KB).
You'll see this process of rapid freezing on the downlink
video from the shuttle during the mission.
The kinds
of metallic solids that we get out of this process are very different than
one can obtain in any other way. One example is a superconducting phase
in Niobium compounds, which cannot be formed by normal cooling. Another
example is metallic glass. In the video (first frame shown at left),
flat plates of titanium alloy, metallic glass, and stainless steel have
been prepared and placed on a table. Then, identical steel balls were dropped
from the same height onto the plates. If you view the video, you'll see
the ball on the metallic glass plate bounce nearly as high on each bounce.
The ball on the stainless steel plate will stop bouncing fairly quickly
- after about 10 seconds, and the ball on the titanium alloy plate lasts
longer - about 20 seconds. However, the metallic glass ball will, like the
Eveready bunny, keep on going! This behavior is due to the arrangement of
the atoms in the metallic glass, which is very different from the arrangement
in the other materials, and results directly from having been formed from
the undercooled state.
On the first flight of MSL-1/STS-83, new records were set for the amount of undercooling in several of the samples. We hope to go to even deeper levels of undercooling on the second flight of MSL-1, inorder to obtain more knowledge about metals and alloys in this fascinating state.
(1.9 MB) |
Diffusion is a familiar process to each of us. Its the process
that helps carry the smell of baked bread from the oven throughout the house,
or allows food coloring to disperse through a glass of water without stirring.
This process is also very important in the study of metals and alloys, and
on the ground in "1-g" (one-gravity), it can be masked or altered
in many ways by gravity-driven flows in molten metals.
Many of the metal products we use everyday are formed when a mixture of molten metals are combined and then allowed to solidify through a variety of processes. The mixture is in many cases related to the strength of the resulting solid alloy. It is therefore important that we understand precisely how metals mix together or mix with themselves. Gravity can often complicate the mixing process, just as it complicates the mixing of oil and vinegar in making salad dressing.
The picture above is from a video clip that simulates the mixing of atoms of two different liquid materials (such as lead and tin) in a low-gravity environment. Chemical diffusion, which is being modeled here, is difficult to observe on the ground, because gravity itself causes convection in the mixture and alters the reaction. (avi movie 864 KB or quicktime movie 352 KB)
Much of the work done in the Japanese Large Isothermal Furnace is dedicated to studying diffusion and measuring a quantity called the diffusion coefficient. Each of these experiments are dedicated to learning more about how metals mix under various conditions. The second flight of MSL-1 will help us build on our knowledge obtained from the limited experimentation time on the first flight.
we study metals and alloys in space!
we study metals and alloys in space!
June 19, 1997
Author: Dr.
John Horack
Curator:Bryan Walls
NASA Official: John M. Horack