Glass From Space

Researchers have discovered that glass formed in space has remarkable properties.

It's easy: mix together some materials like sand, limestone and soda. Heat them above 2000^o 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.

Copyright Dave Bartruff A blob of molten glass comes out of the fire at the Orrefors glassworks in Sweden.

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.