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A Break with Tradition: Fused Silica

All About Glass

After you see something work, then you realize that it’s not so complicated after all.
     — J. Franklin Hyde

It’s exquisitely pure and remarkably transparent. It expands and contracts very little with changes in temperature. It is the simplest of all glasses, yet for years it was nearly impossible to make: pure silica glass. In 1934, Corning organic chemist J. Franklin Hyde came up with a brilliant solution.

fused silica

Glass had always been made by melting dry mineral ingredients. Making a pure silica glass required melting the purest quartz at incredibly high temperatures. Hyde’s unprecedented idea was to synthesize the glass from liquid chemicals. In a crude experiment, he sprayed liquid silicon tetrachloride into the flame of a welder’s torch. It reacted with the water vapor produced by the burning fuel to form an extremely pure glass—fused silica.

Hyde had invented a radical new way to make glass—the first in more than 4,000 years—and he hadn’t even been given the assignment. Today, his process is used to make fused-silica glasses for the most demanding applications.

Stepping down the size

A “stepper” lens assembly is the most sophisticated lens system in the world. It allows circuit patterns to be printed on computer chips like images on photographic film. Its dozen or more lenses, all made of fused silica, reduce a circuit’s pattern and focus it—in lines as fine as a wavelength of light—onto the chip.

Fused silica transmits more ultraviolet (UV) light than any other kind of glass. The extremely short wavelength of UV light makes it possible to print nearly 9 million transistors on a silicon chip that is smaller than a postage stamp.

In cold and heat

Space shuttle windows are made from fused silica

Some telescope mirrors are made from Ultra Low Expansion (ULETM) glass—fused silica that contains the element titanium. Fused silica is very resistant to thermal changes, but titanium gives it great thermal stability.

A telescope mirror made from ULETM glass won’t change its shape at all, even with extreme shifts in temperature. That’s critical. Changes in a mirror’s shape will distort the image.

Space shuttle windows made from fused silica are tough and can withstand the tremendous heat of takeoff and re-entry.

The Corning Museum of Glass
This article was originally published in Innovations in Glass, 1999, pp. 36–37.

Published on October 24, 2011