[PA-NJ Glassblowers] NASA article about glass-making in zero-gravity outer space

Tony Patti gaffer at glassblower.info
Thu Feb 20 23:45:23 EST 2014



Glass from Space

NASA-supported researchers have discovered that glass formed in space has
remarkable properties.

 <http://www.nasa.gov/> NASA

April 14, 2003: It's easy: mix together some materials like sand, limestone
and soda. Heat them above 2000o F. Then cool the incandescent liquid
carefully so that crystals cannot form.


That's how you make glass.


Craftsmen on Earth have followed this basic recipe for millennia. It works.
"Now we know it works even better in space," says glass and ceramics expert
Delbert Day, who has been experimenting with glass melts on space shuttles
over the past twenty years. Day is the Curators' Professor Emeritus of
Ceramic Engineering at the University of Missouri-Rolla.


Going into those first experiments, he says, he expected to end up with a
purer glass. That's because on Earth, the melts--the molten liquid from
which glass is formed--must be held in some kind of container. That's a
problem. "At high temperatures," says Day, "these glass melts are very
corrosive toward any known container." As the melt attacks and dissolves the
crucible, the melt--and thus the glass--becomes contaminated.


In microgravity, though, you don't need a container. In Day's initial
experiments, the melt--a molten droplet about 1/4 inch in diameter--was held
in place inside a hot furnace simply by the pressure of sound waves emitted
by an acoustic levitator.


With that acoustic levitator, explains Day, "we could melt and cool and melt
and cool a molten droplet without letting it touch anything." As Day had
hoped, containerless processing produced a better glass. To his surprise,
though, the glass was of even higher quality than theory had predicted.


When most people think of glass, they think of that transparent stuff in
window panes. But glass doesn't have to be transparent nor is it always
found in windows. Among researchers there's a different definition: "glass"
is a solid material with an amorphous internal structure. The atoms in
solids are usually arranged in regular, predictable patterns, like bricks
fitted into a wall. But if the atoms are just jumbled together in a
disorganized way, like bricks dumped on the ground... that's glass.


The window glass that we're so familiar with is made mostly of silica--a
compound of silicon and oxygen. It's essentially melted sand. But in theory,
a melt of any chemical composition can produce a glass as long as the melt
can be cooled quickly enough that the atoms don't have time to hook
themselves up into patterns, or crystals.


In Earth-orbit, it turns out, these molten liquids don't crystallize as
easily as they do on Earth. It's easier for glass to form. So not only can
you make glass that's less contaminated, you can also form it from a wider
variety of melts.


But why is that important? What's wrong with glass made of silica?


For windows silica is just fine. But glass made from other chemical
compositions offers a panoply of unexpected properties. For example, there
are "bioactive glasses" that can be used to repair human bones. These
glasses eventually dissolve when their work is done. On the other hand, Day
has developed glasses which are so insoluble in the body that they are being
used to treat cancer by delivering high doses of radiation directly to a
tumor site.


 <http://science.nasa.gov/msl1/themes/manda_over> see captionAnother
example: Glass made of metal can be remarkably strong and
corrosion-resistant. And you don't need to machine it into the precise,
intricate shapes needed, say, for a motor. You can just mold or cast it.


Right: Steel balls bounce on flat plates of titanium alloy, metallic glass,
and stainless steel. The ball bouncing on metallic glass keep going for a
remarkably long time. [ <http://science.nasa.gov/msl1/themes/manda_over>


Also intriguing to space researchers is fluoride glass. A blend of
zirconium, barium, lanthanum, sodium and aluminum, this type of glass (also
known as "ZBLAN") is a hundred times more transparent than silica-based
glass. It would be exceptional for fiber optics.


A fluoride fiber would be so transparent, says Day, that light shone into
one end, say, in New York City, could be seen at the other end as far away
as Paris. With silicon glass fibers, the light signal degrades along the


Unfortunately, fluoride glass fibers are very difficult to produce on Earth.
The melts tend to crystallize before glass can form.


see captionRight: The surfaces of ZBLAN fibers formed in near-weightlessness
(upper panel) and in normal Earth-gravity (lower panel). [


The reason, says Day, is that gravity causes convection or mixing in a melt.
In effect, gravity "stirs" it, and, in a process known as
ids> shear thinning, the melt becomes more fluid. This same process works in
peanut butter: the faster you stir it, the more easily it moves.

In melts that are more fluid, like those stirred by gravity, the atoms move
rapidly, so they can get into geometric arrangements more quickly. In
thicker, more viscous melts, the atoms move more slowly. It's harder for
regular patterns to form. It's more likely that the melt will produce a


In microgravity, Day believes, melts may be more viscous than they are on


While this theory has not yet been confirmed, some experimental results
suggest that it is correct. NASA researcher Dennis Tucker worked with
fluoride melts on the KC-135, a plane that provides short bursts of near
zero-gravity interspersed with periods of high gravity.


"He did some glass-melting experiments, trying to pull thin fibers out of
melts," recounts Day. "During the low-gravity portion of the plane's flight,
when g was almost zero, the fibers came out with no trouble. But during the
double-gravity portion of the plane's flight, the fiber that he was pulling
totally crystallized."


That result, says Day, could be explained by shear thinning. "A melt in low
gravity doesn't experience much shear. But as you increase g, there'll be
more and more movement in the melt." Shear stresses increase. The effective
viscosity of the melt decreases. Crystallization becomes more likely.


see captionRight: (left panel) a defect-free ZBLAN fiber pulled during a
low-g arc aboard the KC-135; (right panel) a crystallized fiber pulled from
the same apparatus under 1-g. [


Day is currently planning his next experiment in space--onboard the
International Space Station--which he hopes will confirm his ideas. He'll be
melting and cooling identical glass samples in the same way on Earth and in
microgravity. Then he'll count the number of crystals that appear in each
sample. If shear-thinning exists, he says, there will be fewer crystals in
the space-melted samples than in the ones produced on Earth.


Eventually, Day hopes to take these lessons learned from space and apply
them to glass production on the ground. Metallic glasses. Bioactive glasses.
Super-clear fiber optics. The possible applications go on and on.... which
makes the value of this research crystal clear.


more information


NASA's  <http://spaceresearch.nasa.gov/> Office of Biological and Physical
Research (OBPR) supports studies like Day's for the benefit of humans in
space and on Earth

 <http://www.glassnotes.com/WindowPanes.html> The "Glass Flows" Myth
(Glassnotes.com) --learn more about the basics of glass.

ZBLAN continues to show promise (Science at NASA) Thin fibers of an exotic
glass called ZBLAN are clearer when made in near weightlessness than on
Earth under gravity's effects. [

 <http://web.umr.edu/~day/> Delbert E. Day -- (University of Missouri) home

 <http://www.eweek.org/site/News/Features/microspheres.shtml> Fighting
Cancer with Radioactive Glass Microspheres (National Engineers Week) Tiny
glass spheres are proving an effective way of safely delivering large doses
of radiation to cancerous tumors -- researchers see multiple medical

 <http://microgravity.msfc.nasa.gov/MG_PRODUCTS/FS-2001-06-97-MSFC.pdf> The
Bare Bones of Bioactive Glass (Microgravity News) researchers are learning
how to use glass beads to improve bone growth.

 <http://www.nasatech.com/Briefs/Dec98/MFS26503.html> Microgravity
Fiber-Pulling Apparatus (NASA) Thber-processing method provides a way to
produce optical fiber composed of glass systems in low gravity.

 <http://science.nasa.gov/msl1/themes/manda_over> Materials Science Overview
- Metals and Alloys (Science at NASA)





Tony Patti
gaffer at glassblower.info

 <http://www.glassblower.info/qr-code.html> QR Code for Tony Patti -



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