MILFORD – The items that Saint-Gobain Crystals has been delivering to the Army and Marine Corps for their mobile rocket-launchers might look like windows and function as windows, but the company has a more descriptive term: “transparent armor.”

“A typical armor solution is to have many layers of glass adhered together with different polymers. We replace a number of those glass layers with a sheet of sapphire … which is second in hardness only to diamond; a very dense, transparent material,” said Russell Wooddell, program manager for the Powers Street company.

Transparent? Yes; sapphires in jewelry stores have various colors, but that’s because of impurities. Sapphires grown by Saint-Gobain for military and semiconductor applications are grown from a single, pure crystal, so light passes right through.

The Power Street firm recently celebrated the delivery of the 100th set of this “transparent armor” for the M142 High Mobility Artillery Rocket Launcher as part of a three-year, $20 million contract that allowed them expand the workforce in Milford by about 30 percent. Roughly 100 people work at the factory, which long-timers will remember as Saphikon, an independent firm that dates back to 1974 which Saint-Gobain bought in 2000.

“This was the first contract of its kind. We were first to commercialize sapphire-based transparent armor,” he said.

Sapphire works for windows because it resists scratching and pitting caused by the exhaust from missiles as well as the rocks and dust of desert operations, and also because it is lighter than glass, Wooddell said. These launchers (whose acronym is often pronounced “high-MARL”) are sometimes carried into operation aboard C-130 transport planes, so weight is an issue.

Sapphire is also chemically inert, although that trait is more valuable in semiconductor creation than military operations.

Growing large sheets of crystal isn’t easy. Sapphire has a melting point of about 3,700 degrees Fahrenheit, so specialized equipment is required, and cooling rates can greatly affect crystal structure.

“Over the years, building on the Saphikon heritage, we’re tried a number of different things: growing them faster, slower, wider, thinner,” Wooddell said. “I’d equate almost to a Formula 1 racecar. There’s a lot of precision required – a certain amount of analytics, but a lot of fine-tuning is required.”

This contract grew out of prior window work done for Air Force and Navy’s Joint Strike Fighter Program.

As would be expected, sapphire is more expensive to make than glass.

“Cost is typically 5 to 10 times more than a glass solution, in terms of acquisition cost,” Wooddell said. “When you examine life cycle or total ownership costs, that’s where you start to see a lot of the value.”

Still, don’t expect to see sapphire-hardened windows for sale at your local hardware store, he said: “The one-in-every-home solution may not be sapphire.”

Saint-Gobain Crystals is a division of Saint-Gobain, a French firm that is one of the world’s largest building materials companies, with approximately 19,000 employees in the U.S.

Saint-Gobain Crystals is headquartered in Hiram, Ohio, and handles crystal-based technologies for radiation detection, optics, and sapphire components for industrial, aerospace and defense applications.

David Brooks can be reached at 594-6531 or dbrooks@nashua
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