Corning produces some of the world's purest glass through a process that, for a while, doesn't seem to involve glass at all.
It's called vapor deposition – a high-temperature process that creates glass by depositing layer after layer of tiny glass particles on a growing surface, rather than cooling a molten liquid.
Vapor deposition is key to Corning's worldwide leadership in optical fiber. It's also the process Corning uses to produce other specialized glass technology products, like sophisticated telescope mirrors.
And it represents a classic Corning combination of deep materials understanding, process control expertise, cutting-edge equipment design, and automation.
How it works
There are various forms of the process, but the one most commonly used at Corning is Outside Vapor Deposition (OVD), which "builds" the new glass in miniscule layers on top of (or around) a solid substrate. Michelle King and Greg Gausman, who manage Technology Delivery at the optical fiber plant in Wilmington, North Carolina, explain it this way.
"In very simple terms, imagine the teakettle on your stove," Gausman said. "As you raise the temperature of the water, but not so high that it boils, you still create steam, or vapor, that's above the liquid itself. Rather than just allowing that steam to escape out of the teakettle, you're actually conveying it through piping to a burner where that vapor is burned."
The vapor comes not from boiling water, but from liquids that contain silicon, and sometimes also controlled additives known as dopants. So the combustion process produces a mixture of very small, oxidized glass particles – called soot -- and un-combusted vapor. That vapor, in turn, can condense around the particles, which then aggregate further and adhere to a substrate.
With optical fiber, the vapor is meticulously deposited around a long ceramic bait rod. Layer after layer of vapor reaction to microscopic glass particles results in the formation of ultra-pure glass. And with the bait rod removed, the perfect glass tube -- known as a preform -- is then consolidated in intense heat and drawn into hair-thin optical fiber. Watch this video to learn more.
In the case of lenses, mirrors, and – for many years – windows for U.S. spacecraft, the vapor deposition takes place in a "direct to glass" process, resulting in large, dense, glass monoliths. Making a large telescope mirror is a process that can last for more than a year.